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Simulation study on propagation characteristics of gas explosion in Y-shaped ventilated coal face
LIU Jiajia, ZHANG Yang, ZHANG Xiang, NIE Zishuo
, Available online  , doi: 10.11883/bzycj-2023-0018
To study the propagation law of gas explosion in a Y-shaped ventilated coal face, the simulation software of Fluent was used to carry out numerical simulation research combined with the actual situation of the N2105 working face in the Yuwu Coal Mine. First, the reliability of the mathematical model in this paper was demonstrated. In addition, the simulation parameters were optimized to make the results fit the actual situation. Finally, a numerical simulation was carried out. The results show that the maximum error between the simulation results and the previous experimental results is 11.3%, and the minimum error is only 1.7%, which verifies the reliability of the mathematical model in this paper. The most reasonable key parameters for the numerical simulation of gas explosion were determined including mesh size, iteration step size and ignition temperature, which are 0.4 m, 0.10 ms and 1 800 K, respectively. The overpressure peak of the gas explosion in the air inlet channel, belt fluting, return airway, and working face and its distance from the explosion source accords with an exponential function, and the relationship between the time required to reach the overpressure peak and the distance from the explosion source is linear. The overpressure attenuation ratio of the working face is 41.03% at 7.5 m away from the tunnel bifurcation, and the overpressure attenuation ratio of the belt fluting is 25.99%. Belt fluting is more dangerous in the event of a gas explosion. In the bifurcation of the working face, the turbulent flow zone gradually moves from the right side to the left side, and the overpressure peak at the bifurcation of the roadway increases. The flame dissipation of the return airway is the fastest, followed by the flame dissipation of the belt fluting, and the flame dissipation of the working face is the slowest. The direction of the flame dissipation in the belt fluting and return airway is opposite to the direction of the flame propagation in the early stage of the gas explosion, while the direction of the flame dissipation in the working face is consistent with the direction of the flame propagation in the early stage of the gas explosion.
Characteristics of the impact pressure of the hole wall by interval charge in the hole bottom
LOU Xiaoming, GUAN Xuhui, ZENG Lingfeng, GUO Wenkang, YUE Bin, LU Wei
, Available online  , doi: 10.11883/bzycj-2022-0109
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 interface, 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.
Preliminary theoretical study on the rebound effect of projectiles penetrating ultra-high performance concrete targets
ZHU Qing, LI Shutao, CHEN Yeqing, MA Shang
, Available online  , doi: 10.11883/bzycj-2022-0513
It is a developing trend of protection engineering to use high resistance materials such as ultra-high performance concrete to construct bullet-shielding structures. The phenomenon of projectile body rebound was found in the tests of projectile body penetrating ultra-high performance concrete. The projectile rebound effect is very important in the study of engineering protection, weapon damage and warhead design. In order to study the rebound velocity of projectile body after penetration and its influencing factors, the stress of projectile body from penetration to rebound was analyzed. Based on the expression of penetration resistance given by the cavity expansion theory, a one-dimensional elastic bar potential energy model was established from the perspective of the accumulation of deformation energy by penetration resistance, and a one-dimensional stress wave model was established from the perspective of stress wave generated by penetration resistance. The analytical solutions of the rebound velocity were derived from the two models respectively, and the physical quantities affecting the rebound velocity were analyzed. Through numerical simulation, the rebound phenomenon of the projectile body after penetrating the ultra-high performance concrete is reproduced, and the numerical results of the rebound velocity agree well with the two analytical solutions. Through numerical calculation of the same penetration model with different material parameters, the relationship between the rebound velocity and the material parameters in the analytical solution is verified, and the reliability of the theoretical model is proved. The results show that the projectile body accumulates deformation potential energy due to penetration resistance, and the projectile body bounces back due to the release of deformation potential energy after penetration. The initial rebound velocity is independent of the target velocity, proportional to the target material, yield strength and warhead shape coefficient, and inversely proportional to the elastic modulus and density of the projectile body. The results can preliminarily predict the rebound velocity and provide a reference for the design of ultra-high performance concrete protective structure and warhead.
Cook-off experiment on the JH-14C booster explosive with a shell and numerical simulation on its cook-off response
XIAO Youcai, WANG Ruisheng, FAN Chengyan, ZHANG Hong, WANG Zhijun, SUN Yi
, Available online  , doi: 10.11883/bzycj-2022-0555
In order to explore the cook-off response characteristics of the JH-14C booster explosive with a shell under different external temperatures, a set of experimental equipment was designed to measure the cook-off response temperatures at multiple points of the JH-14C booster explosive and to monitor the deformation of the shell. The explosive temperatures were measured from its edge to its center. The strain-time curves of the shell were recorded by a dynamic strain indicator and a high-temperature strain gauge. The cook-off experiments with the heating rates of 1.0 ℃/min and 3.3℃/h were conducted. And the temperature rises at different points of the explosive and the strains at different points of the shell were obtained. The intensity of the shock wave in the process of the slow cook-off experiment was calculated by using the thin-walled cylinder principle, and the violence of the reaction of the JH-14C booster explosive with a shell was quantitatively characterized by using the intensity of blast loading. The response characteristics of the JH-14C booster explosive with a shell in the slow cook-off experiment was revealed. Though the relationship between the shell strain results and the reaction intensities, a method was proposed to describe the reaction level of the JH-14C booster explosive with a shell. Based on the thermodynamics and the chemical reaction of the explosive, the heat conduction model was established. The decomposition reaction of the explosive was described by the Arrhenius equation. A back propagation (BP) neural network was used to invert the heat reaction parameters of the JH-14C booster explosive. Comparison between the experimental and simulated results shows that the presented model can be used to obtain the cook-off response characteristics of the explosive by simulation in high precision. The internal temperature field response of the projectile body was studied under different heating rates. The results display that the lower the heating rate, the higher the response temperature of the charge and the more intense the reaction. With the decrease of the heating rate, the ignition area of the explosive gradually shifts from the outer edges of both ends to the inside of the explosive.
Numerical simulation of the structural response of a torpedo at the moment of vertical water entry
HE Zheng, GAO Ziqing, GU Xuan, GAO Zishu
, Available online  , doi: 10.11883/bzycj-2022-0506
The torpedo may be damaged by impact while entering the water. Due to changes in shape, the place where cabins are connected is more stressed and is usually more dangerous. The trajectory of a torpedo is stable when it enters the water vertically for a short time. Based on this, the axial motion and mechanical characteristics of the torpedo's cabins and connecting parts were studied. Firstly, the arbitrary Lagrangian-Eulerian (ALE) algorithm and penalty function method were used to establish the numerical model of fluid-structure coupling calculation, and its effectiveness was then verified by comparing it with the existing experiment. Next, four sets of solid grids and five sets of fluid grids were established, and the rate of change of maximum acceleration and maximum pressure was analyzed. The independence of the grid was verified through comparison. The vertical water entry processes of torpedoes with different head shapes and connection forms were simulated and compared with those of integral torpedoes. The results show that the acceleration increases instantaneously after the torpedo hits the water, then fluctuates in the positive and negative directions around zero and becomes smaller and smaller. The sharper the head, the smaller the impact. The response characteristics of each cabin are different. Since the stress is transmitted backward in the form of waves, the response order of each cabin depends on the distance from the head, and the strength will gradually decrease. The adjacent shells are no longer relatively stationary, and the connector between them will be continuously pulled and pressed, leading to significant changes in their appearance and position. When the adjacent shells tend to move away from each other, there will be gaps, and the stress of the connectors will also reach the maximum, which is dangerous to the torpedo. It is recommended to add sealing rings or other fixed devices in the project to strengthen the protection of connection parts.
Influences of negative pressure conditions on the explosion temperature field and harmful effects of emulsion explosive
LI Zihan, CHENG Yangfan, WANG Hao, ZHU Shoujun, SHEN Zhaowu
, Available online  , doi: 10.11883/bzycj-2023-0106
In order to explore the mechanism of the detonation reaction of emulsion explosives under negative pressure conditions, a self-made visualized spherical explosion tank was designed, and the explosion flame propagation process, detonation wave pressure and explosion noise of emulsion explosive were measured by a high-speed camera, a pressure sensor and a noise meter, respectively. Furthermore, the two-dimensional temperature field of explosion fireball was reconstructed using the colorimetric temperature measurement technology, and the effects of the initial vacuum degree on the explosion temperature field, the detonation wave characteristic parameters and the explosion noise of emulsion explosives were studied in depth. Combined with the simulation results of the AUTODYN software, the influences of negative pressures on the explosive pressure fields were analyzed, and the detonation mechanism of the emulsion explosive in the negative pressure environment was also discussed. The experimental results showed that with the increase of the initial vacuum degree , the explosion fireball became brighter, lasted longer and had a more stable morphology; when the vacuum degree was 0 kPa, the fireball began to rupture at 19.35 μs, while the vacuum degree was −100 kPa, the fireball began to rupture at 58.05 μs; a low initial vacuum degree had little effect on the fireball temperature, while the initial vacuum degree above −60 kPa would significantly increase the explosion temperature of emulsion explosives. The peak pressure and specific impulse of shock wave decreased with the increase of initial vacuum degree, while the effect of initial vacuum degree on the positive pressure action time of shock wave was not obvious. AUTODYN numerical simulation results showed that the peak pressure of the shock wave decreased with the increase of the vacuum degree, the shock wave velocity gradually decreased to be close to the expansion velocity of the detonation product. In addition, the increase of initial vacuum degree was beneficial for the reduction of the explosion noise, compared with atmospheric pressure, when the vacuum pressure in the tank was −100 kPa, the sound pressure level of explosion noise was reduced by 35.9 dB, with a reduction of 29.8%.
Failure mechanism and dynamic response of a composite lattice structure under intense explosion loadings
SHI Shengbo, WANG Renzhi, TANG Jiabin, GAN Yundan, YUAN Jianfei, CHEN Yong
, Available online  , doi: 10.11883/bzycj-2022-0430
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. This work is of great scientific significance. A composite lattice sandwich structure with pyramidal truss core was designed, which was consisted of carbon fiber reinforced composite panels and metal cores. The explosion experimental tests 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 composite panels and the Johnson-Cook damage model of metal cores were constructed. Combining with the finite element method, a numerical model for predicting explosion shock response of composite lattice structure was developed. Both the bonding properties between layers of composite panels, and the performances of adhesive layer between panels and 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 and used to characterize the attenuation degree of stiffness properties of 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 which influencing on the explosion protection properties of 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 closed to explosion loadings. The main failure modes are the debonding between composite panels and 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 is discussed. The feasible domain for this structure design is given. These research results could provide theoretical basis and technical support for the designing and safety evaluation of lightweight, explosion protection structure of key equipment components.
Numerical and theoretical investigations on crashworthiness of star-shaped hybrid multi-cell tubes
KONG Zhicheng, HU Jun, GUO Zhiping
, Available online  , doi: 10.11883/bzycj-2022-0549
In order to develop a lightweight and efficient energy absorption device, a novel type of the star-shaped hybrid multi-cell (SHM) tubes based on the hybrid design of polygonal cross-section and star-shaped cross-section was proposed. The finite element (FE) models of the polygonal thin-walled (PT) tubes, the star-shaped thin-walled (ST) tubes and the SHM tubes were established by ABAQUS, and the reliability of the FE model was verified by simulating quasi-static axial crush tests. Then, the energy absorption characteristics and deformation modes of three kinds of thin-walled tubes under axial loading conditions were studied by numerical simulation. Based on the simplified super folding element (SSFE) theory, the theoretical formula of the mean crushing force of the SHM tubes under the progressive folding deformation mode is established. The numerical results show that there is a synergistic effect between the polygonal cross-section and the star-shaped cross-section of the SHM tubes. Compared with the PT tubes and the ST tubes, the energy absorption of the SHM tubes is significantly improved. When the number of polygon edges N=6, the cross-section synergistic effect of the SHM tubes is the best, and the energy absorption efficiency is the highest when N=8. Subsequently, the investigations on geometric parameters of the SHM tubes are carried out, and the effects of wall thickness and star angle on crashworthiness are discussed respectively. It is found that the wall thickness has obvious influence on the crashworthiness of the SHM tubes, and the crushing force level increases linearly with the increase of the wall thickness. In addition, the change of the star angle has little influence on crashworthiness. The crushing load efficiency and the specific energy absorption increase first and then decrease with the increase of the star angles. When the star angle α=120°, the SHM tubes has the most excellent crashworthiness. The research results can provide design methods and theoretical guidance for the cross-section design of multi-cell structures.
Dynamic properties and constitutive model of basalt after high-temperature treatment and water cooling under constant dynamic load
XU Zehui, HE Tong, DU Guanggang, LIU Lei
, Available online  , doi: 10.11883/bzycj-2022-0421
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.
Numerical analysis of dynamic response of ceramic particle reinforced polyurethane composites under explosive loading
ZOU Guangping, LIANG Zheng, WU Songyang, CHANG Zhongliang
, Available online  , doi: 10.11883/bzycj-2022-0254
As a traditional energy absorbing and shock absorbing protective material, polyurethane has high requirements for its dynamic mechanical properties. An effective way to improve the impact resistance of polyurethane is to add ceramic balls as reinforcement in polyurethane matrix. The existing research on ceramic ball reinforced materials mainly focuses on nano and micro scale. The dynamic response of Al2O3 ceramic ball reinforced polyurethane matrix composites under small equivalent explosion load was simulated by establishing a numerical model of polyurethane embedded millimeter ceramic ball and using ALE algorithm of LS-DYNA and the correctness of the numerical model was verified by the empirical formula of henrych’s free field explosion overpressure and the penetration experiment of polyurethane-ceramic sphere composite plate. The deformation process of the composite plate was obtained and through the comparison of the acceleration of the composite plate and the pure polyurethane, it was found that the acceleration of the ceramic ball and the polyurethane always maintain the opposite direction, which proves that the existence of the ceramic ball reduces the overall acceleration fluctuation range; Furthermore, the effects of explosion equivalent on the velocity, displacement and energy absorption of composite plates and the effects of different explosion equivalent and ceramic ball size on the properties of composite materials under a certain areal density were discussed. The results show that the overall acceleration fluctuation range of polyurethane-ceramic balls composite material is about 1×105 m·s-2 lower than that of pure polyurethane. With the increase of explosive equivalent, the deflection of the composite increased steadily to 1mm, and the energy absorption proportion of polyurethane increased from 69.6% to 80.3%; Under the same areal density, both the deformation resistance of the composite plate and the overall acceleration fluctuation range increases with the increase of the diameter of the ceramic ball.
Influence of the ignition energy on combustion and explosion characteristics of single-base propellant
KANG Penglin, LI Xiaodong, LIU Wenjie, SUN Yantao, GUAN Yunfei, MA Zhigang, ZHAO Ziwen
, Available online  , doi: 10.11883/bzycj-2022-0452
A device was developed to experimentally explore the influences of the ignition energy on the combustion and explosion characteristics of single-base propellant. In order to control the ignition energy on the single-base propellant, the black powders with different masses were used to ignite the propellant in the combustion and explosion experiment. By analyzing the ablative traces on the inner wall of the witness plate and the confining steel cylinder, the combustion and explosion development process of the single-base propellant was discussed, and the influences of different ignition energies on the combustion and explosion characteristics of the single base-propellant were obtained. The results show that, at the beginning of ignition, the combustion reaction of the propellant in the confining steel cylinder is incomplete and the reaction is weak according to the larger ablation trace diameter and lighter ablation trace color. After propagating a distance away from the ignition side, the combustion reaction becomes stronger, but the reaction is still incomplete at this time, smaller ablation diameter and deeper ablation color. While propagating to the end of the confinging steel cylinder, the propellant reaction is complete and the severity of reaction is relatively large, seen from the smaller ablation diameter and the lighter ablation color. At the ignition energies of 4.0, 5.0 and 8.0 kJ, the growth distances from initial ignition to rapid increase of reaction intensity were 54.66, 53.95 and 19.38 cm, respectively. At the ignition energy of 20.0 kJ, the propellant reaction is already strong at the beginning and grows stronger enough to produce obvious dents on the witness plate while propagating to the end. Also at this ignition energy, slow combustion, fast combustion and deflagration occur in the reacion of the propellant, respectively at different positions in the confining steel cylinder. The study enlights that the ignition energy has reference significance for the design of propellant charge.
Sub-texture in adiabatic shear bands from arc additively manufactured stainless steel under dynamic loads
CHEN Jie, WANG Kehong, PENG Yong, KONG Jian, LIU Chuang, DONG Kewei, WANG Qipeng, ZHANG Xianfeng
, Available online  , doi: 10.11883/bzycj-2022-0493
Adiabatic shearing is a common failure mechanism for additively manufactured metals and alloys under dynamic loads. Cylindrical samples (\begin{document}$\varnothing $\end{document}4 mm×4 mm) along building and scanning directions were extracted from 316L stainless steel plate fabricated by cold metal transfer wire and arc additive manufacturing process (AM 316L). Cylindrical AM 316L samples were subjected to dynamic impacts to introduce adiabatic shear bands (ASBs) at high strain rates from 4000 to 6000 s−1 by using split Hopkinson press bar. Deformed AM 316L samples were cut along compression direction. Multiple methods including scanning electron microscope, electron-back-scatter diffraction, focused ion beam, transmission electron microscope, transmission kikuchi diffraction were applied to characterize the microstructure of ASBs. The dynamic flow stress of AM 316L increases with forward strain due to strain hardening at first, and then comes an obvious flat stage for the balance between adiabatic thermal softening and strain hardening followed by adiabatic shearing prevailing causing the last failure. The sub-grains in ASBs experienced a dynamic recrystallization process, present fully distinct equiaxed crystal morphology with high angle grain boundaries from the matrix, of which the grain size is about 200~300 nm. The complex thermal and mechanical processes during adiabatic shearing lead to the formation of duplex components in sub-texture, which conclude not only the <110>-fiber along the compression direction similar with the matrix, but also the crystallographic texture related to shear direction with plane (111) along shear plane and orientation <112> along shear direction. The residual large amount of Σ3 60° grain boundaries and twin-symmetry texture in ASBs prove that twinning recrystallization is the main dynamic recrystallization mechanism. The ASB propagating paths of AM 316L along different directions under dynamic loadings are the similar, which is that both ASBs successively extend along the symmetrical path of angles 35° with respect to the loading surface. These two paths are the locations of the maximum strain and thermal distribution during the dynamic loadings consistent with previous simulation work. In addition to the external physical conditions of the maximum strain and thermal field distribution in the sample under dynamic loading, the paths conform to the crystallographic condition that the intersection angle between the shear plane (111) and the matrix (110) is 35.2°. Accompanied with macro adiabatic shear bands, micro-strain localization bands are formed to accommodate more strain, wherein the sub-grains take distinct orientation from matrix.
Study on the vulnerability of concrete obstacle under contact explosion
MA Shixin, JI Yangziyi, ZHONG Mingshou, LI Xiangdong
, Available online  , doi: 10.11883/bzycj-2022-0538
Contact explosion experiments were conducted to assess the damage capacity of a cylindrical charge contact explosion on a concrete obstacle. A characterization method for the damage level of a concrete obstacle was proposed based on the experimental results. Subsequently, numerical simulations were performed to study the influence of charge mass and placement location on the residual height of a concrete obstacle. To validate the numerical model and applied material parameters, the results of the numerical simulations were compared with the experimental results. Based on the numerical results, the vulnerability of the concrete obstacle under contact explosions of different charge placements was characterized using the damage iso-curve method. The shape and center position of the damage zone on the top and side of the obstacle were obtained. Considering the randomness of charge placement after deployment in actual use, a model for calculating the vulnerable area was established to investigate the overall vulnerability of the obstacle. The relationship between the charge mass and the vulnerable area of different damage levels of the obstacle when the charge exploded on the top and side was obtained. The research results indicate that the shape of the damage zone on the top of the obstacle is approximately a square, with the center coinciding with the center of the top surface. The shape of the damage zone on the side is approximately a rounded trapezoid, with the center located about 10 cm below the geometric center of the side surface. Based on the calculated results of the vulnerable area, the difference in vulnerability between the top and side of the obstacle under contact explosion was compared. When the mass of the cylindrical charge is between 0.5 kg and 10.79 kg, the concrete obstacle is more vulnerable to damage when subjected to a contact explosion on the side. The findings of this research can provide support and guidance for the demolition of concrete obstacles, the design of obstacle-breaking projectiles, and the evaluation of their damage effectiveness.
Advances in numerical simulation of blast-induced traumatic brain injury: modeling, mechanical mechanism and protection
KANG Yue, MA Tian, HUANG Xiancong, ZHUANG Zhuo, LIU Zhanli, ZENG Fan, HUANG Chao
, Available online  , doi: 10.11883/bzycj-2022-0521
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.
Dynamic response and energy dissipating characteristics of shale under cyclic impact loadings
WANG Yu, ZHAI Cheng, TANG Wei, SHI Kelong
, Available online  , doi: 10.11883/bzycj-2022-0248
The formation of complex fracture networks in shale by cyclic impact loading is an important scientific problem for water-free fracturing technology of shale reservoirs such as explosive fracturing and high-energy-gas-fracturing. In this paper, two cyclic impact experiments based on the Hopkinson rod experimental system (SHPB) were conducted on freshly exposed black mud shale of the Wufeng Formation-Longmaxi Formation taken from 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 revealed the energy evolution law of 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 of impact pressure, the number of times of impacts required to rupture the specimen decreases, the fragmentation and the peak stress increase; the specimen undergoes cyclic impact showing the mechanical response characteristics of compaction first and then gradual damage. The damage degree of shale specimens during cyclic impact was calculated by a dynamic damage model based on the Weibull distribution, and the results showed 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, which showed 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 cycle impact gas pressure gradient and the positive cycle impact gas pressure gradient is greater than that of the zero gradients, and the absolute value of the pressure gradient shows a positive correlation with the energy absorption ratio. This indicates that under the same condition of total impact energy, increasing the absolute value of the cyclic impact gradient can produce 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.
Simulation on the defending effect of composite structure of body armor under the combined action of blast wave and fragments
WANG Zhi, CHANG Lijun, HUANG Xingyuan, CAI Zhihua
, Available online  , doi: 10.11883/bzycj-2022-0515
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 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 wave and fragments, but continued increase in thickness has limited gain in protection performance.
Upper explosion limit of C3H8/C2H4 mixtures in air at high temperatures and pressures
CHEN Sheng, NING Ye, HE Meng, QI Chang, WANG Yalei, YAN Xingqing, YU Jianliang
, Available online  , doi: 10.11883/bzycj-2022-0475
In order to prevent the potential explosive risks of flammable gas mixtures in the process of high temperatures and pressures, it is necessary to understand the upper explosion limits of C3H8/C2H4 mixtures. An experimental device with high pressure 20 L spherical vessel placed in a high temperature oven were 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 certain concentration. The 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 experiments. The effects of temperature, pressure and concentration 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 large than 0.3 MPa. The amplitude and rate on the increase of the upper explosion limit at high temperatures and pressures are higher than those at normal conditions with the increase of C2H4. The influences of temperature and pressure on the upper explosion limit are much greater than the sum of two effects alone, which can indicate 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 relationships 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.
Energy absorption characteristics of composite thin-walled Ω-shaped tubes with different ply orientations
WANG Yu, LI Lihang, HOU Bing, DOU Qingbo, ZHANG Xinyue, SUO Tao, LI Yulong
, Available online  , doi: 10.11883/bzycj-2022-0525
Composite Ω-shaped tubes have certain application potential in terms of collision energy absorption and lightweight. In order to study the effects of ply orientation and loading rate on the energy absorption characteristics of the composite Ω-shaped tubes, quasi-static and dynamic axial compression experiments were carried out on carbon-fiber-reinforced composite Ω-shaped tubes by using an electronic universal testing machine and a high-speed hydraulic servo testing machine, respectively. In addition, the failure modes and evaluation index connected with energy absorption were analyzed based on the crushing load-displacement curves and failure morphologies. In the experiments, the Ω-shaped tubes with three ply orientations, including [0/90]3s, [0/45/90/−45]3 and [±45]3s, were compressed under quasi-static and dynamic loading rates. Under quasi-static loading, the specimens with [0/90]3s and [0/45/90/−45]3 ply orientation both show progressive failure, while the specimens with [±45]3s ply orientation show a catastrophic failure mode. The specific energy absorption (SEA) of the specimens with [±45,]3s ply orientation is about half of those of the above two specimens due to different failure modes. Under the dynamic loading, the Ω-shaped tubes with three ply orientations, where the SEA almost remains the same, are featured by the progressive crushing. Moreover, the SEAs of the specimens with [0/90]3s and [0/45/90/−45]3 ply orientations under dynamic loading are reduced by 29.70% and 20.97%, respectively, compared with those under quasi-static loading. However, the SEA of the specimens with [±45]3s ply orientation is 46.10% higher than that under quasi-static loading. The change of failure modes is the main reason for the increase of the SEA. Under quasi-static loading, the ply orientation has a certain effect on the SEA of the Ω-shaped tube, while under dynamic loading, its influence is relatively weak. The main reasons are as follows. At a low loading rate, buckling fracture and interlaminar delamination of fiber and matrix gradually occur, which is a global response of the structure. However, at a higher loading rate, the contact time between the Ω-shaped tubes and the indenter is short, which is a local response, causing the dominant influence to be the loading rate, and the failure mode is less affected by the ply orientations.
Experimental studies on crack propagation behaviors of rock materials under dynamic loads: a review
GAO Weiting, ZHU Zheming, ZHU Wei, ZOU Ming
, Available online  , doi: 10.11883/bzycj-2022-0526
Dynamic fracture behavior is a crucial aspect of rock mechanics and engineering, with significant implications for the safety and effectiveness of structures in fields such as mining and civil engineering. In recent years, significant progress has been made in the study of dynamic crack propagation in rock materials, and the purpose of this paper is to provide a comprehensive review and summary of the latest achievements in testing techniques, experimental equipment, and experimental methods. Various measurement techniques have been developed for dynamic rock crack propagation testing, including X-ray computed tomography, caustics method, digital image correlation method, crack propagation gauge, conductive carbon film test method and acoustic emission. Each of these techniques has advantages and limitations, and the selection of the appropriate technique depends on the specific experimental requirements and constraints. The dynamic fracture behaviors of rock at different strain rates have been studied extensively by numerous researchers. The strain rate is a crucial parameter that determines the deformation and failure mechanisms of rocks under dynamic load. The dynamic fracture properties of rock under middle and low strain rates, high strain rates, and ultra-high strain rates have been summarized systematically. The experimental methods used for dynamic fracture testing include the drop-hammer impact device, split Hopkinson pressure bar, and explosion experiments. The failure properties of crack initiation, propagation, arrest behaviors, and dynamic fracture toughness of rocks under different strain rates have been investigated. In conclusion, the study of dynamic crack propagation in rock is a challenging and important field of research in rock mechanics and rock engineering. The development of new experimental techniques and methods has enabled researchers to gain a deeper understanding of the complex behavior of cracks in rock under dynamic loads. The findings of these studies have important implications for the design of safe and reliable structures in various fields of actual engineering.
Parameter design of a new thin-diaphragm pressure sensor
WANG Zhao, WU Zutang, YANG Jun, LI Yan, LIU Wenxiang
, Available online  , doi: 10.11883/bzycj-2022-0392
In recent years, the new measurement method of shock wave reflection overpressure peak by using the direct proportional relationship between the pressure to be measured and the diaphragm acceleration has been verified by shock-tube verification experiments. This method has the advantages of no calibration, simple fabrication, low cost and high measurement accuracy. In order to optimize the main parameters of the thin-diaphragm pressure sensor and to obtain the uncertainty of pressure measurement, numerical simulations were carried out. Specifically, the numerical simulation based on step pressure was carried out to analyze the influences of diaphragm thickness, pressure to be measured, fitting parameters and other factors on the pressure measurement. The numerical simulation based on blast pressure was carried out to analyze the influence of rapid pressure drop on measurement. The displacement or velocity signal of the thin diaphragm was fitted to obtain the diaphragm’s acceleration value at the beginning of impact, which was further used to calculate the pressure peak to be measured. By comparing the calculated pressure with the standard pressure, the optimum values of fitting time, fitting polynomial degree, diaphragm thickness and other factors were obtained. And the main technical specifications of the thin diaphragm pressure sensor were obtained. In particular, the polynomial fitting method was applied to carry out data processing, which can effectively avoid the model error introduced by linear fitting. This method obviously improved the measurement accuracy of the sensor and was a great improvement. In addition, shock-tube experiments were carried out to verify some conclusions by numerical simulation. In summary, the optimal parameters of the diaphragm pressure sensor were obtained: the thickness of the stainless steel diaphragm is 50-70 µm, velocity data is fitted by second-order polynomial, and fitting time is about 0.8 µs. And the relative error of shock wave reflection overpressure peak measurement can be controlled within 3%. Relevant conclusions can provide references for the popularization and application of the diaphragm pressure sensors.
Dynamic cratering process during penetration of rigid projectile into concrete target
LI Pengcheng, ZHANG Xianfeng, WANG Guiji, LIU Chuang, LIU Junwei, DENG Yuxuan, SHENG Qiang
, Available online  , doi: 10.11883/bzycj-2022-0512
In order to study the cratering stage in the dynamic penetration process of projectiles into the concrete targets, the cratering stage is further divided into two phases according to the damage of the projectile during penetration. Combined with the shape function of projectile head, streamline field of Z model and normal expansion theory (NET), an analytical and calculation model of penetration resistance during the cratering stage is established, which considers the influence of concrete ejection process. Reliability of penetration resistance model during the cratering stage is then verified by test data taken from published papers. The advantages of the present model compared with the existing classical model are analyzed, while the influences of initial impact velocity of projectile, the caliber-radius-head and uniaxial compressive strength of concrete on the dynamic process during the cratering stage are analyzed. With the increase of the initial impact velocity of projectile, the diameter and depth of the ejection region gradually increase, the time of the ejection region to reach the maximum size is gradually shortened, and the time of the dynamic process during the cratering stage is also shortened. With the increase of the caliber-radius-head of the projectile, the diameter and depth of the ejection region gradually decrease, the time of the ejection region to reach the maximum size gradually increases, and the time of the dynamic process during the cratering stage increases, too. With the increase of uniaxial compressive strength of concrete, the diameter and depth of the ejection region are gradually reduced, the time of the ejection region to reach the maximum size is gradually shortened, and the time of the dynamic process during the cratering stage is also shortened. The velocity has the greatest influence on the dynamic process during the cratering stage of the projectile penetration into the concrete target, followed by the caliber-radius-head of the projectile and uniaxial compressive strength of concrete.
Experimental study on explosion cratering and coupled ground shock in clay
SHI Benjun, LI Jie, GUO Wei, XU Tianhan, XU Xiaohui, LI Gan, JIANG Haiming
, Available online  , doi: 10.11883/bzycj-2022-0445
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}1500 mm×1490 mm layered blast test apparatus. The real volume of the crater under different burial depths was recorded by using a three-dimensional scanning equipment, and the pressure data under different distances from the blast center were measured by earth pressure sensors to obtain the blast wave propagation law. Meanwhile, the law of energy distribution of coupled ground impact was theoretically revealed, which is proportional to the volume of medium damage. Three conversion relations of coupling coefficient were given, and the coupling coefficient curve of clay was drawn using the Boltzmann function. The experimental results show that in the range of −0.056 m/kg1/3h≤0.37 m/kg1/3, as the burial depth of the charge increases, the attenuation coefficient increases, and the peak pressure of the blast core distance also increases, and the share of the explosion impact coupling medium also increases with the increase of the charging burial depth. This indicates that the increase of the charging proportion burial depth intensifies the effects of the explosion. This finding implies that the change in burial depth has a negligible impact on the energy of the explosion impact coupling medium. The critical depth of ground shock effect of compacted clay is about 0.55 m/kg1/3, which is slightly larger than the radius of underground closed explosion cavity. The experimental value of visible diameter is in good agreement with the corresponding ConWep predicted value. The macroscopic failure critical depth is about 1.46 m/kg1/3. Combined with the test results, the variation law of the energy distribution of explosion coupling ground impact in clay with the buried depth of the charge ratio is given, and the calculation method of the equivalent closed equivalent of underground explosion is established. This provides a load basis for underground engineering blast resistance research and structural design.
Numerical simulation of flat-nosed projectile with attack angle across aramid laminates having varying thickness
JI Haibo, WANG Xin, ZHAO Zhenyu, ZHAO Zhongnan, LI Xue, HAN Jiatong, LU Tianjian
, Available online  , doi: 10.11883/bzycj-2022-0231
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 mm, 8 mm, 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 method for synchronous shock calibration of triaxial accelerometers based on vector decomposition
WANG Qinghua, ZHANG Yuanyuan, GAO Meng, XU Feng, GUO Weiguo
, Available online  , doi: 10.11883/bzycj-2023-0007
The triaxial accelerometer can simultaneously detect and measure shock loads along the three coordinate axes in the three-dimensional space. Therefore, it has a wide range of applications in the fields of spatial vibration test, spatial impact test, and so on. Before being put into practical use, triaxial accelerometers must be calibrated for their sensitivity coefficients to ensure the validity and accuracy of measurements. Unlike the calibration of single-axis accelerometers, there is a major difficulty in the calibration technologies of the triaxial accelerometer, that is, how to realize the excitation of three-dimensional shock loads synchronously, since the pulse width of the shock loads are usually as short as a few milliseconds. On the other hand, tracing and measuring the acceleration excited during shock process is also the key to the shock calibration of accelerometers. In order to address the aforementioned problems, a drop table equipped with a shock amplifier was used to excite acceleration loads vertically upward. Then, with the help of an anvil which has a bevel, the vertical acceleration excited on shock amplifier was decomposed to each sensitive axis of the triaxial accelerometer based the principle of vector decomposition. By means of this approach, synchronous shock loading of the triaxial accelerometer was then realized. High-speed camera and image processing based on MATLAB were used to trace and measure the acceleration excited in the synchronous shock calibration of triaxial accelerometers. Experiments were conducted to verify the effectiveness of the motion measurement method based on high-speed camera and MATLAB image processing. The sensitivity matrix of the triaxial accelerometer, which takes into consideration both the main sensitivity coefficients and the coupling sensitivity coefficients, was solved using the least-square method. At last, the measurement accuracy of the accelerometer calibrated using the synchronous method was compared with the measurement accuracy of the accelerometer calibrated using the conventional asynchronous method. The research results indicate that the conventional drop table could excite a wide range (102g~104g) of acceleration by equipping a shock amplifier. In addition, the motion measurement method based on high-speed camera and MATLAB image processing is valid in acceleration traceability or measurement in the shock calibration of accelerometer. Furthermore, compared to the measurement accuracy of the accelerometer calibrated by the asynchronous method, the measurement accuracy of the triaxial accelerometer could be guaranteed and improved by using the synchronous method. Therefore, in engineering, the triaxial accelerometer ought to be calibrated using synchronous methods rather than asynchronous methods to guarantee the validity and accuracy of measurements.
Experimental study on blast resistance performance and damage repair of precast concrete column under close-in explosion
LYU Chenxu, YAN Qiushi, LI Liang
, Available online  , doi: 10.11883/bzycj-2022-0225
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.
GPa-level slow-front ramp wave loading technology driven by non-shock initiation reaction
YANG Tianhao, CHONG Tao, LI Tao, FU Hua, HU Haibo
, Available online  , doi: 10.11883/bzycj-2022-0238
To study the ignition behavior of micro-mesoscopic hot spots in the matrix of pressed PBXs under GPa and 10μs-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 1.6GPa, and the front of the ramp wave is 25μs, which preliminarily proved the feasibility of realizing GPa and 10μs-level ramp wave pressure output by using the non-shock initiation reaction of heavily constrained pressed PBX explosives.
A study of the circumferential propagation law of the shock wave produced by the near ground dynamic explosion of cylindrical charge
WANG Zhenning, YIN Jianping, YI Jianya, LI Xudong
, Available online  , doi: 10.11883/bzycj-2022-0313
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.
Effect of initial void ratio on phase transition of confined HMX-based PBX-3 in slow cook-off test
HU Pingchao, LI Tao, LIU Cangli, FU Hua
, Available online  , doi: 10.11883/bzycj-2022-0489
In order to understand the effect of initial void ratio on the thermal phase transformation and ignition response characteristics of HMX based PBX-3 in slow cook-off condition, it has been designed and conducted a series of experiments of confined PBX-3 with initial void ratio of 1.0%, 4.2% and 13.8% during slow cook-off test. For each test, the PBX-3 sample composed of two cylindrical pieces of explosive, 25mm in diameter and 10mm in height for each, were stacked. The temperature was monitored by the five small size Type K thermocouples, 0.25mm 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°C, and then heated at 0.25℃/min until thermal explosion occurred. During the process, the temperature of different location inside of explosive and surface of shell were acquired. The process of HMX phase transition, the mechanism of the effect of initial void ratio on HMX phase transition and the effect of HMX phase transition process on the thermal explosion temperature were analyzed in detail. The result shows that the smaller the initial void ratio is, the greater 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 slow cook-off. Due to the higher thermal sensitivity of δ-HMX, the slower the phase transition process of HMX in the slow cook-off is, the slower the heat accumulation resulted from the δ-HMX exothermic decomposition reaction, and the higher the confined shell temperature at the time of thermal explosion.