Deformation and fragmentation behaviour of exploded metal cylinders and the effects of wall materials,configuration, explosive energy and initiated locations

Tubular metal specimens are explosively expanded to fragmentation, and the effects of wall materials, thicknesses, notches in walls, explosive driver diameters and the initiated locations are investigated on the deformation and fracture behavior of the cylinders experimentally and numerically. In the standard tests, the driver is a column of low density powder of high explosive PETN, inserted coaxially into the bore of a smooth-walled cylinder and initiated by exploding a bundle of fine copper wires at the column axis using a discharge current from a high-voltage capacitor bank. Notched cylinders with single axial slit, various grooves in the walls, and smooth cylinders with varied wall thicknesses were tested. Low-carbon steels and an aluminum alloy A5052 were provided in addition to the standard smooth-walled 304 stainless steel cylinder, and they were fully or partially charged with varying explosive column diameters. The initiated locations in the explosive column are changed for comparison, placing the bundle of fine copper wires eccentrically from the central axis or replacing the fine wire bundle into a bold wire line except the middle portion at the central axis for central point initiation. Additionally an explosive-filled cylindrical vessel with welded endplate at the one end is initiated at the other end explosive surface exploding wire-rows and expanded by axially propagating explosive detonation to fracture for comparison with the uniform expansion. Deformation and crack initiation of expanding cylinders are observed with high speed camera, and most of the fragments have been recovered successfully. Recovered fragments have been measured and investigated using a fragmentation model. The effects of test parameters on the deformation and fracture behavior of metallic cylinders are discussed with use of numerical simulations, indicating applicability of the fragmentation model and suggesting future necessary studies.     

Computational modeling of explosive-filled cylinders

A time-dependent, two-dimensional, finite-difference code can be used to model fragmenting cylinders. Strictly hydrodynamic treatment of the casing material generally overpredicts the final fragment velocity. A more definitive final fragment velocity is predicted when the casing material is treated as an elastic-plastic material, but the final fragment velocities occur at unrealistically high cylindrical expansion ratios. To remove some of these objections and, at the same time, model the casing motion more realistically, a gas leakage model has been developed to simulate explosive gas leakage around fragments after casing breakup. Comparisons have been made between code calculations and experimental data. The experimental data include different length-to-diameter ratios, natural and discrete fragmenting cylinders, different charge-to-casing mass ratios, and different initiation postures. The gas leakage model predicts definitive final fragment velocities in excellent agreement with the experimental data.     

Effect of heat treatment on small scale fragmentation of aluminium alloy

Abstract

Small scale explosions, using a detonator, of 7075 aluminium alloy cylinders, 15–100 mm outside diameter, were carried out to investigate the effects of heat treatment on fragmentation. This was the finest for the strongest as received alloy and coarsest for the softest overaged alloy. This effect was similar to that seen in investigations of the fragmentation of steel. Cylinders of 50 and 100 mm in diameter did not fragment but plastically deformed with maximum deformation at the cylinder bottom. Fragmentation of 33 and 42 mm diameter cylinders produced long fragments typical of the break-up of thick walled cylinders. At smaller diameters, break-up gave fragments of several shapes, finer fragments being largely associated with the smallest diameter cylinders and the highest strength alloys. Results followed those seen in large scale studies of cylinder break-up and suggest the possibility of using small scale fragmentation experiments in the investigation of the effects of composition, heat treatment and processing on natural fragmentation.     

充填聚氨酯泡沫的薄壁金属筒的力学性能研究

通过充填聚氨酯泡沫的薄壁金属圆筒的力学性能试验,研究薄壁金属圆筒内充填聚氨酯泡沫的作用和效果。试验比较了空心薄壁金属圆筒和充填聚氨酯的薄壁金属圆筒的轴向抗压荷载一位移曲线和破坏模式．试验结果表明充填聚氨酯后可大大改善薄壁金属筒的力学性能,提高其抗变形和吸收能量的能力．     

Fragmentation model for expanding cylinder

A two-dimensional energy-based model of fragmentation of rapidly expanding cylinder under plane strain conditions is proposed. The model allows us to estimate the average fragment length and the number of fragments produced by ductile fracture of the cylinder. Comparison of obtained results with published experimental data on the fragmentation of the aluminum rings and cylinders shows that they are in good agreement.     

一种圆筒试验不同数据处理新方法？

对标准圆筒试验的两种数据处理方法进行了系统阐述和研究,并以一种PBX炸药（ HMX/黏结剂：95/5）的？50 mm圆筒试验为例,分别采用两种数据处理方法得到试验圆筒的壁膨胀速度、比动能、格尼系数等参量,详细分析和对比了圆筒壁膨胀速度与位移曲线、膨胀比动能与位移曲线。结果表明,在圆筒膨胀早期,新处理方法比传统处理方法能更准确地描述圆筒壁膨胀速度的变化过程,而在膨胀的中后期,两种处理方法所得圆筒壁速曲线偏差较小,且所获得的格尼系数相差很小。     

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.     

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.     

Study on the fragmentation of shells

Fragmentation can be observed in nature and in everyday life on a wide range of length scales and for all kinds of technical applications. Most studies on dynamic failure focus on the behaviour of bulk systems in one, two and three dimensions under impact and explosive loading, showing universal power law behaviour of fragment size distribution. However, hardly any studies have been devoted to fragmentation of shells. We present a detailed experimental and theoretical study on the fragmentation of closed thin shells of various materials, due to an excess load inside the system and impact with a hard wall. Characteristic fragmentation mechanisms are identified by means of a high speed camera and fragment shapes and mass distributions are evaluated. Theoretical rationalisation is given by means of stochastic break-up models and large-scale discrete element simulations with spherical shell systems under different extreme loading situations. By this we explain fragment shapes and distributions and prove a power law for the fragment mass distribution. Satisfactory agreement between experimental findings and numerical predictions of the exponents of the power laws for the fragment shapes is obtained     

Numerical simulation on the interaction of blast waves with a series of aluminum cylinders at near-field

This paper demonstrates the application of numerical simulation in predicting the interaction of blast waves with a series of aluminum cylinders at near-field. The results from the experiments performed by Held [Held M. Impulse method for the blast contour of cylindrical high explosive charges. Propellants Explos Pyrotech 1999;24:17–26] are used as a benchmark for comparison. This numerical simulation, performed using the fluid-structure coupling feature in AUTODYN-3D^®, predicts the initial velocities of the aluminum cylinders in the vicinity of the blast field. Results from the numerical simulation yield relatively good agreement with those obtained from experiments, and also provide insight and explanations to some of the surprising results observed in the experiments. An understanding of these results from the experiments is crucial in determining the effects of close-in explosions from high explosive. The paper also includes the study of the momentum transfer to these cylinders when the explosive charge is initiated at two ends simultaneously. The results from this simulation are then compared with a case when it is initiated at two ends with different initiation times. In an effort to investigate the effects of high length-to-diameter ratios on the momentum transfer, simulation for a cylindrical charge with L/D = 3.0 is also included.     

Response of simulated propellant and explosives to projectile impact—II. Fragmentation

This paper is the second of a series concerned with the penetration and perforation phenomena in two types of propellant and explosive simulant, named Propergol, due to the impact at normal incidence of both blunt and conically-tipped steel strikers. The collision results in fragmentation, plug formation and generation of a cloud of debris that includes particles of measurable dimensions traveling with significant velocities. Both the fragment size and area as well as the ejecta mass are determined experimentally as a function of Propergol specimen thickness and impact velocity or energy. The cumulative number of fragments as a function of size for the Propergol is uniformly found to be a bi-linear semi-logarithmic relationship with the bifurcation occurring at the mean crystal radius. Individual crystals and the crater generated are examined by means of a scanning electron microscope.

A phenomenological model of the fragmentation process is constructed, based on an assumed spherical shape of the fragments and the bi-linear fragment distribution, using energy methods. This is combined with a perforation analysis that considers the process to be sequentially composed of initial indentation, fragmentation, and sliding and deflection of the Propergol disks. An evaluation of this model providing fragment volumes as a function of impact velocity is compared with experimental results and found to be in good agreement.     

Fragmentation from spallation of RC slabs due to airblast loads

Terrorist attacks using improvised explosive devices on reinforced concrete buildings create a rapid release of energy in the form of a shock wave. Most casualties and injuries resulting from such an attack are not caused by the blast itself, but rather by the disintegration and fragmentation of the RC member due to concrete spallation on the opposite side of the member and which is propelled at high velocities depending on the size of the fragments. Therefore, it is important to analyze the size distributions of the concrete fragments from spallation. In this paper, two RC specimens were tested under explosive loading in a blast chamber: the first, a reinforced concrete (RC) specimen; and the second, an identical RC specimen retrofitted with 6 near surface mounted (NSM) carbon fibre reinforced polymer (CFRP) plates on both the top and bottom faces. Both specimens were subjected to the equivalent 2.1 kg of TNT at a standoff distance of 0.6 m, resulting in significant scabbing of the concrete. All fragments resulting from the blast tests were collected and analyzed. A sieve analysis was carried out to investigate the size distributions of the fragments from the two specimens. It was found that the fragment size followed both a Weibull distribution and a Rosin–Rammler–Sperling–Bennet (RRSB) distribution. The distribution of the fragment shape factor was also studied. The fragment shape factors were distributed according to the lognormal distribution. Furthermore, the influence of fragment size distribution on energy density dissipation was evaluated.     

Isotropic scattering by penetrable cylinders

Isotropic scattering is considered for infinite cylinders thin in the sense that ka < 1, although ?k'a? and cross-sectional shape can be arbitrary within limits (k and k' are, respectively, free-space and interior propagation constants, and a is a characteristic dimension of the cylinder). For circular cylinders, scattering width is found to saturate at its perfectly conducting value, and absorption width is found to peak, when skin depth becomes comparable with cylinder diameter. For a variety of cylinders with and without edges, both scattering and absorption widths are then found to be effectively identical to those of the circular cylinder with equal cross-sectional area. A new analytical formula is obtained for high but not infinite conductivity, and the connection with scattering cross sections of corresponding finite cylinders is discussed.     

乳化炸药圆筒试验研究

对乳化炸药进行了？25.4 mm的圆筒试验,测试了圆筒在乳化炸药爆轰产物驱动下的膨胀过程R（t）关系.在圆筒的初始膨胀阶段（t＜15μs）,圆筒筒壁膨胀较为缓慢,此后筒壁膨胀半径与时间几乎呈直线增长关系.随着膨胀半径的增大,圆筒壁膨胀速度有着显著的变化,在5～10mm内,筒壁膨胀速度从0.77 mm/μs迅速增大至0.84 mm/μs,而后增速明显变缓.24 mm以后,膨胀速度几乎不再增大.在开始阶段,随着膨胀半径的增大,筒壁的膨胀加速度急剧下降,乳化炸药爆炸能量的释放速度或传递速度急剧下降.此后筒壁加速度下降的趋势变缓,直到零.筒壁的比动能、炸药的能量利用率随膨胀半径及膨胀时间的变化趋势与速度随膨胀半径及膨胀时间的变化趋势基本一致,各变化阶段与速度的变化阶段完全相同.炸药能量利用率在膨胀半径为19 mm时维持在约51%的最高值,剩余的49%的能量主要消耗在爆轰产物的动能和位能上.     

壁厚对HR2钢柱壳爆轰加载下膨胀断裂行为的影响

通过对6、12 mm两种不同壁厚的HR2钢柱壳进行爆轰加载实验,对其断裂碎片的宏观形貌、断口的微观形貌以及横截面的变形微观结构进行系统表征,研究了金属柱壳在爆轰加载下的膨胀断裂机理。结果表明,在膨胀断裂过程中壳壁厚度的增大导致HR2钢柱壳由纯剪切断裂变为拉剪混合的断裂模式。断裂碎片的微观结构分析结果表明,柱壳的断裂实际上是剪切裂纹从样品内部剪切带形核并扩展、和拉伸裂纹沿柱壳外表面的形核扩展的共同作用及竞争的结果。薄壁柱壳断裂由样品内裂纹沿剪切带的形核和扩展主导发生剪切断裂,而厚壁柱壳中内侧的裂纹沿剪切带的形核和扩展,但是最外侧则为环向拉应力主导发生拉伸断裂,因此表现出拉剪结合的断裂模式。     

氢气瓶爆炸原理及其防范措施探讨

通过对一起氢气瓶爆炸事故处理,总结了处置潜在爆炸危险气瓶的成功方案,应用事故树分析方法,结合生产装置实际情况和前后爆炸的3只气瓶,探讨分析了引起氢气瓶爆炸的直接原因,有针对性的提出了防止同类事故发生的措施.     

Tangential velocity profiles of granular material within horizontal rotating cylinders modelled using the DEM

Flow regimes of granular materials in horizontal rotating cylinders are industrially important since they have a strong influence on the rates of heat and mass transfer within these systems. The tangential velocity profile, which describes how the average particle velocity in the direction parallel to the surface of the bed varies along a radius perpendicular to the surface of the bed, has been examined for many experimental and simulated systems. This paper is concerned with tangential velocity profiles within rotating cylinders simulated using the discrete element method. For high fill levels good agreement is found between the simulated velocity profiles and the equation proposed by Nakagawa et al. (Exp Fluids 16:54–60, 1993) based on magnetic resonance measurements. At lower fill levels slip is observed between the cylinder wall and the particles in contact with it and also between the outer layer of particles and the bulk of the bed. It is demonstrated that this slip occurs when the particles in contact with the wall are able to rotate and that it may be prevented either by using non-spherical particles or by attaching “lifters” to the cylinder wall.     

Fragmentation of Spherical Shells under Internal Blast Loading

We present experimental data on the fragmentation, scattering, and penetration into barriers of fragments of thin-walled spherical shells made of soft steel or an aluminum alloy, which are loaded internally by blasting a sphere-shaped explosive charge. The speed, number, and average sizes of fragments formed of shells of different sizes as well as the maximum depths of penetration of fragments into barriers made of a number of homogeneous and heterogeneous materials have been determined. Some characteristic features of the fragmentation of spherical shells under internal blast loading have been elucidated. An attempt has been made to describe the characteristic (average) fragment size by a formula derived from the balance of elastic energy and the work of fracture. Thicknesses of fragmentation protective layers of some structural materials have been chosen, which enable catching soft steel or aluminum alloy fragments which are formed by the explosion of particular sphere-shaped explosive charges.     

高雷诺数下错列双圆柱气动干扰的机理研究

为了进一步澄清小间距错列双圆柱的气动干扰机理,该文采用大涡模拟方法,在高雷诺数下（Re=1.4×105）,研究了间距为2倍圆柱直径的错列双圆柱的气动性能和流场特性随风攻角的变化规律,分析了两个圆柱气动力系数相关性,探讨了下游圆柱气动力与流场结构的内在联系,对下游圆柱平均升力的流场机理提出了新的解释。研究表明,大涡模拟得到的结果与风洞试验值吻合良好;下游圆柱的气动性能、流场结构和两个圆柱气动力相关性均会随风攻角发生剧烈变化;风攻角在0°~10°时,下游圆柱受平均负阻力作用,其原因分别为两圆柱间的回流区和间隙流;风攻角在10°附近时,下游圆柱受很大平均升力作用,风压停滞点偏移、两圆柱间高速间隙流、下游圆柱间隙侧剪切层的提前分离和再附是平均升力出现的三个因素。