粒状发射药动态破碎研究进展

综述了落锤冲击试验、空气炮试验、分离式霍普金森压杆试验和动态挤压物理仿真试验等在发射药动态破碎研究中的应用状况,介绍了破碎度法、动态活度比法和燃烧渐增因子法等发射药破碎程度的描述方法,并提出建议:在冲击载荷条件下发射药床不同位置药粒的受力特点以及药粒的本构模型和破碎模型还需进一步研究,为描述发射过程中发射药破碎规律提供理论基础。     

基于燃气生成速率比的发射药破碎程度 定量表征方法

为定量表征发射药的破碎程度，引入了燃气生成速率比的概念。通过理论推导,得出燃气生成速率比即为破碎发射装药与相应未破碎发射装药的燃烧表面积比。提出采用破碎发射药燃烧前期的燃气生成速率比的平均值来定量表征发射药的破碎程度。对标准发射药、大块发射药、小块发射药和粉末发射药进行了密闭爆发器试验，获得了不同发射药的p-t曲线，数据处理得到不同发射药破碎程度的量化值。结果表明，基于燃气生成速率比的发射药破碎程度定量表征方法是可行的。     

Predicting the fragmentation onset velocity for different metallic projectiles using numerical simulations

For cubes and spheres under high velocity impact there exists for each system of projectile and target, a threshold velocity that is just sufficient to shatter the projectile. This velocity, usually above 2km/s for metallic projectiles, is known as the fragmentation onset velocity. To determine the fragmentation onset velocity experimentally, a number of experiments in which the impact velocity of the projectile is varied in a controlled manner needs to be conducted [1]. In the work described in this paper, the numerical analysis code AUTODYN was used to simulate the impact of stainless steel and tantalum projectiles onto transparent targets in an attempt to simulate the onset of fragmentation. Using the meshfree SPH method for discretizing the spatial domain of the projectile and a simple failure model that allows the critical spall stress of the material to vary with the local material and loading conditions, encouraging results were obtained, with the fragmentation onset velocity for both projectile/target configurations being reasonably well predicted. In addition, further experiments conducted at TNO-PML, to determine the fragmentation onset velocity for tungsten projectiles, will be reported.     

CD-3发射装药低易损性能试验研究

为了降低发射药的敏感性,以Bu-NENA为增塑剂,FOX-7和RDX作为填充物研制了一种新型硝化棉(NC)基发射药(GD-3发射药),对其装药进行了低易损性能测试研究。试验结果表明,GD-3发射装药在慢速烤燃和快速烤燃、子弹撞击刺激源下发生了V类燃烧反应,在特定的空心装药射流刺激下发生了III类爆炸反应。GD-3发射药在刺激源下易损性响应剧烈程度弱于硝基胍发射药和单基发射药,该新型装药符合低易损性弹药的性能评定要求。     

Experimental testing and phenomenological modelling of the fragmentation process of braided carbon/epoxy composite tubes under axial and oblique impact

A new simulation technique is presented for the phenomenological modelling of stable fragmentation in fibre reinforced composite structures under dynamic compressive loading. An explicit crash code is used for implementation of a hybrid modelling technique, in which two distinct material models act simultaneously. The first model is implemented in a multi-layered shell element and uses a unidirectional composites fracture criterion to predict potential ply fracture mechanisms on a macroscopic scale. This model is, however, unable to represent the complex localised fracture mechanisms that occur on a meso (sub-ply) scale under compression fragmentation loading. Therefore, a second constitutive model is added to capture the energy absorbing process within the fragmentation zone, utilising an Energy Absorbing Contact (EAC) formulation between the composite structure and the impacting body. The essential benefits of the procedure are that it requires minimal input data that can be obtained from simple fragmentation tests, and that the procedure is computationally efficient enabling application to large scale industrial structures. The EAC theory is discussed, together with the required material model parameters. A series of dynamic axial and oblique impact tests and simulations of cylindrical continuous carbon fibre reinforced composite tubes have been performed to validate the approach. Furthermore, the application to more complex load cases including combinations of fragmentation and global structural fracture have also shown a good correlation with test results.     

Investigation of impact fracture behavior of automobile laminated glass by 3D discrete element method

A three-dimensional discrete element model of laminated glass plane is presented and a 3D numerical analysis code, which can simulate the impact fracture behavior of automobile laminated glass, is developed. The impact process of a single glass plane and a laminated glass plane are calculated in the elastic range by the code. Comparing its results with those calculated by the commercial FEM code LS-DYNA in the same condition, the validity of the 3D laminated glass model and the 3D discrete element method are proved. Furthermore, the impact fracture process of a single glass plane and a laminated glass plane are simulated respectively. The entire failure processes in detail are presented. By comparing the impact force and reduction of kinetic energy of impact body between those two models, the numerical method is applied to demonstrate the advantage of laminated glass in passenger’s safety.     

Response of simulated propellant and explosives to projectile impact—III. Experimental and numerical results of warhead penetration and fragmentation

This paper is the third of a series concerned with the effects of projectile impact on a simulated explosive or propellant, called Propergol. Experiments were conducted to study the fragmentation and perforation response of disks of this material when subjected to impact by blunt and cylindro-conical strikers. Similar tests were conducted on layered targets of Propergol and steel, and also for a simulated warhead that was struck by armor-piercing projectiles. Data were obtained by velocity measurement, high-speed photography and post-mortem target examination including collected fragments.

A fragmentation oriented penetration code, AUTODYN(frag) was developed from the interfacing of a two-dimensional commercial finite difference code, AUTODYN, with a fragmentation subroutine, BFRACT, developed by other investigators. This program was utilized to study the microfracture and fragmentation processes in both monolithic and composite Propergol plates during their penetration by projectiles. In addition, numerical evaluations of the effects of simulated warhead penetration by armor-piercing bullets were conducted using the publicly available finite-element code DYNA2D.

The numerical results were compared with corresponding experimental data and also with the predictions of an analytical representation of the phenomenon, described in the second paper of the series. Reasonable agreement was obtained in the domain where the hypotheses concerning the structure of the analysis and of the computations were applicable.     

A three‐dimensional atomistic‐based process zone model simulation of fragmentation in polycrystalline solids

A three‐dimensional atomistic‐based process zone model (APZM) is used to simulate high‐speed impact induced dynamic fracture process such as fragmentation and spall fracture. This multiscale simulation model combines the Cauchy–Born rule, colloidal crystal process model, and micromechanics homogenization technique to construct constitutive relations in both grains and grain boundary at mesoscale. The proposed APZM has some inherent advantages to describe mechanical behaviors of polycrystalline solids. First, in contrast to macroscale phenomenological constitutive models, the APZM takes into account atomistic binding energy and atomistic lattice structure. In particular, the electron density related embedded atom method (EAM) potential has been adopted to describe interatomistic interactions of metallic polycrystalline solids in bulk elements; second, a mixed type of EAM potential and colloidal crystal depletion potential is constructed to describe heterogeneous microstructure in the process zone; third, the atomistic potential in both bulk material and process zone has the same atomistic origin, and hence, the bulk and process potentials are self‐consistent. The simulation of dynamic fracture process of a cylinder made of aluminum powder metallurgy (P/M) alloy during high‐speed impact/penetration is carried out, and numerical results demonstrate that APZM finite element method has remarkable ability to accurately capture complex three‐dimensional fragmentation formation and damage morphology. Copyright © 2012 John Wiley & Sons, Ltd.     

PAFRAG modeling of explosive fragmentation munitions performance

A technique for predicting performance of explosive fragmentation munitions presented in this work is based on integrating three-dimensional axisymmetric hydrocode analyses with analyses from a newly developed fragmentation computer code PAFRAG. The validation of the PAFRAG code fragmentation model was accomplished using the existing munition arena test data. After having established the crucial parameters of the model, a new explosive fragmentation munition was designed and optimized. Upon fabrication of the developed munition, the performance of the new charge was tested in a series of small-scale experiments including the flash radiography, the high-speed photography, and the sawdust fragment recovery. Considering relative simplicity of the model, the accuracy of the PAFRAG code predictions is rather remarkable.     

A model for fracture of explosively driven metal shells

A model for fracture of explosively driven metal shells presented in this work is based on integrating three-dimensional axisymmetric arbitrary Lagrangian-Eulerian hydrocode analyses with analyses from a newly developed fragmentation computer code MOTT. The developed model was based on the Mott’s theory of break-up of cylindrical “ring-bombs”, in which the length of the average fragment is a function of the radius and the expansion velocity of the shell at the moment of break-up, and the mechanical properties of the metal. The validation of the MOTT code fragmentation model was accomplished using existing explosive fragmentation munition arena test data. After having established the crucial parameters of the model, a new explosive fragmentation munition was designed and optimized. Upon fabrication of the developed munition, the performance of the new charge was tested in a series of small-scale experiments including flash radiography, high-speed photography, and sawdust fragment recovery. The accuracy of the MOTT code predictions is excellent.     

低温感包覆火药装药的两相流内弹道数值模拟

本文分析了低温感包覆火药装药在火炮膛内点传火和燃烧的物理过程，建立了具有主装药、包覆药、可燃药筒、中心传火管和尾翼管状药等五种装药原件这一复杂装药结构的两相流内弹道物理模型和数学模型，编写了相应的计算程序，并以某线膛炮为例进行了计算，结果表明：计算值与实验值吻合较好。     

Simulation of particle bed breakage by slow compression and impact using a DEM particle replacement model

The present work introduces a particle replacement model implemented in the commercial software EDEM to describe breakage of particles. Several model parameters were initially estimated on the basis of single-particle breakage tests on iron ore pellets. The model was then used to simulate breakage of particle beds by both slow compression and impact. Model predictions were compared to experiments in terms of compressive force versus packing density, breakage probability of the particles versus compressive force applied to the bed, and the product size distribution in compression and impact. The model showed the expected trends as well as some agreement with the measured product size distributions both from confined and unconfined stressing conditions of the bed of particles, being a simple and effective approach to describe breakage in systems where particles are stressed as assemblies.     

Fragment mass distribution of metal cased explosive charges

Fragmentation of metal casings is an important issue in a variety of problems like weapon effectiveness, safety distances or collateral damage. To be able to describe the intended or unintended effects of naturally fragmenting shells, one needs to know the mass distribution of the fragments produced after detonation of the explosive charge. In the present study the fragmentation behavior of very light and heavier casings has been investigated. The data collection method is outlined and applied to the fragment mass distribution of four different shells. The results are given in diagrams. It was found that an existing fragmentation model adequately predicts the dependence of circumferential fragment size on material strength. Fracture in axial direction should also be considered to predict correct fragment masses, but currently a suitable model for this purpose is not available.     

Ion trap versus low-energy beam-type collision-induced dissociation of protonated ubiquitin ions

The beam-type and ion trap collision-induced dissociation (CID) behaviors of protonated bovine ubiquitin ions were studied for charge states ranging from +6 to +12 on a modified triple quadrupole/linear ion trap tandem mass spectrometer. Both beam-type CID and ion trap CID were conducted in a high-pressure linear ion trap, followed by proton-transfer ion/ion reactions to reduce the charge states of product ions mostly to +1. The product ions observed under each activation condition were predominantly b- and y-type ions. Fragmentation patterns showed a much stronger dependence on parent ion charge state with ion trap CID than with beam-type CID using nitrogen as the collision gas, with preferential cleavages C-terminal to aspartic acid at relatively low charge states, nonspecific fragmentation at moderate charge states, and favored cleavages N-terminal to proline residues at high charge states. In the beam-type CID case, extensive cleavage along the protein backbone was noted, which yielded richer sequence information (77% of backbone amide bond cleavages) than did ion trap CID (52% of backbone amide bond cleavages). Collision gas identity and collision energy were also evaluated in terms of their effects on the beam-type CID spectrum. The use of helium as collision gas, as opposed to nitrogen, resulted in CID behavior that was sensitive to changes in collision energy. At low collision energies, the beam-type CID data resembled the ion trap CID data with preferential cleavages predominant, while at high collision energies, nonspecific fragmentation was observed with increased contributions from sequential fragmentation.     

A combined physical and DEM modelling approach to investigate particle shape effects on load movement in tumbling mills

The discrete element method (DEM) which is used to simulate granular flows often assumes spherical shape for particles. This assumption is legitimized by the added complexity of non-spherical shape representation, contact detection and computational cost. In this work, the difference between the dynamics of non-spherical and spherical particles was studied in detail by a combined physical and DEM modeling approach. An in-house developed DEM software called KMPC_DEM©, which was coded to handle non-spherical particles, was used to simulate the behavior of particles. To calibrate the model parameters, a model tumbling mill (100 cm diameter and 10.8 cm length) with one transparent end was used which made accurate photography possible. The tests were performed at filling of 20% and mill speed of 85% of critical speed with steel balls and wood cubes. In the simulation, each cubical particle was represented with clusters of spheres (with identical size) by particle packing algorithm for contact detection and contact-force calculation. Comparison of the simulation and experimental results showed that the difference between the measured and predicted impact toe, shoulder angle and bulk toe angle were 3, 4 and 5°, respectively. The significant change in the charge movement and structure on account of non-spherical particles was reflected in the amount of in-flight charge, and positions of shoulder, impact toe and bulk toe. It found that there was a 17% difference in the amount of in-flight of charge between cubical and spherical particles. The marked difference was attributed to higher interlocking of non-spherical particles in comparison to spherical balls. The results showed that cubical particles participated 5% more in the high energy impact action compared to that of the spherical particles. The simulation computation time increased by 35 times when the shape of particles changed from spherical to cubical.     

结构性岩体的爆破破碎分形

讨论了结构性岩体内部结构和岩石破碎的分形特性，建立了岩体结构体的分布函数；用概率统计的方法证明了结构性岩体破碎的实质是一个分维数逐渐增加的分形过程，破碎体块度分布的分形特性是岩体结构性分形和破碎分形的必然结果。同时给出了结构体分形和破碎块度分形之间的关系。通过分析结构性岩体爆破破碎的模拟试验结果，进一步验证了文中的结论。     

Numerical Investigation of Crater Phenomena in a Particle Stream Impact onto a Granular Bed

This paper presents an experimental and numerical study of the impact of a particle stream onto a particle bed using a 2D slot model. The numerical simulation is performed by means of the discrete element method (DEM). The results show that the DEM simulation can reproduce the experimental results well under comparative conditions. The dynamics in the formation of a crater is then analyzed in terms of velocity field, force structure, bottom stress distribution and energy exchange based on the DEM results. It is shown that as a result of impact by the falling particles, the particles in the top central region of the particle bed have relatively large velocities and contact forces. The velocities and forces propagate into the bed, and reach the bottom of the base layer quickly. They then continue to propagate leftwards and rightwards to create a crater. During the impact process, most of the energy from the falling particles is dissipated due to the inelastic collision and frictional contacts between particles, and only a small amount of the energy contributes to the formation of the crater. The crater size is shown to be affected by the discharging rate, discharging height and materials properties, and be related to the ratio of the input energy from the falling stream to the inertial energy from the original packing.     

CFD-DEM numerical study on air impacted packing densification of equiaxed cylindrical particles

A CFD-DEM model was developed to reproduce the packing densification process of mono-sized equiaxed cylindrical particles under air impact. The effects of operating parameters on packing density were firstly studied. Then various microscopic properties of packing structures such as coordination number (CN), contact types, particle orientations, pore features were characterized and compared. And corresponding densification mechanisms were analysed based on particle motion behaviour, local structure evolution, and forces. Results indicate that the air impact can realize the packing densification of cylindrical particles under appropriate conditions. The pore size distribution in the packing of cylindrical particles shows a tail at larger pore sizes compared with that in the packing of equal spheres. Both the size and the sphericity of the pores decrease in the final dense packing; also, more surface-surface and less surface-edge contacts between two particles therein can be formed. More cylindrical particles tend to be in parallel or perpendicular contact with each other to form more stable local structures during air impact. Most particles at higher position move down (direction of gravity/air impact) with about one particle length during the densification process and most particles exhibit translational motion to realize the local rearrangement for pore filling through air impact induced inter-particle forces.     

Nuclear fragmentation and the number of particle tracks in tissue

For high energy nuclei, the number of particle tracks per cell is modified by local nuclear reactions that occur, with large fluctuations expected for heavy ion tracks. Cells near the interaction site of a reaction will experience a much higher number of tracks than estimated by the average fluence. Two types of reaction products are possible and occur in coincidence; projectile fragments, which generally have smaller charge and similar velocity to that of the projectile, and target fragments, which are produced from the fragmentation of the nuclei of water atoms or other cellular constituents with low velocity. In order to understand the role of fragmentation in biological damage a new model of human tissue irradiated by heavy ions was developed. A box of the tissue is modelled with periodic boundary conditions imposed, which extrapolates the technique to macroscopic volumes of tissue. The cross sections for projectile and target fragmentation products are taken from the quantum multiple scattering fragmentation code previously developed at NASA Johnson Space Center. Statistics of fragmentation pathways occurring in a cell monolayer, as well as in a small volume of 10 x 10 x 10 cells are given. A discussion on approaches to extend the model to describe spatial distributions of inactivated or other cell damage types, as well as highly organised tissues of multiple cell types, is presented.