2023 Vol. 43, No. 6
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2023, 43(6): 061101.
doi: 10.11883/bzycj-2022-0521
Abstract:
Blast-induced traumatic brain injury (bTBI) is a prevalent consequence of modern warfare and explosion hazards. In recent years, mild primary brain injury caused by blast waves has become the predominant form of injury, garnering significant attention from researchers. Due to ethical and technical limitations, human testing is challenging to conduct; therefore, numerical simulation has emerged as one of the most critical methods for studying bTBI. By combining reasonable physical modeling with reliable modes, we can quantitatively predict the biomechanical response of the human head and brain to blast waves. This approach reveals the mechanical mechanisms underlying brain injury, which is essential for understanding bTBI's biomechanical characteristics and designing protective equipment for individuals. The aim of this review is to furnish a comprehensive overview of the current research on numerical simulation of primary bTBI, encompassing advancements in computational modeling, mechanical mechanisms and protective measures. Focusing on the multi-scale nature of the human brain and biomechanical modeling of bTBI, this article introduces linear elastic, hyper-elastic, and viscoelastic constitutive models for brain tissue; development and evolution of finite element models for the human head in terms of brain structure and mesh size; as well as macroscopic, mesoscopic, and multi-scale modeling methods along with numerical simulation techniques for bTBI. Aiming at the direct effects of wave propagation, cerebral vasculature influence, and the continuous process of bodily response, the mechanical mechanism obtained through numerical simulation is analyzed and discussed. The advancements in numerical simulation of protective strategies for bTBI, including the significance of enhancing head closure and the implementation of novel structures and materials, are expounded upon. Ultimately, a summary is provided regarding current research and application of numerical simulation for bTBI, along with an assessment of future development and improvement.
Blast-induced traumatic brain injury (bTBI) is a prevalent consequence of modern warfare and explosion hazards. In recent years, mild primary brain injury caused by blast waves has become the predominant form of injury, garnering significant attention from researchers. Due to ethical and technical limitations, human testing is challenging to conduct; therefore, numerical simulation has emerged as one of the most critical methods for studying bTBI. By combining reasonable physical modeling with reliable modes, we can quantitatively predict the biomechanical response of the human head and brain to blast waves. This approach reveals the mechanical mechanisms underlying brain injury, which is essential for understanding bTBI's biomechanical characteristics and designing protective equipment for individuals. The aim of this review is to furnish a comprehensive overview of the current research on numerical simulation of primary bTBI, encompassing advancements in computational modeling, mechanical mechanisms and protective measures. Focusing on the multi-scale nature of the human brain and biomechanical modeling of bTBI, this article introduces linear elastic, hyper-elastic, and viscoelastic constitutive models for brain tissue; development and evolution of finite element models for the human head in terms of brain structure and mesh size; as well as macroscopic, mesoscopic, and multi-scale modeling methods along with numerical simulation techniques for bTBI. Aiming at the direct effects of wave propagation, cerebral vasculature influence, and the continuous process of bodily response, the mechanical mechanism obtained through numerical simulation is analyzed and discussed. The advancements in numerical simulation of protective strategies for bTBI, including the significance of enhancing head closure and the implementation of novel structures and materials, are expounded upon. Ultimately, a summary is provided regarding current research and application of numerical simulation for bTBI, along with an assessment of future development and improvement.
2023, 43(6): 062201.
doi: 10.11883/bzycj-2022-0430
Abstract:
In order to comply with the requirements of explosive shock wave protection for the new generation of equipment structures, it is necessary to design a lightweight, high energy absorption ratio structure and further systematically understand its dynamic responses under explosion loadings. A composite lattice sandwich structure with pyramidal truss core was designed, which consisting of carbon fiber reinforced composite panels and metal cores. The explosion experiments were carried out. The failure mechanism and damage mode of this composite lattice structure under intense explosion shock loadings were analyzed. Based on the failure mechanism in mesoscale of the material, both the three-dimensional progressive damage model of the composite panels and the Johnson-Cook damage model of the metal cores were constructed. By combining with the finite element method, a numerical model for predicting explosion shock response of the composite lattice structure was developed. Both the bonding properties between layers of the composite panels, and the performances of the adhesive layer between the panels and the cores were considered in the numerical model. The initial damage criterion based on strain description was established, and the damage dynamic evolution equations corresponding to different damage modes were given. A damage variable was introduced to characterize the attenuation degree of stiffness properties of the damaged elements. Furthermore, the stress of damaged elements could be obtained. The dynamic responses of this structure under different loadings were analyzed using the developed model. The main mechanisms influencing the explosion protection properties of the composite lattice structure were discussed based on both simulated and experimental results. It is revealed that the local failures occur when the composite lattice structure is exposed and close to explosion loadings. The main failure modes are the debonding between the composite panels and the pyramidal truss cores in the edge area, and the fracture of local struts. However, the overall configuration of this composite lattice sandwich structure is basically intact and it still has a good carrying capacities. The damage function considering various variables of load conditions and structural parameters was discussed. The feasible domain for this structure design was given. These research results can provide theoretical basis and technical support for the designing and safety evaluation of lightweight, explosion protection structure of key equipment components.
In order to comply with the requirements of explosive shock wave protection for the new generation of equipment structures, it is necessary to design a lightweight, high energy absorption ratio structure and further systematically understand its dynamic responses under explosion loadings. A composite lattice sandwich structure with pyramidal truss core was designed, which consisting of carbon fiber reinforced composite panels and metal cores. The explosion experiments were carried out. The failure mechanism and damage mode of this composite lattice structure under intense explosion shock loadings were analyzed. Based on the failure mechanism in mesoscale of the material, both the three-dimensional progressive damage model of the composite panels and the Johnson-Cook damage model of the metal cores were constructed. By combining with the finite element method, a numerical model for predicting explosion shock response of the composite lattice structure was developed. Both the bonding properties between layers of the composite panels, and the performances of the adhesive layer between the panels and the cores were considered in the numerical model. The initial damage criterion based on strain description was established, and the damage dynamic evolution equations corresponding to different damage modes were given. A damage variable was introduced to characterize the attenuation degree of stiffness properties of the damaged elements. Furthermore, the stress of damaged elements could be obtained. The dynamic responses of this structure under different loadings were analyzed using the developed model. The main mechanisms influencing the explosion protection properties of the composite lattice structure were discussed based on both simulated and experimental results. It is revealed that the local failures occur when the composite lattice structure is exposed and close to explosion loadings. The main failure modes are the debonding between the composite panels and the pyramidal truss cores in the edge area, and the fracture of local struts. However, the overall configuration of this composite lattice sandwich structure is basically intact and it still has a good carrying capacities. The damage function considering various variables of load conditions and structural parameters was discussed. The feasible domain for this structure design was given. These research results can provide theoretical basis and technical support for the designing and safety evaluation of lightweight, explosion protection structure of key equipment components.
2023, 43(6): 062301.
doi: 10.11883/bzycj-2022-0489
Abstract:
In order to understand the effect of initial void ratio on the thermal phase transformation and ignition response characteristics of HMX-based PBX-3 under slow cook-off condition, a series of experiments were designed and conducted on the confined PBX-3 explosives with the initial void ratios of 1.0%, 4.2% and 13.8%. In each test, the PBX-3 sample composed of two cylindrical pieces of explosive, 25 mm in diameter and 10 mm in height for each, was prepared. The temperature was monitored by the five small-size type-K thermocouples, 0.25 mm in width and 0.15 mm in thickness for each, among which four were arranged at the different positions in the interior of the PBX-3 and one was positioned on the surface of the shell. The experimental apparatus was positioned in a slow cook-off chamber with a transparent glass cover. The slow cook-off setup was heated to 150 ℃ within 30 minutes, followed by a 45-minute soak at 150 ℃, and then heated at 0.25 ℃/min until thermal explosion occurred. During the process, the temperatures at different locations inside the explosive and at the surface of the shell were acquired. The process of the HMX phase transition, the mechanisms exhibiting the effect of the initial void ratio on the HMX phase transition and the effect of the HMX phase transition process on the thermal explosion temperature were analyzed in detail. The result shows that the lower the initial void ratio is, the higher the thermal stress the PBX-3 is subjected to when it is heated to the HMX phase transition temperature, which delays the transformation process of β-HMX into δ-HMX during the slow cook-off. Due to the higher thermal sensitivity of δ-HMX, the longer the phase transition process of HMX in the slow cook-off is, the slower the heat accumulation resulting from the δ-HMX exothermic decomposition reaction, and the higher the temperature of the confined shell at the time of thermal explosion.
In order to understand the effect of initial void ratio on the thermal phase transformation and ignition response characteristics of HMX-based PBX-3 under slow cook-off condition, a series of experiments were designed and conducted on the confined PBX-3 explosives with the initial void ratios of 1.0%, 4.2% and 13.8%. In each test, the PBX-3 sample composed of two cylindrical pieces of explosive, 25 mm in diameter and 10 mm in height for each, was prepared. The temperature was monitored by the five small-size type-K thermocouples, 0.25 mm in width and 0.15 mm in thickness for each, among which four were arranged at the different positions in the interior of the PBX-3 and one was positioned on the surface of the shell. The experimental apparatus was positioned in a slow cook-off chamber with a transparent glass cover. The slow cook-off setup was heated to 150 ℃ within 30 minutes, followed by a 45-minute soak at 150 ℃, and then heated at 0.25 ℃/min until thermal explosion occurred. During the process, the temperatures at different locations inside the explosive and at the surface of the shell were acquired. The process of the HMX phase transition, the mechanisms exhibiting the effect of the initial void ratio on the HMX phase transition and the effect of the HMX phase transition process on the thermal explosion temperature were analyzed in detail. The result shows that the lower the initial void ratio is, the higher the thermal stress the PBX-3 is subjected to when it is heated to the HMX phase transition temperature, which delays the transformation process of β-HMX into δ-HMX during the slow cook-off. Due to the higher thermal sensitivity of δ-HMX, the longer the phase transition process of HMX in the slow cook-off is, the slower the heat accumulation resulting from the δ-HMX exothermic decomposition reaction, and the higher the temperature of the confined shell at the time of thermal explosion.
2023, 43(6): 063101.
doi: 10.11883/bzycj-2022-0421
Abstract:
Experimental and theoretical investigations on basalt rock were implemented to explore the dynamic characteristics of rocks subjected to crustal stress, geothermal environment, and dynamic disturbance and to enrich the theoretical research of underground rock mass engineering. First, a split Hopkinson pressure bar (SHPB) device with a confining pressure loading system was used to carry out constant-pressure dynamic compression tests on basalt samples at room temperature (25 ℃) and those that have experienced high-temperature treatment (100, 300, 450, and 600 ℃) and water-cooling processes, with confining pressures of 2, 4 and 6 MPa. Second, static and microscopic tests were conducted to understand the effects of temperature and confining pressure on the dynamic mechanical properties and failure characteristics of basalt, respectively. Third, a dynamic constitutive model for basalt under confining pressure, high-temperature treatment, and water-cooling was constructed based on the Weibull distribution theory. The results show there is a temperature degradation effect on the dynamic peak stress and elastic modulus of basalt under the three sets of confining pressures. And the higher the confining pressure, the more significant the temperature degradation effect. In addition, a confining-pressure-induced strengthening effect on the dynamic peak stress and elastic modulus was observed for basalt samples at room temperature and those that have undergone the process of high-temperature treatment followed by water cooling, though the effect tends to be weak for the sample that has been subject to 600 ℃ treatment. For a given confining pressure, the degree of fragmentation of the sample increases with the heat-treatment temperature. For a given heat-treatment temperature, the degree of fragmentation of the sample decreases with the increase of confining pressure. The established dynamic constitutive model of basalt has good consistency with the experimental results and can be used to predict the dynamic mechanical behavior of basalt under the coupling effect of high-temperature treatment, water cooling and active confining pressure, thus providing theoretical support for underground resource development and protection of underground engineering.
Experimental and theoretical investigations on basalt rock were implemented to explore the dynamic characteristics of rocks subjected to crustal stress, geothermal environment, and dynamic disturbance and to enrich the theoretical research of underground rock mass engineering. First, a split Hopkinson pressure bar (SHPB) device with a confining pressure loading system was used to carry out constant-pressure dynamic compression tests on basalt samples at room temperature (25 ℃) and those that have experienced high-temperature treatment (100, 300, 450, and 600 ℃) and water-cooling processes, with confining pressures of 2, 4 and 6 MPa. Second, static and microscopic tests were conducted to understand the effects of temperature and confining pressure on the dynamic mechanical properties and failure characteristics of basalt, respectively. Third, a dynamic constitutive model for basalt under confining pressure, high-temperature treatment, and water-cooling was constructed based on the Weibull distribution theory. The results show there is a temperature degradation effect on the dynamic peak stress and elastic modulus of basalt under the three sets of confining pressures. And the higher the confining pressure, the more significant the temperature degradation effect. In addition, a confining-pressure-induced strengthening effect on the dynamic peak stress and elastic modulus was observed for basalt samples at room temperature and those that have undergone the process of high-temperature treatment followed by water cooling, though the effect tends to be weak for the sample that has been subject to 600 ℃ treatment. For a given confining pressure, the degree of fragmentation of the sample increases with the heat-treatment temperature. For a given heat-treatment temperature, the degree of fragmentation of the sample decreases with the increase of confining pressure. The established dynamic constitutive model of basalt has good consistency with the experimental results and can be used to predict the dynamic mechanical behavior of basalt under the coupling effect of high-temperature treatment, water cooling and active confining pressure, thus providing theoretical support for underground resource development and protection of underground engineering.
2023, 43(6): 063102.
doi: 10.11883/bzycj-2022-0248
Abstract:
The formation of complex fracture networks in the shale subjected to cyclic impact loading is an important scientific problem for water-free fracturing technologies of shale reservoirs, such as explosive fracturing and high-energy gas fracturing. Two cyclic impact experiments based on a split Hopkinson pressure bar (SHPB) system were conducted on the freshly exposed black mud shale taken from the Wufeng Formation-Longmaxi Formation in Changning County, Sichuan Province, to investigate the kinetic response and damage evolution characteristics of the shale under different cyclic impact gas pressure and different cyclic impact gas pressure gradients, respectively, and to reveal the energy evolution law of the cyclic impact shale using different impact gas pressure gradients under the condition of controlling the constant total incident energy. The main conclusions are as follows. With the increase in impact pressure, the number of impacts required to rupture the specimen decreases, and the fragmentation and peak stress increase. The specimen undergoes cyclic impact showing the mechanical response characteristics of compaction first and then gradual damage. The damage degree of the shale specimens during cyclic impact was calculated by a dynamic damage model based on the Weibull distribution, and the results show that the damage of the specimen gradually changes from slow deterioration to sudden damage by increasing the cyclic impact pressure. Different cyclic impact experiments with different impact gas pressure gradients were conducted. The results show that under the condition of constant total incident energy, different cyclic incident energy gradients could produce different damage effects, and the energy absorption ratio of the negative or positive gas pressure gradient of cycle impact is greater than that of the zero ones. The absolute value of the pressure gradient shows a positive correlation with the energy absorption ratio. It indicates that under the condition of constant total impact energy, increasing the absolute value of the cyclic impact gradient can produce a better damage effect. The findings of the shale cyclic impact experiments can provide theoretical support for the technological design of multi-stage pulsed high-energy-gas-fracturing.
The formation of complex fracture networks in the shale subjected to cyclic impact loading is an important scientific problem for water-free fracturing technologies of shale reservoirs, such as explosive fracturing and high-energy gas fracturing. Two cyclic impact experiments based on a split Hopkinson pressure bar (SHPB) system were conducted on the freshly exposed black mud shale taken from the Wufeng Formation-Longmaxi Formation in Changning County, Sichuan Province, to investigate the kinetic response and damage evolution characteristics of the shale under different cyclic impact gas pressure and different cyclic impact gas pressure gradients, respectively, and to reveal the energy evolution law of the cyclic impact shale using different impact gas pressure gradients under the condition of controlling the constant total incident energy. The main conclusions are as follows. With the increase in impact pressure, the number of impacts required to rupture the specimen decreases, and the fragmentation and peak stress increase. The specimen undergoes cyclic impact showing the mechanical response characteristics of compaction first and then gradual damage. The damage degree of the shale specimens during cyclic impact was calculated by a dynamic damage model based on the Weibull distribution, and the results show that the damage of the specimen gradually changes from slow deterioration to sudden damage by increasing the cyclic impact pressure. Different cyclic impact experiments with different impact gas pressure gradients were conducted. The results show that under the condition of constant total incident energy, different cyclic incident energy gradients could produce different damage effects, and the energy absorption ratio of the negative or positive gas pressure gradient of cycle impact is greater than that of the zero ones. The absolute value of the pressure gradient shows a positive correlation with the energy absorption ratio. It indicates that under the condition of constant total impact energy, increasing the absolute value of the cyclic impact gradient can produce a better damage effect. The findings of the shale cyclic impact experiments can provide theoretical support for the technological design of multi-stage pulsed high-energy-gas-fracturing.
2023, 43(6): 063201.
doi: 10.11883/bzycj-2022-0313
Abstract:
The complex terminal ballistic parameters of the warhead will affect the circumferential propagation law of the near ground explosive wave and the damage degree to the target. Studying the propagation law of the near ground explosive wave of the cylindrical charge has important engineering significance to accurately evaluate the damage efficiency. By using AUTODYN-3D software, the near ground explosion of cylindrical charge with different terminal ballistic parameters is simulated and calculated, and the data of shock wave pressure in the front, back and side directions produced by the near ground explosion of cylindrical charge are obtained by modeling in two directions respectively. Thus, the influences of four parameters, namely, the velocity of the battle group, the impact angle, the height of the explosion center and the ratio of the length to diameter of the charge, on the propagation of the shock wave produced by the near ground explosion of the cylindrical charge are studied. The evolution process of the shock wave, the peak pressure and the height of the Mach stem are analyzed. The results show that the height of the explosion center is the main factor affecting the height of the shock wave Mach stem during static explosion, and the impact angle and the length-to-diameter ratio of the charge are the main factors affecting the difference in the height direction of the Mach stem. During dynamic explosion, the height of circumferential Mach stem can be increased, especially in the front; in addition, the peak value of forward shock wave increases linearly with the increase of dynamic detonation velocity. The results of orthogonal optimization show that the dynamic detonation velocity has the largest range to the front peak pressure of the cylindrical charge among the four variables; the impact angle has the largest range to the rear peak pressure; and the height of explosion center has the greatest influence on the height of Mach stem. By studying the circumferential propagation law of the shock wave produced by near ground dynamic explosion of the cylindrical charge, the results show that reasonable adjustment of the charge parameters and the front of the near ground explosion can be used for reference to achieve the maximum damage or reduce the hyper-pressure damage in a certain direction.
The complex terminal ballistic parameters of the warhead will affect the circumferential propagation law of the near ground explosive wave and the damage degree to the target. Studying the propagation law of the near ground explosive wave of the cylindrical charge has important engineering significance to accurately evaluate the damage efficiency. By using AUTODYN-3D software, the near ground explosion of cylindrical charge with different terminal ballistic parameters is simulated and calculated, and the data of shock wave pressure in the front, back and side directions produced by the near ground explosion of cylindrical charge are obtained by modeling in two directions respectively. Thus, the influences of four parameters, namely, the velocity of the battle group, the impact angle, the height of the explosion center and the ratio of the length to diameter of the charge, on the propagation of the shock wave produced by the near ground explosion of the cylindrical charge are studied. The evolution process of the shock wave, the peak pressure and the height of the Mach stem are analyzed. The results show that the height of the explosion center is the main factor affecting the height of the shock wave Mach stem during static explosion, and the impact angle and the length-to-diameter ratio of the charge are the main factors affecting the difference in the height direction of the Mach stem. During dynamic explosion, the height of circumferential Mach stem can be increased, especially in the front; in addition, the peak value of forward shock wave increases linearly with the increase of dynamic detonation velocity. The results of orthogonal optimization show that the dynamic detonation velocity has the largest range to the front peak pressure of the cylindrical charge among the four variables; the impact angle has the largest range to the rear peak pressure; and the height of explosion center has the greatest influence on the height of Mach stem. By studying the circumferential propagation law of the shock wave produced by near ground dynamic explosion of the cylindrical charge, the results show that reasonable adjustment of the charge parameters and the front of the near ground explosion can be used for reference to achieve the maximum damage or reduce the hyper-pressure damage in a certain direction.
2023, 43(6): 063202.
doi: 10.11883/bzycj-2022-0515
Abstract:
In the complex battlefield environment, soldiers will not only face the impact damage of bullets and fragments, but also be subjected to the combined effect of shock wave and bullets caused by explosion. In order to enhance the performance of existing protective gears and better protect the safety of soldiers, a human chest composite protective structure composed of polyurea, Kevlar and foam was designed. Based on the LS-DYNA software platform, a finite element model of the chest composite protective structure is established, and the validity of the model is verified by experimental data drawn from open literature. On this basis, air domain, improvised explosive device and transmissive pressure test platform models are established, and the formation of blast shock wave and fragments and their interaction with the protective structure are simulated by the arbitrary Lagrange-Euler method. The transmittance pressures of different protective structures are compared, while the effects of the arrangement types of protective structures and the thickness on the chest protection are analyzed. The results show that under the action of blast shock wave alone, all three protective structures can effectively reduce the overpressure of blast shock wave; different arrangement types of protective structures have less influence on the anti-blast effect, among which polyurea-Kevlar-foam arrangement structure has better anti-blast effect, and Kevlar-polyurea-foam structure has poor anti-blast effect, and the difference between the two pressure peaks is 2.42%. Under the combined action of blast shock wave and fragments, the peak transmissive pressure of all three protective structures is larger than that of the blast alone; the polyurea-Kevlar-foam arrangement structure has a better protective effect, and the peak transmissive pressure is reduced by 18.49% compared with that of the polyurea-Kevlar-polyurea-foam structure, which has the largest peak transmissive pressure. Appropriate increase in structure thickness can reduce the damage to human chest caused by the combined action of blast shock waves and fragments, but continued increase in thickness has limited gain in protection performance.
In the complex battlefield environment, soldiers will not only face the impact damage of bullets and fragments, but also be subjected to the combined effect of shock wave and bullets caused by explosion. In order to enhance the performance of existing protective gears and better protect the safety of soldiers, a human chest composite protective structure composed of polyurea, Kevlar and foam was designed. Based on the LS-DYNA software platform, a finite element model of the chest composite protective structure is established, and the validity of the model is verified by experimental data drawn from open literature. On this basis, air domain, improvised explosive device and transmissive pressure test platform models are established, and the formation of blast shock wave and fragments and their interaction with the protective structure are simulated by the arbitrary Lagrange-Euler method. The transmittance pressures of different protective structures are compared, while the effects of the arrangement types of protective structures and the thickness on the chest protection are analyzed. The results show that under the action of blast shock wave alone, all three protective structures can effectively reduce the overpressure of blast shock wave; different arrangement types of protective structures have less influence on the anti-blast effect, among which polyurea-Kevlar-foam arrangement structure has better anti-blast effect, and Kevlar-polyurea-foam structure has poor anti-blast effect, and the difference between the two pressure peaks is 2.42%. Under the combined action of blast shock wave and fragments, the peak transmissive pressure of all three protective structures is larger than that of the blast alone; the polyurea-Kevlar-foam arrangement structure has a better protective effect, and the peak transmissive pressure is reduced by 18.49% compared with that of the polyurea-Kevlar-polyurea-foam structure, which has the largest peak transmissive pressure. Appropriate increase in structure thickness can reduce the damage to human chest caused by the combined action of blast shock waves and fragments, but continued increase in thickness has limited gain in protection performance.
2023, 43(6): 063301.
doi: 10.11883/bzycj-2022-0225
Abstract:
In order to investigate the anti-explosion performance and post-blast performance after reinforcement/repair of precast concrete (PC) columns under close-in explosion, the explosion test of full-scale PC column and axial compression test of repaired blast-induced damage PC column were conducted. The PC columns with the two widely used assembly connections, i.e., half grout sleeve connection and slurry anchor lap connection, were selected to investigate the effect of connection type on blast resistance and to compare the damage and dynamic response with the reinforced concrete (RC) column of the same specification. The explosion test results show that PC columns had a local damage failure mode. The concrete spalling and oblique cracks occurred near the explosion center and penetrating cracks appeared on the interface of the assembly position. The damage of the anchor slurry lapped PC column was more severe than the grouting sleeve PC column. The PC columns of the two assembly forms had comparable dynamic response and damage characteristics as the RC column in general, but the assembly interface weakened the integrity and shear resistance of the PC column because of its discontinuity. It is the typical weak position of the PC column and should be noticed in design and protection. The axial compression test results show that the axial bearing capacity of the PC column repaired by concrete replacement exceeds 20.8% and 30.6% compared to the undamaged column test value and the calculated value of the same specification respectively. The exceeding proportion of the PC column repaired by concrete replacement and wrapping carbon fiber reinforcement polymer (CFRP) sheet is 38.3% and 49.6% respectively. The results show that it is feasible to reinforce and repair the damaged PC column using the concrete replacement or combining concrete replacement with the wrapping CFRP sheet method, which can meet the requirements of axial bearing capacity.
In order to investigate the anti-explosion performance and post-blast performance after reinforcement/repair of precast concrete (PC) columns under close-in explosion, the explosion test of full-scale PC column and axial compression test of repaired blast-induced damage PC column were conducted. The PC columns with the two widely used assembly connections, i.e., half grout sleeve connection and slurry anchor lap connection, were selected to investigate the effect of connection type on blast resistance and to compare the damage and dynamic response with the reinforced concrete (RC) column of the same specification. The explosion test results show that PC columns had a local damage failure mode. The concrete spalling and oblique cracks occurred near the explosion center and penetrating cracks appeared on the interface of the assembly position. The damage of the anchor slurry lapped PC column was more severe than the grouting sleeve PC column. The PC columns of the two assembly forms had comparable dynamic response and damage characteristics as the RC column in general, but the assembly interface weakened the integrity and shear resistance of the PC column because of its discontinuity. It is the typical weak position of the PC column and should be noticed in design and protection. The axial compression test results show that the axial bearing capacity of the PC column repaired by concrete replacement exceeds 20.8% and 30.6% compared to the undamaged column test value and the calculated value of the same specification respectively. The exceeding proportion of the PC column repaired by concrete replacement and wrapping carbon fiber reinforcement polymer (CFRP) sheet is 38.3% and 49.6% respectively. The results show that it is feasible to reinforce and repair the damaged PC column using the concrete replacement or combining concrete replacement with the wrapping CFRP sheet method, which can meet the requirements of axial bearing capacity.
2023, 43(6): 063302.
doi: 10.11883/bzycj-2022-0231
Abstract:
A three-dimensional finite element (FE) model was developed to quantify the effect of attack angle on the penetration resistance of aramid laminates having varying thickness against flat-nosed projectile. The model was created through a macroscopic approach, which did not take into account the internal microscopic structure of the laminate and macroscopically equated each laminate as a homogeneous orthotropic anisotropic material. The validity of FE simulation results was compared with existing experimental data, with good agreement achieved in terms of residual velocities of the project and damage patterns of the aramid laminates. The validated FE model was subsequently employed to simulate the ballistic responses of 4, 8 and 16 mm target plates in the range of 0°～30° attack angle. The residual velocity of the projectile, energy absorption rate of target, ballistic limit, and perforation energy threshold were calculated to characterize the ballistic performance of aramid laminates. By comparing the damage patterns of the aramid laminates and the contact forces applied to the project under different conditions, the mechanical mechanism by which the attack angle affected the ballistic performance of the aramid laminates at different impact velocities and different target thicknesses was explained. Within the studied working conditions, obtained results revealed that: the attack angle affects significantly the ballistic performance of aramid laminates, depending upon projectile impact velocity and target thickness; the ballistic limit and perforation energy threshold decrease with increasing attack angle, and the degree of such decrease is reduced as target thickness is increased; the residual velocity of projectile increases with increasing attack angle when the impact velocity is close to the ballistic limit and decreases with increasing attack angle when the velocity is well above the ballistic limit; the influencing mechanism of attack angle on ballistic performance varies with the damage pattern of aramid laminates.
A three-dimensional finite element (FE) model was developed to quantify the effect of attack angle on the penetration resistance of aramid laminates having varying thickness against flat-nosed projectile. The model was created through a macroscopic approach, which did not take into account the internal microscopic structure of the laminate and macroscopically equated each laminate as a homogeneous orthotropic anisotropic material. The validity of FE simulation results was compared with existing experimental data, with good agreement achieved in terms of residual velocities of the project and damage patterns of the aramid laminates. The validated FE model was subsequently employed to simulate the ballistic responses of 4, 8 and 16 mm target plates in the range of 0°～30° attack angle. The residual velocity of the projectile, energy absorption rate of target, ballistic limit, and perforation energy threshold were calculated to characterize the ballistic performance of aramid laminates. By comparing the damage patterns of the aramid laminates and the contact forces applied to the project under different conditions, the mechanical mechanism by which the attack angle affected the ballistic performance of the aramid laminates at different impact velocities and different target thicknesses was explained. Within the studied working conditions, obtained results revealed that: the attack angle affects significantly the ballistic performance of aramid laminates, depending upon projectile impact velocity and target thickness; the ballistic limit and perforation energy threshold decrease with increasing attack angle, and the degree of such decrease is reduced as target thickness is increased; the residual velocity of projectile increases with increasing attack angle when the impact velocity is close to the ballistic limit and decreases with increasing attack angle when the velocity is well above the ballistic limit; the influencing mechanism of attack angle on ballistic performance varies with the damage pattern of aramid laminates.
2023, 43(6): 064101.
doi: 10.11883/bzycj-2022-0238
Abstract:
To study the ignition behavior of micro-mesoscopic hot spots in the matrix of pressed PBXs under GPa and 10 μs-level slow-front ramp wave loading, a ramp wave loading device driven by non-shock initiation reaction of pressed PBX with heavy constraint was designed. With the help of the output pressure from the explosion reaction of the donor explosive, the acceptor explosive was loaded by a ramp wave. A two-dimensional axisymmetric finite difference program was developed based on the burn rate equation of laminar combustion on the explosive surface to guide the structural design of the device. The pressure history during the combustion process of the explosive crack surface formed by the explosive fragmentation in the late stage of the non-shock initiation reaction of the donor explosive in the device configuration and the pressure waveform acting on the acceptor explosive are analyzed. And the influence of crushing degree of donor explosive and device structure parameters (thickness of case and interlayer) on output pressure waveform during the combustion process is discussed. The calculation results show that the specific combustion surface area formed by the crushing of the donor explosive is the key factor affecting the pressure evolution of the non-shock initiation reaction. The larger the specific combustion surface area, the greater the ramp wave pressure is. The ramp wave pressure can reach above GPa, and the corresponding rising front of the pressure wave can be reduced from tens of milliseconds to several milliseconds. The thickness of the case of the donor explosive, namely the constraint strength, has a significant effect on the pressure during the non-shock initiation reaction. As the thickness of the interlayer increases, the output ramp wave pressure decays approximately exponentially. The structural design of the device was completed according to the calculation results, and the ramp wave loading experiment was carried out on the tested PBX. The pressure at the incident interface of the tested explosive measured by PVDF is 1.6 GPa, and the front of the ramp wave is 25 μs, which preliminarily proved the feasibility of realizing GPa and 10 μs-level ramp wave pressure output by using the non-shock initiation reaction of heavily constrained pressed PBX explosives.
To study the ignition behavior of micro-mesoscopic hot spots in the matrix of pressed PBXs under GPa and 10 μs-level slow-front ramp wave loading, a ramp wave loading device driven by non-shock initiation reaction of pressed PBX with heavy constraint was designed. With the help of the output pressure from the explosion reaction of the donor explosive, the acceptor explosive was loaded by a ramp wave. A two-dimensional axisymmetric finite difference program was developed based on the burn rate equation of laminar combustion on the explosive surface to guide the structural design of the device. The pressure history during the combustion process of the explosive crack surface formed by the explosive fragmentation in the late stage of the non-shock initiation reaction of the donor explosive in the device configuration and the pressure waveform acting on the acceptor explosive are analyzed. And the influence of crushing degree of donor explosive and device structure parameters (thickness of case and interlayer) on output pressure waveform during the combustion process is discussed. The calculation results show that the specific combustion surface area formed by the crushing of the donor explosive is the key factor affecting the pressure evolution of the non-shock initiation reaction. The larger the specific combustion surface area, the greater the ramp wave pressure is. The ramp wave pressure can reach above GPa, and the corresponding rising front of the pressure wave can be reduced from tens of milliseconds to several milliseconds. The thickness of the case of the donor explosive, namely the constraint strength, has a significant effect on the pressure during the non-shock initiation reaction. As the thickness of the interlayer increases, the output ramp wave pressure decays approximately exponentially. The structural design of the device was completed according to the calculation results, and the ramp wave loading experiment was carried out on the tested PBX. The pressure at the incident interface of the tested explosive measured by PVDF is 1.6 GPa, and the front of the ramp wave is 25 μs, which preliminarily proved the feasibility of realizing GPa and 10 μs-level ramp wave pressure output by using the non-shock initiation reaction of heavily constrained pressed PBX explosives.
2023, 43(6): 065101.
doi: 10.11883/bzycj-2022-0445
Abstract:
To study the distribution of the coupled ground impact energy due to underground explosions, the key is to obtain the experimental parameters of the volume of the crater compression zone under the coupling effect between the clay medium and explosion energy. To reveal the relationship between the distribution of the blast coupling ground impact energy in clay and the compression volume of the crater, 10.5 g TNT explosive spheres were used as the blast source, and blast experiments under variable burial depths were conducted in a\begin{document}$\varnothing $\end{document} ![]()
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To study the distribution of the coupled ground impact energy due to underground explosions, the key is to obtain the experimental parameters of the volume of the crater compression zone under the coupling effect between the clay medium and explosion energy. To reveal the relationship between the distribution of the blast coupling ground impact energy in clay and the compression volume of the crater, 10.5 g TNT explosive spheres were used as the blast source, and blast experiments under variable burial depths were conducted in a
2023, 43(6): 065201.
doi: 10.11883/bzycj-2022-0109
Abstract:
On the premise of a good crushing effect, reducing the rock mass vibration above the bottom of the upward fan-shaped deep hole by reducing the peak pressure of the shock wave at the bottom of the hole is an effective measure to protect the superstructure. To determine the reasonable length of the air column at the bottom of the hole, the influence of air column length on the impact pressure of the hole wall without consideration of air column coupling is studied by combining the theoretical analysis with the field model blast experiment. Based on the theories of one-dimensional unsteady hydrodynamics and theoretical detonation physics, the action process and propagation law of the shock wave in the blast hole in different stages after the explosion of the bottom air interval cylindrical charge column are discussed. Considering the reflection and transmission of shock waves at different media interfaces, the parameters of the shock wave propagating in different directions, the initial shock pressure, and the action time of the hole wall pressure in each stage are analyzed. Thus, the calculation formula and variation curves of the pressure on the hole wall in each stage are obtained. Six groups of twelve cylindrical thick wall concrete models of different sizes were designed and made, and the bottom air interval blasting model experiments were carried out to verify the above results. The air column lengths were 200, 400, 600, 800, 1 000 and 1 200 mm. During the blasting process, an ultra-high-speed multi-channel dynamic strain testing system was used to monitor the hole wall impact pressure. The monitoring data are then analyzed, and the theoretical results are verified. Finally, the variation curves of the peak pressures with the axial uncoupling factor and the variation curves of hole wall impact pressure with time and measurement point under different uncoupling factors are obtained. Based on the dynamic compressive strength of rock, reasonable length ranges of bottom axial air interval suitable for soft, medium, and hard rocks are determined. A field industrial blasting experiment was carried out with the air interval at the hole bottom to verify the rationality of the conclusion. The roof forming and the blasting pile size after the blast are observed and analyzed by photography. The research results show that the existence of air interval significantly increases the action time of the impact pressure. The peak value of the impact pressure decreases obviously. When the uncoupling factor is 1.5 and the length of the air column is 200 mm, the attenuation ratio of the peak pressure at the hole bottom is 73.4%; when the uncoupling factor is 4 and the length of the air column is 1.2 m, the attenuation ratio of the peak pressure at the hole bottom reaches 96.7%. When the air interval is greater than 60 cm, an area with low pressure appears at the bottom of the blast hole. A reasonable bottom air interval length can not only ensure good blasting fragmentation but also reduce blasting vibration by reducing the peak pressure at the hole bottom, thus protecting the stope roof and other protected objects.
On the premise of a good crushing effect, reducing the rock mass vibration above the bottom of the upward fan-shaped deep hole by reducing the peak pressure of the shock wave at the bottom of the hole is an effective measure to protect the superstructure. To determine the reasonable length of the air column at the bottom of the hole, the influence of air column length on the impact pressure of the hole wall without consideration of air column coupling is studied by combining the theoretical analysis with the field model blast experiment. Based on the theories of one-dimensional unsteady hydrodynamics and theoretical detonation physics, the action process and propagation law of the shock wave in the blast hole in different stages after the explosion of the bottom air interval cylindrical charge column are discussed. Considering the reflection and transmission of shock waves at different media interfaces, the parameters of the shock wave propagating in different directions, the initial shock pressure, and the action time of the hole wall pressure in each stage are analyzed. Thus, the calculation formula and variation curves of the pressure on the hole wall in each stage are obtained. Six groups of twelve cylindrical thick wall concrete models of different sizes were designed and made, and the bottom air interval blasting model experiments were carried out to verify the above results. The air column lengths were 200, 400, 600, 800, 1 000 and 1 200 mm. During the blasting process, an ultra-high-speed multi-channel dynamic strain testing system was used to monitor the hole wall impact pressure. The monitoring data are then analyzed, and the theoretical results are verified. Finally, the variation curves of the peak pressures with the axial uncoupling factor and the variation curves of hole wall impact pressure with time and measurement point under different uncoupling factors are obtained. Based on the dynamic compressive strength of rock, reasonable length ranges of bottom axial air interval suitable for soft, medium, and hard rocks are determined. A field industrial blasting experiment was carried out with the air interval at the hole bottom to verify the rationality of the conclusion. The roof forming and the blasting pile size after the blast are observed and analyzed by photography. The research results show that the existence of air interval significantly increases the action time of the impact pressure. The peak value of the impact pressure decreases obviously. When the uncoupling factor is 1.5 and the length of the air column is 200 mm, the attenuation ratio of the peak pressure at the hole bottom is 73.4%; when the uncoupling factor is 4 and the length of the air column is 1.2 m, the attenuation ratio of the peak pressure at the hole bottom reaches 96.7%. When the air interval is greater than 60 cm, an area with low pressure appears at the bottom of the blast hole. A reasonable bottom air interval length can not only ensure good blasting fragmentation but also reduce blasting vibration by reducing the peak pressure at the hole bottom, thus protecting the stope roof and other protected objects.
2023, 43(6): 065401.
doi: 10.11883/bzycj-2022-0475
Abstract:
It is necessary to understand the upper explosion limits of C3H8/C2H4 mixtures to prevent the potential explosive risks of flammable gas mixtures in the process of high temperatures and pressures. An experimental device of a 20 L spherical vessel with high pressure placed in a high-temperature oven was set up to test the upper explosion limits of C3H8/C2H4 mixtures at high pressure and temperature. The partial pressure method was used to prepare the mixtures of C3H8, C2H4, and air with a certain concentration. A pressure rise amplitude of 5% was adopted to judge whether the explosion occurred. The initial temperature ranged from 20 ℃ to 200 ℃, and the initial pressure ranged from 0.1 MPa to 1.5 MPa in the experiments. The effects of temperature, pressure, and volume fraction of C2H4 on the upper explosion limit of C3H8/C2H4 mixtures were analyzed. The results show that the upper explosion limit of C3H8/C2H4 mixtures increases with the rises of temperature and pressure, but the increase rate of the upper explosion limit decreases significantly with the increase of C2H4 concentration when the initial pressure is higher than 0.3 MPa. The amplitude increase and rate of the upper explosion limit with C2H4 at high temperatures and pressures are higher than those at normal conditions. The influences of temperature and pressure on the upper explosion limit are much greater than the sum of the two effects alone, indicating that the C3H8/C2H4 mixtures have a higher explosion risk under the synergistic effect of high temperature and pressure, and it will be further enhanced with the increase of C2H4 concentration. The influence of the temperature, pressure, and their synergistic effects on the upper explosion limit of C3H8/C2H4 mixtures in different proportions are comprehensively analyzed, and the corresponding functional relations of the temperature-upper explosion limit, pressure-upper explosion limit, and temperature-pressure-upper explosion limit in different volume fractions of C2H4 are summarized by the non-linear regression of surface.
It is necessary to understand the upper explosion limits of C3H8/C2H4 mixtures to prevent the potential explosive risks of flammable gas mixtures in the process of high temperatures and pressures. An experimental device of a 20 L spherical vessel with high pressure placed in a high-temperature oven was set up to test the upper explosion limits of C3H8/C2H4 mixtures at high pressure and temperature. The partial pressure method was used to prepare the mixtures of C3H8, C2H4, and air with a certain concentration. A pressure rise amplitude of 5% was adopted to judge whether the explosion occurred. The initial temperature ranged from 20 ℃ to 200 ℃, and the initial pressure ranged from 0.1 MPa to 1.5 MPa in the experiments. The effects of temperature, pressure, and volume fraction of C2H4 on the upper explosion limit of C3H8/C2H4 mixtures were analyzed. The results show that the upper explosion limit of C3H8/C2H4 mixtures increases with the rises of temperature and pressure, but the increase rate of the upper explosion limit decreases significantly with the increase of C2H4 concentration when the initial pressure is higher than 0.3 MPa. The amplitude increase and rate of the upper explosion limit with C2H4 at high temperatures and pressures are higher than those at normal conditions. The influences of temperature and pressure on the upper explosion limit are much greater than the sum of the two effects alone, indicating that the C3H8/C2H4 mixtures have a higher explosion risk under the synergistic effect of high temperature and pressure, and it will be further enhanced with the increase of C2H4 concentration. The influence of the temperature, pressure, and their synergistic effects on the upper explosion limit of C3H8/C2H4 mixtures in different proportions are comprehensively analyzed, and the corresponding functional relations of the temperature-upper explosion limit, pressure-upper explosion limit, and temperature-pressure-upper explosion limit in different volume fractions of C2H4 are summarized by the non-linear regression of surface.
