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, Available online , doi: 10.11883/bzycj-2024-0282
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Hydrogen-doped natural gas technology has been gradually used in pipeline transportation, but hydrogen-doped natural gas is prone to leakage and explosion accidents. The study used a 20L spherical device to investigate the effects of hydrogen blending ratio and CO2 addition on the explosion pressure and flame propagation characteristics of hydrogen-doped natural gas, and the chemical reaction kinetics method was used to analyse the explosion mechanism. The results showed that the hydrogen doping ratio has a promoting effect on the hydrogen-doped natural gas explosion pressure parameters and flame propagation speed. As the hydrogen doping ratio increases, the maximum explosion pressure gradually increases, the rapid burn time and sustained burn time are gradually decreasing. The maximum explosion pressure rise rate and flame propagation speed gradually increase when the hydrogen doping ratio is less than 0.5. When the hydrogen doping ratio is greater than 0.5, the maximum explosion pressure rise rate and flame propagation speed rise rapidly. The addition of CO2 has an inhibitory effect on the explosion pressure and flame propagation speed of the mixed gas, but the suppression effect on pressure parameters with high hydrogen doping ratio is poor. Through reaction kinetic analysis, it can be seen that as the hydrogen doping ratio increases, the laminar burning velocity and adiabatic flame temperature gradually increase, the mole fraction of active free radicals and the rate of product increase significantly, and the mixing of hydrogen changes the reaction path of methane. When the hydrogen doping ratio is greater than 0.5, reactions R84, R46 and R3 enter the top ten steps of the reaction, producing H and OH radicals, which promotes the reaction. CO2 can reduce the laminar burning velocity, adiabatic flame temperature, active free radical mole fraction and rate of production of the mixed gas, but adding CO2 does not change the reaction path of methane.
Hydrogen-doped natural gas technology has been gradually used in pipeline transportation, but hydrogen-doped natural gas is prone to leakage and explosion accidents. The study used a 20L spherical device to investigate the effects of hydrogen blending ratio and CO2 addition on the explosion pressure and flame propagation characteristics of hydrogen-doped natural gas, and the chemical reaction kinetics method was used to analyse the explosion mechanism. The results showed that the hydrogen doping ratio has a promoting effect on the hydrogen-doped natural gas explosion pressure parameters and flame propagation speed. As the hydrogen doping ratio increases, the maximum explosion pressure gradually increases, the rapid burn time and sustained burn time are gradually decreasing. The maximum explosion pressure rise rate and flame propagation speed gradually increase when the hydrogen doping ratio is less than 0.5. When the hydrogen doping ratio is greater than 0.5, the maximum explosion pressure rise rate and flame propagation speed rise rapidly. The addition of CO2 has an inhibitory effect on the explosion pressure and flame propagation speed of the mixed gas, but the suppression effect on pressure parameters with high hydrogen doping ratio is poor. Through reaction kinetic analysis, it can be seen that as the hydrogen doping ratio increases, the laminar burning velocity and adiabatic flame temperature gradually increase, the mole fraction of active free radicals and the rate of product increase significantly, and the mixing of hydrogen changes the reaction path of methane. When the hydrogen doping ratio is greater than 0.5, reactions R84, R46 and R3 enter the top ten steps of the reaction, producing H and OH radicals, which promotes the reaction. CO2 can reduce the laminar burning velocity, adiabatic flame temperature, active free radical mole fraction and rate of production of the mixed gas, but adding CO2 does not change the reaction path of methane.
, Available online , doi: 10.11883/bzycj-2024-0277
Abstract:
The explosion limit serves as a key parameter for assessing explosion risks and prevention strategies of combustible gases. Through a self-developed 5-liter experimental platform for flammable gas explosion characteristics, the upper explosive limits (UELs) of CH4/C2H6 andC2H6/H2O gas mixtures under high-temperature and high-pressure conditions were investigated, revealing the influence mechanisms of methane blending ratios and steam concentrations on the UELs of ethane under such extreme environments. The results demonstrate that methane blending ratios (0-0.5) exhibit minimal influence on the UELs of CH4/C2H6 mixtures at 200℃ and 0.4-0.6 MPa, and the UELs of CH4/C2H6 mixtures increase with increasing initial pressure, while exhibiting a progressively diminishing rate of UEL increment. Under identical thermal conditions (200℃, 0.4-0.6 MPa), the UELs of C2H6/H2O mixtures decrease approximately linearly with increasing water vapor concentrations (0-40%). Conversely, higher initial pressures enhance the UELs of C2H6/H2O mixtures. Notably, under 0.5 MPa pressure, as temperature increases from 200℃ to 270℃, the UELs of both pure ethane and C2H6/H2O mixtures containing 40% water vapor increase with a rise in temperature, with pure ethane demonstrating an accelerating UEL increase rate.
The explosion limit serves as a key parameter for assessing explosion risks and prevention strategies of combustible gases. Through a self-developed 5-liter experimental platform for flammable gas explosion characteristics, the upper explosive limits (UELs) of CH4/C2H6 andC2H6/H2O gas mixtures under high-temperature and high-pressure conditions were investigated, revealing the influence mechanisms of methane blending ratios and steam concentrations on the UELs of ethane under such extreme environments. The results demonstrate that methane blending ratios (0-0.5) exhibit minimal influence on the UELs of CH4/C2H6 mixtures at 200℃ and 0.4-0.6 MPa, and the UELs of CH4/C2H6 mixtures increase with increasing initial pressure, while exhibiting a progressively diminishing rate of UEL increment. Under identical thermal conditions (200℃, 0.4-0.6 MPa), the UELs of C2H6/H2O mixtures decrease approximately linearly with increasing water vapor concentrations (0-40%). Conversely, higher initial pressures enhance the UELs of C2H6/H2O mixtures. Notably, under 0.5 MPa pressure, as temperature increases from 200℃ to 270℃, the UELs of both pure ethane and C2H6/H2O mixtures containing 40% water vapor increase with a rise in temperature, with pure ethane demonstrating an accelerating UEL increase rate.
, Available online , doi: 10.11883/bzycj-2024-0417
Abstract:
To investigate the dynamic shear mechanical response and post-damage permeability characteristics of rough structural planes, a dynamic shear system was utilized to conduct shear tests on rough structural planes of sandstone under varying shear rate conditions. The effects of shear rate and roughness coefficient on peak shear strength and slip behaviors were analyzed. After the shear test, the influence of dynamic shear on the damage characteristics of rough structural surfaces was analyzed using three-dimensional scanning technology. Subsequently, seepage tests were conducted on damaged structural surfaces under different confining pressures to further investigate the subsequent seepage characteristics of damaged structural surfaces after dynamic shearing. The results of dynamic shear tests show that the dynamic peak shear strength of sandstone structural planes exhibits a decreasing trend with the shear rate, and shear rate influence on shear stiffness is insignificant. As the shear rate increases from 50 mm/s to 210 mm/s, the peak shear strength of structural planes with joint roughness coefficient of 12.43 declines from 8.49 MPa to 6.88 MPa. In addition, the dynamic peak shear strength of structural planes increases with the roughness under the same shear rate condition. The frequency of height distribution of damaged structural planes decreases with the shear rate. Under the same roughness condition, the damage degree of the structural plane generally increases with the shear rate, resulting in a decline in crack opening and thus affecting the permeability properties of the structural plane. The flow test results indicate that the relationship between the hydraulic gradient and the volumetric flow rate of the damaged structural plane adheres to Forchheimer’s law. In addition, the transmissivity of the damaged structural plane decreases with the shear rate under the same confining pressure condition, while increasing with the joint roughness coefficient.
To investigate the dynamic shear mechanical response and post-damage permeability characteristics of rough structural planes, a dynamic shear system was utilized to conduct shear tests on rough structural planes of sandstone under varying shear rate conditions. The effects of shear rate and roughness coefficient on peak shear strength and slip behaviors were analyzed. After the shear test, the influence of dynamic shear on the damage characteristics of rough structural surfaces was analyzed using three-dimensional scanning technology. Subsequently, seepage tests were conducted on damaged structural surfaces under different confining pressures to further investigate the subsequent seepage characteristics of damaged structural surfaces after dynamic shearing. The results of dynamic shear tests show that the dynamic peak shear strength of sandstone structural planes exhibits a decreasing trend with the shear rate, and shear rate influence on shear stiffness is insignificant. As the shear rate increases from 50 mm/s to 210 mm/s, the peak shear strength of structural planes with joint roughness coefficient of 12.43 declines from 8.49 MPa to 6.88 MPa. In addition, the dynamic peak shear strength of structural planes increases with the roughness under the same shear rate condition. The frequency of height distribution of damaged structural planes decreases with the shear rate. Under the same roughness condition, the damage degree of the structural plane generally increases with the shear rate, resulting in a decline in crack opening and thus affecting the permeability properties of the structural plane. The flow test results indicate that the relationship between the hydraulic gradient and the volumetric flow rate of the damaged structural plane adheres to Forchheimer’s law. In addition, the transmissivity of the damaged structural plane decreases with the shear rate under the same confining pressure condition, while increasing with the joint roughness coefficient.
, Available online , doi: 10.11883/bzycj-2024-0477
Abstract:
K447A, a nickel-based superalloy, is widely used in critical hot-end components of aerospace engines due to its excellent high-temperature performance. Through quasi - static and high strain rate compression experiments within the temperature range of 25 ℃ to1000 ℃, the dynamic mechanical properties of K447A superalloy were systematically investigated. The effects of temperature and strain rate on its plastic flow behavior and material microstructure were analyzed. By examining the stress-strain curves under quasi-static conditions and utilizing electron backscatter diffraction (EBSD), the microstructural characteristics of specimens deformed at various strain rates and temperatures were analyzed. The results reveal that during the plastic deformation of K447A, strain hardening, temperature softening, and strain rate strengthening phenomena coexist. As the strain rate increases from quasi-static levels to 5000 s−1, the temperature sensitivity index (s) gradually decreases, indicating a diminishing temperature softening effect at higher strain rates. Notably, at an elevated strain rate of 800 ℃, an anomalous stress peak appears in the flow stress-strain curve of the K447A alloy, suggesting complex interactions between temperature and strain rate during deformation. Furthermore, the strain rate sensitivity coefficient (p) increases with temperature, highlighting a more pronounced strain rate strengthening effect at elevated temperatures. Microstructural changes within the material, which are influenced by the coupling of strain rate and temperature, are also examined. An increase in strain rate leads to grain refinement, while higher temperatures result in a decrease in the proportion of low-angle grain boundaries, facilitating dynamic recrystallization within the material. To accurately describe the flow stress influenced by the interplay of temperature and strain rate, a modified Johnson-Cook (J-C) constitutive model was developed. This revised model demonstrates improved predictive capability compared to the original formulation, effectively capturing the plastic flow behavior of K447A across a broad range of temperatures and strain rates. The predictive error is significantly reduced from 26.36% to 9.05%, underscoring the model's enhanced accuracy and reliability in simulating the mechanical performance of K447A alloy under varying operational conditions.
K447A, a nickel-based superalloy, is widely used in critical hot-end components of aerospace engines due to its excellent high-temperature performance. Through quasi - static and high strain rate compression experiments within the temperature range of 25 ℃ to
, Available online , doi: 10.11883/bzycj-2024-0355
Abstract:
The characteristics of flash radiation during hypervelocity impact processes were investigated using a flash radiation test system established on a two-stage light gas gun platform. The study explored how impact velocity, projectile diameter, and target chamber vacuum level affect the frequency and time characteristics of flash radiation. The flash radiation test system was designed to precisely measure the frequency and time domain of the flash radiation emitted during hypervelocity impacts. The system is composed of a two-stage light gas gun capable of achieving high impact velocities, a vacuum chamber to control the environmental pressure, and a high-speed spectrometer to capture the emitted radiation. The experimental setup enabled the systematic variation of impact velocity, projectile diameter, and target chamber vacuum level, allowing for a comprehensive study of their individual and combined effects on flash radiation characteristics. The results indicate that the flash radiation in the frequency domain exhibits a dual-component structure, comprising discrete line spectra with fixed wavelengths and continuous spectra. Higher impact velocities and larger projectile diameters, which increase the initial kinetic energy of the impact, enhance the radiation intensity of the flash. Additionally, higher environmental pressures of target chamber increase the frictional heating between the projectile and the gas, further increasing flash radiation intensity. During the decay phase of the flash, increasing the impact velocity raises the plasma concentration, prolongs the duration of the flash, but accelerates the flash temperature decay. In contrast, the projectile diameter has an insignificant effect on the duration and temperature of the flash. Reducing the environmental pressure of target chamber decreases the attenuation during the flash radiation process and extends the duration of the flash. In conclusion, the study provides a comprehensive understanding of the factors influencing flash radiation during hypervelocity impacts. The findings highlight the importance of impact velocity and projectile diameter in determining the intensity and duration of flash radiation and reveal the significant role of environmental pressure of target chamber in modifying the radiation characteristics. These results offer valuable insights for the design and analysis of hypervelocity impact experiments and contribute to the broader understanding of impact physics.
The characteristics of flash radiation during hypervelocity impact processes were investigated using a flash radiation test system established on a two-stage light gas gun platform. The study explored how impact velocity, projectile diameter, and target chamber vacuum level affect the frequency and time characteristics of flash radiation. The flash radiation test system was designed to precisely measure the frequency and time domain of the flash radiation emitted during hypervelocity impacts. The system is composed of a two-stage light gas gun capable of achieving high impact velocities, a vacuum chamber to control the environmental pressure, and a high-speed spectrometer to capture the emitted radiation. The experimental setup enabled the systematic variation of impact velocity, projectile diameter, and target chamber vacuum level, allowing for a comprehensive study of their individual and combined effects on flash radiation characteristics. The results indicate that the flash radiation in the frequency domain exhibits a dual-component structure, comprising discrete line spectra with fixed wavelengths and continuous spectra. Higher impact velocities and larger projectile diameters, which increase the initial kinetic energy of the impact, enhance the radiation intensity of the flash. Additionally, higher environmental pressures of target chamber increase the frictional heating between the projectile and the gas, further increasing flash radiation intensity. During the decay phase of the flash, increasing the impact velocity raises the plasma concentration, prolongs the duration of the flash, but accelerates the flash temperature decay. In contrast, the projectile diameter has an insignificant effect on the duration and temperature of the flash. Reducing the environmental pressure of target chamber decreases the attenuation during the flash radiation process and extends the duration of the flash. In conclusion, the study provides a comprehensive understanding of the factors influencing flash radiation during hypervelocity impacts. The findings highlight the importance of impact velocity and projectile diameter in determining the intensity and duration of flash radiation and reveal the significant role of environmental pressure of target chamber in modifying the radiation characteristics. These results offer valuable insights for the design and analysis of hypervelocity impact experiments and contribute to the broader understanding of impact physics.
, Available online , doi: 10.11883/bzycj-2024-0409
Abstract:
The influence of reflected explosion stress waves on dynamic crack propagation behavior , as well as the connection between dynamic cracks and pre-existing cracks, was studied using dynamic photoelastic experiments. A high-speed camera was used to capture the full field photoelastic isochromatic fringe pattern of horizontally expanding explosive cracks. The explosive crack is a directional crack generated by detonating explosives in a blast hole containing a horizontal V-shaped groove. The propagation process of explosive cracks can be divided into three different stages. In the first stage, explosive detonation produces dynamic cracks. Simultaneously incident explosion stress waves propagate and interact with prefabricated vertical cracks. In the second stage, the reflected explosion stress waves interact with dynamic cracks. In the third stage, dynamic cracks connect with pre-existing cracks and release unloading stress waves. Considering both singular and non-singular stresses in the near-crack-tip region, three far-field-controlled constant stresses were adopted. The mixed mode stress intensity factor of dynamic cracks under the action of reflected stress waves was analyzed and calculated using the Newton-Raphson iteration method. The results indicate that the leading edge of the reflected pressure wave acts as a stretching wave and the trailing edge behaves as a compression wave. The tensile component of the reflected pressure wave applies tensile stress to the crack tip, increasing the dynamic stress intensity factor KⅠ and promoting crack propagation. On the contrary, the compressive component of the reflected pressure wave applies compressive stress to the crack tip, resulting in a decrease in the dynamic stress intensity factor KⅠ and suppressing crack propagation. Reflected shear waves can cause unstable crack propagation. It causes changes in the direction and velocity of crack propagation, resulting in a wavy crack trajectory. After the penetration of dynamic cracks and prefabricated cracks, the elastic energy stored near the crack tip is rapidly released to generate unloading waves. Due to the action of the unloading wave, stress is concentrated at the tip of the pre-existing crack, causing the formation of a secondary crack at the tip of the pre-existing crack.
The influence of reflected explosion stress waves on dynamic crack propagation behavior , as well as the connection between dynamic cracks and pre-existing cracks, was studied using dynamic photoelastic experiments. A high-speed camera was used to capture the full field photoelastic isochromatic fringe pattern of horizontally expanding explosive cracks. The explosive crack is a directional crack generated by detonating explosives in a blast hole containing a horizontal V-shaped groove. The propagation process of explosive cracks can be divided into three different stages. In the first stage, explosive detonation produces dynamic cracks. Simultaneously incident explosion stress waves propagate and interact with prefabricated vertical cracks. In the second stage, the reflected explosion stress waves interact with dynamic cracks. In the third stage, dynamic cracks connect with pre-existing cracks and release unloading stress waves. Considering both singular and non-singular stresses in the near-crack-tip region, three far-field-controlled constant stresses were adopted. The mixed mode stress intensity factor of dynamic cracks under the action of reflected stress waves was analyzed and calculated using the Newton-Raphson iteration method. The results indicate that the leading edge of the reflected pressure wave acts as a stretching wave and the trailing edge behaves as a compression wave. The tensile component of the reflected pressure wave applies tensile stress to the crack tip, increasing the dynamic stress intensity factor KⅠ and promoting crack propagation. On the contrary, the compressive component of the reflected pressure wave applies compressive stress to the crack tip, resulting in a decrease in the dynamic stress intensity factor KⅠ and suppressing crack propagation. Reflected shear waves can cause unstable crack propagation. It causes changes in the direction and velocity of crack propagation, resulting in a wavy crack trajectory. After the penetration of dynamic cracks and prefabricated cracks, the elastic energy stored near the crack tip is rapidly released to generate unloading waves. Due to the action of the unloading wave, stress is concentrated at the tip of the pre-existing crack, causing the formation of a secondary crack at the tip of the pre-existing crack.
, Available online , doi: 10.11883/bzycj-2024-0466
Abstract:
The gradient stresses in the surrounding rock caused by deep excavation and the naturally occurring slow-dipping hard structural planes of the rock are critical factors influencing the characteristics of rockburst.Through triaxial loading-unidirectional unloading tests conducted on large-scale (400 mm×600 mm×1 000 mm) artificial rock specimens containing prefabricated hard slow-dipping structural planes using a gas-liquid composite loading rockburst simulation system, this study systematically investigated rockburst evolution mechanisms and mechanisms of damage. A multi-modal monitoring approach incorporating digital image correlation (DIC), acoustic emission (AE) detection, infrared thermography, and high-speed photography was employed to capture critical parameters including energy released patterns, surface infrared radiation characteristics, DIC strain field evolution, and crack propagation dynamics during rockburst development. The results of the study show that the presence of the slow-dipping structural plane has a controlling effect on the damage pattern of the specimen,greatly constrains the boundaries and morphology of rockburst craters, and accelerates the occurrence of rockburst. It is verified that the location of rockbursts in the specimens is mainly in the area between the structural planes of the specimens. The infrared radiation values and DIC strain fields in this area are much higher than those in the rest of the unloading surface before the damage. As the angle of the slow-dipping structural plane increases, the peak and cumulative acoustic emission energy of the specimen increases, the proportion of shear damage to total damage produced increaces, intensity of rockburst spawned increaces. The research results can provide an important reference for the prevention, control and treatment of disasters in deep-buried high-stress underground engineering.
The gradient stresses in the surrounding rock caused by deep excavation and the naturally occurring slow-dipping hard structural planes of the rock are critical factors influencing the characteristics of rockburst.Through triaxial loading-unidirectional unloading tests conducted on large-scale (400 mm×600 mm×1 000 mm) artificial rock specimens containing prefabricated hard slow-dipping structural planes using a gas-liquid composite loading rockburst simulation system, this study systematically investigated rockburst evolution mechanisms and mechanisms of damage. A multi-modal monitoring approach incorporating digital image correlation (DIC), acoustic emission (AE) detection, infrared thermography, and high-speed photography was employed to capture critical parameters including energy released patterns, surface infrared radiation characteristics, DIC strain field evolution, and crack propagation dynamics during rockburst development. The results of the study show that the presence of the slow-dipping structural plane has a controlling effect on the damage pattern of the specimen,greatly constrains the boundaries and morphology of rockburst craters, and accelerates the occurrence of rockburst. It is verified that the location of rockbursts in the specimens is mainly in the area between the structural planes of the specimens. The infrared radiation values and DIC strain fields in this area are much higher than those in the rest of the unloading surface before the damage. As the angle of the slow-dipping structural plane increases, the peak and cumulative acoustic emission energy of the specimen increases, the proportion of shear damage to total damage produced increaces, intensity of rockburst spawned increaces. The research results can provide an important reference for the prevention, control and treatment of disasters in deep-buried high-stress underground engineering.
, Available online , doi: 10.11883/bzycj-2024-0363
Abstract:
The hose-drogue aerial refueling process involves the complex coupling of aerodynamic force, fuel flow, and flexible structure deformation. Solving these interactions requires advanced simulation techniques and significant computational resources, which posed challenges to the accuracy and safety of practical implementations. A novel fluid-solid coupling model and methodology integrating aerodynamic loads, wake vortex effects, hose flexibility, airflow and internal fuel flow were developed to analyze structural deformation of hose-drogue assembly during docking and fuel transfer phases, overcoming limitations of traditional kinetic equation modeling. The aerodynamic forces of the paradrogue were obtained by performing separate CFD modeling on the paradrogue and conducting steady-state calculations. Meanwhile, the stabilizing moment of the paradrogue was equivalently converted into the lateral and rotational boundary condition at the center point of the paradrogue. Subsequently, based on the Hallock-Burnham model, the analytical expressions of the aerodynamic loads on the hose-drogue assembly under the action of the wake vortex alone were derived, and the aerodynamic loads were applied to hose-drogue assembly by ABAQUS subroutine. With the proposed model, the multi-stage operational processes of hose-drogue aerial refueling including steady-state, docking-state and refueling-state were calculated. Fluid-solid coupling simulations, which were conducted through co-simulation, demonstrated excellent agreement with experimental data, particularly under the steady-state. Furthermore, the influence of fuel flow characteristics, docking parameters and flight parameters were systematically identified. The results show that the matching relationship between the docking speed and retracting acceleration is the main influencing factor of whiplash load, and the retracting acceleration is positively correlated with the magnitude of the optimally matched docking velocity. In addition, the flight parameters are the secondary influencing factors. When the fuel flow is not considered, it is established at each altitude that the higher the flight speed, the lower the whiplash load. Fuel flow dynamics acts as a disturbing factor that partially perturbs the established relationship between whiplash loads and key operational parameters. However, these disturbances do not fundamentally alter the overall trend, and therefore, analyses under specific conditions are imperative to account for the effects of the fuel flow in different situations.
The hose-drogue aerial refueling process involves the complex coupling of aerodynamic force, fuel flow, and flexible structure deformation. Solving these interactions requires advanced simulation techniques and significant computational resources, which posed challenges to the accuracy and safety of practical implementations. A novel fluid-solid coupling model and methodology integrating aerodynamic loads, wake vortex effects, hose flexibility, airflow and internal fuel flow were developed to analyze structural deformation of hose-drogue assembly during docking and fuel transfer phases, overcoming limitations of traditional kinetic equation modeling. The aerodynamic forces of the paradrogue were obtained by performing separate CFD modeling on the paradrogue and conducting steady-state calculations. Meanwhile, the stabilizing moment of the paradrogue was equivalently converted into the lateral and rotational boundary condition at the center point of the paradrogue. Subsequently, based on the Hallock-Burnham model, the analytical expressions of the aerodynamic loads on the hose-drogue assembly under the action of the wake vortex alone were derived, and the aerodynamic loads were applied to hose-drogue assembly by ABAQUS subroutine. With the proposed model, the multi-stage operational processes of hose-drogue aerial refueling including steady-state, docking-state and refueling-state were calculated. Fluid-solid coupling simulations, which were conducted through co-simulation, demonstrated excellent agreement with experimental data, particularly under the steady-state. Furthermore, the influence of fuel flow characteristics, docking parameters and flight parameters were systematically identified. The results show that the matching relationship between the docking speed and retracting acceleration is the main influencing factor of whiplash load, and the retracting acceleration is positively correlated with the magnitude of the optimally matched docking velocity. In addition, the flight parameters are the secondary influencing factors. When the fuel flow is not considered, it is established at each altitude that the higher the flight speed, the lower the whiplash load. Fuel flow dynamics acts as a disturbing factor that partially perturbs the established relationship between whiplash loads and key operational parameters. However, these disturbances do not fundamentally alter the overall trend, and therefore, analyses under specific conditions are imperative to account for the effects of the fuel flow in different situations.
, Available online , doi: 10.11883/bzycj-2024-0424
Abstract:
Propagation features of blast-induced stress waves undergo substantial alterations as they traverse heterogeneous interfaces. In rock engineering, the prevalence of discontinuous structural planes, such as joints and fissures, becomes increasingly pronounced with increasing burial depth. To gain a comprehensive insight into the dynamic response and damage mechanism, an explicit dynamics numerical method incorporating the ALE algorithm and fluid-solid coupling technology was adopted, which allows for precise simulation of the fracture process within jointed rock mass under the combined effects of confining pressure and blasting load. Based on the time-domain recurrence theory, the transmission and reflection coefficients of the stress wave were calculated, and the propagation process and features of the stress wave were then analyzed by the explosion photoelasticity test using an epoxy resin plate. Additionally, the Riedel-Hiermaier-Thoma (RHT) damage model was used to investigate the influence of different joint angles and confining pressures on cracking behavior. Furthermore, the cracks were quantitatively assessed using the FracPaQ program. Finally, the damage mechanism of the jointed rock mass was revealed by analyzing the principal stress distribution and displacement change as well as the dynamic stress intensity factors (DSIFs) of the joint tip. The results show that both the joint and the anisotropic pressure have a guiding effect on crack extension, and the effect of the anisotropic pressure will be weakened by the presence of the joint. For the anisotropic pressure condition, the stress wave transmission and reflection coefficients tended to decrease and increase, respectively, with increasing pressure in the horizontal direction. From the change rule of normal and tangential displacement on both sides of the joint surface, it is found that shear stress is the main cause of tip-wing crack expansion. An analysis of the DSIFs reveals that tensile cracks predominantly contribute to damage at the joint tip during the initial phase of blasting, with shear cracks becoming the dominant form of damage in the later stages.
Propagation features of blast-induced stress waves undergo substantial alterations as they traverse heterogeneous interfaces. In rock engineering, the prevalence of discontinuous structural planes, such as joints and fissures, becomes increasingly pronounced with increasing burial depth. To gain a comprehensive insight into the dynamic response and damage mechanism, an explicit dynamics numerical method incorporating the ALE algorithm and fluid-solid coupling technology was adopted, which allows for precise simulation of the fracture process within jointed rock mass under the combined effects of confining pressure and blasting load. Based on the time-domain recurrence theory, the transmission and reflection coefficients of the stress wave were calculated, and the propagation process and features of the stress wave were then analyzed by the explosion photoelasticity test using an epoxy resin plate. Additionally, the Riedel-Hiermaier-Thoma (RHT) damage model was used to investigate the influence of different joint angles and confining pressures on cracking behavior. Furthermore, the cracks were quantitatively assessed using the FracPaQ program. Finally, the damage mechanism of the jointed rock mass was revealed by analyzing the principal stress distribution and displacement change as well as the dynamic stress intensity factors (DSIFs) of the joint tip. The results show that both the joint and the anisotropic pressure have a guiding effect on crack extension, and the effect of the anisotropic pressure will be weakened by the presence of the joint. For the anisotropic pressure condition, the stress wave transmission and reflection coefficients tended to decrease and increase, respectively, with increasing pressure in the horizontal direction. From the change rule of normal and tangential displacement on both sides of the joint surface, it is found that shear stress is the main cause of tip-wing crack expansion. An analysis of the DSIFs reveals that tensile cracks predominantly contribute to damage at the joint tip during the initial phase of blasting, with shear cracks becoming the dominant form of damage in the later stages.
, Available online , doi: 10.11883/bzycj-2024-0395
Abstract:
The viscous characteristics of fault granular interlayers have a significant impact on the dynamic mechanical behavior of faults. The problem of determining the viscosity of fault granular interlayers at different slip velocities has not yet been solved. This article conducts theoretical research on this issue. Firstly, the Maxwell relaxation model was used to study the evolution of force chains for slow shearing of granular gouge, and the dependence of force chain length on shear strain rate, effective extension speed of shear bands, and strength of granular medium was derived. Further the relaxation time of the shear band, the expression of the viscosity coefficient of the granular medium, the conditions for the transformation of solid-liquid mechanical behavior of the granular medium were established. The comparison with existing experimental data has verified the validity of this model. For high-speed slip shear, the motion of granular medium exhibits turbulent characteristics. Statistical physics was used to describe the interaction between granular particles, and it is obtained that the viscosity coefficient is inversely proportional to the shear rate at high slip rate. The research results have fundamental significance for understanding the viscous and other physico-mechanical properties of granular gouge in faults.
The viscous characteristics of fault granular interlayers have a significant impact on the dynamic mechanical behavior of faults. The problem of determining the viscosity of fault granular interlayers at different slip velocities has not yet been solved. This article conducts theoretical research on this issue. Firstly, the Maxwell relaxation model was used to study the evolution of force chains for slow shearing of granular gouge, and the dependence of force chain length on shear strain rate, effective extension speed of shear bands, and strength of granular medium was derived. Further the relaxation time of the shear band, the expression of the viscosity coefficient of the granular medium, the conditions for the transformation of solid-liquid mechanical behavior of the granular medium were established. The comparison with existing experimental data has verified the validity of this model. For high-speed slip shear, the motion of granular medium exhibits turbulent characteristics. Statistical physics was used to describe the interaction between granular particles, and it is obtained that the viscosity coefficient is inversely proportional to the shear rate at high slip rate. The research results have fundamental significance for understanding the viscous and other physico-mechanical properties of granular gouge in faults.
, Available online , doi: 10.11883/bzycj-2024-0448
Abstract:
To enhance the evaluation and prediction for service performance of hot-end components in equipment under the dynamic loads, a comprehensive study was conducted on Ni-based single crystal superalloys with diverse microstructures. This study involved a series of split Hopkinson tensile bar (SHTB) tests and related scanning electron microscopy (SEM) characterization. The influences of various factors, including the volume fraction of precipitation particles, phase coarsening, loading angle and strain rate, etc., on the dynamic tensile properties of superalloys were systematically investigated. Moreover, the relationships between these factors and the fracture morphology of alloys were thoroughly discussed. The results indicated that the microstructural features and strain rate have significant effect on the dynamic tensile properties of alloys, leading to a complex anisotropic characteristic occur in their dynamic tensile behaviors after phase coarsening. In general, the yielding strength displays a positive relationship with the tensile strength. As the volume fraction of precipitation particles or the strain rate increases, the alloy specimen gradually exhibits brittle fracture characteristics, with an increase in strength and a decrease in elongation. Besides, phase coarsening derived from the aging treatment significantly weakens the strength of alloys while enhancing their elongation, i.e., the specimens progressively show mixed fracture characteristics after phase coarsening, and both yielding strength and tensile ultimate strength gradually decrease while the elongation increases with the degree of phase coarsening. Furthermore, the strength and elongation of alloys at the loading angle of 55° are lower than those at the loading angle of 0°. Comparatively, for alloys with high volume fraction of precipitation particles and high degree of phase coarsening, the elongation achieves the maximum value at the loading angle of 55°. The corresponding variation characteristics are closely related to the fibrous zone and the cleavage plane on the fracture surface. Meanwhile, the variations in microstructure of materials and loading conditions affect the microcrack nucleation and fracture mode within the specimen, leading to various dynamic tensile properties in Ni-based single crystal superalloys. The present research and related results provide theoretical guidance and experimental data support for improving the mechanical performance of Ni-based single crystal superalloys and optimizing the design of hot-end components.
To enhance the evaluation and prediction for service performance of hot-end components in equipment under the dynamic loads, a comprehensive study was conducted on Ni-based single crystal superalloys with diverse microstructures. This study involved a series of split Hopkinson tensile bar (SHTB) tests and related scanning electron microscopy (SEM) characterization. The influences of various factors, including the volume fraction of precipitation particles, phase coarsening, loading angle and strain rate, etc., on the dynamic tensile properties of superalloys were systematically investigated. Moreover, the relationships between these factors and the fracture morphology of alloys were thoroughly discussed. The results indicated that the microstructural features and strain rate have significant effect on the dynamic tensile properties of alloys, leading to a complex anisotropic characteristic occur in their dynamic tensile behaviors after phase coarsening. In general, the yielding strength displays a positive relationship with the tensile strength. As the volume fraction of precipitation particles or the strain rate increases, the alloy specimen gradually exhibits brittle fracture characteristics, with an increase in strength and a decrease in elongation. Besides, phase coarsening derived from the aging treatment significantly weakens the strength of alloys while enhancing their elongation, i.e., the specimens progressively show mixed fracture characteristics after phase coarsening, and both yielding strength and tensile ultimate strength gradually decrease while the elongation increases with the degree of phase coarsening. Furthermore, the strength and elongation of alloys at the loading angle of 55° are lower than those at the loading angle of 0°. Comparatively, for alloys with high volume fraction of precipitation particles and high degree of phase coarsening, the elongation achieves the maximum value at the loading angle of 55°. The corresponding variation characteristics are closely related to the fibrous zone and the cleavage plane on the fracture surface. Meanwhile, the variations in microstructure of materials and loading conditions affect the microcrack nucleation and fracture mode within the specimen, leading to various dynamic tensile properties in Ni-based single crystal superalloys. The present research and related results provide theoretical guidance and experimental data support for improving the mechanical performance of Ni-based single crystal superalloys and optimizing the design of hot-end components.
, Available online , doi: 10.11883/bzycj-2024-0381
Abstract:
To investigate the propagation process of shock waves within a channel under different explosive yields and charge positions, this study established an experimental channel designed for individual soldier transit. Through experiments and simulations, it is found that the quantity and position of the charge affect the time history of overpressure and shock wave parameters. Within the tunnel, the propagation velocity and overpressure peak of the shock wave decreased with increasing of distance, while the duration and impulse of positive overpressure continuously extend and increase. When the charge equivalent increases, all shock wave parameters are enhanced, though the influence on the rate of overpressure peak attenuation is minimal. As the distance between the explosion center and the interior of the tunnel increases, all parameters decline. Both experiments and simulations reveal a unique change in the time history of overpressure and shock wave parameters near the 9 m measurement point inside the tunnel. By analyzing pressure contour maps and overpressure time history, it is discovered that wavefront movement is the primary cause. Based on the fundamental shock wave theory, a higher overpressure peak of shock wave results in faster wavefront motion. Fro m the 3 m to 7 m section inside the entrance, the leading wavefront overpressure continuously attenuates with increasing distance, and its motion speed significantly decreases. However, the overpressure values of subsequent reflected waves attenuate more slowly or even exceed those of the leading wavefront due to continuous collision and superposition. Between the 7 m and 9 m sections inside the entrance, the reflected waves formed by later superposition catch up with and overlap the leading wavefront, resulting in an increase in the first peak value with increasing distance. This process is also clearly understood through the simulated overpressure contour map. Based on the experimental and numerical simulation results, a predictive model for shock wave overpressure within the channel, which has practical engineering reference significance, has been developed.
To investigate the propagation process of shock waves within a channel under different explosive yields and charge positions, this study established an experimental channel designed for individual soldier transit. Through experiments and simulations, it is found that the quantity and position of the charge affect the time history of overpressure and shock wave parameters. Within the tunnel, the propagation velocity and overpressure peak of the shock wave decreased with increasing of distance, while the duration and impulse of positive overpressure continuously extend and increase. When the charge equivalent increases, all shock wave parameters are enhanced, though the influence on the rate of overpressure peak attenuation is minimal. As the distance between the explosion center and the interior of the tunnel increases, all parameters decline. Both experiments and simulations reveal a unique change in the time history of overpressure and shock wave parameters near the 9 m measurement point inside the tunnel. By analyzing pressure contour maps and overpressure time history, it is discovered that wavefront movement is the primary cause. Based on the fundamental shock wave theory, a higher overpressure peak of shock wave results in faster wavefront motion. Fro m the 3 m to 7 m section inside the entrance, the leading wavefront overpressure continuously attenuates with increasing distance, and its motion speed significantly decreases. However, the overpressure values of subsequent reflected waves attenuate more slowly or even exceed those of the leading wavefront due to continuous collision and superposition. Between the 7 m and 9 m sections inside the entrance, the reflected waves formed by later superposition catch up with and overlap the leading wavefront, resulting in an increase in the first peak value with increasing distance. This process is also clearly understood through the simulated overpressure contour map. Based on the experimental and numerical simulation results, a predictive model for shock wave overpressure within the channel, which has practical engineering reference significance, has been developed.
, Available online , doi: 10.11883/bzycj-2024-0405
Abstract:
To investigate the effect of high temperature on the energy characteristics of marble, ANSYS/LS-DYNA was used to carry out dynamic compression simulation tests on marble with six temperature gradients at five impact velocities to analyze the mechanical properties of marble under high-temperature dynamic loading and the temperature effect on energy evolution, and to explore the energy criterion for strength failure of high-temperature marble from the perspective of energy dissipation. The results show that the Holmquist-Johnson-Cook (HJC) constitutive model can reasonably and effectively simulate the dynamic damage process of marble under different temperatures. With the increase in temperature, the dynamic peak strength and dynamic elastic modulus of marble exhibit a quadratic negative correlation with temperature, the dynamic peak strain exhibits a quadratic positive correlation with temperature, and the damage morphology is changed from X-type to conjugate shear damage. The increase in temperature reduces the energy storage capacity of the marble specimen to a certain extent, while the effect of high temperature on the energy dissipation capacity of marble is transformed from a facilitating effect to an inhibiting effect with 600 ℃ as the cut-off point. When the temperature reaches 600 ℃, the peak strength is significantly reduced, the ductility of the marble increases, crushing damage is presented, and the dissipated strain energy reaches the maximum value. 600 ℃ can be used as the threshold temperature for the brittle-delayed transformation of the marble. Based on the characteristics of the energy evolution process, the point of a steep increase in dissipated strain energy is regarded as a precursor information point of the precursor of overall instability and damage of marble. The inflection point at which the growth rate of the elastic energy consumption ratio first appears is defined according to the curve of the stress-elastic energy consumption ratio-strain relationship as the energy criterion of the strength failure of marble.
To investigate the effect of high temperature on the energy characteristics of marble, ANSYS/LS-DYNA was used to carry out dynamic compression simulation tests on marble with six temperature gradients at five impact velocities to analyze the mechanical properties of marble under high-temperature dynamic loading and the temperature effect on energy evolution, and to explore the energy criterion for strength failure of high-temperature marble from the perspective of energy dissipation. The results show that the Holmquist-Johnson-Cook (HJC) constitutive model can reasonably and effectively simulate the dynamic damage process of marble under different temperatures. With the increase in temperature, the dynamic peak strength and dynamic elastic modulus of marble exhibit a quadratic negative correlation with temperature, the dynamic peak strain exhibits a quadratic positive correlation with temperature, and the damage morphology is changed from X-type to conjugate shear damage. The increase in temperature reduces the energy storage capacity of the marble specimen to a certain extent, while the effect of high temperature on the energy dissipation capacity of marble is transformed from a facilitating effect to an inhibiting effect with 600 ℃ as the cut-off point. When the temperature reaches 600 ℃, the peak strength is significantly reduced, the ductility of the marble increases, crushing damage is presented, and the dissipated strain energy reaches the maximum value. 600 ℃ can be used as the threshold temperature for the brittle-delayed transformation of the marble. Based on the characteristics of the energy evolution process, the point of a steep increase in dissipated strain energy is regarded as a precursor information point of the precursor of overall instability and damage of marble. The inflection point at which the growth rate of the elastic energy consumption ratio first appears is defined according to the curve of the stress-elastic energy consumption ratio-strain relationship as the energy criterion of the strength failure of marble.
, Available online , doi: 10.11883/bzycj-2024-0454
Abstract:
Impact damage and fatigue are emerging challenges in the defense industry and civil infrastructure. The more pronounced material size effect induced by advanced manufacturing processes makes mechanical analysis and life prediction in these contexts more complex. Currently, there is no convenient and effective method for predicting and designing the cross-scale impact damage and fatigue performance of metal materials. This research is based on the metallic plasticity mechanisms in the impact damage and fatigue processes, investigating the material performance under the influence of the material size effect during the impact damage process. A non-local, cross-scale impact and damage constitutive theory for metallic materials was developed, and an impact damage and fatigue simulation method for advanced manufactured metals was established. This method used the conventional theory of mechanism-based strain gradient (CMSG) to describe the size effect and was built on the Johnson-Cook impact dynamics model and Lemaitre impact damage model to describe cross-scale impact dynamics and damage evolution. This approach could be conveniently implemented in finite element analysis with the VUMAT and relevant subroutines. The present work established uniaxial and U-notch bending finite element models and verified the influence of work hardening, strain rate hardening, size effect, and damage effect on static and impact dynamic response of metals. Simulation results indicated the material behavior corresponds to the material characteristic and constitutive design. The distribution and evolution of the stress, strain, strain gradient, and damage before and after material failure are also discussed. The results show that the inhomogeneous deformation caused by advanced manufacturing processes leads to higher strain gradients, which further increase the flow stress through work hardening and strain rate hardening effects and strengthen the material. However, this also causes the material to enter the damage stage earlier, leading to reduced impact and fatigue-bearing capacity or premature failure. These findings are consistent with the inherent trade-off between strength and toughness of metallic materials.
Impact damage and fatigue are emerging challenges in the defense industry and civil infrastructure. The more pronounced material size effect induced by advanced manufacturing processes makes mechanical analysis and life prediction in these contexts more complex. Currently, there is no convenient and effective method for predicting and designing the cross-scale impact damage and fatigue performance of metal materials. This research is based on the metallic plasticity mechanisms in the impact damage and fatigue processes, investigating the material performance under the influence of the material size effect during the impact damage process. A non-local, cross-scale impact and damage constitutive theory for metallic materials was developed, and an impact damage and fatigue simulation method for advanced manufactured metals was established. This method used the conventional theory of mechanism-based strain gradient (CMSG) to describe the size effect and was built on the Johnson-Cook impact dynamics model and Lemaitre impact damage model to describe cross-scale impact dynamics and damage evolution. This approach could be conveniently implemented in finite element analysis with the VUMAT and relevant subroutines. The present work established uniaxial and U-notch bending finite element models and verified the influence of work hardening, strain rate hardening, size effect, and damage effect on static and impact dynamic response of metals. Simulation results indicated the material behavior corresponds to the material characteristic and constitutive design. The distribution and evolution of the stress, strain, strain gradient, and damage before and after material failure are also discussed. The results show that the inhomogeneous deformation caused by advanced manufacturing processes leads to higher strain gradients, which further increase the flow stress through work hardening and strain rate hardening effects and strengthen the material. However, this also causes the material to enter the damage stage earlier, leading to reduced impact and fatigue-bearing capacity or premature failure. These findings are consistent with the inherent trade-off between strength and toughness of metallic materials.
, Available online , doi: 10.11883/bzycj-2024-0346
Abstract:
To investigate the fracture and permeability characteristics of sandstone-type uranium ore under cyclic impact, a Hopkinson bar experimental system was used to load sandstone samples by cyclic impacts. The dynamic mechanical properties of the sandstone samples were measured after 3, 6 and 9 impacts. Subsequently, the impacted sandstone samples were subjected to CT scanning, and the crack images obtained from the scans were reconstructed in three-dimensions to measure the changes in pore and fracture parameters. The internal structures and damages in the impacted samples were then analyzed. Furthermore, a microscopic seepage simulation was performed to analyze the permeability of the samples, revealing the changes in the simulated permeability. Finally, permeability tests were conducted on the impacted samples to measure the variations in the actual permeability. Results show that cyclic impacts cause cumulative damage in the specimens, reducing their dynamic mechanical properties. As the number of impacts increases, energy in the specimens accumulates and releases cyclically. This cyclic accumulation and release of energy lead to a process of crack "expansion, compaction, re-expansion, re-compaction". During the cyclic impact process, small and isolated cracks inside the specimen gradually develop into larger, interconnected fractures. Simultaneously, medium-sized cracks exhibit dual effects of faulting and connectivity, presenting nonlinear characteristics. Cyclic impacts induce more complex fractures in the specimens, leading to an increased number of fluid seepage pathways and a larger scale of seepage. When subjected to three cycles of impact, the sample forms a single crack, resulting in a permeability increase of 340.91%−380.00%. After six cycles of impact, the cracks begin to connect, leading to a permeability increase of1468.18 %−2893.33 %. With nine cycles of impact, a connected network of cracks forms, resulting in a permeability increase of 4718.18 %−9380.00 %. The cyclic impact significantly enhances the permeability of sandstone, with crack propagation and connectivity being the key driving factors for the increase in permeability.
To investigate the fracture and permeability characteristics of sandstone-type uranium ore under cyclic impact, a Hopkinson bar experimental system was used to load sandstone samples by cyclic impacts. The dynamic mechanical properties of the sandstone samples were measured after 3, 6 and 9 impacts. Subsequently, the impacted sandstone samples were subjected to CT scanning, and the crack images obtained from the scans were reconstructed in three-dimensions to measure the changes in pore and fracture parameters. The internal structures and damages in the impacted samples were then analyzed. Furthermore, a microscopic seepage simulation was performed to analyze the permeability of the samples, revealing the changes in the simulated permeability. Finally, permeability tests were conducted on the impacted samples to measure the variations in the actual permeability. Results show that cyclic impacts cause cumulative damage in the specimens, reducing their dynamic mechanical properties. As the number of impacts increases, energy in the specimens accumulates and releases cyclically. This cyclic accumulation and release of energy lead to a process of crack "expansion, compaction, re-expansion, re-compaction". During the cyclic impact process, small and isolated cracks inside the specimen gradually develop into larger, interconnected fractures. Simultaneously, medium-sized cracks exhibit dual effects of faulting and connectivity, presenting nonlinear characteristics. Cyclic impacts induce more complex fractures in the specimens, leading to an increased number of fluid seepage pathways and a larger scale of seepage. When subjected to three cycles of impact, the sample forms a single crack, resulting in a permeability increase of 340.91%−380.00%. After six cycles of impact, the cracks begin to connect, leading to a permeability increase of
, Available online , doi: 10.11883/bzycj-2024-0500
Abstract:
In order to study crashworthy performance and energy absorption characteristics of the aircraft fuselage substructure and carry out structural crashworthy design, a typical metal aircraft fuselage was taken as the research object in this paper. A typical fuselage substructure drop test was conducted. The energy-absorbing characteristics of the fuselage substructure were evaluated based on the experimental results and simulation analysis results. On this basis, the energy absorption design of fuselage substructure was carried out. The influence of the structural layout parameters of the new fuselage substructure on the crash response was studied through the simulation analysis. The structural deformation, the impact force-time curve, the acceleration response and the energy absorption of fuselage substructure with different layout parameters were compared. The research results show that in the crash process of the original structure, the main energy absorption modes include plastic deformation and fracture of the column, frame and beam connection area, bending deformation of cabin floor beams and failure of the connectors. Since all the columns bend and break in the area near the connection area, the other areas of the column are almost not involved in plastic deformation. The energy absorption of the column is limited. The new substructure proposed in this paper has new configuration and also make full use of advantages of metal plastic deformation. Compared with the original configuration, the deformation of new substructure proposed in this paper is more adequate while maintaining the same total mass of the fuselage structure. The peak load and acceleration at the early stage of the crash can be significantly reduced. The proportion of energy absorption by the frame and the energy-absorbing component has increased significantly. After optimization, the average overload of the new fuselage substructure decrease by 30.8% compared with the original configuration. The average acceleration of the two mass points on the cabin floor of the new fuselage substructure decrease by 25% and 37.6% respectively compared with the original configuration. The research results can provide a reference for the fuselage substructure crashworthy design.
In order to study crashworthy performance and energy absorption characteristics of the aircraft fuselage substructure and carry out structural crashworthy design, a typical metal aircraft fuselage was taken as the research object in this paper. A typical fuselage substructure drop test was conducted. The energy-absorbing characteristics of the fuselage substructure were evaluated based on the experimental results and simulation analysis results. On this basis, the energy absorption design of fuselage substructure was carried out. The influence of the structural layout parameters of the new fuselage substructure on the crash response was studied through the simulation analysis. The structural deformation, the impact force-time curve, the acceleration response and the energy absorption of fuselage substructure with different layout parameters were compared. The research results show that in the crash process of the original structure, the main energy absorption modes include plastic deformation and fracture of the column, frame and beam connection area, bending deformation of cabin floor beams and failure of the connectors. Since all the columns bend and break in the area near the connection area, the other areas of the column are almost not involved in plastic deformation. The energy absorption of the column is limited. The new substructure proposed in this paper has new configuration and also make full use of advantages of metal plastic deformation. Compared with the original configuration, the deformation of new substructure proposed in this paper is more adequate while maintaining the same total mass of the fuselage structure. The peak load and acceleration at the early stage of the crash can be significantly reduced. The proportion of energy absorption by the frame and the energy-absorbing component has increased significantly. After optimization, the average overload of the new fuselage substructure decrease by 30.8% compared with the original configuration. The average acceleration of the two mass points on the cabin floor of the new fuselage substructure decrease by 25% and 37.6% respectively compared with the original configuration. The research results can provide a reference for the fuselage substructure crashworthy design.
, Available online , doi: 10.11883/bzycj-2024-0513
Abstract:
Cortical bone, as a critical component of the human skeletal system, effectively disperses and absorbs external impact forces, protecting the internal medullary cavity, surrounding soft tissues, and organs from damage. To investigate the mechanical response of cortical bone under impact loading, quasi-static and dynamic compression experiments were conducted on porcine cortical bone at varying strain rates using a universal material testing machine and a Split Hopkinson Pressure Bar (SHPB) apparatus. The compression deformation characteristics of cortical bone were observed employing ultra-depth three-dimensional microscopy and Digital Image Correlation (DIC) techniques. A damage-integrated viscoelastic constitutive model was applied to fit the experimental data, and the constitutive parameters of the model were determined. The results demonstrate that the compression process of cortical bone is characterized by the initiation and propagation of microcracks, with its mechanical properties exhibiting significant strain-rate dependence. The elastic modulus, yield stress, and compressive strength increase markedly with higher strain rates. Under quasi-static loading, the stress-strain curve consists of distinct elastic and plastic deformation stages. In contrast, under high-strain-rate loading, the stress-strain response remains purely elastic at strains below 0.2%, but transitions into a highly nonlinear regime with increasing compression. Notably, no significant plastic deformation occurs under dynamic loading, revealing pronounced viscoelastic behavior. Comparison between the experimental data and theoretical curves from the constitutive model shows good agreement, with minimal deviations between predicted and measured values. The model accurately captures the compressive mechanical behavior of cortical bone across different strain rates, validating its reliability for simulating impact scenarios. These findings provide valuable theoretical insights for the treatment of impact-related injuries and the design of protective equipment. The strain-rate-dependent mechanical properties of cortical bone highlight the importance of considering dynamic loading conditions in biomechanical studies. This research contributes to a deeper understanding of bone fracture mechanisms under traumatic impacts and supports advancements in injury prevention strategies.
Cortical bone, as a critical component of the human skeletal system, effectively disperses and absorbs external impact forces, protecting the internal medullary cavity, surrounding soft tissues, and organs from damage. To investigate the mechanical response of cortical bone under impact loading, quasi-static and dynamic compression experiments were conducted on porcine cortical bone at varying strain rates using a universal material testing machine and a Split Hopkinson Pressure Bar (SHPB) apparatus. The compression deformation characteristics of cortical bone were observed employing ultra-depth three-dimensional microscopy and Digital Image Correlation (DIC) techniques. A damage-integrated viscoelastic constitutive model was applied to fit the experimental data, and the constitutive parameters of the model were determined. The results demonstrate that the compression process of cortical bone is characterized by the initiation and propagation of microcracks, with its mechanical properties exhibiting significant strain-rate dependence. The elastic modulus, yield stress, and compressive strength increase markedly with higher strain rates. Under quasi-static loading, the stress-strain curve consists of distinct elastic and plastic deformation stages. In contrast, under high-strain-rate loading, the stress-strain response remains purely elastic at strains below 0.2%, but transitions into a highly nonlinear regime with increasing compression. Notably, no significant plastic deformation occurs under dynamic loading, revealing pronounced viscoelastic behavior. Comparison between the experimental data and theoretical curves from the constitutive model shows good agreement, with minimal deviations between predicted and measured values. The model accurately captures the compressive mechanical behavior of cortical bone across different strain rates, validating its reliability for simulating impact scenarios. These findings provide valuable theoretical insights for the treatment of impact-related injuries and the design of protective equipment. The strain-rate-dependent mechanical properties of cortical bone highlight the importance of considering dynamic loading conditions in biomechanical studies. This research contributes to a deeper understanding of bone fracture mechanisms under traumatic impacts and supports advancements in injury prevention strategies.
, Available online , doi: 10.11883/bzycj-2024-0102
Abstract:
In order to reduce the great threat of gas explosion to coal mine operators and coal safety mining, the law of explosion overpressure and impact airflow velocity attenuation with the propagation distance of different volumes of gas-air mixed gas in roadway was deeply studied. Firstly, based on dimensional analysis, factors affecting the single-direction propagation attenuation of gas explosion overpressure in roadway were comprehensively considered, such as mixed gas energy, gas accumulation amount, measuring point distance and related parameters of roadway, and a dimensionless formula of single-direction propagation attenuation of gas explosion overpressure in roadway was obtained. Based on the regression analysis of the experimental data of gas explosion overpressure in large-size roadway, the mathematical model of unidirectional overpressure propagation attenuation in roadway was established, and the mathematical model of bidirectional overpressure propagation attenuation in roadway was established according to the law of energy similarity. According to the analysis process of influencing factors of single-direction propagation attenuation of gas explosion overpressure in roadway, a dimensionless formula of single-direction propagation attenuation of impact airflow velocity in roadway was obtained. Through regression analysis of experimental data of gas explosion impact airflow velocity in large-size roadway, a mathematical model of single-direction propagation attenuation of impact airflow velocity in roadway was established. According to the law of energy similarity, the mathematical model of the bidirectional propagation attenuation of the impact airflow velocity in the roadway was established. Secondly, according to the establishment process of the mathematical model of the unidirectional and bidirectional propagation attenuation of overpressure and impact airflow velocity in the roadway, the impact airflow velocity was included as one of the influencing factors in the consideration of the unidirectional propagation attenuation of gas explosion overpressure in the roadway in addition to the mixed gas energy, gas accumulation amount, measuring point distance and relevant parameters of the roadway. Based on the energy similarity law, the overpressure-airflow velocity relation of overpressure propagation attenuation in roadway was established. According to the establishment process of the overpressure-airflow velocity relation of the single and bidirectional propagation attenuation of gas explosion overpressure in roadway, the airflow velocity relation of the single and bidirectional propagation attenuation of the impact airflow velocity in roadway was established. Finally, the attenuation model and the mathematical relationship between overpressure and impact airflow velocity were verified. The results show that the energy of gas mixture, gas accumulation amount, the distance of measuring point, the hydraulic diameter and the cross-sectional area of roadway are the main factors affecting the attenuation of overpressure and impact airflow velocity. Both overpressure and impact airflow velocity are positively correlated with the amount of mixed gas accumulation. The greater the initial overpressure and impact airflow velocity, the faster the attenuation. The relative errors between the theoretical value and the test value of the attenuation model and the relative errors between the theoretical value and the test value of the relation are controlled at about 10%, and the overall consistency of the data is high, which verifies the reliability of the model and the mathematical relation, and can describe the law of gas explosion propagation more simply and intuitively, and realize the rapid calculation of overpressure and impact airflow velocity.
In order to reduce the great threat of gas explosion to coal mine operators and coal safety mining, the law of explosion overpressure and impact airflow velocity attenuation with the propagation distance of different volumes of gas-air mixed gas in roadway was deeply studied. Firstly, based on dimensional analysis, factors affecting the single-direction propagation attenuation of gas explosion overpressure in roadway were comprehensively considered, such as mixed gas energy, gas accumulation amount, measuring point distance and related parameters of roadway, and a dimensionless formula of single-direction propagation attenuation of gas explosion overpressure in roadway was obtained. Based on the regression analysis of the experimental data of gas explosion overpressure in large-size roadway, the mathematical model of unidirectional overpressure propagation attenuation in roadway was established, and the mathematical model of bidirectional overpressure propagation attenuation in roadway was established according to the law of energy similarity. According to the analysis process of influencing factors of single-direction propagation attenuation of gas explosion overpressure in roadway, a dimensionless formula of single-direction propagation attenuation of impact airflow velocity in roadway was obtained. Through regression analysis of experimental data of gas explosion impact airflow velocity in large-size roadway, a mathematical model of single-direction propagation attenuation of impact airflow velocity in roadway was established. According to the law of energy similarity, the mathematical model of the bidirectional propagation attenuation of the impact airflow velocity in the roadway was established. Secondly, according to the establishment process of the mathematical model of the unidirectional and bidirectional propagation attenuation of overpressure and impact airflow velocity in the roadway, the impact airflow velocity was included as one of the influencing factors in the consideration of the unidirectional propagation attenuation of gas explosion overpressure in the roadway in addition to the mixed gas energy, gas accumulation amount, measuring point distance and relevant parameters of the roadway. Based on the energy similarity law, the overpressure-airflow velocity relation of overpressure propagation attenuation in roadway was established. According to the establishment process of the overpressure-airflow velocity relation of the single and bidirectional propagation attenuation of gas explosion overpressure in roadway, the airflow velocity relation of the single and bidirectional propagation attenuation of the impact airflow velocity in roadway was established. Finally, the attenuation model and the mathematical relationship between overpressure and impact airflow velocity were verified. The results show that the energy of gas mixture, gas accumulation amount, the distance of measuring point, the hydraulic diameter and the cross-sectional area of roadway are the main factors affecting the attenuation of overpressure and impact airflow velocity. Both overpressure and impact airflow velocity are positively correlated with the amount of mixed gas accumulation. The greater the initial overpressure and impact airflow velocity, the faster the attenuation. The relative errors between the theoretical value and the test value of the attenuation model and the relative errors between the theoretical value and the test value of the relation are controlled at about 10%, and the overall consistency of the data is high, which verifies the reliability of the model and the mathematical relation, and can describe the law of gas explosion propagation more simply and intuitively, and realize the rapid calculation of overpressure and impact airflow velocity.
, Available online , doi: 10.11883/bzycj-2024-0414
Abstract:
To understand the interaction between joints and blasting stresses and optimizing blasting parameters in jointed rock, the impact of different joint inclinations on blasting fragmentation was studied through a combination of tests and numerical simulations. In this study, a group of concrete model specimens containing joints with different angles was used in the blasting tests to investigate the effect of joint inclination on blast fragmentation. During tests, detonators were placed in vertical boreholes in the specimens and detonated, while high-speed camera was used to capture the fragmentation process. The dynamic responses of joint surfaces at different time intervals after detonation was observed, and blasting fragmentation distribution was extracted using image processing techniques. The effect of joint inclination on blasting fragmentation was analyzed. The propagation of stress waves and the evolution of strain fields within the specimens was obtained in finite element numerical simulations by using LS-DYNA. Experimental and numerical results indicated that the joints have a significant influence on the distribution of blasting fragmentation and the propagation of stress waves. The impact of the joints on the blasting performance was mainly attributed to the reflection of blasting waves from the joints, which was related to the deformation characteristics of the joints. With the increase of joint inclination, the blasting fragmentation initially decreased followed by an increase. The effective stress and peak particle velocity transmission in the joints decreased overall with the increase of joint inclination, but showed a rebound between 45° and 60°. This suggests approximately 45° is the most favorable condition for rock fragmentation under blasting. Moreover, the results obtained from numerical crack network reconstruction and image processing revealed that there was an upsurge in the occurrence of vertical cracks in the specimen as the joint inclination increased, while a decline was observed in the presence of horizontal cracks.
To understand the interaction between joints and blasting stresses and optimizing blasting parameters in jointed rock, the impact of different joint inclinations on blasting fragmentation was studied through a combination of tests and numerical simulations. In this study, a group of concrete model specimens containing joints with different angles was used in the blasting tests to investigate the effect of joint inclination on blast fragmentation. During tests, detonators were placed in vertical boreholes in the specimens and detonated, while high-speed camera was used to capture the fragmentation process. The dynamic responses of joint surfaces at different time intervals after detonation was observed, and blasting fragmentation distribution was extracted using image processing techniques. The effect of joint inclination on blasting fragmentation was analyzed. The propagation of stress waves and the evolution of strain fields within the specimens was obtained in finite element numerical simulations by using LS-DYNA. Experimental and numerical results indicated that the joints have a significant influence on the distribution of blasting fragmentation and the propagation of stress waves. The impact of the joints on the blasting performance was mainly attributed to the reflection of blasting waves from the joints, which was related to the deformation characteristics of the joints. With the increase of joint inclination, the blasting fragmentation initially decreased followed by an increase. The effective stress and peak particle velocity transmission in the joints decreased overall with the increase of joint inclination, but showed a rebound between 45° and 60°. This suggests approximately 45° is the most favorable condition for rock fragmentation under blasting. Moreover, the results obtained from numerical crack network reconstruction and image processing revealed that there was an upsurge in the occurrence of vertical cracks in the specimen as the joint inclination increased, while a decline was observed in the presence of horizontal cracks.
, Available online , doi: 10.11883/bzycj-2024-0353
Abstract:
In practical engineering, rock frequently suffers from recurrent dynamic disturbances, posing serious threats to engineering safety. To investigate the dynamic mechanical behavior of jointed rock under cyclic dynamic disturbances, cyclic impact tests of single-jointed gabbro (SJG) were conducted using a split Hopkinson pressure bar (SHPB) test system. The stress equilibrium during the tests was verified using the three-wave method and the force balance coefficient method. The dynamic mechanical behavior of the specimens was comprehensively analyzed in terms of impact resistance, stress-strain relationships, energy and damage evolution, as well as dynamic failure mechanisms. The results show that single-jointed rock specimens can achieve stress equilibrium under cyclic impact conditions. The failure mode of the specimens under cyclic impacts is splitting, and the joint inclination angle significantly influences the impact resistance of the specimens. As the joint inclination angle increases, the impact resistance of the specimens also increases. During the cyclic impact process, strain rebound occurs in all specimens, and their mechanical properties do not monotonically degrade with an increasing number of impacts. The peak stress of the specimens generally exhibits a decreasing trend with the number of impacts. The cumulative damage coefficient, represented by dissipated energy, increases approximately linearly with the number of impacts, while the increase rate decreases with larger joint inclination angles. Under low-stress impact loading, the compressive-shear stress within single-jointed specimens is insufficient to generate shear cracks. The failure of specimens primarily results from the progressive propagation of tensile cracks induced by tensile stress, which eventually coalesce with the joint. The failure mechanism of multi-jointed rock masses resembles that of single-jointed rock masses. During cyclic impact loading, both compaction of micro-defects and initiation of micro-cracks at joints occur simultaneously. However, the impact resistance of multi-jointed specimens depends on whether the cracks can interconnect the joints. For intact rock specimens, the failure process initially involves compaction of micro-defects, followed by probabilistic activation of micro-cracks, ultimately leading to specimen failure.
In practical engineering, rock frequently suffers from recurrent dynamic disturbances, posing serious threats to engineering safety. To investigate the dynamic mechanical behavior of jointed rock under cyclic dynamic disturbances, cyclic impact tests of single-jointed gabbro (SJG) were conducted using a split Hopkinson pressure bar (SHPB) test system. The stress equilibrium during the tests was verified using the three-wave method and the force balance coefficient method. The dynamic mechanical behavior of the specimens was comprehensively analyzed in terms of impact resistance, stress-strain relationships, energy and damage evolution, as well as dynamic failure mechanisms. The results show that single-jointed rock specimens can achieve stress equilibrium under cyclic impact conditions. The failure mode of the specimens under cyclic impacts is splitting, and the joint inclination angle significantly influences the impact resistance of the specimens. As the joint inclination angle increases, the impact resistance of the specimens also increases. During the cyclic impact process, strain rebound occurs in all specimens, and their mechanical properties do not monotonically degrade with an increasing number of impacts. The peak stress of the specimens generally exhibits a decreasing trend with the number of impacts. The cumulative damage coefficient, represented by dissipated energy, increases approximately linearly with the number of impacts, while the increase rate decreases with larger joint inclination angles. Under low-stress impact loading, the compressive-shear stress within single-jointed specimens is insufficient to generate shear cracks. The failure of specimens primarily results from the progressive propagation of tensile cracks induced by tensile stress, which eventually coalesce with the joint. The failure mechanism of multi-jointed rock masses resembles that of single-jointed rock masses. During cyclic impact loading, both compaction of micro-defects and initiation of micro-cracks at joints occur simultaneously. However, the impact resistance of multi-jointed specimens depends on whether the cracks can interconnect the joints. For intact rock specimens, the failure process initially involves compaction of micro-defects, followed by probabilistic activation of micro-cracks, ultimately leading to specimen failure.
, Available online , doi: 10.11883/bzycj-2024-0283
Abstract:
Steel-concrete-steel composite (SCS) wall has been applied in high-rise buildings and nuclear power plants. Its performance under accidental and extreme loads during the whole life cycle deserves attention. Considering that fires and explosions often occur simultaneously, and that the mechanical properties of steel and concrete are deteriorated significantly at high temperatures, this leads to serious degradation of blast resistance of structural members. In this context, a total of 120 finite element (FE) models of SCS walls under combined fire and explosion were established using ABAQUS software. First, the FE models were verified based on existing fire resistance tests and explosion tests at room temperature on SCS walls. Then, the blast resistance mechanism of SCS walls was analyzed, and the influences of key parameters, including fire duration, explosion charge, steel plate ratio, material strength, tie bars spacing and axial compression ratio, on the explosion resistance were investigated. Finally, based on the single-degree of freedom method, the formulas were proposed to predict the maximum deformation of SCS walls under combined fire exposure and explosion. The results show that SCS walls primarily exhibit overall bending failure under coupled fire exposure and explosion. With the increase of fire duration, the contribution of the steel plate on the fire-exposed side to the energy dissipation decreases, and the plastic deformation of the steel plate on the non-fire-exposed side gradually becomes the main energy dissipation component. Fire duration, explosion charge and steel strength significantly affect the blast resistance of SCS walls under fire conditions. When exposed to fire for 90 minutes, the maximum mid-span deformation decreases by approximately 22%, as the steel yield strength increases from 235MPa to 460MPa. However, the influence of the concrete strength is minor. The maximum deformation of SCS walls can be reasonably predicted by the proposed formulas based on the single-degree of freedom method under coupled fire exposure and explosion.
Steel-concrete-steel composite (SCS) wall has been applied in high-rise buildings and nuclear power plants. Its performance under accidental and extreme loads during the whole life cycle deserves attention. Considering that fires and explosions often occur simultaneously, and that the mechanical properties of steel and concrete are deteriorated significantly at high temperatures, this leads to serious degradation of blast resistance of structural members. In this context, a total of 120 finite element (FE) models of SCS walls under combined fire and explosion were established using ABAQUS software. First, the FE models were verified based on existing fire resistance tests and explosion tests at room temperature on SCS walls. Then, the blast resistance mechanism of SCS walls was analyzed, and the influences of key parameters, including fire duration, explosion charge, steel plate ratio, material strength, tie bars spacing and axial compression ratio, on the explosion resistance were investigated. Finally, based on the single-degree of freedom method, the formulas were proposed to predict the maximum deformation of SCS walls under combined fire exposure and explosion. The results show that SCS walls primarily exhibit overall bending failure under coupled fire exposure and explosion. With the increase of fire duration, the contribution of the steel plate on the fire-exposed side to the energy dissipation decreases, and the plastic deformation of the steel plate on the non-fire-exposed side gradually becomes the main energy dissipation component. Fire duration, explosion charge and steel strength significantly affect the blast resistance of SCS walls under fire conditions. When exposed to fire for 90 minutes, the maximum mid-span deformation decreases by approximately 22%, as the steel yield strength increases from 235MPa to 460MPa. However, the influence of the concrete strength is minor. The maximum deformation of SCS walls can be reasonably predicted by the proposed formulas based on the single-degree of freedom method under coupled fire exposure and explosion.
, Available online , doi: 10.11883/bzycj-2024-0399
Abstract:
As the global demand for resources continues to rise, the scale of deep underground engineering development expands, facing increasingly complex geological conditions and high-stress environments. This shift has made the study of the dynamic characteristics of deep rock masses with structural planes a hot and challenging research topic in recent years. Firstly, a systematic summary of the dynamic shear and tensile characteristics of structural planes was conducted, along with an in-depth analysis of the impact of various factors on their dynamic behavior. Additionally, the effect of structural plane effects on the dynamic properties of rock masses was explored, particularly regarding dynamic strength and deformation. Furthermore, the triggering mechanisms and prevention technologies for common deep dynamic disasters, such as rock bursts, large deformations, and dynamic pressure, have been reviewed, emphasizing the importance of establishing an effective theoretical and technical system. Finally, a forward-looking perspective on future research directions for the dynamic characteristics of deep rock masses with structural planes and disaster prevention technologies is offered, calling for the integration of emerging technologies and theoretical methods to enhance the depth and breadth of research, thereby promoting the safety and effectiveness in engineering practice.
As the global demand for resources continues to rise, the scale of deep underground engineering development expands, facing increasingly complex geological conditions and high-stress environments. This shift has made the study of the dynamic characteristics of deep rock masses with structural planes a hot and challenging research topic in recent years. Firstly, a systematic summary of the dynamic shear and tensile characteristics of structural planes was conducted, along with an in-depth analysis of the impact of various factors on their dynamic behavior. Additionally, the effect of structural plane effects on the dynamic properties of rock masses was explored, particularly regarding dynamic strength and deformation. Furthermore, the triggering mechanisms and prevention technologies for common deep dynamic disasters, such as rock bursts, large deformations, and dynamic pressure, have been reviewed, emphasizing the importance of establishing an effective theoretical and technical system. Finally, a forward-looking perspective on future research directions for the dynamic characteristics of deep rock masses with structural planes and disaster prevention technologies is offered, calling for the integration of emerging technologies and theoretical methods to enhance the depth and breadth of research, thereby promoting the safety and effectiveness in engineering practice.
, Available online , doi: 10.11883/bzycj-2024-0336
Abstract:
Based on continuum damage mechanics, a rock dynamic constitutive model with coupled elastic-plastic damage was established. This model took the unified strength theory as the yield criterion and introduces the dynamic tensile-compressive ratio to fully reflect the strain rate effect. The effective plastic strain and volumetric plastic strain were used to represent the compressive damage variable, and the effective plastic strain was used to represent the tensile damage variable, thereby reflecting the different damage evolution laws of rocks under tensile and compressive conditions. A piecewise function was adopted to describe the different plastic hardening behaviors of rocks under tensile and compressive conditions. The established constitutive model was numerically implemented based on Fortran language and the LS-DYNA user material customization interface (Umat). The established constitutive model is verified by three classical calculation examples, namely, the uniaxial and triaxial compression tests of rocks, the uniaxial tensile test of rocks, and the ballistic test of rocks. The results showed that this constitutive model can comprehensively describe the static and dynamic mechanical behaviors of rocks.
Based on continuum damage mechanics, a rock dynamic constitutive model with coupled elastic-plastic damage was established. This model took the unified strength theory as the yield criterion and introduces the dynamic tensile-compressive ratio to fully reflect the strain rate effect. The effective plastic strain and volumetric plastic strain were used to represent the compressive damage variable, and the effective plastic strain was used to represent the tensile damage variable, thereby reflecting the different damage evolution laws of rocks under tensile and compressive conditions. A piecewise function was adopted to describe the different plastic hardening behaviors of rocks under tensile and compressive conditions. The established constitutive model was numerically implemented based on Fortran language and the LS-DYNA user material customization interface (Umat). The established constitutive model is verified by three classical calculation examples, namely, the uniaxial and triaxial compression tests of rocks, the uniaxial tensile test of rocks, and the ballistic test of rocks. The results showed that this constitutive model can comprehensively describe the static and dynamic mechanical behaviors of rocks.
, Available online , doi: 10.11883/bzycj-2024-0335
Abstract:
In order to take into account the influence of the crack roughness, first of all, on basis of the calculation model for the rockmass macroscopic damage variable which can take into account the crack geometry parameter, strength parameter and deformation parameter, a calculation model for the rockmass macroscopic damage variable is proposed by introducing the JRC-JCS shear strength model for the rough crack established by Barton, which can consider the crack roughness. Secondly, the proposed calculation model is introduced into the uniaxial compressive dynamic damage model for the rock mass with the non-persistent crack, which both considers the coupling of the macroscopic and microscopic defects, and then a uniaxial compressive dynamic damage model for the rock mass with the non-persistent crack is established which can consider the crack roughness at the same time. Finally, the effect of crack roughness JRC and crack basic friction angle φb and crack length 2a on rockmass dynamic mechanical property is studied with the parametric sensitivity analysis. The result shows that the rockmass dynamic climax strength increases from 26.42 MPa to 27.28 and 28.37 MPa with JRC increasing from 0 to 10 and 20 respectively. The rockmass dynamic climax strength increases from 26.24 MPa to 27.28 and 28.80 MPa with φb increasing from 0° to 15° and 30° respectively. The rockmass dynamic climax strength decreases from 31.37 MPa to 27.28 and 23.90 MPa with 2a increasing from 1cm to 2 and 3cm respectively. At the same time, in order to describe the influence of the crack roughness more accurately, the crack fractal dimension is introduced into the dynamic damage model for the rock mass, which not only improves the calculation accuracy of the model, but also broadens its application range, which is more convenient for practical engineering application.
In order to take into account the influence of the crack roughness, first of all, on basis of the calculation model for the rockmass macroscopic damage variable which can take into account the crack geometry parameter, strength parameter and deformation parameter, a calculation model for the rockmass macroscopic damage variable is proposed by introducing the JRC-JCS shear strength model for the rough crack established by Barton, which can consider the crack roughness. Secondly, the proposed calculation model is introduced into the uniaxial compressive dynamic damage model for the rock mass with the non-persistent crack, which both considers the coupling of the macroscopic and microscopic defects, and then a uniaxial compressive dynamic damage model for the rock mass with the non-persistent crack is established which can consider the crack roughness at the same time. Finally, the effect of crack roughness JRC and crack basic friction angle φb and crack length 2a on rockmass dynamic mechanical property is studied with the parametric sensitivity analysis. The result shows that the rockmass dynamic climax strength increases from 26.42 MPa to 27.28 and 28.37 MPa with JRC increasing from 0 to 10 and 20 respectively. The rockmass dynamic climax strength increases from 26.24 MPa to 27.28 and 28.80 MPa with φb increasing from 0° to 15° and 30° respectively. The rockmass dynamic climax strength decreases from 31.37 MPa to 27.28 and 23.90 MPa with 2a increasing from 1cm to 2 and 3cm respectively. At the same time, in order to describe the influence of the crack roughness more accurately, the crack fractal dimension is introduced into the dynamic damage model for the rock mass, which not only improves the calculation accuracy of the model, but also broadens its application range, which is more convenient for practical engineering application.
, Available online , doi: 10.11883/bzycj-2024-0453
Abstract:
With the deterioration of the natural climate, hail impact has become a threat that cannot be ignored by civil aircraft. To study the hail impact damage characteristics of high-performance carbon fiber composites used for civil aircraft, we first investigated the impact force characteristics of ice spheres under high-speed impact through experiments, and the impact time history curves of ice spheres under different speeds were obtained using an air cannon test system. At the same time, to make the speed range of the ice sphere more extensive, some existing experiment data are introduced as a comparison to obtain the linear growth relationship between the peak impact force and the kinetic energy of the ice sphere. Subsequently, a single ice sphere impact test was conducted on the T800/3200 carbon fiber composite laminates. It was found that the concave of the front core damage area forms a 45° angle with the boundary of the target plate, which is related to the carbon fiber layup mode, and the damage degree depends on the initial speed of the ice sphere. To further quantify the relationship between the damage degree of the laminate and the kinetic energy of the ice sphere, ultrasonic C-scanning was used to obtain the damaged area of the target plate, and the damage percentage was extracted by software analysis. The results show that the percentage of internal interlayer delamination increases linearly with the kinetic energy of the ice sphere. After that, repeated impact tests of ice spheres were carried out on the target plate with the same thickness, and as expected, the macro damage degree increased with the number of impacts. Finally, the front and back surfaces of the composite laminates were completely delaminated, resulting in a large number of fibers being pulled out and displaying a penetrating through-thickness damage pattern. The deflection of the center point of the target plate was selected as the quantitative damage index, and according to the data analysis of the measured results, it was found that there is a quadratic relationship between the deflection of the center point of the carbon fiber plate and the accumulated kinetic energy of the ice sphere. The apex of the parabola can well reflect the accumulated kinetic energy required for the target plate penetration.
With the deterioration of the natural climate, hail impact has become a threat that cannot be ignored by civil aircraft. To study the hail impact damage characteristics of high-performance carbon fiber composites used for civil aircraft, we first investigated the impact force characteristics of ice spheres under high-speed impact through experiments, and the impact time history curves of ice spheres under different speeds were obtained using an air cannon test system. At the same time, to make the speed range of the ice sphere more extensive, some existing experiment data are introduced as a comparison to obtain the linear growth relationship between the peak impact force and the kinetic energy of the ice sphere. Subsequently, a single ice sphere impact test was conducted on the T800/3200 carbon fiber composite laminates. It was found that the concave of the front core damage area forms a 45° angle with the boundary of the target plate, which is related to the carbon fiber layup mode, and the damage degree depends on the initial speed of the ice sphere. To further quantify the relationship between the damage degree of the laminate and the kinetic energy of the ice sphere, ultrasonic C-scanning was used to obtain the damaged area of the target plate, and the damage percentage was extracted by software analysis. The results show that the percentage of internal interlayer delamination increases linearly with the kinetic energy of the ice sphere. After that, repeated impact tests of ice spheres were carried out on the target plate with the same thickness, and as expected, the macro damage degree increased with the number of impacts. Finally, the front and back surfaces of the composite laminates were completely delaminated, resulting in a large number of fibers being pulled out and displaying a penetrating through-thickness damage pattern. The deflection of the center point of the target plate was selected as the quantitative damage index, and according to the data analysis of the measured results, it was found that there is a quadratic relationship between the deflection of the center point of the carbon fiber plate and the accumulated kinetic energy of the ice sphere. The apex of the parabola can well reflect the accumulated kinetic energy required for the target plate penetration.
, Available online , doi: 10.11883/bzycj-2024-0294
Abstract:
To accurately predict the initial velocity distribution of cylindrical casing under central point detonation at one end with different length-diameter ratios (L/D), it studied the impact of L/D ratios on the initial velocity of fragments and the applicability of existing empirical models for the initial velocity of fragments founded on the numerical model of experimental verification. On this basis, a correction term related to L/D ratio, which was often influenced by the axial rarefaction waves, was added to the fragment initial velocity index model. By fitting the data obtained from numerical simulations, the function expression of the correction term was derived and the calculation model for the initial velocity distribution of cylindrical casing with L/D ratio≥1 was obtained. Finally, the applicability of the established fragment initial velocity calculation model was validated through experimental data and numerical simulations. The research results indicate that the initial velocity distribution of fragments under different L/D ratios exhibits a trend where the initial velocities are lower at both ends and higher in the middle. Additionally, as the L/D ratio raises, the initial velocity of the fragment also increases. When the L/D ratio reaches 5, the relative error between the maximum initial velocity of the fragments and the calculated result using the Gurney formula is only 1.99%. However, the existing models for calculating initial velocities of fragment display significant errors when predicting smaller L/D ratios in cylindrical casing. The average error between the formula calculation results and the experimental and numerical simulation results does not exceed 6%, indicating that the proposed model is reliable for predicting the initial velocity distribution of fragments under different L/D ratios.
To accurately predict the initial velocity distribution of cylindrical casing under central point detonation at one end with different length-diameter ratios (L/D), it studied the impact of L/D ratios on the initial velocity of fragments and the applicability of existing empirical models for the initial velocity of fragments founded on the numerical model of experimental verification. On this basis, a correction term related to L/D ratio, which was often influenced by the axial rarefaction waves, was added to the fragment initial velocity index model. By fitting the data obtained from numerical simulations, the function expression of the correction term was derived and the calculation model for the initial velocity distribution of cylindrical casing with L/D ratio≥1 was obtained. Finally, the applicability of the established fragment initial velocity calculation model was validated through experimental data and numerical simulations. The research results indicate that the initial velocity distribution of fragments under different L/D ratios exhibits a trend where the initial velocities are lower at both ends and higher in the middle. Additionally, as the L/D ratio raises, the initial velocity of the fragment also increases. When the L/D ratio reaches 5, the relative error between the maximum initial velocity of the fragments and the calculated result using the Gurney formula is only 1.99%. However, the existing models for calculating initial velocities of fragment display significant errors when predicting smaller L/D ratios in cylindrical casing. The average error between the formula calculation results and the experimental and numerical simulation results does not exceed 6%, indicating that the proposed model is reliable for predicting the initial velocity distribution of fragments under different L/D ratios.
, Available online , doi: 10.11883/bzycj-2024-0147
Abstract:
In order to improve the quantitative characterization of the penetration process of tungsten alloy projectile into the target, the numerical methods such as FEM (finite element method), SPG (smoothed particle Galerkin), SPH (smoothed particle hydrodynamics), and FE-SPH (finite element-smoothed particle hydrodynamics) adaptive simulation methods were employed to simulate the penetration of tungsten alloy projectiles into Q235A steel targets. Based on numerical simulations, a comparison was made of the advantages and disadvantages of the four numerical simulation methods for calculating the residual velocity of the projectile after penetrating the target, the perforation diameter of the target, and the distribution of secondary fragments by the projectile penetration. The results show that, for calculating the residual velocity of the projectile, FEM and FE-SPH adaptive methods strictly rely on the selection of failure criteria and corresponding parameters, as FEM employs an element erosion algorithm to model material failure, while SPG method, as it does not require adjusting the failure parameters in bond failure mode, can obtain relatively accurate calculations; for predicting perforation diameter, FEM and FE-SPH adaptive methods accurately represent material boundaries and perforation morphology, although the perforation diameter varies significantly under different failure criteria, while the SPG method can accurately predict the perforation diameter of target plates due to its insensitive to failure parameters; for analzing secondary fragments generation and distribution, both FE-SPH adaptive and SPH methods effectively characterize these phenomena, while the FE-SPH adaptive method provides detailed information on large fragments, it is less computationally efficient than the SPH method.
In order to improve the quantitative characterization of the penetration process of tungsten alloy projectile into the target, the numerical methods such as FEM (finite element method), SPG (smoothed particle Galerkin), SPH (smoothed particle hydrodynamics), and FE-SPH (finite element-smoothed particle hydrodynamics) adaptive simulation methods were employed to simulate the penetration of tungsten alloy projectiles into Q235A steel targets. Based on numerical simulations, a comparison was made of the advantages and disadvantages of the four numerical simulation methods for calculating the residual velocity of the projectile after penetrating the target, the perforation diameter of the target, and the distribution of secondary fragments by the projectile penetration. The results show that, for calculating the residual velocity of the projectile, FEM and FE-SPH adaptive methods strictly rely on the selection of failure criteria and corresponding parameters, as FEM employs an element erosion algorithm to model material failure, while SPG method, as it does not require adjusting the failure parameters in bond failure mode, can obtain relatively accurate calculations; for predicting perforation diameter, FEM and FE-SPH adaptive methods accurately represent material boundaries and perforation morphology, although the perforation diameter varies significantly under different failure criteria, while the SPG method can accurately predict the perforation diameter of target plates due to its insensitive to failure parameters; for analzing secondary fragments generation and distribution, both FE-SPH adaptive and SPH methods effectively characterize these phenomena, while the FE-SPH adaptive method provides detailed information on large fragments, it is less computationally efficient than the SPH method.
, Available online , doi: 10.11883/bzycj-2024-0403
Abstract:
The shear mechanical properties and deformation damage mechanism of the double structural planes of traditional anchor cables and new anchor cables with C-shaped tube structures (abbreviated as ACC) under different loading rate conditions were investigated through experimental and numerical simulation analyses. Dual structural face shear tests were conducted at shear displacement loading rates of 2, 10, 20, 30, and 40 mm/min under 55 MPa concrete specimen strength and 200 kN preload, with shear deformation curves, peak structural shear loads, steel wire damage patterns, and structural plane shear strength contributions as the main parameters considered. The results show that the loading rate significantly affects the shear performance of the structure. Within a certain loading rate interval, influenced by the damage accumulation rate and the strain rate strengthening effect, the structure exhibits characteristics of strength weakening and strengthening, respectively, with a large variation interval in shear load-carrying capacity. Near the structural plane, the support structure shows a combination of tensile and shear damage. However, the ACC structure, due to the presence of the C-shaped tube, exhibits lower stress concentration effects, reduced fluctuation in the test curve, and significantly weakened internal steel wire damage compared to traditional anchor cables. Meanwhile, the numerical model of the double shear test of the ACC structure, constructed based on the test results, exhibits high accuracy. Numerical simulations of dynamic loading tests demonstrate that the anchoring system formed by the ACC structure has a good energy absorption effect, which becomes more pronounced with increasing impact energy. Under high-speed impact, the ACC structure is significantly affected by the strain rate reinforcement effect, with higher shear load capacity at greater impact velocities.
The shear mechanical properties and deformation damage mechanism of the double structural planes of traditional anchor cables and new anchor cables with C-shaped tube structures (abbreviated as ACC) under different loading rate conditions were investigated through experimental and numerical simulation analyses. Dual structural face shear tests were conducted at shear displacement loading rates of 2, 10, 20, 30, and 40 mm/min under 55 MPa concrete specimen strength and 200 kN preload, with shear deformation curves, peak structural shear loads, steel wire damage patterns, and structural plane shear strength contributions as the main parameters considered. The results show that the loading rate significantly affects the shear performance of the structure. Within a certain loading rate interval, influenced by the damage accumulation rate and the strain rate strengthening effect, the structure exhibits characteristics of strength weakening and strengthening, respectively, with a large variation interval in shear load-carrying capacity. Near the structural plane, the support structure shows a combination of tensile and shear damage. However, the ACC structure, due to the presence of the C-shaped tube, exhibits lower stress concentration effects, reduced fluctuation in the test curve, and significantly weakened internal steel wire damage compared to traditional anchor cables. Meanwhile, the numerical model of the double shear test of the ACC structure, constructed based on the test results, exhibits high accuracy. Numerical simulations of dynamic loading tests demonstrate that the anchoring system formed by the ACC structure has a good energy absorption effect, which becomes more pronounced with increasing impact energy. Under high-speed impact, the ACC structure is significantly affected by the strain rate reinforcement effect, with higher shear load capacity at greater impact velocities.
, Available online , doi: 10.11883/bzycj-2024-0315
Abstract:
Structural damages in solid propellants can lead to combustion anomalies and affect ballistic performance. Utilizing synchrotron radiation X-ray computed tomography technology and an in-situ mechanical loading test system, the macro-meso structures of nitrate ester plasticized polyether (NEPE) solid propellant were observed in-situ at compressive rates of 0.1, 1.0, and 5.0 mm/s. The compressive process employed an intermittent loading mode. With loading paused each time the preset displacement was reached to enable scanning imaging, thereby capturing the state of the propellant at specific phases during compression. Following the in-situ imaging experiment, the tomographic images of the samples were processed through projection correction and phase recovery using PITRE and PITRE_BM software, followed by image bit-depth conversion to obtain 8-bit 2D grayscale slices. Through 3D reconstruction, the typical damages and evolutionary behaviors of the solid propellant were analyzed, exploring the macroscopic deformation as well as the distribution and propagation patterns of internal micro-cracks. Results indicate that most micro-cracks nucleate and grow at the interface between filled particles and the matrix, with meso-pore evolution being rate-dependent. Unlike the continuous damage growth under tensile loading, the nucleation, growth, and closure of pores occur simultaneously during compression. Under high-rate uniaxial compressive loading, the solid propellant exhibits characteristic trumpet-shaped deformation, with spatially distributed cracks primarily located around the propellant. Macroscopic surface damage results from micro-crack propagation between near-surface particles and the matrix, with crack propagation related to the spatial location of filled particles. Transversal and axial crack propagation modes exist under dynamic compressive loading, with the transition from vertically to horizontally oriented cracks in the matrix leading to crack closure.
Structural damages in solid propellants can lead to combustion anomalies and affect ballistic performance. Utilizing synchrotron radiation X-ray computed tomography technology and an in-situ mechanical loading test system, the macro-meso structures of nitrate ester plasticized polyether (NEPE) solid propellant were observed in-situ at compressive rates of 0.1, 1.0, and 5.0 mm/s. The compressive process employed an intermittent loading mode. With loading paused each time the preset displacement was reached to enable scanning imaging, thereby capturing the state of the propellant at specific phases during compression. Following the in-situ imaging experiment, the tomographic images of the samples were processed through projection correction and phase recovery using PITRE and PITRE_BM software, followed by image bit-depth conversion to obtain 8-bit 2D grayscale slices. Through 3D reconstruction, the typical damages and evolutionary behaviors of the solid propellant were analyzed, exploring the macroscopic deformation as well as the distribution and propagation patterns of internal micro-cracks. Results indicate that most micro-cracks nucleate and grow at the interface between filled particles and the matrix, with meso-pore evolution being rate-dependent. Unlike the continuous damage growth under tensile loading, the nucleation, growth, and closure of pores occur simultaneously during compression. Under high-rate uniaxial compressive loading, the solid propellant exhibits characteristic trumpet-shaped deformation, with spatially distributed cracks primarily located around the propellant. Macroscopic surface damage results from micro-crack propagation between near-surface particles and the matrix, with crack propagation related to the spatial location of filled particles. Transversal and axial crack propagation modes exist under dynamic compressive loading, with the transition from vertically to horizontally oriented cracks in the matrix leading to crack closure.
, Available online , doi: 10.11883/bzycj-2024-0128
Abstract:
In the near-field explosion of improvised explosive device, the protective structure is often subjected to the combined action of blast wave and fragments. To improve the protection performance of the structure, a composite structural material containing foamed aluminum/fiber sandwich was designed and prepared. The explosion and penetration experiment was carried out to study the failure mode of the composite structure under the combined action of explosion shock wave and high-speed fragments. In the experiment, the time for the explosive shock wave to reach the surface of the composite plate and the pressure attenuation before and after passing through the material were tested by installing PVDF pressure gauges on the upper and lower surfaces of the composite plate. Meanwhile, the time for the shock wave to reach the surface of the composite plate was measured by piezoelectric probes for the purpose of verification. The time for fragments to reach the surface of the composite plate was tested using a comb-shaped target, and the velocity attenuation of fragments after penetrating the target plate was obtained. The influence of the two loading’s timing sequence of explosion shock wave and fragment on the failure mode was discussed, and the energy absorption mechanism of different materials was analyzed. The results show that the change of detonation distance directly affects the timing sequence of the action of explosion shock wave and fragment. In the conditions discussed in this paper, when the detonation distance is greater than 600 mm, the fragment acts before the shock wave. Under the combined action of shock wave and fragment, the aluminum plate is accompanied by local sag deformation in addition to the penetration failure of fragments. The cellular structure of foamed aluminum was crushed and deformed under the impact load. The fibers at the bullet hole are stretched and fractured under the penetration of fragments, and are accompanied by high temperature failure. Under the two sequential effects, the existence of bullet holes weakens the effect of shock wave on the front aluminum plate, and the deformation and damage degree of the later sandwich structural material and the rear aluminum plate are more serious than that of the previous material. This research provides a technical basis for the application and functional design of lightweight composite structural materials in the field of near-burst protection in limited space.
In the near-field explosion of improvised explosive device, the protective structure is often subjected to the combined action of blast wave and fragments. To improve the protection performance of the structure, a composite structural material containing foamed aluminum/fiber sandwich was designed and prepared. The explosion and penetration experiment was carried out to study the failure mode of the composite structure under the combined action of explosion shock wave and high-speed fragments. In the experiment, the time for the explosive shock wave to reach the surface of the composite plate and the pressure attenuation before and after passing through the material were tested by installing PVDF pressure gauges on the upper and lower surfaces of the composite plate. Meanwhile, the time for the shock wave to reach the surface of the composite plate was measured by piezoelectric probes for the purpose of verification. The time for fragments to reach the surface of the composite plate was tested using a comb-shaped target, and the velocity attenuation of fragments after penetrating the target plate was obtained. The influence of the two loading’s timing sequence of explosion shock wave and fragment on the failure mode was discussed, and the energy absorption mechanism of different materials was analyzed. The results show that the change of detonation distance directly affects the timing sequence of the action of explosion shock wave and fragment. In the conditions discussed in this paper, when the detonation distance is greater than 600 mm, the fragment acts before the shock wave. Under the combined action of shock wave and fragment, the aluminum plate is accompanied by local sag deformation in addition to the penetration failure of fragments. The cellular structure of foamed aluminum was crushed and deformed under the impact load. The fibers at the bullet hole are stretched and fractured under the penetration of fragments, and are accompanied by high temperature failure. Under the two sequential effects, the existence of bullet holes weakens the effect of shock wave on the front aluminum plate, and the deformation and damage degree of the later sandwich structural material and the rear aluminum plate are more serious than that of the previous material. This research provides a technical basis for the application and functional design of lightweight composite structural materials in the field of near-burst protection in limited space.
, Available online , doi: 10.11883/bzycj-2024-0356
Abstract:
Axisymmetric conical structures, as a common configuration, induce oblique detonation waves exhibiting significantly greater structural complexity compared to those generated by sharp wedges. Numerical simulations of oblique detonation waves induced by a finite cone were performed using the open-source code OpenFOAM, with analysis conducted on post-detonation flow fields, wavefront structure, and detonation cell structures. The numerical results show that under the effect of the finite cone the flow field behind the detonation wave is successively influenced by Taylor-Maccoll flow and Prandtl-Meyer expansion waves. The pressure and Mach number along the streamlines at different positions on the detonation wave front exhibit oscillatory changes with the influence of these two physical processes and triple points on oblique detonation surfaces, and then tend to stabilize. Depending on the different post-detonation flow field, the detonation wave front structure is divided into four sections: smooth ZND (Zel'dovich- Neumann-Döring)-like structure, single-headed triple points cell-like structure, dual-headed triple points cell structure and dual-headed triple point structure influenced by Prandtl-Meyer. The shock pole curve theory is used to analyze the wave structures. It is found that the upstream-facing triple points exhibits higher detonation intensity, i.e., higher Mach number and pressure, compared to the downstream-facing triple points in dual-headed triple points structure. Finally, based on the above analysis, triple point traces are recorded to obtain four different cell structures: smooth planar structure, parallel line structure, oblique rhombus structure, and irregular oblique rhombus structure.
Axisymmetric conical structures, as a common configuration, induce oblique detonation waves exhibiting significantly greater structural complexity compared to those generated by sharp wedges. Numerical simulations of oblique detonation waves induced by a finite cone were performed using the open-source code OpenFOAM, with analysis conducted on post-detonation flow fields, wavefront structure, and detonation cell structures. The numerical results show that under the effect of the finite cone the flow field behind the detonation wave is successively influenced by Taylor-Maccoll flow and Prandtl-Meyer expansion waves. The pressure and Mach number along the streamlines at different positions on the detonation wave front exhibit oscillatory changes with the influence of these two physical processes and triple points on oblique detonation surfaces, and then tend to stabilize. Depending on the different post-detonation flow field, the detonation wave front structure is divided into four sections: smooth ZND (Zel'dovich- Neumann-Döring)-like structure, single-headed triple points cell-like structure, dual-headed triple points cell structure and dual-headed triple point structure influenced by Prandtl-Meyer. The shock pole curve theory is used to analyze the wave structures. It is found that the upstream-facing triple points exhibits higher detonation intensity, i.e., higher Mach number and pressure, compared to the downstream-facing triple points in dual-headed triple points structure. Finally, based on the above analysis, triple point traces are recorded to obtain four different cell structures: smooth planar structure, parallel line structure, oblique rhombus structure, and irregular oblique rhombus structure.
, Available online , doi: 10.11883/bzycj-2024-0350
Abstract:
In blast-resistant structural design for conventional weapons, previous studies on blast-induced stress waves in solid media have predominantly focused on soil and rock media (i.e., ground shock issues), whereas research on the propagation and attenuation laws of stress waves in concrete remains relatively limited. Based on the KCC constitutive model in conjunction with the multi-material ALE (MMALE) algorithm, the propagation laws of stress waves in concrete induced by cylindrical charge explosion were numerically investigated. Firstly, the applicability of the constitutive model parameters and numerical algorithm were validated by comparing the results with the existing experiments. Subsequently, the peak stress was employed as a criterion to delineate the explosive damage zones in the concrete surrounding the charge. Additionally, the attenuation laws of explosion stress waves in each damage zone were discussed. Finally, the effect of burial depth was taken into further considered, and a formula for calculating the peak stress in concrete induced by cylindrical charge explosion was established. It was found that the attenuation patterns of blast-induced stress waves differ significantly in each explosion failure zone. The stress waves in the near-field zone (quasi-fluid and crushing zones) demonstrates a more rapid attenuation rate compared to that in the mid-field zone (transition and fracture zones). Furthermore, an increase in the aspect ratio of the cylindrical charge leads to an acceleration in the attenuation of the normal peak stress. Moreover, the established formula for calculating the peak stress of blast-induced stress waves enables accurate and rapid determination of the normal peak stress generated by cylindrical charges with varying geometries and burial depths, which can be served as a valuable reference for blast-resistant design of concrete structures.
In blast-resistant structural design for conventional weapons, previous studies on blast-induced stress waves in solid media have predominantly focused on soil and rock media (i.e., ground shock issues), whereas research on the propagation and attenuation laws of stress waves in concrete remains relatively limited. Based on the KCC constitutive model in conjunction with the multi-material ALE (MMALE) algorithm, the propagation laws of stress waves in concrete induced by cylindrical charge explosion were numerically investigated. Firstly, the applicability of the constitutive model parameters and numerical algorithm were validated by comparing the results with the existing experiments. Subsequently, the peak stress was employed as a criterion to delineate the explosive damage zones in the concrete surrounding the charge. Additionally, the attenuation laws of explosion stress waves in each damage zone were discussed. Finally, the effect of burial depth was taken into further considered, and a formula for calculating the peak stress in concrete induced by cylindrical charge explosion was established. It was found that the attenuation patterns of blast-induced stress waves differ significantly in each explosion failure zone. The stress waves in the near-field zone (quasi-fluid and crushing zones) demonstrates a more rapid attenuation rate compared to that in the mid-field zone (transition and fracture zones). Furthermore, an increase in the aspect ratio of the cylindrical charge leads to an acceleration in the attenuation of the normal peak stress. Moreover, the established formula for calculating the peak stress of blast-induced stress waves enables accurate and rapid determination of the normal peak stress generated by cylindrical charges with varying geometries and burial depths, which can be served as a valuable reference for blast-resistant design of concrete structures.
, Available online , doi: 10.11883/bzycj-2024-0268
Abstract:
To investigate the explosion flame development and propagation mechanism of coated aluminum powder, a shell and core structure of stearic acid-coated aluminum powder (SA@Al) was prepared using the solvent evaporation method. The influence of dust cloud concentration on the explosion flame propagation characteristics of SA@Al dust with coating concentrations of 5%, 10%, and 15% was experimentally studied using an improved Hartmann tube. Flame propagation behavior was observed through high-speed photography, and the flame propagation speed was calculated. The kinetic characteristics of the gas-phase explosion reaction were analyzed using CHEMKIN-PRO software to reveal the mechanism of SA@Al dust explosion flame propagation. The results indicated that as the dust cloud concentration increased, the fullness and continuity of the explosion flames for 5%, 10%, and 15% SA@Al dust first increased and then decreased, with the average flame propagation speed showing a trend of first rising and then falling. The flame propagation speed reached its maximum at a dust cloud concentration of 500 g/m³. In contrast, the explosion flame propagation velocity of pure aluminum powder reached its maximum at 750 g/m³, suggesting that the stearic acid coating layer promotes the propagation of the aluminum powder explosion flame. Additionally, under each dust cloud concentration, the explosion flame of 10% coating concentration SA@Al was the most intense, with the highest average flame propagation speed. The temperature rise of the SA@Al explosion flame with different dust cloud concentrations mainly consisted of two stages: a rapid heating stage and a slow heating stage. The rapid heating stage exhibited higher temperature sensitivity for reactions R2, R11, and R10, while the slow heating stage exhibited higher temperature sensitivity for reactions R5 and R11. The dust cloud concentration significantly affected the rate of temperature rise in the slow heating stage, resulting in the highest explosion equilibrium temperature for SA@Al at 500 g/m³. The combustion of the stearic acid coating promoted the oxidation of the aluminum core, thereby strengthening the explosion reaction. However, high dust cloud concentration led to limitations in O radicals, which weakened the reaction intensity to some extent.
To investigate the explosion flame development and propagation mechanism of coated aluminum powder, a shell and core structure of stearic acid-coated aluminum powder (SA@Al) was prepared using the solvent evaporation method. The influence of dust cloud concentration on the explosion flame propagation characteristics of SA@Al dust with coating concentrations of 5%, 10%, and 15% was experimentally studied using an improved Hartmann tube. Flame propagation behavior was observed through high-speed photography, and the flame propagation speed was calculated. The kinetic characteristics of the gas-phase explosion reaction were analyzed using CHEMKIN-PRO software to reveal the mechanism of SA@Al dust explosion flame propagation. The results indicated that as the dust cloud concentration increased, the fullness and continuity of the explosion flames for 5%, 10%, and 15% SA@Al dust first increased and then decreased, with the average flame propagation speed showing a trend of first rising and then falling. The flame propagation speed reached its maximum at a dust cloud concentration of 500 g/m³. In contrast, the explosion flame propagation velocity of pure aluminum powder reached its maximum at 750 g/m³, suggesting that the stearic acid coating layer promotes the propagation of the aluminum powder explosion flame. Additionally, under each dust cloud concentration, the explosion flame of 10% coating concentration SA@Al was the most intense, with the highest average flame propagation speed. The temperature rise of the SA@Al explosion flame with different dust cloud concentrations mainly consisted of two stages: a rapid heating stage and a slow heating stage. The rapid heating stage exhibited higher temperature sensitivity for reactions R2, R11, and R10, while the slow heating stage exhibited higher temperature sensitivity for reactions R5 and R11. The dust cloud concentration significantly affected the rate of temperature rise in the slow heating stage, resulting in the highest explosion equilibrium temperature for SA@Al at 500 g/m³. The combustion of the stearic acid coating promoted the oxidation of the aluminum core, thereby strengthening the explosion reaction. However, high dust cloud concentration led to limitations in O radicals, which weakened the reaction intensity to some extent.
, Available online , doi: 10.11883/bzycj-2024-0002
Abstract:
To understand the dynamic fracture characteristics of nodular cast iron structures such as the spent nuclear fuel storage and transportation vessels under low temperatures and dynamic loads, the mode I dynamic fracture toughness (DFT) of nodular cast iron was tested at different temperatures (20, −40, −60 and −80 ℃) using an improved split Hopkinson pressure bar technique, and focused on studying the ductile-brittle transition behavior of the material. Standard three-point bending specimens with a fatigue crack were pre-fabricated before the experiment. A special fixture was used to replace the transmitter bar, while the temperature was controlled by a specially designed environmental chamber. The crack initiation time of the specimen was determined by the strain gauge method, and the dynamic stress intensity factor (DSIF) at the crack tip was determined using the experimental-numerical method. Mesh refinement and element transition were used at the crack tip region to ensure a high-accuracy result of the displacement field. On this basis, the mode Ⅰ DFT of the material was finally determined. The results show that under the same impact velocity, the DFT and the fracture initiation time of nodular cast iron decrease significantly with the decrease in temperature. As the temperature decreases, the macroscopic fracture surface of nodular cast iron changes from rough to relatively flat, indicating a change in the failure modes of the material. The effect of temperature on the failure mode is further verified by quantitative microscopic analysis of fracture surfaces. As the temperature decreases, the number of dimples on the fracture surface decreases, while river patterns and cleavage steps increase. It means that the ductility of the material is weakened, but the brittleness is enhanced at low temperatures. This ductile-brittle transition phenomenon is consistent with the tendency of the measured toughness of the material.
To understand the dynamic fracture characteristics of nodular cast iron structures such as the spent nuclear fuel storage and transportation vessels under low temperatures and dynamic loads, the mode I dynamic fracture toughness (DFT) of nodular cast iron was tested at different temperatures (20, −40, −60 and −80 ℃) using an improved split Hopkinson pressure bar technique, and focused on studying the ductile-brittle transition behavior of the material. Standard three-point bending specimens with a fatigue crack were pre-fabricated before the experiment. A special fixture was used to replace the transmitter bar, while the temperature was controlled by a specially designed environmental chamber. The crack initiation time of the specimen was determined by the strain gauge method, and the dynamic stress intensity factor (DSIF) at the crack tip was determined using the experimental-numerical method. Mesh refinement and element transition were used at the crack tip region to ensure a high-accuracy result of the displacement field. On this basis, the mode Ⅰ DFT of the material was finally determined. The results show that under the same impact velocity, the DFT and the fracture initiation time of nodular cast iron decrease significantly with the decrease in temperature. As the temperature decreases, the macroscopic fracture surface of nodular cast iron changes from rough to relatively flat, indicating a change in the failure modes of the material. The effect of temperature on the failure mode is further verified by quantitative microscopic analysis of fracture surfaces. As the temperature decreases, the number of dimples on the fracture surface decreases, while river patterns and cleavage steps increase. It means that the ductility of the material is weakened, but the brittleness is enhanced at low temperatures. This ductile-brittle transition phenomenon is consistent with the tendency of the measured toughness of the material.
, Available online , doi: 10.11883/bzycj-2024-0280
Abstract:
Aiming to investigate the performance and design approach of the carbon fiber reinforced polymer (CFRP) sheet strengthened masonry infilled walls subjected to blast loads, the commercial finite element program LS-DYNA is firstly used to develop the simplified micro-finite element model of masonry infilled walls and the corresponding blast-resistant analysis model of the CFRP sheet strengthened walls. By comparing the numerical simulation results with the nine groups field explosion test results of the unstrengthening and CFRP sheet strengthened masonry infilled walls, the applicability of the present simplified micro-modeling approach, as well as the material models and parameters of masonry and CFRP sheet and the corresponding contact algorithm, is thoroughly verified. Furthermore, referring to the CFRP sheet seismic strengthening methods recommended by Chinese standard GB 50608—2020, the dynamic behaviors of the prototype masonry infilled walls strengthened with CFRP sheets under blast loads are analyzed and compared. It is recommended that the diagonal two-way strengthening method be advocated, followed by the vertical two-way and horizontal full-cover strengthening methods. In contrast, the vertical full-cover and mixed three-way strengthening methods are not recommended. Finally, to simultaneously satisfy the conditions of intact CFRP, no scattering debris and the peak central deflection than wall thickness to meet the blast-resistant design goal, the ranges of the scaled distance of the prototype masonry infilled walls with different arrangements of tie bar (non-/cut-off/full-length tie bar) that need to be strengthened under typical sedan (227 kg equivalent TNT) and briefcase bombs (23 kg equivalent TNT) specified by Federal Emergency Management Agency explode at different scaled distances are determined to be 0.8–2.0 m/kg1/3 and 0.2–1.2 m/kg1/3, respectively. The suggestions for the optimal number of CFRP sheet layers for effective blast-resistant design are further provided. The arrangement of the tie bar has little effect on the optimal number of strengthening layers, only affecting the critical scaled distance at which the wall needs to be strengthened.
Aiming to investigate the performance and design approach of the carbon fiber reinforced polymer (CFRP) sheet strengthened masonry infilled walls subjected to blast loads, the commercial finite element program LS-DYNA is firstly used to develop the simplified micro-finite element model of masonry infilled walls and the corresponding blast-resistant analysis model of the CFRP sheet strengthened walls. By comparing the numerical simulation results with the nine groups field explosion test results of the unstrengthening and CFRP sheet strengthened masonry infilled walls, the applicability of the present simplified micro-modeling approach, as well as the material models and parameters of masonry and CFRP sheet and the corresponding contact algorithm, is thoroughly verified. Furthermore, referring to the CFRP sheet seismic strengthening methods recommended by Chinese standard GB 50608—2020, the dynamic behaviors of the prototype masonry infilled walls strengthened with CFRP sheets under blast loads are analyzed and compared. It is recommended that the diagonal two-way strengthening method be advocated, followed by the vertical two-way and horizontal full-cover strengthening methods. In contrast, the vertical full-cover and mixed three-way strengthening methods are not recommended. Finally, to simultaneously satisfy the conditions of intact CFRP, no scattering debris and the peak central deflection than wall thickness to meet the blast-resistant design goal, the ranges of the scaled distance of the prototype masonry infilled walls with different arrangements of tie bar (non-/cut-off/full-length tie bar) that need to be strengthened under typical sedan (227 kg equivalent TNT) and briefcase bombs (23 kg equivalent TNT) specified by Federal Emergency Management Agency explode at different scaled distances are determined to be 0.8–2.0 m/kg1/3 and 0.2–1.2 m/kg1/3, respectively. The suggestions for the optimal number of CFRP sheet layers for effective blast-resistant design are further provided. The arrangement of the tie bar has little effect on the optimal number of strengthening layers, only affecting the critical scaled distance at which the wall needs to be strengthened.
, Available online , doi: 10.11883/bzycj-2024-0225
Abstract:
With its high design freedom and rapid prototyping capabilities, additive manufacturing (AM) offers significant advantages in manufacturing critical components with complex geometries for the aerospace and defense industries. Ti-6Al-4V alloy, leveraging its exceptional combination of low density, high specific strength, and creep resistance, are extensively employed in critical structures that are frequently subjected to impact loading in aerospace and defense systems. A thorough understanding of the mechanical properties and underlying mechanisms of the additively manufactured Ti-6Al-4V alloy under static and dynamic loading is crucial for enhancing the service performance of these components. This paper systematically reviews and summarizes the latest advancements in the mechanical response of AM Ti-6Al-4V titanium alloys. Firstly, a brief overview of the classification and working principles of typical metal additive manufacturing (AM) technologies is provided. Subsequently, research efforts on the quasi-static tensile and dynamic compressive properties of additively manufactured Ti-6Al-4V titanium alloy are systematically reviewed, followed by a comparative analysis of its mechanical performance against cast and forged Ti-6Al-4V components. Furthermore, the mechanisms of correlation between the microstructure and mechanical behaviors of typical metal additive manufactured titanium alloys. Additionally, the commonly used post-processing techniques to mitigate the anisotropic mechanical response of AM Ti-6Al-4V alloy under static loading are summarizes.
With its high design freedom and rapid prototyping capabilities, additive manufacturing (AM) offers significant advantages in manufacturing critical components with complex geometries for the aerospace and defense industries. Ti-6Al-4V alloy, leveraging its exceptional combination of low density, high specific strength, and creep resistance, are extensively employed in critical structures that are frequently subjected to impact loading in aerospace and defense systems. A thorough understanding of the mechanical properties and underlying mechanisms of the additively manufactured Ti-6Al-4V alloy under static and dynamic loading is crucial for enhancing the service performance of these components. This paper systematically reviews and summarizes the latest advancements in the mechanical response of AM Ti-6Al-4V titanium alloys. Firstly, a brief overview of the classification and working principles of typical metal additive manufacturing (AM) technologies is provided. Subsequently, research efforts on the quasi-static tensile and dynamic compressive properties of additively manufactured Ti-6Al-4V titanium alloy are systematically reviewed, followed by a comparative analysis of its mechanical performance against cast and forged Ti-6Al-4V components. Furthermore, the mechanisms of correlation between the microstructure and mechanical behaviors of typical metal additive manufactured titanium alloys. Additionally, the commonly used post-processing techniques to mitigate the anisotropic mechanical response of AM Ti-6Al-4V alloy under static loading are summarizes.
, Available online , doi: 10.11883/bzycj-2024-0119
Abstract:
H-section steel columns have been widely employed in industrial buildings and parking lots, etc., which are vulnerable to crane-loading or vehicle collisions. Based on above background and previous experimental studies, the lateral impact model and residual load-carrying capacity model are established by using Abaqus finite element software to analyze the performance of H-section steel columns during and after impact loading. Firstly, the working mechanism, including the deformation characteristics, stress evolution and energy dissipation, is analyzed. Results indicate that under impact loading, the deformation pattern is mainly dominated by the global deformation, with the local deformation of the upper flange and out-of-plane buckling of the web. The time history curve of impact force exhibits an obvious plateau phase, and the existence of the pre-axial compression clearly reduces the impact resistance of the specimens. In general, H-section steel columns present favorable ductility performance during impact loading. Subsequently, a total of 108 parametric models are constructed, and the effects of load parameters (impact mass, impact velocity and axial load ratio), material parameter (steel yield strength) and geometric parameters (sectional area and specimen length) on the impact force, deformation, and residual load-carrying capacity are emphatically studied. The results show that as the impact mass, impact velocity, and/or pre-axial loading ratio increase, both the global and local deformations of H-section steel column will increase, while the residual load-carrying capacity will decrease. Finally, by considering the multi-factor interactions, the formulas for predicting global deformation and local deformation during impact and the residual load-carrying performance after impact are proposed by using response surface method. Results show that pre-axial loading is a key factor affecting global deformation, while the impact velocity mainly affects local deformation. In addition, both the pre-axial loading and impact velocity significantly interact with other parameters. The proposed formulas can be employed for the damage evaluation and design of H-section steel columns during the whole impact process and after impact event.
H-section steel columns have been widely employed in industrial buildings and parking lots, etc., which are vulnerable to crane-loading or vehicle collisions. Based on above background and previous experimental studies, the lateral impact model and residual load-carrying capacity model are established by using Abaqus finite element software to analyze the performance of H-section steel columns during and after impact loading. Firstly, the working mechanism, including the deformation characteristics, stress evolution and energy dissipation, is analyzed. Results indicate that under impact loading, the deformation pattern is mainly dominated by the global deformation, with the local deformation of the upper flange and out-of-plane buckling of the web. The time history curve of impact force exhibits an obvious plateau phase, and the existence of the pre-axial compression clearly reduces the impact resistance of the specimens. In general, H-section steel columns present favorable ductility performance during impact loading. Subsequently, a total of 108 parametric models are constructed, and the effects of load parameters (impact mass, impact velocity and axial load ratio), material parameter (steel yield strength) and geometric parameters (sectional area and specimen length) on the impact force, deformation, and residual load-carrying capacity are emphatically studied. The results show that as the impact mass, impact velocity, and/or pre-axial loading ratio increase, both the global and local deformations of H-section steel column will increase, while the residual load-carrying capacity will decrease. Finally, by considering the multi-factor interactions, the formulas for predicting global deformation and local deformation during impact and the residual load-carrying performance after impact are proposed by using response surface method. Results show that pre-axial loading is a key factor affecting global deformation, while the impact velocity mainly affects local deformation. In addition, both the pre-axial loading and impact velocity significantly interact with other parameters. The proposed formulas can be employed for the damage evaluation and design of H-section steel columns during the whole impact process and after impact event.
, Available online , doi: 10.11883/bzycj-2024-0393
Abstract:
Traumatic brain injury (TBI) is the neurological disorder with the highest incidence and prevalence, and poses a huge public health burden for the whole society. An in-depth study of the biomechanics of TBI can help to improve the effectiveness of head protection, develop rapid assessment techniques and take timely interventions, thus reducing the risk of injury deterioration. As a numerical analysis tool, the finite element head model (FEHM) is able to simulate the dynamic response of the head during impact, including the spatial and temporal distribution of stress-strain in brain tissues, and the change of intracranial pressure, which provides an important basis for understanding the mechanical mechanism of traumatic brain injury (TBI). This paper summarizes in detail the current status and development of mainstream finite element models of the human head at home and abroad, traces the development of the models, summarises the characteristics of the models and introduces the research progress of TBI mechanisms based on finite element models. The summary and sorting out of related research will be helpful for the development of new FEHMs and provide theoretical guidance and technical support for the risk assessment of traumatic brain injury and the design of protective equipment.
Traumatic brain injury (TBI) is the neurological disorder with the highest incidence and prevalence, and poses a huge public health burden for the whole society. An in-depth study of the biomechanics of TBI can help to improve the effectiveness of head protection, develop rapid assessment techniques and take timely interventions, thus reducing the risk of injury deterioration. As a numerical analysis tool, the finite element head model (FEHM) is able to simulate the dynamic response of the head during impact, including the spatial and temporal distribution of stress-strain in brain tissues, and the change of intracranial pressure, which provides an important basis for understanding the mechanical mechanism of traumatic brain injury (TBI). This paper summarizes in detail the current status and development of mainstream finite element models of the human head at home and abroad, traces the development of the models, summarises the characteristics of the models and introduces the research progress of TBI mechanisms based on finite element models. The summary and sorting out of related research will be helpful for the development of new FEHMs and provide theoretical guidance and technical support for the risk assessment of traumatic brain injury and the design of protective equipment.
, Available online , doi: 10.11883/bzycj-2024-0261
Abstract:
Tolerances in machining and assembly often result in gaps within engineering structures. Under strong dynamic loading, gap jets may form within these gaps, thereby posing a threat to the reliability and safety of the structure. However, the formation mechanism of gap jets differs from that of traditional high-speed metal jets, and its formation process still requires systematic study. Hypervelocity impact loading experiments on tungsten samples with gaps were conducted using a two-stage light gas gun, and the formation and evolution of the gap jet were recorded using a high-speed framing camera. A numerical model for predicting the formation of gap jets was established using ANSYS Autodyn, and the applicability of the numerical simulation method was validated by comparing the numerical results with the jet morphology and head velocity history data obtained from a representative experiment. The effects of flyer velocity, gap width, and gap half-angle on the formation of the gap jet were investigated by adjusting these parameters in the numerical model, and the variations in the gap jet head velocity and mass with respect to these factors were obtained. The limitations of the steady-state jet model were analyzed, and an empirical model was developed to predict the jet head velocity and mass based on the findings from numerical simulations. The results show that the numerical model based on the Eulerian method can accurately predict the formation of the gap jet under strong dynamic loading. Loading pressure is found to be the main factor controlling the jet head velocity and mass; as the loading pressure increases, both the jet head velocity and mass increase accordingly. The gap width and half-angle have little effect on the jet head velocity, but the mass increases linearly with the gap width and half-angle. Due to significant errors in estimating the gap closing velocity, the steady jet model fails to accurately predict the formation of the gap jet. In contrast, the developed empirical model shows good agreement with the numerical results.
Tolerances in machining and assembly often result in gaps within engineering structures. Under strong dynamic loading, gap jets may form within these gaps, thereby posing a threat to the reliability and safety of the structure. However, the formation mechanism of gap jets differs from that of traditional high-speed metal jets, and its formation process still requires systematic study. Hypervelocity impact loading experiments on tungsten samples with gaps were conducted using a two-stage light gas gun, and the formation and evolution of the gap jet were recorded using a high-speed framing camera. A numerical model for predicting the formation of gap jets was established using ANSYS Autodyn, and the applicability of the numerical simulation method was validated by comparing the numerical results with the jet morphology and head velocity history data obtained from a representative experiment. The effects of flyer velocity, gap width, and gap half-angle on the formation of the gap jet were investigated by adjusting these parameters in the numerical model, and the variations in the gap jet head velocity and mass with respect to these factors were obtained. The limitations of the steady-state jet model were analyzed, and an empirical model was developed to predict the jet head velocity and mass based on the findings from numerical simulations. The results show that the numerical model based on the Eulerian method can accurately predict the formation of the gap jet under strong dynamic loading. Loading pressure is found to be the main factor controlling the jet head velocity and mass; as the loading pressure increases, both the jet head velocity and mass increase accordingly. The gap width and half-angle have little effect on the jet head velocity, but the mass increases linearly with the gap width and half-angle. Due to significant errors in estimating the gap closing velocity, the steady jet model fails to accurately predict the formation of the gap jet. In contrast, the developed empirical model shows good agreement with the numerical results.
, Available online , doi: 10.11883/bzycj-2024-0278
Abstract:
In order to investigate the damage mechanisms of zirconium-based amorphous alloy fragments penetrating carbon fiber targets and their subsequent effects on target failure, ballistic experiments were conducted using a 12.7 mm ballistic gun. The experiments involved spherical zirconium-based amorphous alloy fragments impacting a composite target system consisting of a 6-mm thick carbon fiber laminate and a 2-mm thick LY12 alloy plate. These targets were arranged in both stacked and spaced configurations to evaluate the effects of target configuration on the damage caused by fragment impact. To quantitatively assess the subsequent damage, image recognition technology was employed to analyze the damage area of the LY12 target after impact.The results indicated that the damage area of the carbon fiber target was positively correlated with the velocity of the impacting fragment, with no significant hole expansion observed. On the front side, damage primarily resulted from fiber shear failure and compressive deformation, while the back face of the carbon fiber laminate exhibited tensile tearing and interlaminar delamination. These findings suggest that the carbon fiber target experienced a combination of mechanical damage modes, including shear and compressive deformation on the impact side, and tensile and delamination failures on the rear face, as a result of the high-velocity impact.In the case of the LY12 aluminum alloy target, the damage area increased with fragment velocity. When the velocity was below 954.7 m/s, the damage area on the LY12 target in the spaced configuration was smaller than that of the stacked configuration. However, as the fragment velocity increased, the damage area of the LY12 target in the spaced configuration grew rapidly, while the damage area in the stacked configuration increased more gradually. At higher velocities, the damage area in the spaced configuration was significantly larger than that in the stacked configuration. This trend suggests that for high-velocity impacts, the spaced configuration of the targets was more effective in promoting greater damage to the LY12 target.
In order to investigate the damage mechanisms of zirconium-based amorphous alloy fragments penetrating carbon fiber targets and their subsequent effects on target failure, ballistic experiments were conducted using a 12.7 mm ballistic gun. The experiments involved spherical zirconium-based amorphous alloy fragments impacting a composite target system consisting of a 6-mm thick carbon fiber laminate and a 2-mm thick LY12 alloy plate. These targets were arranged in both stacked and spaced configurations to evaluate the effects of target configuration on the damage caused by fragment impact. To quantitatively assess the subsequent damage, image recognition technology was employed to analyze the damage area of the LY12 target after impact.The results indicated that the damage area of the carbon fiber target was positively correlated with the velocity of the impacting fragment, with no significant hole expansion observed. On the front side, damage primarily resulted from fiber shear failure and compressive deformation, while the back face of the carbon fiber laminate exhibited tensile tearing and interlaminar delamination. These findings suggest that the carbon fiber target experienced a combination of mechanical damage modes, including shear and compressive deformation on the impact side, and tensile and delamination failures on the rear face, as a result of the high-velocity impact.In the case of the LY12 aluminum alloy target, the damage area increased with fragment velocity. When the velocity was below 954.7 m/s, the damage area on the LY12 target in the spaced configuration was smaller than that of the stacked configuration. However, as the fragment velocity increased, the damage area of the LY12 target in the spaced configuration grew rapidly, while the damage area in the stacked configuration increased more gradually. At higher velocities, the damage area in the spaced configuration was significantly larger than that in the stacked configuration. This trend suggests that for high-velocity impacts, the spaced configuration of the targets was more effective in promoting greater damage to the LY12 target.
, Available online , doi: 10.11883/bzycj-2024-0227
Abstract:
The small-scale test has several advantages, such as low cost, low risk, and short duration, and has been widely applied in aerospace and other fields. Taking the lower structure of a typical civil aircraft fuselage as the research object, this study conducted theoretical analysis and experimental methodology of scaling on the impact crashworthiness of civil aircraft structures. Using a dimensional analysis, the complex dynamics of the fuselage crash were simplified to identify key physical parameters and processes. The main objects, critical physical parameters, and physical processes involved in the aircraft crash were discussed, leading to the extraction of key basic physical parameters and the derivation of primary dimensionless numbers that control the crash response of the fuselage structure. Based on the Buckingham Π theorem, the scaling factor for civil aircraft crashes was derived, establishing the small-scale experimental methodology. A 1/4 scale experimental model was designed and fabricated, and an impact test at a speed of 6 m/s was performed. The velocity, acceleration, ground impact load, deformation, and failure modes of key components in both full-scale and small-scale crash tests were obtained and compared. The applicability and accuracy of the small-scale theory in the crash experiment of the civil aircraft fuselage frame section were verified. The results show that the deformation and failure modes of the frames and columns of the 1/4 scale model are in good agreement with those of the full-scale model. The peak crash load prediction error of the small-scale structure for the full-scale prototype structure is 14.4%, the peak seat acceleration prediction error is 14.8%, and the peak acceleration prediction error at the beam is 13.1%. The small-scale tests can effectively predict the deformation, failure process, and dynamic response of key parts of the full-scale prototype structure. Therefore, the small-scale test could be used to verify and evaluate the crash performance of civil aircraft structures.
The small-scale test has several advantages, such as low cost, low risk, and short duration, and has been widely applied in aerospace and other fields. Taking the lower structure of a typical civil aircraft fuselage as the research object, this study conducted theoretical analysis and experimental methodology of scaling on the impact crashworthiness of civil aircraft structures. Using a dimensional analysis, the complex dynamics of the fuselage crash were simplified to identify key physical parameters and processes. The main objects, critical physical parameters, and physical processes involved in the aircraft crash were discussed, leading to the extraction of key basic physical parameters and the derivation of primary dimensionless numbers that control the crash response of the fuselage structure. Based on the Buckingham Π theorem, the scaling factor for civil aircraft crashes was derived, establishing the small-scale experimental methodology. A 1/4 scale experimental model was designed and fabricated, and an impact test at a speed of 6 m/s was performed. The velocity, acceleration, ground impact load, deformation, and failure modes of key components in both full-scale and small-scale crash tests were obtained and compared. The applicability and accuracy of the small-scale theory in the crash experiment of the civil aircraft fuselage frame section were verified. The results show that the deformation and failure modes of the frames and columns of the 1/4 scale model are in good agreement with those of the full-scale model. The peak crash load prediction error of the small-scale structure for the full-scale prototype structure is 14.4%, the peak seat acceleration prediction error is 14.8%, and the peak acceleration prediction error at the beam is 13.1%. The small-scale tests can effectively predict the deformation, failure process, and dynamic response of key parts of the full-scale prototype structure. Therefore, the small-scale test could be used to verify and evaluate the crash performance of civil aircraft structures.
Preparation of NiP@Fe-SBA-15 suppressant and its inhibition mechanism on PP dust deflagration flames
, Available online , doi: 10.11883/bzycj-2024-0434
Abstract:
Polypropylene (PP) is widely utilized in industrial production, yet PP dust generated during its production and transportation can form explosive dust clouds, leading to severe dust explosion accidents that threaten personnel and equipment safety. To address this issue, a novel explosion suppressant, NiP@Fe-SBA-15, was synthesized to inhibit the propagation of PP dust combustion flames. The synthesis involved modifying SBA-15 mesoporous silica with Fe ions and subsequently loading NiP, resulting in a composite powder with uniformly dispersed active components and a well-preserved mesoporous structure. Characterization via SEM-Mapping and N2 adsorption-desorption experiments revealed that NiP@Fe-SBA-15 maintains a high specific surface area, exhibits a regulated pore structure, and shows no significant particle agglomeration. The Hartman tube explosive testing system was employed to evaluate the effect of NiP@Fe-SBA-15 on PP dust deflagration. Results indicated that as the NiP@Fe-SBA-15 additive increased, the flame propagation speed, brightness, and flame length of PP deflagration decreased significantly, with flame propagation almost completely inhibited at a suppressant dosage of 70 wt%. The dual explosion suppression mechanism of NiP@Fe-SBA-15 was analyzed. Physically, NiP@Fe-SBA-15 occupies reaction space, reducing oxygen and combustible volatile concentrations, while the SBA-15 molecular sieve, exposed by thermal decomposition of the suppressant, absorbs heat and forms a physical barrier, thereby reducing combustion intensity. Chemically, NiP decomposition releases Ni· and P· radicals that consume key free radicals (H·, O·, OH·) in combustion reactions, interrupting explosion chain reactions. Meanwhile, Fe-based species rapidly oxidize to Fe3O4, reducing oxygen availability and further weakening combustion intensity. In summary, NiP@Fe-SBA-15 was proven to be an effective explosion suppressant for PP dust explosions, reducing combustion intensity through combined physicochemical synergies. This research provides a new approach to enhancing polypropylene industry safety. Future work will focus on optimizing the industrial application of NiP@Fe-SBA-15 explosion suppressants while addressing cost, environmental sustainability, and stability issues to further advance dust explosion prevention technology.
Polypropylene (PP) is widely utilized in industrial production, yet PP dust generated during its production and transportation can form explosive dust clouds, leading to severe dust explosion accidents that threaten personnel and equipment safety. To address this issue, a novel explosion suppressant, NiP@Fe-SBA-15, was synthesized to inhibit the propagation of PP dust combustion flames. The synthesis involved modifying SBA-15 mesoporous silica with Fe ions and subsequently loading NiP, resulting in a composite powder with uniformly dispersed active components and a well-preserved mesoporous structure. Characterization via SEM-Mapping and N2 adsorption-desorption experiments revealed that NiP@Fe-SBA-15 maintains a high specific surface area, exhibits a regulated pore structure, and shows no significant particle agglomeration. The Hartman tube explosive testing system was employed to evaluate the effect of NiP@Fe-SBA-15 on PP dust deflagration. Results indicated that as the NiP@Fe-SBA-15 additive increased, the flame propagation speed, brightness, and flame length of PP deflagration decreased significantly, with flame propagation almost completely inhibited at a suppressant dosage of 70 wt%. The dual explosion suppression mechanism of NiP@Fe-SBA-15 was analyzed. Physically, NiP@Fe-SBA-15 occupies reaction space, reducing oxygen and combustible volatile concentrations, while the SBA-15 molecular sieve, exposed by thermal decomposition of the suppressant, absorbs heat and forms a physical barrier, thereby reducing combustion intensity. Chemically, NiP decomposition releases Ni· and P· radicals that consume key free radicals (H·, O·, OH·) in combustion reactions, interrupting explosion chain reactions. Meanwhile, Fe-based species rapidly oxidize to Fe3O4, reducing oxygen availability and further weakening combustion intensity. In summary, NiP@Fe-SBA-15 was proven to be an effective explosion suppressant for PP dust explosions, reducing combustion intensity through combined physicochemical synergies. This research provides a new approach to enhancing polypropylene industry safety. Future work will focus on optimizing the industrial application of NiP@Fe-SBA-15 explosion suppressants while addressing cost, environmental sustainability, and stability issues to further advance dust explosion prevention technology.
, Available online , doi: 10.11883/bzycj-2024-0359
Abstract:
Oxy-fuel combustion is one of the effective means to reduce greenhouse gases. To grasp the combustion characteristics of the clean fuel acetylene in O2/CO2 atmosphere and to investigate the effect of different CO2 volume fraction on the lower flammable limit of acetylene, the lower flammable limit of acetylene was experimentally measured in a 5 L cylindrical explosive reaction device. With the increase of CO2 volume fraction from 14% to 85%, the experimental value of the lower flammable limit of acetylene increased from 2.64% to 3.93%, which was linearly increased in a small range. Compared with hydrocarbon fuels such as ethylene, ethane, and propylene, the lower flammability limit of alkanes, olefins, alkynes decrease sequentially, indicating that alkynes have a larger combustion range and a higher hazard factor. Based on the calculation model of limiting laminar flame velocity method, a prediction model applicable to the lower flammability limit of acetylene was established. Through the verification of experimental data, the average absolute error of this prediction model using the USC Ⅱ combustion reaction mechanism is at 0.52%, and the model is accurate and reliable. To explain the reason for the existence of the lower flammability limit from the perspective of the competition between the temperature rise of the heat generation from fuel consumption and the temperature drop of the heat dissipation from the expansion of the fuel body, this study examines the thermodynamic, chemical, and transport effects of CO2 on the lower flammability limit. The combustion reaction mechanism of USC Ⅱ is modified to incorporate the virtual substances FCO2, TCO2, and MCO2, and comparing the flammability limits of the three virtual substances as well as those of the five atmospheres of N2 and CO2. The thermodynamic, chemical and transport effects of CO2 on the lower flammability limit were discussed. The results show that the average proportion of thermodynamic effect is 64%, chemical effect is 35% and transportation effect is 1%.
Oxy-fuel combustion is one of the effective means to reduce greenhouse gases. To grasp the combustion characteristics of the clean fuel acetylene in O2/CO2 atmosphere and to investigate the effect of different CO2 volume fraction on the lower flammable limit of acetylene, the lower flammable limit of acetylene was experimentally measured in a 5 L cylindrical explosive reaction device. With the increase of CO2 volume fraction from 14% to 85%, the experimental value of the lower flammable limit of acetylene increased from 2.64% to 3.93%, which was linearly increased in a small range. Compared with hydrocarbon fuels such as ethylene, ethane, and propylene, the lower flammability limit of alkanes, olefins, alkynes decrease sequentially, indicating that alkynes have a larger combustion range and a higher hazard factor. Based on the calculation model of limiting laminar flame velocity method, a prediction model applicable to the lower flammability limit of acetylene was established. Through the verification of experimental data, the average absolute error of this prediction model using the USC Ⅱ combustion reaction mechanism is at 0.52%, and the model is accurate and reliable. To explain the reason for the existence of the lower flammability limit from the perspective of the competition between the temperature rise of the heat generation from fuel consumption and the temperature drop of the heat dissipation from the expansion of the fuel body, this study examines the thermodynamic, chemical, and transport effects of CO2 on the lower flammability limit. The combustion reaction mechanism of USC Ⅱ is modified to incorporate the virtual substances FCO2, TCO2, and MCO2, and comparing the flammability limits of the three virtual substances as well as those of the five atmospheres of N2 and CO2. The thermodynamic, chemical and transport effects of CO2 on the lower flammability limit were discussed. The results show that the average proportion of thermodynamic effect is 64%, chemical effect is 35% and transportation effect is 1%.
, Available online , doi: 10.11883/bzycj-2024-0431
Abstract:
Compared to concrete and steel structures, research on the blast resistance of timber structures is relatively scarce. Although experimental studies on the blast performance of light-frame wood walls have been conducted, relevant numerical studies remain limited. This study addresses the numerical modeling of light-frame wood walls under blast loads, with a focus on the determination of the dynamic increase factor (DIF) for nail connections and the failure criteria for wood studs. Based on the partial composite action theory, an analytical expression was derived to describe the relationship between the DIF for nail connections and other mechanical properties of light-frame wood walls, including the stiffness of studs, the stiffness of sheathing panels, and the stiffness of nail connections. A reasonable value for the DIF of nail connections was provided by introducing experimentally measured DIFs for wood studs and wood-frame walls. On this basis, a finite element (FE) model for blast resistance analysis of light-frame wood walls was developed. In this model, the wood studs, sheathing panels, and nail connections were represented using beam elements, shell elements, and discrete beam elements, respectively. The orthotropic characteristics of wood-based structural panels, the nonlinear dynamic behavior of nail connections, and the dynamic elastic-plastic features of wood studs were also appropriately modeled. Verification of the developed model against experimental data indicates that it can accurately predict the dynamic response of light-frame wood walls under blast loads, as well as the time and corresponding peak displacement when wood studs fracture. FE analyses also show that if the variation of the studs’ material properties is reasonably accounted for, the predictions of the dynamic response and failure mode after the fracture of studs are in good agreement with the experimental results. The developed model paves the way for assessing the blast vulnerability of light-frame wood structures in future research.
Compared to concrete and steel structures, research on the blast resistance of timber structures is relatively scarce. Although experimental studies on the blast performance of light-frame wood walls have been conducted, relevant numerical studies remain limited. This study addresses the numerical modeling of light-frame wood walls under blast loads, with a focus on the determination of the dynamic increase factor (DIF) for nail connections and the failure criteria for wood studs. Based on the partial composite action theory, an analytical expression was derived to describe the relationship between the DIF for nail connections and other mechanical properties of light-frame wood walls, including the stiffness of studs, the stiffness of sheathing panels, and the stiffness of nail connections. A reasonable value for the DIF of nail connections was provided by introducing experimentally measured DIFs for wood studs and wood-frame walls. On this basis, a finite element (FE) model for blast resistance analysis of light-frame wood walls was developed. In this model, the wood studs, sheathing panels, and nail connections were represented using beam elements, shell elements, and discrete beam elements, respectively. The orthotropic characteristics of wood-based structural panels, the nonlinear dynamic behavior of nail connections, and the dynamic elastic-plastic features of wood studs were also appropriately modeled. Verification of the developed model against experimental data indicates that it can accurately predict the dynamic response of light-frame wood walls under blast loads, as well as the time and corresponding peak displacement when wood studs fracture. FE analyses also show that if the variation of the studs’ material properties is reasonably accounted for, the predictions of the dynamic response and failure mode after the fracture of studs are in good agreement with the experimental results. The developed model paves the way for assessing the blast vulnerability of light-frame wood structures in future research.
, Available online , doi: 10.11883/bzycj-2024-0361
Abstract:
To study the damage law of calcareous conglomerate under blasting, firstly, the damage fracture process and mechanism of calcareous conglomerate under blasting load were revealed based on the theory of damage fracture mechanics. A meso-scale model of conglomerate, including filler, conglomerate and interfacial transition zone (ITZ), was established by using LS-DYNA and Fortran programming, and the propagation law of explosive stress wave and its damage characteristics were analyzed. The damage fracture process of calcareous conglomerate under blasting can be divided into four stages, namely: compression damage in both gravel and fill; tensile damage in gravel and compression damage in fill; tensile damage in both gravel and fill; and tensile damage at the intersection of gravel and fill. Numerical results show that under blasting loads, the gravel has higher equivalent stresses, the fill has the lowest, stress concentration is evident at the ITZ, and the stress gap between the gravel and the fill decreases as the distance increases. The conglomerate sustains relatively minor damage, with a notable phenomenon of damage occurring around it. However, and the filler experiences significant damage. The expansion of blasting crack in Calcareous conglomerate forms mainly along the direction of stress wave propagation. Cracks tend to develop along the filler with lower physical and mechanical properties, as well as along the junction surfaces. The damage to the gravel is comparatively less severe. Blasting blockiness is mainly manifested as the filler wrapping gravel, and the distribution of blasting blockiness is affected by the bonding force at the intersection surface and the distribution of gravel.
To study the damage law of calcareous conglomerate under blasting, firstly, the damage fracture process and mechanism of calcareous conglomerate under blasting load were revealed based on the theory of damage fracture mechanics. A meso-scale model of conglomerate, including filler, conglomerate and interfacial transition zone (ITZ), was established by using LS-DYNA and Fortran programming, and the propagation law of explosive stress wave and its damage characteristics were analyzed. The damage fracture process of calcareous conglomerate under blasting can be divided into four stages, namely: compression damage in both gravel and fill; tensile damage in gravel and compression damage in fill; tensile damage in both gravel and fill; and tensile damage at the intersection of gravel and fill. Numerical results show that under blasting loads, the gravel has higher equivalent stresses, the fill has the lowest, stress concentration is evident at the ITZ, and the stress gap between the gravel and the fill decreases as the distance increases. The conglomerate sustains relatively minor damage, with a notable phenomenon of damage occurring around it. However, and the filler experiences significant damage. The expansion of blasting crack in Calcareous conglomerate forms mainly along the direction of stress wave propagation. Cracks tend to develop along the filler with lower physical and mechanical properties, as well as along the junction surfaces. The damage to the gravel is comparatively less severe. Blasting blockiness is mainly manifested as the filler wrapping gravel, and the distribution of blasting blockiness is affected by the bonding force at the intersection surface and the distribution of gravel.
, Available online , doi: 10.11883/bzycj-2024-0232
Abstract:
Applicable buffer-head covers and various open-cell foam buffer configurations were designed to meet the buffering and load reduction challenges during high-speed water entry vehicles. In the arbitrary Lagrangian-Euler method, the grid can move as the material flows within the spatial grid. This unique feature allows the arbitrary Lagrangian-Euler method to harness the advantages of both the Lagrangian and Euler methods. It not only overcomes numerical calculation challenges stemming from element distortion but also facilitates accurate computation of large deformations and displacements in solids and fluids. This makes it particularly well-suited for addressing high-speed water buffer load reduction problems. Based on the arbitrary Lagrangian-Eulerian method and considering the large deformation of the buffer foam and the hood, a numerical calculation model for buffering and load reduction during high-speed water entry of navigational bodies was established. Through numerical simulations, an in-depth study was conducted on the load reduction performance of buffer foams with different open-cell patterns. The results indicate that open-cell buffer foam exhibits significant advantages in dispersing the impact force and absorbing impact energy during water entry of navigational bodies, offering better buffering effects. Simultaneously, the buffer head cover experiences local progressive fragmentation upon water entry. The deformation and rupture of the outer wall surface of the buffer head cover at the connector between the buffer shell and the navigational body are caused by the stress concentration distribution generated during water impact. When the open-cell foam contacts the water surface, the front part enters the collapse stage, absorbing a large amount of energy and undergoing plastic deformation, resulting in a reduction of pores. This stage is the primary energy absorption phase for the buffer foam. In comparison, closed-cell foam exhibits poorer load reduction performance. Therefore, the adoption of open-cell foam represents a superior solution for buffering and load reduction during high-speed water entry of navigational bodies.
Applicable buffer-head covers and various open-cell foam buffer configurations were designed to meet the buffering and load reduction challenges during high-speed water entry vehicles. In the arbitrary Lagrangian-Euler method, the grid can move as the material flows within the spatial grid. This unique feature allows the arbitrary Lagrangian-Euler method to harness the advantages of both the Lagrangian and Euler methods. It not only overcomes numerical calculation challenges stemming from element distortion but also facilitates accurate computation of large deformations and displacements in solids and fluids. This makes it particularly well-suited for addressing high-speed water buffer load reduction problems. Based on the arbitrary Lagrangian-Eulerian method and considering the large deformation of the buffer foam and the hood, a numerical calculation model for buffering and load reduction during high-speed water entry of navigational bodies was established. Through numerical simulations, an in-depth study was conducted on the load reduction performance of buffer foams with different open-cell patterns. The results indicate that open-cell buffer foam exhibits significant advantages in dispersing the impact force and absorbing impact energy during water entry of navigational bodies, offering better buffering effects. Simultaneously, the buffer head cover experiences local progressive fragmentation upon water entry. The deformation and rupture of the outer wall surface of the buffer head cover at the connector between the buffer shell and the navigational body are caused by the stress concentration distribution generated during water impact. When the open-cell foam contacts the water surface, the front part enters the collapse stage, absorbing a large amount of energy and undergoing plastic deformation, resulting in a reduction of pores. This stage is the primary energy absorption phase for the buffer foam. In comparison, closed-cell foam exhibits poorer load reduction performance. Therefore, the adoption of open-cell foam represents a superior solution for buffering and load reduction during high-speed water entry of navigational bodies.
, Available online , doi: 10.11883/bzycj-2024-0191
Abstract:
For the estimation of blast loading in complex structures, traditional numerical simulation methods were computationally intensive whereas rapid estimation methods based on neural networks can only provide estimates at local points without providing confidence intervals for the predicted results. To achieve fast and reliable estimation of the blast loading in complex structures, Bayesian theory was combined with deep learning to develop a Bayesian deep learning approach for rapid estimation of blast loading in complex structures. The approach initially utilized open-source numerical simulation software to generate a dataset of blast loading in complex structures, encompassing a wide range of parameters such as explosion equivalents, locations, and velocities. During this process, mesh sizes that balanced computational accuracy and speed were determined through mesh sensitivity analysis and the verification of the numerical simulation accuracy. Then, the deep learning model was extended into a Bayesian deep learning model based on Bayesian theory. By introducing probability distributions over the weights of the neural network, the model parameters were treated as random variables. Variational Bayesian inference was then employed to efficiently train the model, ensuring the accuracy of rapid blast loading estimation while also equipping the model with the ability to quantify uncertainty. Finally, metrics such as mean absolute percentage error (MAPE), normalized mean prediction interval width (NMPIW) and prediction interval coverage probability (PICP) were adopted to quantitatively assess the model's estimated accuracy and the precision of the uncertainty quantification. Additionally, an error decomposition of the estimation results was conducted to analyze model’s performance based on target parameters and scaled distance. The results indicate that the proposed method achieved an estimation error of 12.2% on the test set, with a confidence interval covering over 81.6% of true values, and less than 20 milliseconds of the estimation time for a single sample point. This method provides a novel approach for fast and accurate estimation of blast loading in complex structures with sufficient confidence for the estimation results.
For the estimation of blast loading in complex structures, traditional numerical simulation methods were computationally intensive whereas rapid estimation methods based on neural networks can only provide estimates at local points without providing confidence intervals for the predicted results. To achieve fast and reliable estimation of the blast loading in complex structures, Bayesian theory was combined with deep learning to develop a Bayesian deep learning approach for rapid estimation of blast loading in complex structures. The approach initially utilized open-source numerical simulation software to generate a dataset of blast loading in complex structures, encompassing a wide range of parameters such as explosion equivalents, locations, and velocities. During this process, mesh sizes that balanced computational accuracy and speed were determined through mesh sensitivity analysis and the verification of the numerical simulation accuracy. Then, the deep learning model was extended into a Bayesian deep learning model based on Bayesian theory. By introducing probability distributions over the weights of the neural network, the model parameters were treated as random variables. Variational Bayesian inference was then employed to efficiently train the model, ensuring the accuracy of rapid blast loading estimation while also equipping the model with the ability to quantify uncertainty. Finally, metrics such as mean absolute percentage error (MAPE), normalized mean prediction interval width (NMPIW) and prediction interval coverage probability (PICP) were adopted to quantitatively assess the model's estimated accuracy and the precision of the uncertainty quantification. Additionally, an error decomposition of the estimation results was conducted to analyze model’s performance based on target parameters and scaled distance. The results indicate that the proposed method achieved an estimation error of 12.2% on the test set, with a confidence interval covering over 81.6% of true values, and less than 20 milliseconds of the estimation time for a single sample point. This method provides a novel approach for fast and accurate estimation of blast loading in complex structures with sufficient confidence for the estimation results.
, Available online , doi: 10.11883/bzycj-2024-0203
Abstract:
The equation of state for the detonation products of explosives is one of the foundations in explosion physics. JWL equation of state has been widely applied to study the properties of various explosives. In order to obtain the equation of state of the detonation products, an underwater explosion method was used to study JWL equation of state for the detonation of RDX. It considered the explosion bubble expansion process based on the conservation of energy including Es0 (initial shock wave energy), Ept (potential energy of water), Ec (kinetic energy of water) and Er (energy loss by bubble expansion), which are related to the underwater explosion bubble radius (R-t) and shock wave front (Rs-t) measured in the underwater explosion experiments as functions of time. Based on the experimental results and using the same method to process the experimental data in cylinder experiment, the time functions of explosion bubble expansion radius and variation of shock wave front position were fitted and the parameters of the JWL equation of state for RDX detonation products were obtained. In order to analyze the accuracy of the parameters of the JWL equation of state obtained by the underwater explosion method, the time history of the underwater explosions bubble pulsating pressure wave was calculated using the bubble dynamics equation. It shows that the calculation results agree well with the bubble expansion radius and bubble pulsation period determined using the underwater explosion experiments in a pool. The calculated bubble radius obtained by the proposed measurement method has a smaller deviation from that obtained by the cylinder experimental value, especially in the low-pressure stage compare with the JWL state parameters obtained from cylinder method. This method provides a testing approach for the equation of state of detonation products with low cost, reduced size limitations and a wide pressure range.
The equation of state for the detonation products of explosives is one of the foundations in explosion physics. JWL equation of state has been widely applied to study the properties of various explosives. In order to obtain the equation of state of the detonation products, an underwater explosion method was used to study JWL equation of state for the detonation of RDX. It considered the explosion bubble expansion process based on the conservation of energy including Es0 (initial shock wave energy), Ept (potential energy of water), Ec (kinetic energy of water) and Er (energy loss by bubble expansion), which are related to the underwater explosion bubble radius (R-t) and shock wave front (Rs-t) measured in the underwater explosion experiments as functions of time. Based on the experimental results and using the same method to process the experimental data in cylinder experiment, the time functions of explosion bubble expansion radius and variation of shock wave front position were fitted and the parameters of the JWL equation of state for RDX detonation products were obtained. In order to analyze the accuracy of the parameters of the JWL equation of state obtained by the underwater explosion method, the time history of the underwater explosions bubble pulsating pressure wave was calculated using the bubble dynamics equation. It shows that the calculation results agree well with the bubble expansion radius and bubble pulsation period determined using the underwater explosion experiments in a pool. The calculated bubble radius obtained by the proposed measurement method has a smaller deviation from that obtained by the cylinder experimental value, especially in the low-pressure stage compare with the JWL state parameters obtained from cylinder method. This method provides a testing approach for the equation of state of detonation products with low cost, reduced size limitations and a wide pressure range.
, Available online , doi: 10.11883/bzycj-2024-0279
Abstract:
Prefabricated concrete bursting layer has a very important application prospect in the field of protective engineering attributed to its technical advantages including high construction efficiency and construction quality. However, compared with the monolithic cast-in-situ concrete bursting layer, the impact resistance of the prefabricated concrete bursting layer may be significantly reduced because of the interfaces between the prefabricated blocks and the cast-in-situ part. Therefore, it is important for engineers to reasonably design the prefabricated concrete bursting layer to make its penetration resistance comparable to the monolithic one. To this end, a kind of prefabricated bursting layer connected by wet joints and rebars was proposed in our previous study. In order to apply the prefabricated bursting layer in protective engineering, a series of numerical models were developed to further study its penetration resistance. Firstly, based on the Kong-Fang model and smoothed particle Galerkin (SPG) method, the numerical models were developed and validated against the experimental data of projectile penetrating monolithic and prefabricated targets. Then, the validated numerical models were further used to investigate the influences of prefabricated block size, wet joint width and anchorage length, spacing and diameter of rebars on the penetration resistance of prefabricated targets. Numerical results indicate that increasing the width of wet joints, reducing the spacing between rebars, and extending the anchorage length of rebars can significantly enhance the penetration resistance of prefabricated targets. After clarifying the influences of these parameters, an engineering design method for a prefabricated concrete bursting layer was proposed. Finally, based on this method, two prefabricated high performance concrete targets subjected to two typical types of warhead penetration were designed. Numerical results show that the penetration resistances of two prefabricated targets were comparable to monolithic targets. The proposed engineering design method can provide a reference for engineering applications of prefabricated concrete bursting layers connected by the wet joints and rebars.
Prefabricated concrete bursting layer has a very important application prospect in the field of protective engineering attributed to its technical advantages including high construction efficiency and construction quality. However, compared with the monolithic cast-in-situ concrete bursting layer, the impact resistance of the prefabricated concrete bursting layer may be significantly reduced because of the interfaces between the prefabricated blocks and the cast-in-situ part. Therefore, it is important for engineers to reasonably design the prefabricated concrete bursting layer to make its penetration resistance comparable to the monolithic one. To this end, a kind of prefabricated bursting layer connected by wet joints and rebars was proposed in our previous study. In order to apply the prefabricated bursting layer in protective engineering, a series of numerical models were developed to further study its penetration resistance. Firstly, based on the Kong-Fang model and smoothed particle Galerkin (SPG) method, the numerical models were developed and validated against the experimental data of projectile penetrating monolithic and prefabricated targets. Then, the validated numerical models were further used to investigate the influences of prefabricated block size, wet joint width and anchorage length, spacing and diameter of rebars on the penetration resistance of prefabricated targets. Numerical results indicate that increasing the width of wet joints, reducing the spacing between rebars, and extending the anchorage length of rebars can significantly enhance the penetration resistance of prefabricated targets. After clarifying the influences of these parameters, an engineering design method for a prefabricated concrete bursting layer was proposed. Finally, based on this method, two prefabricated high performance concrete targets subjected to two typical types of warhead penetration were designed. Numerical results show that the penetration resistances of two prefabricated targets were comparable to monolithic targets. The proposed engineering design method can provide a reference for engineering applications of prefabricated concrete bursting layers connected by the wet joints and rebars.
, Available online , doi: 10.11883/bzycj-2024-0207
Abstract:
To investigate the dynamic mechanical characterization of non-pure and non-intact ice materials under impact loads, a modified split Hopkinson pressure bar (SHPB) was used. Rapid loading, rod end cooling and waveform shaping techniques were used to ensure the stability of the ice material and achieve dynamic stress balance during loading. The impact mechanical properties of complete ice (pure water, containing 2.5%, 3.5%, 4.5% salt, containing 2.0%, 4.5%, 8.5% coconut) and spliced ice (splicing interface inclination 30°, 60°) at freezing temperature of −10 ℃ were studied. The strain rate ranges from 150~250 s−1. The failure process was recorded by using the high-speed camera triggered simultaneously with the pressure rod. The correlation between the stress and strain of the sample, along with the failure process, was determined by analyzing the time history curve of sample. The failure mode of the spliced ice sample was analyzed by combining the Mohr-Coulomb strength criterion. The results show that the pure water ice exhibits the highest compressive strength, followed by the ice with coconut shreds, and both of them show a positive strain rate effect. However, the compressive strength of the ice with salt addition decreases significantly due to its loose structure and the strain rate effect is not obvious. The dynamic compressive strength of ice samples added with coconut fiber increases firstly and then decreases with the increase of coconut fiber content. Ice samples with high coconut fiber content are prone to "double peak" phenomenon due to the binding effect of coconut fiber on broken ice with small particle size. The splicing plane affects the crack growth, resulting in lower compressive strength than the intact ice sample, and affects the failure mode as well. The ice with small interface inclination is mainly damaged by interface slip, while the ice with large interface inclination is mainly damaged by whole ice, which is similar to the intact ice. The research results provide theoretical basis and method reference for the dynamic mechanical properties of non-pure and non-intact ice materials under impact loads.
To investigate the dynamic mechanical characterization of non-pure and non-intact ice materials under impact loads, a modified split Hopkinson pressure bar (SHPB) was used. Rapid loading, rod end cooling and waveform shaping techniques were used to ensure the stability of the ice material and achieve dynamic stress balance during loading. The impact mechanical properties of complete ice (pure water, containing 2.5%, 3.5%, 4.5% salt, containing 2.0%, 4.5%, 8.5% coconut) and spliced ice (splicing interface inclination 30°, 60°) at freezing temperature of −10 ℃ were studied. The strain rate ranges from 150~250 s−1. The failure process was recorded by using the high-speed camera triggered simultaneously with the pressure rod. The correlation between the stress and strain of the sample, along with the failure process, was determined by analyzing the time history curve of sample. The failure mode of the spliced ice sample was analyzed by combining the Mohr-Coulomb strength criterion. The results show that the pure water ice exhibits the highest compressive strength, followed by the ice with coconut shreds, and both of them show a positive strain rate effect. However, the compressive strength of the ice with salt addition decreases significantly due to its loose structure and the strain rate effect is not obvious. The dynamic compressive strength of ice samples added with coconut fiber increases firstly and then decreases with the increase of coconut fiber content. Ice samples with high coconut fiber content are prone to "double peak" phenomenon due to the binding effect of coconut fiber on broken ice with small particle size. The splicing plane affects the crack growth, resulting in lower compressive strength than the intact ice sample, and affects the failure mode as well. The ice with small interface inclination is mainly damaged by interface slip, while the ice with large interface inclination is mainly damaged by whole ice, which is similar to the intact ice. The research results provide theoretical basis and method reference for the dynamic mechanical properties of non-pure and non-intact ice materials under impact loads.
, Available online , doi: 10.11883/bzycj-2024-0254
Abstract:
To address the issues of over-excavation at the tunnel arch foot due to the difficulty of forming the perimeter hole blasting and under-excavation at the tunnel face bottom, the damage characteristics of surrounding rock caused by perimeter hole blasting at the arch foot of a horseshoe-shaped tunnel were studied through a combination of theoretical calculations and numerical simulations. On the theoretical level, an in-depth analysis of the stress distribution and crack radius in the arch foot area was conducted based on the principles of blasting mechanics, and the theoretical charge length for the perimeter holes at the arch foot was derived. Building on this, a 3D numerical model of the perimeter holes at the arch foot was established through numerical simulation. During the modeling process, the damage evolution in the surrounding rock during blasting was simulated by introducing an appropriate damage model, and post-blast damage cloud maps were generated. By comparing the damage cloud maps under different conditions, the relationship between blasting effectiveness and parameters such as free surface shape, charge amount, and void deflection angle was analyzed, further revealing the mechanisms by which these parameters influence the blasting formation results, which were validated through field experiments. The research results indicate that the shape of the free surface significantly impacts the extent of surrounding rock damage and the energy utilization efficiency of explosives. A concave free surface results in a smaller damage range compared to a flat free surface, with greater rock confinement, making it difficult for the explosives to effectively fracture the surrounding rock, leading to an energy utilization rate of only 78%. The blasting effectiveness shows a trend of first increasing and then decreasing with the increase in charge amount, with the optimal blasting effectiveness achieved when the linear charge density of the perimeter holes at the arch foot is 0.624. Additionally, by setting voids and adjusting the void deflection angle, the blasting effectiveness of the perimeter holes at the arch foot can be improved. With the optimized blasting parameters, the maximum linear over-excavation at the arch foot was reduced by 53.1%, resulting in a smooth tunnel contour. The research outcomes are engineeringly feasible and provide valuable insights for similar projects.
To address the issues of over-excavation at the tunnel arch foot due to the difficulty of forming the perimeter hole blasting and under-excavation at the tunnel face bottom, the damage characteristics of surrounding rock caused by perimeter hole blasting at the arch foot of a horseshoe-shaped tunnel were studied through a combination of theoretical calculations and numerical simulations. On the theoretical level, an in-depth analysis of the stress distribution and crack radius in the arch foot area was conducted based on the principles of blasting mechanics, and the theoretical charge length for the perimeter holes at the arch foot was derived. Building on this, a 3D numerical model of the perimeter holes at the arch foot was established through numerical simulation. During the modeling process, the damage evolution in the surrounding rock during blasting was simulated by introducing an appropriate damage model, and post-blast damage cloud maps were generated. By comparing the damage cloud maps under different conditions, the relationship between blasting effectiveness and parameters such as free surface shape, charge amount, and void deflection angle was analyzed, further revealing the mechanisms by which these parameters influence the blasting formation results, which were validated through field experiments. The research results indicate that the shape of the free surface significantly impacts the extent of surrounding rock damage and the energy utilization efficiency of explosives. A concave free surface results in a smaller damage range compared to a flat free surface, with greater rock confinement, making it difficult for the explosives to effectively fracture the surrounding rock, leading to an energy utilization rate of only 78%. The blasting effectiveness shows a trend of first increasing and then decreasing with the increase in charge amount, with the optimal blasting effectiveness achieved when the linear charge density of the perimeter holes at the arch foot is 0.624. Additionally, by setting voids and adjusting the void deflection angle, the blasting effectiveness of the perimeter holes at the arch foot can be improved. With the optimized blasting parameters, the maximum linear over-excavation at the arch foot was reduced by 53.1%, resulting in a smooth tunnel contour. The research outcomes are engineeringly feasible and provide valuable insights for similar projects.
