2024 Vol. 44, No. 6
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2024, 44(6): 061001.
doi: 10.11883/bzycj-2023-0336
Abstract:
The precise control of explosive energy to form an effective radial fracture network in shale is the key of shale gas dynamic extraction. In order to elucidate the damage and fracture mechanisms of shale under directional fracture-controlled blasting and establish a quantifiable relationship for shale damage and destruction under various blasting conditions, explosive tests were conducted on cubic shale specimens with four different fracture angles. The evolution of surface strain fields on the shale specimens was monitored using digital image correlation (DIC) technology. Additionally, the fractal dimensions of surface cracks on the shale specimens at different fracture angles were computed based on the box-counting theory. A programmed analysis of post-blast fragment size distribution was carried out using Matlab software, resulting in the development of a fully automated particle size analysis program with visual delineation of particle sizes. The experimental results demonstrate a negative power-law relationship between crack density and scaled distance within different scaled distances. The angle between the fracture direction and the weak plane of the bedding significantly influences the location of micro-damaged areas. Particularly, when the weak plane of the bedding is parallel to the fracture direction, damaged areas tend to concentrate along the weak plane, affecting the macrocrack propagation path and favoring the formation of a single crack. Energy dissipation at the weak planes of the bedding is identified as a crucial factor leading to suboptimal fracturing effects in shale blasting. When the fracture direction aligns with the weak plane of the bedding, a higher proportion of large fragments is observed in the post-blast specimens. The average fractal dimension of fragment size distribution is the lowest among all groups, measuring only 0.784 3. Conversely, when the fracture direction is perpendicular to the weak plane of the bedding, the distribution of post-blast fragment sizes becomes more uniform. The average fractal dimension of fragment size distribution increases to 2.5233, indicating relatively better blasting fragmentation results in such scenarios.
The precise control of explosive energy to form an effective radial fracture network in shale is the key of shale gas dynamic extraction. In order to elucidate the damage and fracture mechanisms of shale under directional fracture-controlled blasting and establish a quantifiable relationship for shale damage and destruction under various blasting conditions, explosive tests were conducted on cubic shale specimens with four different fracture angles. The evolution of surface strain fields on the shale specimens was monitored using digital image correlation (DIC) technology. Additionally, the fractal dimensions of surface cracks on the shale specimens at different fracture angles were computed based on the box-counting theory. A programmed analysis of post-blast fragment size distribution was carried out using Matlab software, resulting in the development of a fully automated particle size analysis program with visual delineation of particle sizes. The experimental results demonstrate a negative power-law relationship between crack density and scaled distance within different scaled distances. The angle between the fracture direction and the weak plane of the bedding significantly influences the location of micro-damaged areas. Particularly, when the weak plane of the bedding is parallel to the fracture direction, damaged areas tend to concentrate along the weak plane, affecting the macrocrack propagation path and favoring the formation of a single crack. Energy dissipation at the weak planes of the bedding is identified as a crucial factor leading to suboptimal fracturing effects in shale blasting. When the fracture direction aligns with the weak plane of the bedding, a higher proportion of large fragments is observed in the post-blast specimens. The average fractal dimension of fragment size distribution is the lowest among all groups, measuring only 0.784 3. Conversely, when the fracture direction is perpendicular to the weak plane of the bedding, the distribution of post-blast fragment sizes becomes more uniform. The average fractal dimension of fragment size distribution increases to 2.5233, indicating relatively better blasting fragmentation results in such scenarios.
2024, 44(6): 062101.
doi: 10.11883/bzycj-2023-0037
Abstract:
Experiments were carried out on the flame behaviors and overpressure evolutions at the initial stage of ignition and explosion of steady-state hydrogen jet in open space, while a high-speed camera and pressure transducers were employed to record the flame shape and overpressure. The results show that at the early stage of ignition and explosion, the flame propagated outward from the ignition electrode with a spherical shape. After 4-6 ms, the flame front reached its maximum displacement, gradually extinguished, and finally formed a jet flame. The displacement of the flame front was mainly affected by the nozzle diameter and increased with the nozzle diameter. The variations of flame width were basically similar to those of the flame front displacement. The entire explosion process only experienced one overpressure peak, with a positive pressure maintained for approximately 1 ms. At the same ignition distance, the peak overpressure increased with hydrogen flow rate. At the same hydrogen flow rate, the peak overpressure decreased with increasing ignition distance. The maximum peak overpressure was directly proportional to the hydrogen flow rate and inversely proportional to the ignition distance.
Experiments were carried out on the flame behaviors and overpressure evolutions at the initial stage of ignition and explosion of steady-state hydrogen jet in open space, while a high-speed camera and pressure transducers were employed to record the flame shape and overpressure. The results show that at the early stage of ignition and explosion, the flame propagated outward from the ignition electrode with a spherical shape. After 4-6 ms, the flame front reached its maximum displacement, gradually extinguished, and finally formed a jet flame. The displacement of the flame front was mainly affected by the nozzle diameter and increased with the nozzle diameter. The variations of flame width were basically similar to those of the flame front displacement. The entire explosion process only experienced one overpressure peak, with a positive pressure maintained for approximately 1 ms. At the same ignition distance, the peak overpressure increased with hydrogen flow rate. At the same hydrogen flow rate, the peak overpressure decreased with increasing ignition distance. The maximum peak overpressure was directly proportional to the hydrogen flow rate and inversely proportional to the ignition distance.
2024, 44(6): 062301.
doi: 10.11883/bzycj-2023-0267
Abstract:
A charge is usually subjected to multi-pulse loading in the process of projectile penetration. A multi-pulse loading device for charge was proposed, and the stress amplification effect of the charge under multi-pulse loading was studied. An equivalent spring model of the multi-pulse loading device was established based on the lumped mass method. The amplification effect of the equivalent model was studied in the time and frequency domains. Based on the finite element analysis of the multi-pulse loading of the charge, the conditions for generating stress amplification were discussed. The results show that the system resonates when the multi-pulse load frequency matches the natural frequency of the charge, and the charge produces amplification response. The presence of gaps causes the main resonance frequency of the system to deviate towards the lower frequency range. The amplification factor decreases with the increase of the structural gap width. When the impact occurs near the moment when the T-shaped transmission bar and the limit block have just separated, the optimal amplification effect can be produced. Under three pulse loading conditions, the optimal amplification factor for the second and third impact is 1.7 times and 2.1 times, respectively. Multiple pulse loading experiments were conducted on Teflon and PBX explosive simulation materials. The relative motion of bullets, limit blocks, and T-shaped transmission bars was observed using high-speed photography technology. The sample pressure was measured using a PVDF (polyvinylidene fluoride) pressure gauge. The results show that stress amplification occurs when the bullet and the T-shaped transmission bar collide in the same direction, but there is no amplification effect when they collide in the opposite direction, which is consistent with the numerical simulation results. Under the condition of constant total length, the stress amplification factor of the combination of Teflon and PBX simulation material is smaller than that of Teflon due to the presence of interface gaps.
A charge is usually subjected to multi-pulse loading in the process of projectile penetration. A multi-pulse loading device for charge was proposed, and the stress amplification effect of the charge under multi-pulse loading was studied. An equivalent spring model of the multi-pulse loading device was established based on the lumped mass method. The amplification effect of the equivalent model was studied in the time and frequency domains. Based on the finite element analysis of the multi-pulse loading of the charge, the conditions for generating stress amplification were discussed. The results show that the system resonates when the multi-pulse load frequency matches the natural frequency of the charge, and the charge produces amplification response. The presence of gaps causes the main resonance frequency of the system to deviate towards the lower frequency range. The amplification factor decreases with the increase of the structural gap width. When the impact occurs near the moment when the T-shaped transmission bar and the limit block have just separated, the optimal amplification effect can be produced. Under three pulse loading conditions, the optimal amplification factor for the second and third impact is 1.7 times and 2.1 times, respectively. Multiple pulse loading experiments were conducted on Teflon and PBX explosive simulation materials. The relative motion of bullets, limit blocks, and T-shaped transmission bars was observed using high-speed photography technology. The sample pressure was measured using a PVDF (polyvinylidene fluoride) pressure gauge. The results show that stress amplification occurs when the bullet and the T-shaped transmission bar collide in the same direction, but there is no amplification effect when they collide in the opposite direction, which is consistent with the numerical simulation results. Under the condition of constant total length, the stress amplification factor of the combination of Teflon and PBX simulation material is smaller than that of Teflon due to the presence of interface gaps.
2024, 44(6): 062302.
doi: 10.11883/bzycj-2023-0381
Abstract:
In order to study the energy release characteristics of composite charge in confined space, a type of coaxial composite charge was designed with the inner layer of thermobaric explosive JHL-6 and the outer layer of mixed fuel of different components. The mixed fuel was mainly composed of Al/PTFE active material or boron-based fuel. The Al/PTFE active material can undergo a detonation-like reaction and provide energy for shock wave, but its reaction products are all solid. The lack of gaseous medium is not conducive to shock wave propagation. However, boron-based fuel can decompose to produce gas under detonation loading, which can make up for the shortcomings of the Al/PTFE active material. The mixed fuel formulations were designed and the content of boron-based fuel in different formulations was determined. The internal explosion test on composite charge was carried out by using a sealed explosion device. The shock wave overpressure on the device wall and the quasi-static pressure were obtained, which can be used to evaluate the implosion power of the composite charges. The effects of boron-fuel content, secondary ignition energy and reactant concentration on the post-combustion reaction and energy release characteristics of the composite charges were investigated by using the method of implosion power evaluation. The test results show that the quasi-static pressure of the composite charge with the same mass but different boron-based fuel content increases first and then decreases with the increase of boron-based fuel content, and the optimal volume fraction of boron-based fuel decomposition products participating in the secondary reaction is about 1.0%. For the composite charge, because the oxygen content in the confined space is limited, when the concentration of substances involved in the secondary reaction reaches a certain threshold, the quasi-static pressure cannot be effectively improved by increasing the ignition energy or the reactant concentration, so the energy utilization rate is not improved.
In order to study the energy release characteristics of composite charge in confined space, a type of coaxial composite charge was designed with the inner layer of thermobaric explosive JHL-6 and the outer layer of mixed fuel of different components. The mixed fuel was mainly composed of Al/PTFE active material or boron-based fuel. The Al/PTFE active material can undergo a detonation-like reaction and provide energy for shock wave, but its reaction products are all solid. The lack of gaseous medium is not conducive to shock wave propagation. However, boron-based fuel can decompose to produce gas under detonation loading, which can make up for the shortcomings of the Al/PTFE active material. The mixed fuel formulations were designed and the content of boron-based fuel in different formulations was determined. The internal explosion test on composite charge was carried out by using a sealed explosion device. The shock wave overpressure on the device wall and the quasi-static pressure were obtained, which can be used to evaluate the implosion power of the composite charges. The effects of boron-fuel content, secondary ignition energy and reactant concentration on the post-combustion reaction and energy release characteristics of the composite charges were investigated by using the method of implosion power evaluation. The test results show that the quasi-static pressure of the composite charge with the same mass but different boron-based fuel content increases first and then decreases with the increase of boron-based fuel content, and the optimal volume fraction of boron-based fuel decomposition products participating in the secondary reaction is about 1.0%. For the composite charge, because the oxygen content in the confined space is limited, when the concentration of substances involved in the secondary reaction reaches a certain threshold, the quasi-static pressure cannot be effectively improved by increasing the ignition energy or the reactant concentration, so the energy utilization rate is not improved.
2024, 44(6): 062303.
doi: 10.11883/bzycj-2023-0353
Abstract:
In order to study the pressure parameters of HMX-based aluminized pressed explosives at the ignition moment during slow cook-off, slow cook-off tests were designed at 0.1 and 1.0 ℃/min heating rates, and internal multi-point temperature measurements were taken inside explosives. On this foundation, based on the universal cook-off model of explosives, combining the multi-step decomposition reaction mechanism of HMX-based explosives with the reaction of aluminum powder, and considering the phase transition process in the decomposition of HMX-based explosives, a slow cook-off calculation model for pressure-department reaction rate of HMX-based aluminized pressed explosives is proposed. The calculation model is then written as a user defined function and imported into Ansys Fluent to perform calculations. Slow cook-off tests were conducted on large aspect ratio (5∶1) HMX-based aluminized pressed explosive charges with 4 mm shell thickness at heating rates of 0.1 and 1.0 ℃/min and compared with simulation results. And then the numerical simulations of the temperature field and internal pressure changes are performed before ignition of the cook-off bomb at heating rates of 0.055, 0.1, 0.2, 0.3, 0.5, and 1.0 ℃/min. It is found that at the heating rate of 0.1 ℃/min, after the test reaction, the end cover is ejected, the shell is axially cracked, and there is no powder left, so it is judged to be a deflagration reaction; while at the heating rate of 1.0 ℃/min, the shell is slightly deformed, with some powder left, indicating that a combustion reaction has occurred. The numerical calculations show that as the heat stimulus increases, the ignition temperature of the explosive tends to increase logarithmically, while the extent of reaction and internal pressure of the cook-off bomb tend to decrease exponentially. Before the HMX phase transition, the internal pressure inside the cook-off bomb grows slowly, after the HMX phase transition the pressure grow rapidly increases, and finally it rises sharply near the ignition moment.
In order to study the pressure parameters of HMX-based aluminized pressed explosives at the ignition moment during slow cook-off, slow cook-off tests were designed at 0.1 and 1.0 ℃/min heating rates, and internal multi-point temperature measurements were taken inside explosives. On this foundation, based on the universal cook-off model of explosives, combining the multi-step decomposition reaction mechanism of HMX-based explosives with the reaction of aluminum powder, and considering the phase transition process in the decomposition of HMX-based explosives, a slow cook-off calculation model for pressure-department reaction rate of HMX-based aluminized pressed explosives is proposed. The calculation model is then written as a user defined function and imported into Ansys Fluent to perform calculations. Slow cook-off tests were conducted on large aspect ratio (5∶1) HMX-based aluminized pressed explosive charges with 4 mm shell thickness at heating rates of 0.1 and 1.0 ℃/min and compared with simulation results. And then the numerical simulations of the temperature field and internal pressure changes are performed before ignition of the cook-off bomb at heating rates of 0.055, 0.1, 0.2, 0.3, 0.5, and 1.0 ℃/min. It is found that at the heating rate of 0.1 ℃/min, after the test reaction, the end cover is ejected, the shell is axially cracked, and there is no powder left, so it is judged to be a deflagration reaction; while at the heating rate of 1.0 ℃/min, the shell is slightly deformed, with some powder left, indicating that a combustion reaction has occurred. The numerical calculations show that as the heat stimulus increases, the ignition temperature of the explosive tends to increase logarithmically, while the extent of reaction and internal pressure of the cook-off bomb tend to decrease exponentially. Before the HMX phase transition, the internal pressure inside the cook-off bomb grows slowly, after the HMX phase transition the pressure grow rapidly increases, and finally it rises sharply near the ignition moment.
2024, 44(6): 063101.
doi: 10.11883/bzycj-2023-0323
Abstract:
Based on the background of the further requirements for lightweight, explosion and impact resistance, and vibration reduction and noise reduction in the development of honeycomb structure in engineering science, a liquid metal honeycomb sandwich structure was proposed, and the preparation, impact experiments, and numerical simulation research of the liquid metal honeycomb sandwich structure were carried out. A preparation method for the liquid-filled metallic honeycomb sandwich structure was developed to meet the requirements of effective sealing of the internal liquid, adjustable liquid filling content, and controllable filling position within the structure. The first level light gas gun was used to launch foam bullets to simulate the explosion shock wave load, and the dynamic response of the structure under different impact velocities was obtained. At the same time, the commercial finite element software Abaqus/Explicit was used to carry out numerical simulation of the impact response of foam bullets in the metal honeycomb sandwich structure using the smooth particle hydrodynamics method, and the impact speed of foam bullets, the liquid content in the cell on the impact resistance and post-impact vibration characteristics of the structure were discussed further. The results indicate that the liquid-filled structure exhibits superior impact resistance and post-impact vibration performance compared with the unfilled structure. Moreover, with an increase in the liquid content, the displacement response of the liquid-filled structure shows a monotonic decrease, while the damping ratio demonstrates an increasing trend. When the core is fully filled with liquid, the structure achieves optimal impact resistance performance, with a decrease in peak displacement of approximately 13.66% compared to the unfilled structure, and an increase in damping ratio by approximately 1.6 times. The aforementioned research establishes the foundation for the extensive application of liquid-filled metallic honeycomb composite structures in the field of impact protection.
Based on the background of the further requirements for lightweight, explosion and impact resistance, and vibration reduction and noise reduction in the development of honeycomb structure in engineering science, a liquid metal honeycomb sandwich structure was proposed, and the preparation, impact experiments, and numerical simulation research of the liquid metal honeycomb sandwich structure were carried out. A preparation method for the liquid-filled metallic honeycomb sandwich structure was developed to meet the requirements of effective sealing of the internal liquid, adjustable liquid filling content, and controllable filling position within the structure. The first level light gas gun was used to launch foam bullets to simulate the explosion shock wave load, and the dynamic response of the structure under different impact velocities was obtained. At the same time, the commercial finite element software Abaqus/Explicit was used to carry out numerical simulation of the impact response of foam bullets in the metal honeycomb sandwich structure using the smooth particle hydrodynamics method, and the impact speed of foam bullets, the liquid content in the cell on the impact resistance and post-impact vibration characteristics of the structure were discussed further. The results indicate that the liquid-filled structure exhibits superior impact resistance and post-impact vibration performance compared with the unfilled structure. Moreover, with an increase in the liquid content, the displacement response of the liquid-filled structure shows a monotonic decrease, while the damping ratio demonstrates an increasing trend. When the core is fully filled with liquid, the structure achieves optimal impact resistance performance, with a decrease in peak displacement of approximately 13.66% compared to the unfilled structure, and an increase in damping ratio by approximately 1.6 times. The aforementioned research establishes the foundation for the extensive application of liquid-filled metallic honeycomb composite structures in the field of impact protection.
2024, 44(6): 063102.
doi: 10.11883/bzycj-2023-0366
Abstract:
In order to explore the underwater anti-explosion mechanism of different corrugated steel-concrete slab composite structures, the damage process of concrete slab under underwater contact explosion was simulated by smoothed particle hydrodynamics and finite element method (FEM-SPH), and the validity of the numerical method was verified by comparing with the experimental results. The FEM-SPH method was used to explore the damage process and failure mode of the wall panel under different protection schemes, to reveal the underwater explosion-proof mechanism, and to construct the prediction curve of the damage grade of the wall panel. The results show that the simulation results are in good agreement with the experimental results, which verifies the effectiveness of the simulation method. Under different protection schemes, the damage range of the wall panel with 12 mm thick corrugated steel composite structure (T-12), 75o angle corrugated steel composite structure (A-75) and 70 mm corrugated steel composite structure (WH-70) is 83%, 81.6% and 82.5% lower than that of the unreinforced wall panel, respectively. In the composite structure, the explosion shock wave propagates to the corrugated steel in the form of incident wave and then propagates in the structure in the form of transmitted wave and reflected wave. When the transmitted wave reaches the lower surface of the corrugated steel, part of the shock wave will continue to propagate to the wall panel, while the remaining shock wave is reflected to form reflected longitudinal wave and reflected transverse wave, which further attenuates the transmitted shock wave acting on the wall panel to achieve the effect of wave clipping and energy absorption. The prediction curve can directly evaluate the influence of explosive amount and wave height change of corrugated steel in composite structure on the damage grade of wall panel.
In order to explore the underwater anti-explosion mechanism of different corrugated steel-concrete slab composite structures, the damage process of concrete slab under underwater contact explosion was simulated by smoothed particle hydrodynamics and finite element method (FEM-SPH), and the validity of the numerical method was verified by comparing with the experimental results. The FEM-SPH method was used to explore the damage process and failure mode of the wall panel under different protection schemes, to reveal the underwater explosion-proof mechanism, and to construct the prediction curve of the damage grade of the wall panel. The results show that the simulation results are in good agreement with the experimental results, which verifies the effectiveness of the simulation method. Under different protection schemes, the damage range of the wall panel with 12 mm thick corrugated steel composite structure (T-12), 75o angle corrugated steel composite structure (A-75) and 70 mm corrugated steel composite structure (WH-70) is 83%, 81.6% and 82.5% lower than that of the unreinforced wall panel, respectively. In the composite structure, the explosion shock wave propagates to the corrugated steel in the form of incident wave and then propagates in the structure in the form of transmitted wave and reflected wave. When the transmitted wave reaches the lower surface of the corrugated steel, part of the shock wave will continue to propagate to the wall panel, while the remaining shock wave is reflected to form reflected longitudinal wave and reflected transverse wave, which further attenuates the transmitted shock wave acting on the wall panel to achieve the effect of wave clipping and energy absorption. The prediction curve can directly evaluate the influence of explosive amount and wave height change of corrugated steel in composite structure on the damage grade of wall panel.
2024, 44(6): 063201.
doi: 10.11883/bzycj-2023-0391
Abstract:
Different initiation methods directly determine the stress wave propagation and explosion energy transmission law caused by drilling and blasting, thus affecting the effect of rock fragmentations. In this paper, the collision mechanism of stress waves and rock fragmentation characteristics induced by blasting with different initiation methods were studied. Based on the theory of frontal and oblique collision of stress waves, the interaction mechanism of stress waves between holes was studied to prove the stress enhancement effect caused by wave collision under the staggered initiation mode. Using the RHT model for rock and JWL state equation for explosive in the ANSYS/LS-DYNA software, the magnitude of stress waves between holes and the rock fragmentation characteristics were simulated under the staggered, bottom and top initiation modes. Finally, combined with on-site experiments, the interaction of stress waves and the characteristics of fragmentation distribution for blasting of rock mass containing gravel under different initiation modes were compared and analysed. Results show that under the staggered initiation mode, a frontal collision of stress waves happens at the midpoint between two holes, and the pressure after the collision is 2.4 times that of the stable propagation of the stress wave. An oblique collision occurs between 0° and 44°, and the ratio of collision pressure to the stable pressure ranges from 4.1 to 2.3. Mach reflection occurs between 44° and 90°, and the ratio of collision pressure to the stable pressure ranges from 3.5 to 1. The rates of rock fragmentations with a size less than 250 mm under staggered and bottom initiation modes are 25.5% and 20.9%, respectively. The rates of rock fragmentations with a size larger than 750 mm under staggered and bottom initiation modes are 9.2% and 17.5%, respectively. The stress enhancement effect caused by wave collision under the staggered initiation mode can significantly improve the blasting fragmentation of rock mass containing gravel.
Different initiation methods directly determine the stress wave propagation and explosion energy transmission law caused by drilling and blasting, thus affecting the effect of rock fragmentations. In this paper, the collision mechanism of stress waves and rock fragmentation characteristics induced by blasting with different initiation methods were studied. Based on the theory of frontal and oblique collision of stress waves, the interaction mechanism of stress waves between holes was studied to prove the stress enhancement effect caused by wave collision under the staggered initiation mode. Using the RHT model for rock and JWL state equation for explosive in the ANSYS/LS-DYNA software, the magnitude of stress waves between holes and the rock fragmentation characteristics were simulated under the staggered, bottom and top initiation modes. Finally, combined with on-site experiments, the interaction of stress waves and the characteristics of fragmentation distribution for blasting of rock mass containing gravel under different initiation modes were compared and analysed. Results show that under the staggered initiation mode, a frontal collision of stress waves happens at the midpoint between two holes, and the pressure after the collision is 2.4 times that of the stable propagation of the stress wave. An oblique collision occurs between 0° and 44°, and the ratio of collision pressure to the stable pressure ranges from 4.1 to 2.3. Mach reflection occurs between 44° and 90°, and the ratio of collision pressure to the stable pressure ranges from 3.5 to 1. The rates of rock fragmentations with a size less than 250 mm under staggered and bottom initiation modes are 25.5% and 20.9%, respectively. The rates of rock fragmentations with a size larger than 750 mm under staggered and bottom initiation modes are 9.2% and 17.5%, respectively. The stress enhancement effect caused by wave collision under the staggered initiation mode can significantly improve the blasting fragmentation of rock mass containing gravel.
2024, 44(6): 063202.
doi: 10.11883/bzycj-2023-0432
Abstract:
In order to improve the blast resistance performance of engineering structures to ensure the safety of important targets and reduce the adverse effects of high cement content on the environment of cement-based ultra-high performance concrete, a new type of composite slab based on geopolymer ultra-high performance concrete (G-UHPC) is proposed. Three G-UHPC composite slabs were prepared with G-UHPC, steel wire mesh, and energy-absorbing foam materials, and an ordinary concrete slab was prepared with C40 concrete. Explosion tests were carried out in the field to verify the blast resistance performance of the new G-UHPC composite slab. The crater diameter, depth, and spalling of each specimen under a 0.4 kg TNT contact explosion were obtained, and the blast resistance performance and failure mode were analyzed. The effects of G-UHPC, steel wire mesh, and energy-absorbing foam materials on the blast resistance performance of concrete slabs were discussed. Based on the explosion test results, a refined finite element model was established using LS-DYNA finite element analysis software and numerical simulation analysis was conducted. The effectiveness of the numerical model was verified by comparing the experimental results with the simulation analysis results. On this basis, the model was used to further analyze the impact of G-UHPC and steel wire mesh on the blast resistance performance of concrete slabs. The failure process of composite slabs was analyzed by simulating the propagation of explosive waves in energy-absorbing foam-reinforced G-UHPC composite slabs, and the failure mechanism of G-UHPC composite slabs was revealed. A parameter analysis was carried out to further study the blast resistance performance of the G-UHPC composite slab. Based on the damage morphology of the G-UHPC composite plate, the mid-span displacement of the plate bottom and the energy absorption of the energy-absorbing layer, the influence of the energy-absorbing foam material layout on the blast resistance performance of the G-UHPC composite slab was discussed. The research results indicate that replacing ordinary concrete with G-UHPC can effectively improve the blast resistance of concrete slabs, and steel wire mesh can reduce the degree of blast pits and peeling damage of concrete slabs. The blast resistance design of composite slabs must consider the compressibility of energy-absorbing foam material and its matching with the wave impedance of G-UHPC, to have a favorable impact on the blast resistance performance of composite slabs. The high compressibility and low shear strength of energy-absorbing foam are the main reasons for the punching failure of concrete slabs. The increase in the number of polyurethane foam plates will lead to the reduction of the blast resistance performance of the concrete slab, which is specifically reflected in the increase of the depth of the explosion pit and the increase of the displacement of the bottom span of the slab.
In order to improve the blast resistance performance of engineering structures to ensure the safety of important targets and reduce the adverse effects of high cement content on the environment of cement-based ultra-high performance concrete, a new type of composite slab based on geopolymer ultra-high performance concrete (G-UHPC) is proposed. Three G-UHPC composite slabs were prepared with G-UHPC, steel wire mesh, and energy-absorbing foam materials, and an ordinary concrete slab was prepared with C40 concrete. Explosion tests were carried out in the field to verify the blast resistance performance of the new G-UHPC composite slab. The crater diameter, depth, and spalling of each specimen under a 0.4 kg TNT contact explosion were obtained, and the blast resistance performance and failure mode were analyzed. The effects of G-UHPC, steel wire mesh, and energy-absorbing foam materials on the blast resistance performance of concrete slabs were discussed. Based on the explosion test results, a refined finite element model was established using LS-DYNA finite element analysis software and numerical simulation analysis was conducted. The effectiveness of the numerical model was verified by comparing the experimental results with the simulation analysis results. On this basis, the model was used to further analyze the impact of G-UHPC and steel wire mesh on the blast resistance performance of concrete slabs. The failure process of composite slabs was analyzed by simulating the propagation of explosive waves in energy-absorbing foam-reinforced G-UHPC composite slabs, and the failure mechanism of G-UHPC composite slabs was revealed. A parameter analysis was carried out to further study the blast resistance performance of the G-UHPC composite slab. Based on the damage morphology of the G-UHPC composite plate, the mid-span displacement of the plate bottom and the energy absorption of the energy-absorbing layer, the influence of the energy-absorbing foam material layout on the blast resistance performance of the G-UHPC composite slab was discussed. The research results indicate that replacing ordinary concrete with G-UHPC can effectively improve the blast resistance of concrete slabs, and steel wire mesh can reduce the degree of blast pits and peeling damage of concrete slabs. The blast resistance design of composite slabs must consider the compressibility of energy-absorbing foam material and its matching with the wave impedance of G-UHPC, to have a favorable impact on the blast resistance performance of composite slabs. The high compressibility and low shear strength of energy-absorbing foam are the main reasons for the punching failure of concrete slabs. The increase in the number of polyurethane foam plates will lead to the reduction of the blast resistance performance of the concrete slab, which is specifically reflected in the increase of the depth of the explosion pit and the increase of the displacement of the bottom span of the slab.
2024, 44(6): 063301.
doi: 10.11883/bzycj-2023-0379
Abstract:
In order to examine the influence of loads on the penetration behavior of the armor-piercing rod in a steel target, two sets of experiments were performed where both loaded and unloaded rods were used to penetrate 603 armored steel plates. Structural failures of the plates were observed under both loaded and unloaded conditions. Subsequently, numerical simulation methods were employed to analyze the penetration characteristics of both loaded and unloaded armor-piercing rods under various conditions, including incident angles of 45° and 60°, and impact velocities ranging from 1300 to 1600 m/s. An analysis was conducted to evaluate the effects of loads, incident angles, impact velocities, and load centroid positions on both the penetration depth and deflection angle of the rods. The research findings indicate that the inclusion of loads substantially enhances the oblique penetration depth of the armor-piercing rod while simultaneously reducing the ballistic deflection angle, thereby effectively improving the overall penetration efficiency. Conversely, in the case of positive penetration, the energy consumption caused by the load striking the target plate’s surface impedes the armor-piercing rod’s ability to penetrate. It is noteworthy that under an impact velocity of 1400 m/s and an incident angle of 60°, the inclusion of loads results in a decrease in the critical jump velocity of the armor-piercing rod. Moreover, observations revealed that as the distance between the centroid of the armor-piercing rod and its head surpasses half of the rod’s length, there is an increase in penetration depth accompanied by a corresponding decrease in the deflection angle. Specifically, it has been found that an increased distance between the centroid of the armor-piercing rod and its head leads to an improvement in penetration effectiveness. These findings highlight the substantial impact of load position on the penetration effectiveness and offer valuable insights for future design optimization. The research outcomes offer essential support and guidance for the design of high-speed kinetic energy missiles, thereby facilitating the enhancement of their penetration capabilities.
In order to examine the influence of loads on the penetration behavior of the armor-piercing rod in a steel target, two sets of experiments were performed where both loaded and unloaded rods were used to penetrate 603 armored steel plates. Structural failures of the plates were observed under both loaded and unloaded conditions. Subsequently, numerical simulation methods were employed to analyze the penetration characteristics of both loaded and unloaded armor-piercing rods under various conditions, including incident angles of 45° and 60°, and impact velocities ranging from 1300 to 1600 m/s. An analysis was conducted to evaluate the effects of loads, incident angles, impact velocities, and load centroid positions on both the penetration depth and deflection angle of the rods. The research findings indicate that the inclusion of loads substantially enhances the oblique penetration depth of the armor-piercing rod while simultaneously reducing the ballistic deflection angle, thereby effectively improving the overall penetration efficiency. Conversely, in the case of positive penetration, the energy consumption caused by the load striking the target plate’s surface impedes the armor-piercing rod’s ability to penetrate. It is noteworthy that under an impact velocity of 1400 m/s and an incident angle of 60°, the inclusion of loads results in a decrease in the critical jump velocity of the armor-piercing rod. Moreover, observations revealed that as the distance between the centroid of the armor-piercing rod and its head surpasses half of the rod’s length, there is an increase in penetration depth accompanied by a corresponding decrease in the deflection angle. Specifically, it has been found that an increased distance between the centroid of the armor-piercing rod and its head leads to an improvement in penetration effectiveness. These findings highlight the substantial impact of load position on the penetration effectiveness and offer valuable insights for future design optimization. The research outcomes offer essential support and guidance for the design of high-speed kinetic energy missiles, thereby facilitating the enhancement of their penetration capabilities.
2024, 44(6): 065101.
doi: 10.11883/bzycj-2023-0252
Abstract:
A numerical simulation study is carried out on the overall battle damage circumstances of structures and the residual behavior of fragments after the typical parts of aircraft are attacked by high-velocity fragments. An adaptive FEM-SPH coupling simulation method is established by using the LS-DYNA software and combining the advantages of finite element method (FEM) and smoothed particle hydrodynamics (SPH). Using this coupling simulation method, the computational model of two typical parts of the aircraft is set up, and the accurate simulation of the core position is realized by a local refinement method of hexahedral FEM grids. Experiments were carried out to verify the numerical model. A series of high-velocity impact (HVI) battle damage simulations are carried out. The debris cloud and crater appearance formed after fragment impacting on structure at high velocity under different working conditions are compared, while the residual velocity and mass of the fragment are analyzed. The critical ricochet angles of the fragment on the skin are also determined. The major conclusions are given below. The calculation results of the adaptive FEM-SPH coupling algorithm are in good agreement with the experimental results, and it can simulate fragment HVI damage effectively and precisely. The distribution shape of debris cloud becomes narrow and long with the increase of fragment incident velocity, and the incidence angle can change the shape orientation of debris cloud and crater on the structure. The variation trends of height and spread velocity of debris cloud with incident velocity or angle are basically consistent and linear. The velocity reduction of the fragment does not change with the incident velocity, and the mass reduction is positively correlated with it, both of which are negatively correlated with the incidence angle. The critical ricochet angle of fragment varies almost linearly with the incident velocity. The research results can provide a reference for the damage prediction and rapid maintenance of aircraft after air combat.
A numerical simulation study is carried out on the overall battle damage circumstances of structures and the residual behavior of fragments after the typical parts of aircraft are attacked by high-velocity fragments. An adaptive FEM-SPH coupling simulation method is established by using the LS-DYNA software and combining the advantages of finite element method (FEM) and smoothed particle hydrodynamics (SPH). Using this coupling simulation method, the computational model of two typical parts of the aircraft is set up, and the accurate simulation of the core position is realized by a local refinement method of hexahedral FEM grids. Experiments were carried out to verify the numerical model. A series of high-velocity impact (HVI) battle damage simulations are carried out. The debris cloud and crater appearance formed after fragment impacting on structure at high velocity under different working conditions are compared, while the residual velocity and mass of the fragment are analyzed. The critical ricochet angles of the fragment on the skin are also determined. The major conclusions are given below. The calculation results of the adaptive FEM-SPH coupling algorithm are in good agreement with the experimental results, and it can simulate fragment HVI damage effectively and precisely. The distribution shape of debris cloud becomes narrow and long with the increase of fragment incident velocity, and the incidence angle can change the shape orientation of debris cloud and crater on the structure. The variation trends of height and spread velocity of debris cloud with incident velocity or angle are basically consistent and linear. The velocity reduction of the fragment does not change with the incident velocity, and the mass reduction is positively correlated with it, both of which are negatively correlated with the incidence angle. The critical ricochet angle of fragment varies almost linearly with the incident velocity. The research results can provide a reference for the damage prediction and rapid maintenance of aircraft after air combat.
2024, 44(6): 065102.
doi: 10.11883/bzycj-2023-0370
Abstract:
Underwater explosions pose a significant threat to ships and other waterborne structures, jeopardizing their integrity and combat readiness. When ships are subjected to attacks by underwater weapons such as torpedoes or mines, the resulted explosions propagate in multiple directions through the water, severely compromising the ability of the ship to remain afloat. To investigate the distribution characteristics of underwater explosion damage, a real-scale near-field underwater explosion test on a ship was conducted. The test results were analyzed focusing on the acceleration and strain measurements along the length of the ship. An acoustic-solid coupling method was employed to assess the cumulative shock wave and bubble jet load on the entire ship structure. The analysis reveals that the plastically deformed area of the ship exhibited a depression depth of 85 cm, with an L-shaped breach width of 30 cm and an area of 0.2 m2. The model was validated by comparing the experimental and simulation data, with breach size discrepancies below 20% and breach location alignment. Then, simulation calculations at varying blast distances were conducted to examine structural damage distribution patterns. A distributed damage pattern was identified to indicate not only overall structural fractures but also widespread small cracks in bulkheads and outer plate sections. As the impact factor decreases from 5.84 to 1.91, the bilge breach size reduces, alongside a decrease in overall breach size. This reduction validates the accuracy of the model. This model was further used to conduct explosion simulation calculations under different blast distances, and a distributed damage model of the barge under the near-field underwater explosion load was proposed. It is clarified that in addition to overall fracture and local large-scale breaches, the damage to the ship structure also occurs. There are widely distributed small cracks in bulkheads, side outer plating and other parts. When the impact factor decreases from 5.74 to 1.91, the size of the bilge breach decreases and the number of cracks in the cabin increases. When the impact factor is between 1.91 and 2.87, and the bilge damage is scattered small breaches. The connections between the sides, bulkheads and bilges are weak points with many small cracks, so protection can be focused on those weak points during the ship design process.
Underwater explosions pose a significant threat to ships and other waterborne structures, jeopardizing their integrity and combat readiness. When ships are subjected to attacks by underwater weapons such as torpedoes or mines, the resulted explosions propagate in multiple directions through the water, severely compromising the ability of the ship to remain afloat. To investigate the distribution characteristics of underwater explosion damage, a real-scale near-field underwater explosion test on a ship was conducted. The test results were analyzed focusing on the acceleration and strain measurements along the length of the ship. An acoustic-solid coupling method was employed to assess the cumulative shock wave and bubble jet load on the entire ship structure. The analysis reveals that the plastically deformed area of the ship exhibited a depression depth of 85 cm, with an L-shaped breach width of 30 cm and an area of 0.2 m2. The model was validated by comparing the experimental and simulation data, with breach size discrepancies below 20% and breach location alignment. Then, simulation calculations at varying blast distances were conducted to examine structural damage distribution patterns. A distributed damage pattern was identified to indicate not only overall structural fractures but also widespread small cracks in bulkheads and outer plate sections. As the impact factor decreases from 5.84 to 1.91, the bilge breach size reduces, alongside a decrease in overall breach size. This reduction validates the accuracy of the model. This model was further used to conduct explosion simulation calculations under different blast distances, and a distributed damage model of the barge under the near-field underwater explosion load was proposed. It is clarified that in addition to overall fracture and local large-scale breaches, the damage to the ship structure also occurs. There are widely distributed small cracks in bulkheads, side outer plating and other parts. When the impact factor decreases from 5.74 to 1.91, the size of the bilge breach decreases and the number of cracks in the cabin increases. When the impact factor is between 1.91 and 2.87, and the bilge damage is scattered small breaches. The connections between the sides, bulkheads and bilges are weak points with many small cracks, so protection can be focused on those weak points during the ship design process.
2024, 44(6): 065103.
doi: 10.11883/bzycj-2023-0250
Abstract:
The liquid in partially filled tanks is prone to slosh under external excitation, and the additional forces and moments generated by liquid sloshing can have adverse effects on tank trucks. In order to avoid significant sloshing of the liquid in the tank when the tank truck brakes, several types of baffles were proposed, and the influence of baffles and their geometric parameters on the liquid sloshing inside the tank truck was studied. Firstly, a numerical model of liquid sloshing based on the finite volume method was established. Secondly, a series of liquid sloshing experiments were conducted. The effectiveness of the numerical model was verified by comparing the free surface waveforms obtained from the experiments at different times with those obtained from numerical simulations under the same conditions. Finally, the validated numerical model was used to analyze the influence of the geometric parameters of the baffle on the liquid sloshing response parameters under different liquid-filling conditions. The research results indicate that the perforated baffle can not only effectively suppress the peak of the sloshing response parameters in the tank but also significantly shorten the time for liquid sloshing to reach stability. The position and number of baffle orifices have little effect on the peak longitudinal force caused by liquid sloshing during vehicle braking, while the peak pitch moment is more significantly affected by the geometric parameters of the baffle. By studying liquid sloshing in the tank at different filling heights, it is found that the decrease rate of the peak value of the sloshing response parameter will first decrease and then increase with the increase of the filling height. When the peak value of pitch moment reaches its maximum value, the baffle has the worst suppression effect on liquid sloshing in a partially filled tank.
The liquid in partially filled tanks is prone to slosh under external excitation, and the additional forces and moments generated by liquid sloshing can have adverse effects on tank trucks. In order to avoid significant sloshing of the liquid in the tank when the tank truck brakes, several types of baffles were proposed, and the influence of baffles and their geometric parameters on the liquid sloshing inside the tank truck was studied. Firstly, a numerical model of liquid sloshing based on the finite volume method was established. Secondly, a series of liquid sloshing experiments were conducted. The effectiveness of the numerical model was verified by comparing the free surface waveforms obtained from the experiments at different times with those obtained from numerical simulations under the same conditions. Finally, the validated numerical model was used to analyze the influence of the geometric parameters of the baffle on the liquid sloshing response parameters under different liquid-filling conditions. The research results indicate that the perforated baffle can not only effectively suppress the peak of the sloshing response parameters in the tank but also significantly shorten the time for liquid sloshing to reach stability. The position and number of baffle orifices have little effect on the peak longitudinal force caused by liquid sloshing during vehicle braking, while the peak pitch moment is more significantly affected by the geometric parameters of the baffle. By studying liquid sloshing in the tank at different filling heights, it is found that the decrease rate of the peak value of the sloshing response parameter will first decrease and then increase with the increase of the filling height. When the peak value of pitch moment reaches its maximum value, the baffle has the worst suppression effect on liquid sloshing in a partially filled tank.
2024, 44(6): 065401.
doi: 10.11883/bzycj-2023-0363
Abstract:
In the experiment conducted using a custom-built 5-L dust explosion flame propagation apparatus, the focus of the study was the characteristics of the flame propagation of magnesium hydride (MgH2) dust explosions within a semi-enclosed space. The experimental results showed that as the concentration of MgH2 dust increased, the time required for the MgH2 dust explosion flame to transfer from ignition to stable propagation decreased initially, but then increased as the dust concentration further increased. Similarly, the width of the preheating zone followed the same pattern. Initially, it decreased with increasing dust concentration, but once the concentration reached a certain threshold, it started to increase. Beyond that, the flame brightness, smoothness of the flame front, and flame propagation speed all showed similar trends. They initially increased as the MgH2 dust concentration increased, suggesting enhanced combustion activity. However, as the concentration further increased, these characteristics started to decline, indicating a diminishing combustion efficiency. The best combustion state was observed at a dust mass concentration of 800 g/m3. The instantaneous speed of the MgH2 dust explosion flame propagation exhibited a fluctuating pattern across different concentrations. The fluctuation amplitude initially decreased as the dust concentration increased, suggesting a more stable flame propagation. However, beyond a certain concentration, the fluctuation amplitude began to increase again. It is worth noting that the change in instantaneous propagation speed variation displayed different trends as the concentration varied. The exact behaviors were found to be dependent on the particular concentration level. Finally, analysis of the X-ray diffraction (XRD) test results of the MgH2 explosion products revealed a complex reaction mechanism. The MgH2 dust explosion primarily involved the combustion reaction of MgH2 but also included multiple overall reactions such as the decomposition of MgH2 and Mg(OH)2, as well as the oxidation of Mg and H2. The final product of the explosion reaction was identified to be MgO.
In the experiment conducted using a custom-built 5-L dust explosion flame propagation apparatus, the focus of the study was the characteristics of the flame propagation of magnesium hydride (MgH2) dust explosions within a semi-enclosed space. The experimental results showed that as the concentration of MgH2 dust increased, the time required for the MgH2 dust explosion flame to transfer from ignition to stable propagation decreased initially, but then increased as the dust concentration further increased. Similarly, the width of the preheating zone followed the same pattern. Initially, it decreased with increasing dust concentration, but once the concentration reached a certain threshold, it started to increase. Beyond that, the flame brightness, smoothness of the flame front, and flame propagation speed all showed similar trends. They initially increased as the MgH2 dust concentration increased, suggesting enhanced combustion activity. However, as the concentration further increased, these characteristics started to decline, indicating a diminishing combustion efficiency. The best combustion state was observed at a dust mass concentration of 800 g/m3. The instantaneous speed of the MgH2 dust explosion flame propagation exhibited a fluctuating pattern across different concentrations. The fluctuation amplitude initially decreased as the dust concentration increased, suggesting a more stable flame propagation. However, beyond a certain concentration, the fluctuation amplitude began to increase again. It is worth noting that the change in instantaneous propagation speed variation displayed different trends as the concentration varied. The exact behaviors were found to be dependent on the particular concentration level. Finally, analysis of the X-ray diffraction (XRD) test results of the MgH2 explosion products revealed a complex reaction mechanism. The MgH2 dust explosion primarily involved the combustion reaction of MgH2 but also included multiple overall reactions such as the decomposition of MgH2 and Mg(OH)2, as well as the oxidation of Mg and H2. The final product of the explosion reaction was identified to be MgO.
