2020 Vol. 40, No. 1
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2020, 40(1): 011401.
doi: 10.11883/bzycj-2019-0346
Abstract:
The progress in explosive safety studies related to experiment achievements with precise diagnostics and understanding of non-shock initiation of explosive phenomena in recent 20 years is reviewed. Some widespread misconceptions and misleading in non-shock initiation reaction behavior and corresponding process modeling is commented and suggestions for improvement are given. Recent experiments focused on the reaction propagation and violence evolution conducted by the author’s team in recent years are introduced and interpreted in detail as an illustration of the basic mechanism of non-shock initiation reaction. For low porosity explosive, the abnormal reaction behavior is dominated by the surface conductive burning and the convective flow of hot, high pressure gaseous reaction products through confinement slot and cracks in explosive bulk, which should be taken as the basic kinetics during the reaction propagation and reaction violence growth process. The evolution of reaction violence is unstable when the surface combustion is coupled with the dynamic evolution of crack network in explosive, but the utmost violence is usually limited by the mild conductive combustion rate of typical secondary explosive and confinement failure. Especially, the deflagration to detonation transition could hardly come true in low porosity explosive system with confinement of limited strength.
The progress in explosive safety studies related to experiment achievements with precise diagnostics and understanding of non-shock initiation of explosive phenomena in recent 20 years is reviewed. Some widespread misconceptions and misleading in non-shock initiation reaction behavior and corresponding process modeling is commented and suggestions for improvement are given. Recent experiments focused on the reaction propagation and violence evolution conducted by the author’s team in recent years are introduced and interpreted in detail as an illustration of the basic mechanism of non-shock initiation reaction. For low porosity explosive, the abnormal reaction behavior is dominated by the surface conductive burning and the convective flow of hot, high pressure gaseous reaction products through confinement slot and cracks in explosive bulk, which should be taken as the basic kinetics during the reaction propagation and reaction violence growth process. The evolution of reaction violence is unstable when the surface combustion is coupled with the dynamic evolution of crack network in explosive, but the utmost violence is usually limited by the mild conductive combustion rate of typical secondary explosive and confinement failure. Especially, the deflagration to detonation transition could hardly come true in low porosity explosive system with confinement of limited strength.
2020, 40(1): 011402.
doi: 10.11883/bzycj-2019-0348
Abstract:
High temperature gaseous products of conductive burning on explosive surface can penetrate into preformed crack inside explosive bulk under high pressure to form so-called convective burning. The high rising gaseous products pressure resulting from the convective burning in turn will create cracks inside the explosive bulk, leading to the formation of new channels for convective reaction and the more reaction surfaces for burning. In this paper, a new experimental method is designed for a pressed HMX-based PBX, in which a highly confined spherical charge is ignited on center point via non-shock initiation. The propagation of such kind of reactive cracks inside is recorded and evaluated with the total reaction violence growth behavior characterized by reaction pressure and confinement wall velocity profile. In the experiment with a transparent window, the early stage evolution of crack inside explosive sphere is invisible and the crack system after the crack break through to the spherical surface shows a 4 fold symmetric crack pattern which is deduced to be related with outer layer confinement conjunction manner. The violence evolution experiences a sustaining low pressure growing rate stage for 100 μs. Then it is observed that a rapid burst pressure in about 10 μs is up to over 1 GPa during the confinement wall movement stage, which gives to a typical explosion outcome with ～20% of bare explosive detonation calculated by air blast over pressure. In the experiment with a 20 mm steel wall, the velocity of the wall has reached 500 m/s at the moment of confinement wall rupture.
High temperature gaseous products of conductive burning on explosive surface can penetrate into preformed crack inside explosive bulk under high pressure to form so-called convective burning. The high rising gaseous products pressure resulting from the convective burning in turn will create cracks inside the explosive bulk, leading to the formation of new channels for convective reaction and the more reaction surfaces for burning. In this paper, a new experimental method is designed for a pressed HMX-based PBX, in which a highly confined spherical charge is ignited on center point via non-shock initiation. The propagation of such kind of reactive cracks inside is recorded and evaluated with the total reaction violence growth behavior characterized by reaction pressure and confinement wall velocity profile. In the experiment with a transparent window, the early stage evolution of crack inside explosive sphere is invisible and the crack system after the crack break through to the spherical surface shows a 4 fold symmetric crack pattern which is deduced to be related with outer layer confinement conjunction manner. The violence evolution experiences a sustaining low pressure growing rate stage for 100 μs. Then it is observed that a rapid burst pressure in about 10 μs is up to over 1 GPa during the confinement wall movement stage, which gives to a typical explosion outcome with ～20% of bare explosive detonation calculated by air blast over pressure. In the experiment with a 20 mm steel wall, the velocity of the wall has reached 500 m/s at the moment of confinement wall rupture.
2020, 40(1): 011403.
doi: 10.11883/bzycj-2019-0345
Abstract:
The aim of this paper is to deep understand the pressurization behavior in evolution of crack burning, and promote the acknowledge level for transition mechanism of high intensity reaction in projectile fillings under accidental ignition. Based on qualitative analysis for pressure evolution in explosive crack burning, theoretical calculation is carried out for the pressurization process in crack burning of a HMX-based PBX (with a content of 95% for HMX). Simplified flow model for explosive burning products has been set up based on gas dynamic theory. With the hypothesis of one-dimensional isentropic flow, crack pressurization process has been predicted without regard to viscosity and friction resistance. The calculation result is qualitatively accord with experimental result in pressurization stage, providing a theoretical explanation for understanding the pressurization behavior in crack burning.
The aim of this paper is to deep understand the pressurization behavior in evolution of crack burning, and promote the acknowledge level for transition mechanism of high intensity reaction in projectile fillings under accidental ignition. Based on qualitative analysis for pressure evolution in explosive crack burning, theoretical calculation is carried out for the pressurization process in crack burning of a HMX-based PBX (with a content of 95% for HMX). Simplified flow model for explosive burning products has been set up based on gas dynamic theory. With the hypothesis of one-dimensional isentropic flow, crack pressurization process has been predicted without regard to viscosity and friction resistance. The calculation result is qualitatively accord with experimental result in pressurization stage, providing a theoretical explanation for understanding the pressurization behavior in crack burning.
2020, 40(1): 011404.
doi: 10.11883/bzycj-2019-0347
Abstract:
The burn rate-pressure characteristic of explosive is the intrinsic factor of ammunition safety, which reflects the potential tendency of the development of reaction violence. We conducted the experiment to understand the deflagration behavior of PBX-1 explosive by using the method of burn pressure-burn consumption in a closed bomb. The temporal pressure data and burn front time-of-arrival data were respectively recorded by pressure transducer and microthermocouple, allowing direct calculation of burn rate as a function of pressure. The result shows that the burn rate equation of PBX-1 explosive can be expressed as r = (2.16±0.55) p1.08±0.06 with the pressure exponent n＞1, indicating that the burn rate is sensitive to pressure. Over the pressure range 10−100 MPa the burn rate displays exponent dependence on the pressure. In contrast, PBX-1 exhibits erratic burn behaviors with pressures grater than 100 MPa and burn rate rises sharply. The analysis demonstrates that the physical deconsolidation of PBX-1 explosive at high pressure is the main factor, which physically disrupts the sample and results in burn specific surface area increasing over 100 times. PBX-1 explosive has potential tendency of enhancing the reaction violence by convective burning mechanism.
The burn rate-pressure characteristic of explosive is the intrinsic factor of ammunition safety, which reflects the potential tendency of the development of reaction violence. We conducted the experiment to understand the deflagration behavior of PBX-1 explosive by using the method of burn pressure-burn consumption in a closed bomb. The temporal pressure data and burn front time-of-arrival data were respectively recorded by pressure transducer and microthermocouple, allowing direct calculation of burn rate as a function of pressure. The result shows that the burn rate equation of PBX-1 explosive can be expressed as r = (2.16±0.55) p1.08±0.06 with the pressure exponent n＞1, indicating that the burn rate is sensitive to pressure. Over the pressure range 10−100 MPa the burn rate displays exponent dependence on the pressure. In contrast, PBX-1 exhibits erratic burn behaviors with pressures grater than 100 MPa and burn rate rises sharply. The analysis demonstrates that the physical deconsolidation of PBX-1 explosive at high pressure is the main factor, which physically disrupts the sample and results in burn specific surface area increasing over 100 times. PBX-1 explosive has potential tendency of enhancing the reaction violence by convective burning mechanism.
2020, 40(1): 011405.
doi: 10.11883/bzycj-2019-0360
Abstract:
In order to investigate whether the reaction evolution of pressed HMX-based PBXs inside long thick wall steel tube initiated by ignition composition leads to detonation finally or not, a new experiment apparatus was designed based on traditional DDT tube, in which the strength of tube at specific locations is enhanced, and multichannel PDV probes and high speed photography were used to diagnose the expansion process and rupture characteristics of tube wall. Compared with the results initiated by detonator in the same explosives and confinement, the reaction durations of detonation and ignition differed by orders of magnitude; the pressure evolution measured by tube wall velocities, and the propagation process of tube wall movement were significantly different in two reactions. Analysis shows that the convective flow of reaction products along the seam between tube wall and explosives, high temperature and pressure, dominated the reaction evolution of PBX-A initiated by ignition composition under strong confinement, and appeared as laminar burning on explosive surface and structural response of confinement. There is no reaction activated in explosive bulk by the ramp wave caused by upper stream non shock initiation reaction, least of all DDT.
In order to investigate whether the reaction evolution of pressed HMX-based PBXs inside long thick wall steel tube initiated by ignition composition leads to detonation finally or not, a new experiment apparatus was designed based on traditional DDT tube, in which the strength of tube at specific locations is enhanced, and multichannel PDV probes and high speed photography were used to diagnose the expansion process and rupture characteristics of tube wall. Compared with the results initiated by detonator in the same explosives and confinement, the reaction durations of detonation and ignition differed by orders of magnitude; the pressure evolution measured by tube wall velocities, and the propagation process of tube wall movement were significantly different in two reactions. Analysis shows that the convective flow of reaction products along the seam between tube wall and explosives, high temperature and pressure, dominated the reaction evolution of PBX-A initiated by ignition composition under strong confinement, and appeared as laminar burning on explosive surface and structural response of confinement. There is no reaction activated in explosive bulk by the ramp wave caused by upper stream non shock initiation reaction, least of all DDT.
2020, 40(1): 012101.
doi: 10.11883/bzycj-2019-0004
Abstract:
This paper is aimed at revealing the couplings of flame instabilities and explosion pressure. By introducing flame wrinkling factor into the smooth flame model, the wrinkled flame model and turbulent flame model are developed to predict explosion pressure evolution. The effects of adiabatic and isothermal compression on explosion pressure prediction are also compared. The results demonstrate that the expanding flame tends to be more unstable under enhancing hydrodynamic instability and the cellular flame will be formed in the constant-volume stage. Since the smooth flame neglects the flame instabilities, the predicted explosion pressure is lower than experimental value. For the smooth flame model, the predicted pressure in the adiabatic condition is higher than that in the isothermal condition. The explosion pressure behavior could be overpredicted significantly using the turbulent flame model due to the fact that the turbulent flame model overestimates the flame wrinkling level. When the wrinkled flame model is considered, the explosion pressure behavior could be reproduced relatively satisfactorily for stoichiometric propane-air mixture and stoichiometric methane-air mixture in V=25.6 m3. When V≤1.25 m3, the experimental explosion pressure is lied within the predicted value using wrinkled flame model and adiabatic smooth flame model.
This paper is aimed at revealing the couplings of flame instabilities and explosion pressure. By introducing flame wrinkling factor into the smooth flame model, the wrinkled flame model and turbulent flame model are developed to predict explosion pressure evolution. The effects of adiabatic and isothermal compression on explosion pressure prediction are also compared. The results demonstrate that the expanding flame tends to be more unstable under enhancing hydrodynamic instability and the cellular flame will be formed in the constant-volume stage. Since the smooth flame neglects the flame instabilities, the predicted explosion pressure is lower than experimental value. For the smooth flame model, the predicted pressure in the adiabatic condition is higher than that in the isothermal condition. The explosion pressure behavior could be overpredicted significantly using the turbulent flame model due to the fact that the turbulent flame model overestimates the flame wrinkling level. When the wrinkled flame model is considered, the explosion pressure behavior could be reproduced relatively satisfactorily for stoichiometric propane-air mixture and stoichiometric methane-air mixture in V=25.6 m3. When V≤1.25 m3, the experimental explosion pressure is lied within the predicted value using wrinkled flame model and adiabatic smooth flame model.
2020, 40(1): 013101.
doi: 10.11883/bzycj-2019-0038
Abstract:
In this paper, dynamic compression response of metal orthogonal corrugated sandwich structures under impact loading is investigated theoretically and numerically. Considering the effect of strain rate of material, analytical models of dynamic response of metal orthogonal corrugated sandwich structure is developed. Finite element simulation of its dynamic compressive response is carried out. It is shown that there is a good agreement between the results based on the analytical model and finite element simulation. Furthermore, the dynamic compressive response of multi-layer orthogonal corrugated sandwich structure is studied using finite element method. Deformation modes under different impact velocities are obtained and the influence of the number of layers on the dynamic response is analyzed. It is found that the mitigation and energy absorption capacity of the sandwich structures can be effectively enhanced by increasing the number of layers while the number of layers have mild influence after exceeding four.
In this paper, dynamic compression response of metal orthogonal corrugated sandwich structures under impact loading is investigated theoretically and numerically. Considering the effect of strain rate of material, analytical models of dynamic response of metal orthogonal corrugated sandwich structure is developed. Finite element simulation of its dynamic compressive response is carried out. It is shown that there is a good agreement between the results based on the analytical model and finite element simulation. Furthermore, the dynamic compressive response of multi-layer orthogonal corrugated sandwich structure is studied using finite element method. Deformation modes under different impact velocities are obtained and the influence of the number of layers on the dynamic response is analyzed. It is found that the mitigation and energy absorption capacity of the sandwich structures can be effectively enhanced by increasing the number of layers while the number of layers have mild influence after exceeding four.
2020, 40(1): 013102.
doi: 10.11883/bzycj-2019-0041
Abstract:
Solids will be broken into multiple fragments under dynamic tension loadings. The Mott-Grady model based on linear cohesive fracture can predict the lower limits of average fragment size during fragmentation process. However, the damage evolution of ductile materials is diversified. In this paper, the ductile fracture processes influenced by different damage evolutions were studied by numerical simulation. Using ABAQUS/Explicit dynamic finite element, we reproduced the tensile fracture process of ductile metal bar (45 steel) at high strain rates. The effects of linear/nonlinear damage evolutions on ductile fracture process were analyzed. The numerical results show that the damage evolution law has a significant influence on the fragmentation process of ductile metals. As the nonlinear parameter increases, the number of fragments decreases during fragmentation process. The Grady-Kipp formula can still reasonably predict the lower limits of the ductile fragment sizes in a certain range. When the non-linear index α was far greater than zero, there are conspicuous deviations between the numerical experiments and the Grady-Kipp model under the low impact loading. With increasing strain rate, the results by the numerical simulations are in agreement with the ones by the Grady-Kipp theoretical model.
Solids will be broken into multiple fragments under dynamic tension loadings. The Mott-Grady model based on linear cohesive fracture can predict the lower limits of average fragment size during fragmentation process. However, the damage evolution of ductile materials is diversified. In this paper, the ductile fracture processes influenced by different damage evolutions were studied by numerical simulation. Using ABAQUS/Explicit dynamic finite element, we reproduced the tensile fracture process of ductile metal bar (45 steel) at high strain rates. The effects of linear/nonlinear damage evolutions on ductile fracture process were analyzed. The numerical results show that the damage evolution law has a significant influence on the fragmentation process of ductile metals. As the nonlinear parameter increases, the number of fragments decreases during fragmentation process. The Grady-Kipp formula can still reasonably predict the lower limits of the ductile fragment sizes in a certain range. When the non-linear index α was far greater than zero, there are conspicuous deviations between the numerical experiments and the Grady-Kipp model under the low impact loading. With increasing strain rate, the results by the numerical simulations are in agreement with the ones by the Grady-Kipp theoretical model.
2020, 40(1): 013201.
doi: 10.11883/bzycj-2019-0029
Abstract:
When warheads such as missiles and artillery bombs explode with a certain velocity, such velocity of motion will change the field of blast wave and thus affect the damage power of ammunition. In this paper, numerical simulation of shock wave field of spherical TNT explosion is carried out by using AUTODYN with velocities of 0, 272, 340, 680, 1 020 and 1 700 m/s, respectively. The peak overpressure, specific impulse and positive pressure time of blast wave field are studied quantitatively. The results show that when the azimuth angle is less than 90°, the velocity of the propellant is positively correlated with the shock wave overpressure and specific impulse, and negatively correlated with the positive pressure time; when the azimuth angle is greater than 90°, the velocity of the propellant is negatively correlated with the shock wave overpressure and specific impulse, and positively correlated with the positive pressure time. The peak overpressure presents sinusoidal variation along azimuth. A calculation model of dynamic detonation shock wave overpressure is established by analyzing the peak overpressure data of shock wave. The calculation results of the model are in good agreement with the simulation and experimental results.
When warheads such as missiles and artillery bombs explode with a certain velocity, such velocity of motion will change the field of blast wave and thus affect the damage power of ammunition. In this paper, numerical simulation of shock wave field of spherical TNT explosion is carried out by using AUTODYN with velocities of 0, 272, 340, 680, 1 020 and 1 700 m/s, respectively. The peak overpressure, specific impulse and positive pressure time of blast wave field are studied quantitatively. The results show that when the azimuth angle is less than 90°, the velocity of the propellant is positively correlated with the shock wave overpressure and specific impulse, and negatively correlated with the positive pressure time; when the azimuth angle is greater than 90°, the velocity of the propellant is negatively correlated with the shock wave overpressure and specific impulse, and positively correlated with the positive pressure time. The peak overpressure presents sinusoidal variation along azimuth. A calculation model of dynamic detonation shock wave overpressure is established by analyzing the peak overpressure data of shock wave. The calculation results of the model are in good agreement with the simulation and experimental results.
2020, 40(1): 014201.
doi: 10.11883/bzycj-2018-0467
Abstract:
A simple and stable wavelet method, which is based on adaptive wavelet collocation methods and artificial viscosity techniques, was proposed to compute shock waves. Dynamic multiscale grids generated by wavelet threshold filtering adaptive to the flow field were used. The shock waves can be checked out by the shock locator functions with power formula, which are constructed through using the magnitudes of the wavelet coefficients on the finest level in the density fields. Then, the artificial viscous terms including viscosity and shock locator functions strictly control the magnitudes and distributions of the artificial viscosity according to the gradients in the flow field. A strong and a weak shock tubes were computed, which shows that the method can accurately capture shock fronts and effectively restrain numerical oscillations. By the way, it is easy to manipulate, high of resolution and small of computational costs.
A simple and stable wavelet method, which is based on adaptive wavelet collocation methods and artificial viscosity techniques, was proposed to compute shock waves. Dynamic multiscale grids generated by wavelet threshold filtering adaptive to the flow field were used. The shock waves can be checked out by the shock locator functions with power formula, which are constructed through using the magnitudes of the wavelet coefficients on the finest level in the density fields. Then, the artificial viscous terms including viscosity and shock locator functions strictly control the magnitudes and distributions of the artificial viscosity according to the gradients in the flow field. A strong and a weak shock tubes were computed, which shows that the method can accurately capture shock fronts and effectively restrain numerical oscillations. By the way, it is easy to manipulate, high of resolution and small of computational costs.
2020, 40(1): 015201.
doi: 10.11883/bzycj-2018-0495
Abstract:
Aiming at the unevenness of the root bottom and the low power capacity of the explosive in the present stage of smooth blasting, a kind of spiral tube shaped charge was put forward. In order to explore the rock-breaking mechanism of the charge, LS-DYNA numerical simulation and borehole blasting test were used to study the rock-breaking mechanism of the charge. Firstly, the numerical simulation results show that the spiral pipe shaped charge can form a continuous metal jet penetrating the borehole wall, and the borehole wall was penetrated out of the crack in the direction of the vertical borehole. The results show that there are helical perforation cracks in the borehole wall of the residual sample of spiral tube, which confirmed the penetration results of numerical simulation. In addition, the perforation utilization rate and reaming rate were increased by 7.2% and 8.4%, respectively, compared with the normal columnar charge. Finally, this charge was applied to the reclamation area of Zhoushan. The results showed that the average root height of the spiral pipe charge blasting area was 14 cm lower than that of the common charge, and the standard deviation of the root height was 12 cm less than that of the common charge, that is, the cumulative charge saved 14 cm hole depth and charge length and reduced the roughness of 12 cm.The research results are of great value in the application of blasting engineering, which can reduce the construction cost, speed up the construction progress and improve the blasting effect.
Aiming at the unevenness of the root bottom and the low power capacity of the explosive in the present stage of smooth blasting, a kind of spiral tube shaped charge was put forward. In order to explore the rock-breaking mechanism of the charge, LS-DYNA numerical simulation and borehole blasting test were used to study the rock-breaking mechanism of the charge. Firstly, the numerical simulation results show that the spiral pipe shaped charge can form a continuous metal jet penetrating the borehole wall, and the borehole wall was penetrated out of the crack in the direction of the vertical borehole. The results show that there are helical perforation cracks in the borehole wall of the residual sample of spiral tube, which confirmed the penetration results of numerical simulation. In addition, the perforation utilization rate and reaming rate were increased by 7.2% and 8.4%, respectively, compared with the normal columnar charge. Finally, this charge was applied to the reclamation area of Zhoushan. The results showed that the average root height of the spiral pipe charge blasting area was 14 cm lower than that of the common charge, and the standard deviation of the root height was 12 cm less than that of the common charge, that is, the cumulative charge saved 14 cm hole depth and charge length and reduced the roughness of 12 cm.The research results are of great value in the application of blasting engineering, which can reduce the construction cost, speed up the construction progress and improve the blasting effect.
2020, 40(1): 015901.
doi: 10.11883/bzycj-2018-0348
Abstract:
Blast-induced traumatic brain injury (b-TBI) is a signature injury in the current military conflicts. However, the relevant mechanism of injury has not been fully elucidated. In this paper, numerical simulation study is carried out to investigate the dynamic response of brain injury mechanics during the blast loading. Firtstly, the 3D numerical head model is established based on magnetic resonance imaging (MRI) of the human head, whose physiological characteristics and detailed structures are included. The numerical model is adopted to simulate the head collision and the results are in good agreement with the experimental data, demonstrating the validity of the numerical model. Based on the coupled Eulerian-Lagrangian (CEL) theory, a fluid-solid coupling model of explosive shock wave-head is developed. The coupled model is used to simulate the situation of head subjected to frontal impacts by explosion shock wave. The dynamic response of the head is analyzed from the pressure distribution of flow field, brain pressure, skull deformation and acceleration. The peak pressure of explosion shock wave increases 3.5 times as much as that of incident wave under fluid-structure interaction, resulting in high-frequency vibration of skull and brain tissue at the site of direct shock. The corresponding vibration frequency is as high as 8 kHz, which is completely different from the dynamic response of brain tissue under head collision. At the same time, the local bending deformation will “propagate” along the skull, affecting the whole skull configuration, which determines the evolution process of brain tissue pressure and injury.
Blast-induced traumatic brain injury (b-TBI) is a signature injury in the current military conflicts. However, the relevant mechanism of injury has not been fully elucidated. In this paper, numerical simulation study is carried out to investigate the dynamic response of brain injury mechanics during the blast loading. Firtstly, the 3D numerical head model is established based on magnetic resonance imaging (MRI) of the human head, whose physiological characteristics and detailed structures are included. The numerical model is adopted to simulate the head collision and the results are in good agreement with the experimental data, demonstrating the validity of the numerical model. Based on the coupled Eulerian-Lagrangian (CEL) theory, a fluid-solid coupling model of explosive shock wave-head is developed. The coupled model is used to simulate the situation of head subjected to frontal impacts by explosion shock wave. The dynamic response of the head is analyzed from the pressure distribution of flow field, brain pressure, skull deformation and acceleration. The peak pressure of explosion shock wave increases 3.5 times as much as that of incident wave under fluid-structure interaction, resulting in high-frequency vibration of skull and brain tissue at the site of direct shock. The corresponding vibration frequency is as high as 8 kHz, which is completely different from the dynamic response of brain tissue under head collision. At the same time, the local bending deformation will “propagate” along the skull, affecting the whole skull configuration, which determines the evolution process of brain tissue pressure and injury.
