Dynamics and scaling of explosion cratering in granular media

Granular cratering is a ubiquitous phenomenon occurring in various natural and industrial contexts. Although impact‐induced granular cratering has been extensively studied, fewer experiments have been conducted on granular cratering via low‐energy explosions. Here, we study the dynamics and scaling of explosion granular cratering by injecting short pulses of pressurized air in quasi‐two‐dimensional granular media. Through an analysis of the dynamics of explosion processes at different explosion pressures, explosion durations, and burial depths, we identify two regimes, the bubbling and the eruption regimes, in explosion granular cratering. Our experiments explore the distinctive dynamics and crater morphologies of these regimes and show the energy scaling of the size of explosion craters. We compare high‐energy and low‐energy explosion cratering as well as explosion and impact cratering in terms of their energy scalings. Our work illustrates complex granular flows in explosion cratering and provides new insights into the general scaling of granular cratering processes. © 2017 American Institute of Chemical Engineers AIChE J, 64: 2972–2981, 2018     

混凝土中的爆坑实验研究

利用爆炸相似理论讨论了固体介质中的相同装药量在不同埋深爆炸情况时的爆坑、炸深与埋深的关系，将传统理论的1／3比例因子修正为1／3．4或1／3．6比例因子。据此设计了混凝土中的炸坑效应缩比实验，并利用某原型实验进行了验证。将实验结果与修正后的比例因子计算值进行了对比，符合较好，其精度可用于工程设计计算。     

Effect of the method used to detonate the borehole charges on the breakdown characteristics

Conclusions The change in the method of detonation is an effective means of controlling the energy of the explosion.By choosing an appropriate method of detonating it is possible not only to concentrate the explosive energy in a specified direction but also to increase the total effect of the explosion in various media.Using the bilateral cord detonation it is possible to achieve a 10–40% increase in the work-effectiveness of the charge depending on the type of rock by comparison with detonation from the end; effectiveness can also be increased 17–80% by comparison with detonation along the charge. This will enable the parameters of drilling and explosive work to be changed and make it possible to have a 30% reduction in costs as has been shown in preliminary analysis.Translated from Ogneupory, No. 6, pp. 28–32, June, 1984.     

Effects of charge strength on ignition parameters for solids on impact

A model has been used for thermoplastic failure and ignition in a thin layer of viscoplastic material on impact with the normal law for the strength distribution in an explosive charge in order to perform numerical calculations on the initiation parameters and explosion curves as functions of charge dimensions and impact energy.Moscow. Translated from Fizika Goreniya i Vzryva, Vol. 27, N. 4, pp. 99–104, July–August, 1991.     

Simulation of shock wave impact due to explosion on a flying flexible aircraft

This paper describes the results obtained by a computational simulation of the impact of shock waves due to explosion on a flying flexible aircraft of commercial type. An explicit three-dimensional dynamic nonlinear coupled analysis has been conducted by means of the software MSC.Dytran. A Lagrangian mesh has been used for the structural parts, and a Eulerian domain is used for the surrounding fluid. The fluid-dynamic solver uses a Eulerian approach and employs a finite volume method to discretize the governing equations. Structural elements are discretized by the Finite Element Method. The impact of the related shock waves on a simple panel and a wing box has been considered. The vibration of an aircraft as a whole, caused by its flexibility, has been analyzed. The analysis has mainly shown that the conducted investigation can be used to evaluate the loads on the aircraft for various initial positions of the explosion as well as for various amounts of the explosive charge. The method could permit a better design of the aircraft with respect to explosion phenomena and simulation of aircraft accidents, aimed at understanding their causes. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 6, pp. 121–130, November–December, 2007.     

Optimal parameters of borehole charges

Experimental data on full-scale borehole-charge explosions are outlined, with a view to establishing the optimal relation between the basic sinkhole parameters and the charge elongation coefficient. It is shown that the results of full-scale explosion are in good agreement with laboratory data.Krasnodar. Translated from Fizika Goreniya i Vzryva, Vol. 28, No. 4, pp. 127–129, July–August, 1992.     

An Analytical Model for the Particulation of a Jet from a shaped charge liner

A new model is presented to predict the cumulative breakup time of the jet from a shaped charge liner. The model invokes a plastic instability criterion, kinematic considerations, and a material constitutive equation. Very good agreement of the cumulative breakup time and jet length with experimental data for several copper liner geometries is shown. The results are dependent on the initial strain rate and jet temperature distribution.     

Effect of Properties of the Source on the Action of Explosions in Air and Water

Results of an experimental study of parameters of the shock wave and explosion products in the near zone of explosions in air and water with a wide range of variation of explosion heat and charge density of high explosives are presented. It is shown that the influence of these characteristics on the action of explosions in the near zone can be characterized by one parameter: volume concentration of energy in the source. A change in this parameter involves a significant redistribution of energy between the explosion products and the shock wave, which can affect brisance and violate the energy similarity of explosions.     

钨合金破片撞击复合靶后装药的实验研究

利用杀伤战斗部所产生的高速钨合金破片撞击复合靶后装药(铸装H-6炸药),以期观测复合靶后装药是否产生爆燃现象。利用工业CT分析了钨合金破片对复合靶后装药的侵彻情况。结果表明,虽然钨合金破片具有了较高的速度,但在贯穿一定厚度复合靶时,其动能急剧下降并产生了破裂,这是未能起爆靶后装药的一个主要原因。     

Considerations about the Analytical Modelling of Shaped Charges

The problem of building and using analytical codes for shaped charge simulation is reviewed. The basic physics of the whole shaped charge functioning is considered, starting from explosive liner interaction, going through jet formation and jet break-up, down to cratering into the target. For each stage of the phenomenon, a critical look is given to the existing analytical models, with the idea of determining which models are able to adequately predict the shaped charge behavior with keeping an as low as possible degree of complexity. On reviewing these analytical models, it is shown that some parameters have to be taken into account for a better understanding of what governs shaped charge performance.     

Fragment Velocity Distribution of Cylindrical Rings Under Eccentric Point Initiation

A design mode, in which a casing is filled with a charge initiated off‐centre (eccentric point initiation), is common in the field of explosion and structural protection. The fragment velocity distribution along the circumference of the casing is distinctly non‐uniform due to the difference in blast loading around the circumference of the casing. To quantify the fragment velocity distribution, two kinds of cylindrical rings with different structural parameters were adopted. Static explosive experiments with three eccentric coefficients (0, 0.5, 1.0) were conducted with pulsed X‐ray diagnostics. Using coefficients derived from experimental data and calculating the effects of both the eccentricity of initiation and angle around the circumference, an angle‐dependent ratio β_θ of charge mass to casing mass has been derived as a mean to modify the fragment velocity formula of Gurney for this application. The derived formula was shown to correctly predict the fragment velocity distribution around the circumference of the cylindrical ring. The calculated velocity distributions show good agreement with the experimental results.     

破甲战斗部新型装药--聚奥黑炸药

一种新型的破甲战斗部装药-聚奥黑炸药是以HMX/RDX二种单质炸药为主体炸药的压装高聚物粘结炸药,其主要特点是可以通过改变HMX/RDX的组成比例,得到不同爆炸能量的系列化产品;更为突出的是,合理选择HMX/RDX比例,使PBX装药具有与HMX相近的高爆炸能量,而成本费用大幅度降低.经过在破甲战斗部中应用试验表明,聚奥黑炸药的装药密度高、破甲威力大,是一种适合装填各类破甲战斗部的新型装药.     

Experimental Study on the Dynamic Strain of a Thin-Walled Pipe in the Gas Cloud Explosion with Ignition Energy

This paper describes an experimental study of the flame propagation mechanism for the combustible gas explosion in a closed pipe with a length of 12 m and an internal diameter of 0.125 m, which is carried out for different values of the ignition energy. The results show that an increase in the ignition energy results in greater explosive intensity, maximum peak pressure, and dynamic strain of the thin wall in the whole process. Moreover, the dynamic strain of the thin-walled pipe increases suddenly owing to arrival of a precursor shock wave and then vibrates for a long time, which is induced by the wave reflected back and forth. In addition, there is good agreement between the dynamic strain signals and pressure wave signals. These research results can provide a theoretical basis for industrial explosion accident assessments as well as explosion and shock resistance designs, which provides guidance not only for industrial safety, but also for prevention and mitigation of explosion accidents.     

含NaCl荷电细水雾对甲烷爆炸火焰传播的抑制特性

为进一步提高细水雾抑制甲烷爆炸的效率,搭建了小尺寸细水雾抑制甲烷爆炸实验平台,在普通细水雾中添加NaCl添加剂,并对其荷电,进行含NaCl添加剂荷电细水雾抑制甲烷爆炸火焰传播特性的实验研究。结果表明,含NaCl添加剂荷电细水雾对甲烷爆炸火焰传播的抑制效果,优于普通细水雾单独添加NaCl添加剂和荷电作用的抑制效果之和。随着NaCl浓度和荷电电压的增大,甲烷爆炸火焰传播速度明显减小;其中荷电8 kV、NaCl浓度12.5%的工况抑制效果最佳,甲烷爆炸火焰传播速度二次峰值较普通细水雾作用时下降了10.747 m·s^-1,下降比例高达60.26%;分析认为,在细水雾抑制甲烷爆炸火焰传播的过程中,NaCl添加剂和荷电作用之间存在相互促进抑制效果的耦合作用。     

The experimental and theoretical study on the spatial-temporal distribution of electromagnetic radiation from JO-8 explosions.

The detonating fuse in the multistage warhead will be subjected to strong electromagnetic interference, derived from electromagnetic radiation generated by explosion of the shaped charge warhead, which may cause premature detonation or misfire. In order to explore the possible electromagnetic environment surrounded the detonating fuse, the spatial-temporal distribution of electromagnetic radiation after the explosion of JO-8 explosive was investigated in this paper. The electromagnetic radiation signal was collected and its frequency coverage was analyzed in the far-field area by the field blast test. Moreover, based on electromagnetic theory, a theoretical model of electromagnetic radiation generated by the explosion of JO-8 explosive was established, and the spatial-temporal distribution of the electric field intensity was illustrated in detail for several typical positions after the explosion. The better agreement between experimental and theoretical results indicates that the proposed theoretical model and computational method are reasonable. On this basis, the distributions of electric field intensity for different positions and various explosive weights were predicted respectively by using distance and explosive weight as variables. This study is expected to provide a reference for the research on the electromagnetic radiation for explosive explosion and anti-explosive electromagnetic interference.     

Comparison of the Explosion Thermodynamics of TNT and Black Powder Using Le Chatelier Diagrams

Le Chatelier diagrams may be adopted for the definition of thermodynamic loci of explosion in terms of internal energy with respect to the temperature for either the primary explosion or for the deflagrative, post‐combustion of the products of the first reaction with air, the afterburning reaction. In this paper, Le Chatelier diagrams are produced for TNT and black powder by using the CEA code. Pressure plots with respect to density or air/fuel ratio are also shown. These results are useful for the simulation of explosion (hydrodynamic codes), and more generally for the definition of safety of storage, transportation, and production of explosives and pyrotechnics. Furthermore, the method can be easily extended to any deflagrative pyrotechnic substances, for which information on explosion and afterburning effects are needed.     

周向液体层对战斗部破片加速过程的影响

为研究外部液体介质对杀伤战斗部破片加速过程的影响,设计了液体层厚度与装药直径之比为1∶1的模拟样机,开展了满腔、半满和空腔3种状态下的模拟样机静爆试验,得到周向液体层包覆下战斗部的破片速度,并利用LS-DYNA软件对3种状态下装药加速破片的过程进行了分析,与试验结果进行了对比。结果表明,外部液体介质影响了战斗部装药爆轰能量的分配,进而降低了装药加载破片的性能,在满腔状态下破片的速度仅能达到空腔状态下的55%~60%;半满状态时,水介质的径向惯性约束作用使得爆轰产物并未均等地向各个方向膨胀作功,而是向无水方向流动较快(类似于局部泄爆),其能量出现不均衡分配,进而有效提高了无水一侧破片的速度,达到空腔状态下的1.65倍。数值模拟的结果与实验结果相吻合,进一步验证了周向液体层对战斗部破片加速过程的影响。     

Afterburn Ignition Delay and Shock Augmentation in Fuel Rich Solid Explosives

We present experimental and computational results that explain some aspects of measured energy release in explosions of unconfined trinitrotoluene [TNT, C₆H₂(NO₂)₃CH₃], and an aluminum‐containing explosive formulation, and show how this energy release can influence shock wave velocities in air. In our interpretation, energy release is divided into early, middle, and late time regimes. An explanation is provided for the interdependence of the time regimes and their influence on the rate at which energy (detonation/explosion and afterburn) is released. We use a merging of the thermodynamic and chemical kinetic processes that predicts how chemical kinetics may determine the time delay of the afterburn of combustible gases produced by the initial detonation/explosion/fast reaction. The thermodynamic computer code CHEETAH is used to predict gaseous and solid products of early time energy release, and a chemical kinetic reaction mechanism (CHEMKIN format) is used to describe the subsequent afterburn of the gas phase products in air. Results of these calculations are compared with field measurements of unconfined explosions of 2 kg charge weights of TNT and an aluminum‐containing explosive formulation.     

Initiation of detonation of a porous high explosive by a high-enthalpy gas flow

Loose packed PETN initiation by a hot gas flow generated by an explosion of an active charge separated by an air gap is studied. Experimental data obtained by means of synchrotron radiography are compared with simulations employing a two-phase two-velocity two-temperature model. Reasonable agreement is reached by taking into account two processes accelerating the reaction: particle fragmentation during powder compaction and combustion intensification due to instability of the evaporating surface layer excited by a high-velocity gas flow around the particles.