2023 Vol. 43, No. 8
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2023, 43(8): 081101.
doi: 10.11883/bzycj-2022-0526
Abstract:
Dynamic fracture behavior is a crucial aspect in rock mechanics and engineering, with significant implications to the safety and effectiveness of structures in fields such as mining and civil engineering. In recent years, significant progress has been made in the study of dynamic crack propagation in rock materials, and the aim of this study is to provide a comprehensive review and summary on the latest achievements in testing techniques, experimental facility, and experimental methods. Various measurement techniques have been developed for dynamic rock crack propagation testing, including X-ray computed tomography, caustics method, digital image correlation method, crack propagation gauge, conductive carbon film test method and acoustic emission. Each of these techniques has advantages and limitations, and the selection of the appropriate technique depends on the specific experimental requirements and constraints. The dynamic fracture behavior in rock under different strain rates has been studied extensively by numerous researchers. The strain rate is a crucial parameter that determines the deformation and failure mechanisms of rocks under dynamic load. The dynamic fracture properties in rock under middle and low strain rates, high strain rates, and ultra-high strain rates have been systematically summarized. The experimental methods used for dynamic fracture testing include the drop-hammer impact device, split Hopkinson pressure bar system, and explosion tests. The failure properties of crack initiation, propagation, arrest behaviors, and dynamic fracture toughness of rocks under different strain rates have been investigated. In conclusion, the study of dynamic crack propagation in rock is a challenging and important field of research in rock mechanics and rock engineering. The development of new experimental techniques and methods has been enabling researchers to gain a deeper understanding of the complex behavior of cracks in rock under dynamic loads. The findings of these studies have important implications for the design of safe and reliable structures in various fields of practical engineering.
Dynamic fracture behavior is a crucial aspect in rock mechanics and engineering, with significant implications to the safety and effectiveness of structures in fields such as mining and civil engineering. In recent years, significant progress has been made in the study of dynamic crack propagation in rock materials, and the aim of this study is to provide a comprehensive review and summary on the latest achievements in testing techniques, experimental facility, and experimental methods. Various measurement techniques have been developed for dynamic rock crack propagation testing, including X-ray computed tomography, caustics method, digital image correlation method, crack propagation gauge, conductive carbon film test method and acoustic emission. Each of these techniques has advantages and limitations, and the selection of the appropriate technique depends on the specific experimental requirements and constraints. The dynamic fracture behavior in rock under different strain rates has been studied extensively by numerous researchers. The strain rate is a crucial parameter that determines the deformation and failure mechanisms of rocks under dynamic load. The dynamic fracture properties in rock under middle and low strain rates, high strain rates, and ultra-high strain rates have been systematically summarized. The experimental methods used for dynamic fracture testing include the drop-hammer impact device, split Hopkinson pressure bar system, and explosion tests. The failure properties of crack initiation, propagation, arrest behaviors, and dynamic fracture toughness of rocks under different strain rates have been investigated. In conclusion, the study of dynamic crack propagation in rock is a challenging and important field of research in rock mechanics and rock engineering. The development of new experimental techniques and methods has been enabling researchers to gain a deeper understanding of the complex behavior of cracks in rock under dynamic loads. The findings of these studies have important implications for the design of safe and reliable structures in various fields of practical engineering.
2023, 43(8): 082301.
doi: 10.11883/bzycj-2023-0106
Abstract:
In order to explore the mechanism of the detonation reaction of emulsion explosives under negative pressure conditions, a self-made visualized spherical explosion tank was designed, and the explosion flame propagation process, detonation wave pressure and explosion noise of emulsion explosive were measured by a high-speed camera, a pressure sensor and a noise meter, respectively. Furthermore, the two-dimensional temperature field of explosion fireball was reconstructed by using the colorimetric temperature measurement technology and the effects of the initial vacuum degree on the explosion temperature field, while the detonation wave characteristic parameters and the explosion noise of emulsion explosives were studied in depth. Combined with the simulation results of the AUTODYN software, the influences of negative pressures on the explosive pressure fields were analyzed, and the detonation mechanism of the emulsion explosive in the negative pressure environment was also discussed. The experimental results show that with the increase of the initial vacuum degree, the explosion fireball became brighter, lasted longer and had a more stable morphology; when the vacuum degree was 0 kPa, the fireball began to rupture at 19.35 μs, while the vacuum degree was 100 kPa, the fireball began to rupture at 58.05 μs; a low initial vacuum degree had little effect on the fireball temperature, while the initial vacuum degree above 60 kPa would significantly increase the explosion temperature of emulsion explosives. The peak pressure and specific impulse of shock wave decreased with the increase of initial vacuum degree, while the effect of initial vacuum degree on the positive pressure action time of shock wave was not obvious. AUTODYN numerical simulation results show that the peak pressure of the shock wave decreases with the increase of the vacuum degree, the shock wave velocity gradually decreases, being closer to the expansion velocity of the detonation product. In addition, the increase of the initial vacuum degree was beneficial for the reduction of the explosion noise, compared with atmospheric pressure, when the vacuum degree in the tank was 100 kPa, the sound pressure level of explosion noise was reduced by 35.9 dB, with a reduction of 29.8%.
In order to explore the mechanism of the detonation reaction of emulsion explosives under negative pressure conditions, a self-made visualized spherical explosion tank was designed, and the explosion flame propagation process, detonation wave pressure and explosion noise of emulsion explosive were measured by a high-speed camera, a pressure sensor and a noise meter, respectively. Furthermore, the two-dimensional temperature field of explosion fireball was reconstructed by using the colorimetric temperature measurement technology and the effects of the initial vacuum degree on the explosion temperature field, while the detonation wave characteristic parameters and the explosion noise of emulsion explosives were studied in depth. Combined with the simulation results of the AUTODYN software, the influences of negative pressures on the explosive pressure fields were analyzed, and the detonation mechanism of the emulsion explosive in the negative pressure environment was also discussed. The experimental results show that with the increase of the initial vacuum degree, the explosion fireball became brighter, lasted longer and had a more stable morphology; when the vacuum degree was 0 kPa, the fireball began to rupture at 19.35 μs, while the vacuum degree was 100 kPa, the fireball began to rupture at 58.05 μs; a low initial vacuum degree had little effect on the fireball temperature, while the initial vacuum degree above 60 kPa would significantly increase the explosion temperature of emulsion explosives. The peak pressure and specific impulse of shock wave decreased with the increase of initial vacuum degree, while the effect of initial vacuum degree on the positive pressure action time of shock wave was not obvious. AUTODYN numerical simulation results show that the peak pressure of the shock wave decreases with the increase of the vacuum degree, the shock wave velocity gradually decreases, being closer to the expansion velocity of the detonation product. In addition, the increase of the initial vacuum degree was beneficial for the reduction of the explosion noise, compared with atmospheric pressure, when the vacuum degree in the tank was 100 kPa, the sound pressure level of explosion noise was reduced by 35.9 dB, with a reduction of 29.8%.
2023, 43(8): 083101.
doi: 10.11883/bzycj-2022-0549
Abstract:
In order to develop a lightweight and efficient energy absorption device, a novel type of the star-shaped hybrid multi-cell (SHM) tubes based on the hybrid design of polygonal cross-section and star-shaped cross-section was proposed. The finite element (FE) models of the polygonal thin-walled (PT) tubes, the star-shaped thin-walled (ST) tubes and the SHM tubes were established by ABAQUS, and the reliability of the FE model was verified by simulating quasi-static axial crush tests. Then, the energy absorption characteristics and deformation modes of three kinds of thin-walled tubes under axial loading conditions were studied by numerical simulation. Based on the simplified super folding element (SSFE) theory, the theoretical formula of the mean crushing force of the SHM tubes under the progressive folding deformation mode is established. The numerical results show that there is a synergistic effect between the polygonal cross-section and the star-shaped cross-section of the SHM tubes. Compared with the PT tubes and the ST tubes, the energy absorption of the SHM tubes is significantly improved. When the number of polygon edges N=6, the cross-section synergistic effect of the SHM tubes is the best, and the energy absorption efficiency is the highest when N=8. Subsequently, the investigations on geometric parameters of the SHM tubes are carried out, and the effects of wall thickness and star angle on crashworthiness are discussed respectively. It is found that the wall thickness has obvious influence on the crashworthiness of the SHM tubes, and the crushing force level increases linearly with the increase of the wall thickness. In addition, the change of the star angle has little influence on crashworthiness. The crushing load efficiency and the specific energy absorption increase first and then decrease with the increase of the star angles. When the star angle α=120°, the SHM tubes has the most excellent crashworthiness. The research results can provide design methods and theoretical guidance for the cross-section design of multi-cell structures.
In order to develop a lightweight and efficient energy absorption device, a novel type of the star-shaped hybrid multi-cell (SHM) tubes based on the hybrid design of polygonal cross-section and star-shaped cross-section was proposed. The finite element (FE) models of the polygonal thin-walled (PT) tubes, the star-shaped thin-walled (ST) tubes and the SHM tubes were established by ABAQUS, and the reliability of the FE model was verified by simulating quasi-static axial crush tests. Then, the energy absorption characteristics and deformation modes of three kinds of thin-walled tubes under axial loading conditions were studied by numerical simulation. Based on the simplified super folding element (SSFE) theory, the theoretical formula of the mean crushing force of the SHM tubes under the progressive folding deformation mode is established. The numerical results show that there is a synergistic effect between the polygonal cross-section and the star-shaped cross-section of the SHM tubes. Compared with the PT tubes and the ST tubes, the energy absorption of the SHM tubes is significantly improved. When the number of polygon edges N=6, the cross-section synergistic effect of the SHM tubes is the best, and the energy absorption efficiency is the highest when N=8. Subsequently, the investigations on geometric parameters of the SHM tubes are carried out, and the effects of wall thickness and star angle on crashworthiness are discussed respectively. It is found that the wall thickness has obvious influence on the crashworthiness of the SHM tubes, and the crushing force level increases linearly with the increase of the wall thickness. In addition, the change of the star angle has little influence on crashworthiness. The crushing load efficiency and the specific energy absorption increase first and then decrease with the increase of the star angles. When the star angle α=120°, the SHM tubes has the most excellent crashworthiness. The research results can provide design methods and theoretical guidance for the cross-section design of multi-cell structures.
2023, 43(8): 083301.
doi: 10.11883/bzycj-2022-0464
Abstract:
In order to meet the demand of low collateral damage, a cross-shape built-in fragmentation directional warhead was invented, which can select different detonation modes according to the target orientation and then control the radial dispersion characteristics of the fragmentation, in which the formation of anti-personnel fragmentation in the target area to achieve directional damage, while in the non-target area to achieve low collateral damage. Numerical simulation was used to study the fragmentation driving process during the detonation of the directional warhead in two modes: adjacent two-point detonation and adjacent three-point detonation. The characteristic parameters such as fragment dispersion velocity and radial dispersion angle were given at each position. Then, two principle samples were prepared and ground static explosion tests were conducted. The fragment velocity and radial dispersion angle were measured through high-speed photography and the distribution characteristics of fragment perforation on the target plate. The accuracy of the simulation is verified by comparing with the numerical simulation results, based on which the fragmentation velocity correction formula is established by introducing the energy distribution angle, and the parameters of the formula are fitted and analyzed according to the simulation results. The results show that the radial dispersion angle of fragments in the directed killing zone is controlled within 145° and 65° under adjacent two-point initiation and adjacent three-point initiation modes respectively, and the proportion of fragments in this area reaches 50.4% and 43% of the total number, respectively. The fragment velocity shows a graded distribution between 535 and 770 m/s. The penetration rate of 1.5 mm thick Q235A steel plate reaches 94.4% and 84.6% respectively, which can achieve the destruction of light vehicle type targets, while the rest of the area is a low incidental safety zone. The calculation result of fragment velocity based on the energy distribution model is basically consistent with the simulation data. The research results can provide new design ideas to the development of low collateral damage warhead.
In order to meet the demand of low collateral damage, a cross-shape built-in fragmentation directional warhead was invented, which can select different detonation modes according to the target orientation and then control the radial dispersion characteristics of the fragmentation, in which the formation of anti-personnel fragmentation in the target area to achieve directional damage, while in the non-target area to achieve low collateral damage. Numerical simulation was used to study the fragmentation driving process during the detonation of the directional warhead in two modes: adjacent two-point detonation and adjacent three-point detonation. The characteristic parameters such as fragment dispersion velocity and radial dispersion angle were given at each position. Then, two principle samples were prepared and ground static explosion tests were conducted. The fragment velocity and radial dispersion angle were measured through high-speed photography and the distribution characteristics of fragment perforation on the target plate. The accuracy of the simulation is verified by comparing with the numerical simulation results, based on which the fragmentation velocity correction formula is established by introducing the energy distribution angle, and the parameters of the formula are fitted and analyzed according to the simulation results. The results show that the radial dispersion angle of fragments in the directed killing zone is controlled within 145° and 65° under adjacent two-point initiation and adjacent three-point initiation modes respectively, and the proportion of fragments in this area reaches 50.4% and 43% of the total number, respectively. The fragment velocity shows a graded distribution between 535 and 770 m/s. The penetration rate of 1.5 mm thick Q235A steel plate reaches 94.4% and 84.6% respectively, which can achieve the destruction of light vehicle type targets, while the rest of the area is a low incidental safety zone. The calculation result of fragment velocity based on the energy distribution model is basically consistent with the simulation data. The research results can provide new design ideas to the development of low collateral damage warhead.
2023, 43(8): 083302.
doi: 10.11883/bzycj-2022-0482
Abstract:
Accurate predictions of the penetration depth and critical perforation thickness of earth penetration weapons into concrete materials are key issues in the field of protective engineering. However, the widely-used formulas have limited predictive accuracy for penetration depth when earth penetration weapons have a large diameter and a high aspect ratio, and are lack of theoretical basis for critical perforation thickness. To resolve the two issues above, the engineering calculation models of rigid ogive-nose shape projectile penetrating and/or perforating into concrete targets are investigated in this paper on the basis of 145 sets of penetration data and 32 sets of perforation data. Firstly, based on the resistance analysis of rigid projectile penetrating into concrete target, a two-stage resistance model is proposed, and then a practical calculation model of penetration depth with the consideration of scaling effect is proposed. The reliability of the proposed model is verified by comparing it with 15 sets of penetration data with large diameter and high aspect ratio as well as the predictions by widely-used ACE formula and NDRC formula. The results show that the average errors of the proposed formula, ACE formula and NDRC formula are 5.5%, 15.7% and 24.9%, respectively. Secondly, based on the assumption that the scabbing is caused by the tensile failure of concrete, a formula for the scabbing height is derived based on the force equilibrium between the stress produced by the projectile and the tensile strength of concrete target. Then, the formulas for the critical perforation thickness, ballistic limit and residual velocity are deduced, which are validated by the relevant experimental data. Besides, the coefficients of concrete targets in preventing perforation for four typical earth penetration weapons are compared and analyzed. The accuracy of proposed calculation models for penetration depth and critical perforation thickness shows a great improvement, providing reliable reference for engineering design.
Accurate predictions of the penetration depth and critical perforation thickness of earth penetration weapons into concrete materials are key issues in the field of protective engineering. However, the widely-used formulas have limited predictive accuracy for penetration depth when earth penetration weapons have a large diameter and a high aspect ratio, and are lack of theoretical basis for critical perforation thickness. To resolve the two issues above, the engineering calculation models of rigid ogive-nose shape projectile penetrating and/or perforating into concrete targets are investigated in this paper on the basis of 145 sets of penetration data and 32 sets of perforation data. Firstly, based on the resistance analysis of rigid projectile penetrating into concrete target, a two-stage resistance model is proposed, and then a practical calculation model of penetration depth with the consideration of scaling effect is proposed. The reliability of the proposed model is verified by comparing it with 15 sets of penetration data with large diameter and high aspect ratio as well as the predictions by widely-used ACE formula and NDRC formula. The results show that the average errors of the proposed formula, ACE formula and NDRC formula are 5.5%, 15.7% and 24.9%, respectively. Secondly, based on the assumption that the scabbing is caused by the tensile failure of concrete, a formula for the scabbing height is derived based on the force equilibrium between the stress produced by the projectile and the tensile strength of concrete target. Then, the formulas for the critical perforation thickness, ballistic limit and residual velocity are deduced, which are validated by the relevant experimental data. Besides, the coefficients of concrete targets in preventing perforation for four typical earth penetration weapons are compared and analyzed. The accuracy of proposed calculation models for penetration depth and critical perforation thickness shows a great improvement, providing reliable reference for engineering design.
2023, 43(8): 083303.
doi: 10.11883/bzycj-2022-0496
Abstract:
Based on the brittle fracture model of rock materials, from the perspective of improving the conversion efficiency of explosive energy to the fracture surface energy of rock materials, it is proposed to use pre-cutting and multi-point shaped charge jet impact on rocks for crack fracturing and propagation, achieving directional rock splitting. A shaped charge that can be used for rock splitting was designed, while the directional splitting mechanism of rock-like brittle materials under the impact of shaped charge jet is studied using numerical method, by which the impact splitting effects of different shapes of high-speed metal rods on rocks are calculated and compared. The formation of the shaped charge jet and the impact fracture process on the rock are analyzed by using numerical simulation, and the optimal shaped charge structure and explosion height for splitting are obtained. In the experiment, 2 shaped charges were used to successfully split the rock samples followed the design direction, and the peak stress on the rock surface obtained from the test were about 0.5−0.8 MPa. The results show that using this shaped charge can form a wedge-shaped metal rod with a length-to-diameter ratio of about 1∶3 at an explosion offset of 25 mm. The shaped charges are set at multiple points along the pre-cutting direction of the designed rock control interface, and at the same time, the wedge-shaped metal rod jets are formed after explosion, which impact the rock and produce a good directional splitting effect. This technology accurately introduces explosive energy into the control interface and converts it into rock fracture surface energy effectively, thereby improving the effective utilization rate of explosives, providing reference for the design of precise control blasting cutting devices for large-scale rock excavation and reducing blasting hazards.
Based on the brittle fracture model of rock materials, from the perspective of improving the conversion efficiency of explosive energy to the fracture surface energy of rock materials, it is proposed to use pre-cutting and multi-point shaped charge jet impact on rocks for crack fracturing and propagation, achieving directional rock splitting. A shaped charge that can be used for rock splitting was designed, while the directional splitting mechanism of rock-like brittle materials under the impact of shaped charge jet is studied using numerical method, by which the impact splitting effects of different shapes of high-speed metal rods on rocks are calculated and compared. The formation of the shaped charge jet and the impact fracture process on the rock are analyzed by using numerical simulation, and the optimal shaped charge structure and explosion height for splitting are obtained. In the experiment, 2 shaped charges were used to successfully split the rock samples followed the design direction, and the peak stress on the rock surface obtained from the test were about 0.5−0.8 MPa. The results show that using this shaped charge can form a wedge-shaped metal rod with a length-to-diameter ratio of about 1∶3 at an explosion offset of 25 mm. The shaped charges are set at multiple points along the pre-cutting direction of the designed rock control interface, and at the same time, the wedge-shaped metal rod jets are formed after explosion, which impact the rock and produce a good directional splitting effect. This technology accurately introduces explosive energy into the control interface and converts it into rock fracture surface energy effectively, thereby improving the effective utilization rate of explosives, providing reference for the design of precise control blasting cutting devices for large-scale rock excavation and reducing blasting hazards.
2023, 43(8): 083304.
doi: 10.11883/bzycj-2023-0005
Abstract:
A single waterjet impact test platform was established based on the first-stage light gas gun in order to study the rain erosion damage behavior, to explore the damage mechanism, and to establish the rain erosion damage criterion of the aircraft skin coating. The gas gun launched a lead bullet to impact the nozzle and squeeze the water in the sealing chamber to produce a high-speed jet. Different impact speeds and angles were achieved by adjusting the air pressure and clamp angle. The samples were composed of carbon fiber T300 woven substrate with three types of coatings of the same thickness, and their mechanical properties were measured using the nano-indentation instrument. The test results show that the impact force on the sample increases with the continuous growth of the impact speed of raindrops, resulting in the extension of the damage area and volume loss of the sample. The typical morphology of all the three coating samples is a circular damaged region surrounding the central undamaged area, and presents a circular peeling with the damage increasing. The damage threshold velocity is 360 m/s. With the impact angle increasing , the normal velocity component gradually decreases, and the damage area and volume of the specimen decrease gradually due to the decrease of the instantaneous impact force on the surface of a liquid droplet. Besides, the coating with superior mechanical properties is more prone to damage than the other two coatings due to its rougher surface, the result proves that surface roughness has more significant influence on rain erosion damage of coatings compared to hardness and modulus.
A single waterjet impact test platform was established based on the first-stage light gas gun in order to study the rain erosion damage behavior, to explore the damage mechanism, and to establish the rain erosion damage criterion of the aircraft skin coating. The gas gun launched a lead bullet to impact the nozzle and squeeze the water in the sealing chamber to produce a high-speed jet. Different impact speeds and angles were achieved by adjusting the air pressure and clamp angle. The samples were composed of carbon fiber T300 woven substrate with three types of coatings of the same thickness, and their mechanical properties were measured using the nano-indentation instrument. The test results show that the impact force on the sample increases with the continuous growth of the impact speed of raindrops, resulting in the extension of the damage area and volume loss of the sample. The typical morphology of all the three coating samples is a circular damaged region surrounding the central undamaged area, and presents a circular peeling with the damage increasing. The damage threshold velocity is 360 m/s. With the impact angle increasing , the normal velocity component gradually decreases, and the damage area and volume of the specimen decrease gradually due to the decrease of the instantaneous impact force on the surface of a liquid droplet. Besides, the coating with superior mechanical properties is more prone to damage than the other two coatings due to its rougher surface, the result proves that surface roughness has more significant influence on rain erosion damage of coatings compared to hardness and modulus.
2023, 43(8): 085101.
doi: 10.11883/bzycj-2022-0456
Abstract:
To investigate the sympathetic detonation (SD) response and protection method of shell explosive in the packaging box, the sympathetic detonation experiment of JHL-2 (RDX/Al/binder = 65.5/30/4.5) explosive charges in the packaging box was carried out. The response of the acceptor charges was characterized by the residual of explosive and the breakage of the shell. A calculation model for the sympathetic detonation of shell explosives in packaging box is established, and the numerical simulation of the sympathetic detonation experiment is carried out by using the nonlinear finite element method. The calculation model is verified to be reliable according to the test results. The results of the simulation study show that the main cause for SD of charges in packaging box is the impact of high-speed fragments. According to the experiment result, simulation result and the fragmentation impact initiation criteria of explosive charge, the anti-sympathetic detonation design is implemented for the packaging box. The anti-sympathetic detonation design considering weight and price is as follows: 20 mm wooden partition is set in the adjacent explosive charge, and 2 mm aluminum partition is set on the bottom of the packaging box. A new sympathetic detonation experiment was performed with anti-sympathetic detonation modifications on the packaging box included. The results show that under the unprotected condition, two acceptor charges in the same packaging box with the donor charge and one acceptor charge in the packaging box below the donor charge detonated, and one acceptor charge in the lower packaging box didn’t react; when 20 mm wooden partition was set between adjacent charges and a 2 mm aluminum plate was set on the bottom of the packaging box, only one of the acceptor charges adjacent to the donor charge had a reaction from deflagration to explosion level, and the other three acceptor charges did not react. The research result proves that the installation of partitions inside the packaging box can effectively reduce the possibility of sympathetic detonation, so as to avoid the disastrous consequences caused by sympathetic detonation.
To investigate the sympathetic detonation (SD) response and protection method of shell explosive in the packaging box, the sympathetic detonation experiment of JHL-2 (RDX/Al/binder = 65.5/30/4.5) explosive charges in the packaging box was carried out. The response of the acceptor charges was characterized by the residual of explosive and the breakage of the shell. A calculation model for the sympathetic detonation of shell explosives in packaging box is established, and the numerical simulation of the sympathetic detonation experiment is carried out by using the nonlinear finite element method. The calculation model is verified to be reliable according to the test results. The results of the simulation study show that the main cause for SD of charges in packaging box is the impact of high-speed fragments. According to the experiment result, simulation result and the fragmentation impact initiation criteria of explosive charge, the anti-sympathetic detonation design is implemented for the packaging box. The anti-sympathetic detonation design considering weight and price is as follows: 20 mm wooden partition is set in the adjacent explosive charge, and 2 mm aluminum partition is set on the bottom of the packaging box. A new sympathetic detonation experiment was performed with anti-sympathetic detonation modifications on the packaging box included. The results show that under the unprotected condition, two acceptor charges in the same packaging box with the donor charge and one acceptor charge in the packaging box below the donor charge detonated, and one acceptor charge in the lower packaging box didn’t react; when 20 mm wooden partition was set between adjacent charges and a 2 mm aluminum plate was set on the bottom of the packaging box, only one of the acceptor charges adjacent to the donor charge had a reaction from deflagration to explosion level, and the other three acceptor charges did not react. The research result proves that the installation of partitions inside the packaging box can effectively reduce the possibility of sympathetic detonation, so as to avoid the disastrous consequences caused by sympathetic detonation.
2023, 43(8): 085102.
doi: 10.11883/bzycj-2023-0099
Abstract:
To improve the design and evaluation system of liquid storage structure (LSS) in protection engineering, theoretical research on the dynamic response of LSS subjected to explosion-induced ground shock has been carried out. The rectangular LSS was simplified into a generalised single-degree-of-freedom system with distributed elasticity. The motion equation under horizontal ground shock was established based on the virtual work principle. The vibration mode function, vibration frequency, and dynamic response of the rectangular plate were obtained using the two-way beam function combination, the Rayleigh method, and the Duhamel’s integration method, respectively. The influences of liquid filling ratio, and ground-shock essentials (i.e. the peak, duration, waveform of ground acceleration) on the dynamic response of the model LSS were analysed by calculation examples. The maximum deflection was used as an index to build the dynamic response spectrum of the LSS subjected to explosion-induced ground shocks. The results showed that, with the increase of liquid filling ratio, the fundamental frequency of the structure decreases, and the characteristic factor of ground motion excitation first increase and then decrease. The latter reflects that the strengthening effect of fluid-structure interaction on seismic action is first enhanced and then weakened. Within the elastic range, as the peak value of ground acceleration increases, the deflection response of the LSS increases linearly. The varations in the duration and waveform of ground acceleration affect the spectrum characteristics, causing the nonlinear changes of deflection response. The effects of explosion-induced ground shocks featured by various typical waveforms can be divided into the mitigation, enhancement, and equality regions relative to the equivalent static action. It is conservative to take the peak of response spectrum as the most adverse response for protection design, whereas the calculation considering the range of site explosion parameters would improve the economy of engineering design. The proposed simplified theoretical method meets the requirement of preliminary rapid calculation and provides a reference for the protection design of LSS.
To improve the design and evaluation system of liquid storage structure (LSS) in protection engineering, theoretical research on the dynamic response of LSS subjected to explosion-induced ground shock has been carried out. The rectangular LSS was simplified into a generalised single-degree-of-freedom system with distributed elasticity. The motion equation under horizontal ground shock was established based on the virtual work principle. The vibration mode function, vibration frequency, and dynamic response of the rectangular plate were obtained using the two-way beam function combination, the Rayleigh method, and the Duhamel’s integration method, respectively. The influences of liquid filling ratio, and ground-shock essentials (i.e. the peak, duration, waveform of ground acceleration) on the dynamic response of the model LSS were analysed by calculation examples. The maximum deflection was used as an index to build the dynamic response spectrum of the LSS subjected to explosion-induced ground shocks. The results showed that, with the increase of liquid filling ratio, the fundamental frequency of the structure decreases, and the characteristic factor of ground motion excitation first increase and then decrease. The latter reflects that the strengthening effect of fluid-structure interaction on seismic action is first enhanced and then weakened. Within the elastic range, as the peak value of ground acceleration increases, the deflection response of the LSS increases linearly. The varations in the duration and waveform of ground acceleration affect the spectrum characteristics, causing the nonlinear changes of deflection response. The effects of explosion-induced ground shocks featured by various typical waveforms can be divided into the mitigation, enhancement, and equality regions relative to the equivalent static action. It is conservative to take the peak of response spectrum as the most adverse response for protection design, whereas the calculation considering the range of site explosion parameters would improve the economy of engineering design. The proposed simplified theoretical method meets the requirement of preliminary rapid calculation and provides a reference for the protection design of LSS.
2023, 43(8): 085103.
doi: 10.11883/bzycj-2023-0147
Abstract:
Masonry-infilled walls (MIWs) are prone to crack, fragment, and even collapse under blast loads, attributed to their low strength and weak ductility, which threatens the safety of building structures and the inside occupants and equipment. Aiming to study the dynamic behaviors and failure mechanism of one-way solid MIWs under far-field range explosion, the out-of-plane loading tests on two one-way solid MIWs with different thicknesses were first carried out based on the developed compressed air-driven large cross-section (3 m×3 m) shock tube. The reflected overpressures-time histories that acted on the MIWs, the deflection-time histories, and the deformation failure mode of MIWs were obtained. Then, a refined finite element model of the shock tube was established, and the simplified micro finite element modeling approach of MIWs, as well as the parameter calculation methods of the Riedel-Hiermaier-Thoma material model for expanded masonry blocks and the cohesive contact model for joints, were proposed. The pressure propagation in the shock tube and the out-of-plane dynamic responses and damage of MIWs were further numerically simulated. Finally, the central deflection-time histories of test walls were predicted based on the out-of-plane resistance function and equivalent single-degree-of-freedom model of one-way MIWs under blast loads. It indicated that reducing the height-to-thickness ratio of walls can increase the frame arch thrust, which could significantly improve the blast resistance performance of the MIWs. A105-mm-thick MIW collapsed after one shot, while a 235-mm-thick MIW was slightly damaged after six shots. Both the test and simulation results of reflected overpressure-time histories acted on the surface of MIWs were uniform pulse loads and in good agreement, which validated the reasonability of the design and refined finite element model of the shock tube. The predicted dynamic behaviors of MIWs by the numerical simulation and theoretical calculation method were in good accordance with test data, which can provide a reference for blast-resistant assessment and analysis of MIWs.
Masonry-infilled walls (MIWs) are prone to crack, fragment, and even collapse under blast loads, attributed to their low strength and weak ductility, which threatens the safety of building structures and the inside occupants and equipment. Aiming to study the dynamic behaviors and failure mechanism of one-way solid MIWs under far-field range explosion, the out-of-plane loading tests on two one-way solid MIWs with different thicknesses were first carried out based on the developed compressed air-driven large cross-section (3 m×3 m) shock tube. The reflected overpressures-time histories that acted on the MIWs, the deflection-time histories, and the deformation failure mode of MIWs were obtained. Then, a refined finite element model of the shock tube was established, and the simplified micro finite element modeling approach of MIWs, as well as the parameter calculation methods of the Riedel-Hiermaier-Thoma material model for expanded masonry blocks and the cohesive contact model for joints, were proposed. The pressure propagation in the shock tube and the out-of-plane dynamic responses and damage of MIWs were further numerically simulated. Finally, the central deflection-time histories of test walls were predicted based on the out-of-plane resistance function and equivalent single-degree-of-freedom model of one-way MIWs under blast loads. It indicated that reducing the height-to-thickness ratio of walls can increase the frame arch thrust, which could significantly improve the blast resistance performance of the MIWs. A105-mm-thick MIW collapsed after one shot, while a 235-mm-thick MIW was slightly damaged after six shots. Both the test and simulation results of reflected overpressure-time histories acted on the surface of MIWs were uniform pulse loads and in good agreement, which validated the reasonability of the design and refined finite element model of the shock tube. The predicted dynamic behaviors of MIWs by the numerical simulation and theoretical calculation method were in good accordance with test data, which can provide a reference for blast-resistant assessment and analysis of MIWs.
2023, 43(8): 085104.
doi: 10.11883/bzycj-2022-0260
Abstract:
The failure law of shallow buried reinforced concrete straight wall arch structure in soil under secondary explosion of conventional weapons was studied by explosion test and numerical simulation. Test structure adopts scale model based on similarity principle. Three groups of six shots were set up in the test. LS-DYNA is used to simulate the three groups of working conditions. By comparing the pressure of the measuring point in the soil, the speed of the structural measuring point, the structural deflection and other data, it is found that the simulation results are basically consistent with the experimental results. After comparing the numerical simulation results with the test, the numerical simulation conditions of the secondary explosion are expanded. When the comparison verifies that the numerical simulation is consistent with the experimental results, the secondary explosion conditions under the action of conventional weapons are simulated to study the dynamic response of structures under repeated impacts. Through calculation, it is found that when the proportional distance is set between 0.4-0.6 m/kg1/3, the damage of the structure is mainly caused by the overall damage. Combined with the macroscopic description of structural damage and the maximum deflection span ratio, the damage grade of the structure under the overall effect is divided. By discussing the initial damage of the structure and the failure law of reinforced concrete straight wall arch structure under different explosion sequences, the following conclusions are obtained: when the structure is damaged by explosion, such as cracking and bending, some concrete is out of work due to cracking or entering plasticity, resulting in the change of stiffness of the structure. The final damage degree of the structure is affected by the strike sequence, and the effect of initial explosion on the final damage of structure is greater than that of secondary explosion.
The failure law of shallow buried reinforced concrete straight wall arch structure in soil under secondary explosion of conventional weapons was studied by explosion test and numerical simulation. Test structure adopts scale model based on similarity principle. Three groups of six shots were set up in the test. LS-DYNA is used to simulate the three groups of working conditions. By comparing the pressure of the measuring point in the soil, the speed of the structural measuring point, the structural deflection and other data, it is found that the simulation results are basically consistent with the experimental results. After comparing the numerical simulation results with the test, the numerical simulation conditions of the secondary explosion are expanded. When the comparison verifies that the numerical simulation is consistent with the experimental results, the secondary explosion conditions under the action of conventional weapons are simulated to study the dynamic response of structures under repeated impacts. Through calculation, it is found that when the proportional distance is set between 0.4-0.6 m/kg1/3, the damage of the structure is mainly caused by the overall damage. Combined with the macroscopic description of structural damage and the maximum deflection span ratio, the damage grade of the structure under the overall effect is divided. By discussing the initial damage of the structure and the failure law of reinforced concrete straight wall arch structure under different explosion sequences, the following conclusions are obtained: when the structure is damaged by explosion, such as cracking and bending, some concrete is out of work due to cracking or entering plasticity, resulting in the change of stiffness of the structure. The final damage degree of the structure is affected by the strike sequence, and the effect of initial explosion on the final damage of structure is greater than that of secondary explosion.
2023, 43(8): 085201.
doi: 10.11883/bzycj-2022-0547
Abstract:
In order to reduce blasting vibration reasonably and determine the damage range of single hole, it is necessary to study the impact pressure changing law of different bore diameters. By analyzing the movement process of the hole wall under the action of detonation, a simplified calculation model for three stages of dynamic expansion of the incompressible fluid, rock-breaking, and dynamic expansion of the hole wall under the action of the explosive shock wave is established, and the time history subsection function of the hole wall pressure in each stage is determined. Based on the ideal gas expansion equation, the theoretical amplification factor of peak pressure on the bore wall is determined, the stage characteristics of bore wall pressure change were mathematically unified, and the impact pressure characteristic curves of impact pressure on the bore wall of blast-hole coupling charge were obtained. Based on LS-DYNA numerical simulation software and field industrial model test, the calculation model results were compared and validated by numerical analysis and super-dynamic strain test model test. The impact pressure curves of five different pore diameters (51−200 mm) under the coupled charge condition were obtained, and the theoretical amplification coefficient of the peak pore pressure was verified by experiments. The theoretical model error is controlled between 0.7% and 6.4%. The comparison and analysis of theoretical calculation, historical point of numerical analysis, and measured point data of model test under two specific conditions of 76 and 90 mm show that the theoretical piecewise function can effectively fit the data of numerical analysis and model test. The error of peak pressure is 6.8% and 4.9%, and that of time is 7.6% and 4.8%, respectively.
In order to reduce blasting vibration reasonably and determine the damage range of single hole, it is necessary to study the impact pressure changing law of different bore diameters. By analyzing the movement process of the hole wall under the action of detonation, a simplified calculation model for three stages of dynamic expansion of the incompressible fluid, rock-breaking, and dynamic expansion of the hole wall under the action of the explosive shock wave is established, and the time history subsection function of the hole wall pressure in each stage is determined. Based on the ideal gas expansion equation, the theoretical amplification factor of peak pressure on the bore wall is determined, the stage characteristics of bore wall pressure change were mathematically unified, and the impact pressure characteristic curves of impact pressure on the bore wall of blast-hole coupling charge were obtained. Based on LS-DYNA numerical simulation software and field industrial model test, the calculation model results were compared and validated by numerical analysis and super-dynamic strain test model test. The impact pressure curves of five different pore diameters (51−200 mm) under the coupled charge condition were obtained, and the theoretical amplification coefficient of the peak pore pressure was verified by experiments. The theoretical model error is controlled between 0.7% and 6.4%. The comparison and analysis of theoretical calculation, historical point of numerical analysis, and measured point data of model test under two specific conditions of 76 and 90 mm show that the theoretical piecewise function can effectively fit the data of numerical analysis and model test. The error of peak pressure is 6.8% and 4.9%, and that of time is 7.6% and 4.8%, respectively.
2023, 43(8): 085401.
doi: 10.11883/bzycj-2023-0018
Abstract:
To study the propagation law of gas explosion in a Y-shaped ventilated coal face, the simulation software of Fluent was used to carry out numerical simulation research combined with the actual situation of the N2105 working face in the Yuwu Coal Mine. Firstly, the reliability of the mathematical model in this paper was demonstrated. In addition, the simulation parameters were optimized to make the results fit the actual situation. Finally, a numerical simulation was carried out. The results show that the maximum error between the simulation results and the previous experimental results is 11.3%, and the minimum error is only 1.7%, which verifies the reliability of the mathematical model in this paper. The most reasonable key parameters for the numerical simulation of gas explosion were determined including mesh size, iteration step size and ignition temperature, which are 0.4 m, 0.10 ms and 1 800 K, respectively. The overpressure peak of the gas explosion in the air inlet channel, belt fluting, return airway, and working face and its distance from the explosion source accords with an exponential function, and the relationship between the time required to reach the overpressure peak and the distance from the explosion source is linear. The overpressure attenuation ratio of the working face is 41.03% at 7.5 m away from the tunnel bifurcation, and the overpressure attenuation ratio of the belt fluting is 25.99%. Belt fluting is more dangerous in the event of a gas explosion. In the bifurcation of the working face, the turbulent flow zone gradually moves from the right side to the left side, and the overpressure peak at the bifurcation of the roadway increases. The flame dissipation of the return airway is the fastest, followed by the flame dissipation of the belt fluting, and the flame dissipation of the working face is the slowest. The direction of the flame dissipation in the belt fluting and return airway is opposite to the direction of the flame propagation in the early stage of the gas explosion, while the direction of the flame dissipation in the working face is consistent with the direction of the flame propagation in the early stage of the gas explosion.
To study the propagation law of gas explosion in a Y-shaped ventilated coal face, the simulation software of Fluent was used to carry out numerical simulation research combined with the actual situation of the N2105 working face in the Yuwu Coal Mine. Firstly, the reliability of the mathematical model in this paper was demonstrated. In addition, the simulation parameters were optimized to make the results fit the actual situation. Finally, a numerical simulation was carried out. The results show that the maximum error between the simulation results and the previous experimental results is 11.3%, and the minimum error is only 1.7%, which verifies the reliability of the mathematical model in this paper. The most reasonable key parameters for the numerical simulation of gas explosion were determined including mesh size, iteration step size and ignition temperature, which are 0.4 m, 0.10 ms and 1 800 K, respectively. The overpressure peak of the gas explosion in the air inlet channel, belt fluting, return airway, and working face and its distance from the explosion source accords with an exponential function, and the relationship between the time required to reach the overpressure peak and the distance from the explosion source is linear. The overpressure attenuation ratio of the working face is 41.03% at 7.5 m away from the tunnel bifurcation, and the overpressure attenuation ratio of the belt fluting is 25.99%. Belt fluting is more dangerous in the event of a gas explosion. In the bifurcation of the working face, the turbulent flow zone gradually moves from the right side to the left side, and the overpressure peak at the bifurcation of the roadway increases. The flame dissipation of the return airway is the fastest, followed by the flame dissipation of the belt fluting, and the flame dissipation of the working face is the slowest. The direction of the flame dissipation in the belt fluting and return airway is opposite to the direction of the flame propagation in the early stage of the gas explosion, while the direction of the flame dissipation in the working face is consistent with the direction of the flame propagation in the early stage of the gas explosion.
