Thermonuclear fusion under high-velocity cluster impact

Numerical investigations have been carried out for thermonuclear fusion processes under hypervelocity impact of micro-projectile composed of deuterium-tritium mixture on a surface of solid target. The results are discussed. Crucial thermonuclear fusion initiation parameters are defined.     

Destruction of organic glass under high-velocity impact

The results are given of experimental investigations of the interaction between a 2.5-g polyethylene impactor and a massive target of organic glass. The impact velocity ranges from 1 to 3.2 km/s. A statistical analysis is made of masses and sizes of fragments of the impact and spallation craters of the target.     

Mathematical simulation of fracture of ceramic obstacles in axially symmetric high-velocity impact

Calculations were made by the finite element method of the high-velocity interaction of cylindrical steel strikers with ceramic obstacles in the range of impact velocities up to 1500 m/sec. A kinetic model of active type fracture was used for numerical simulation of fracture of the ceramic. Chronograms of the process and distribution of the isolines of specific volume of cracks at different moments of time are given. Features of penetration of ceramic obstacles with different initial impact velocities are described.Translated from Problemy Prochnosti, Nos. 5–6, pp. 87–94, May–June, 1995.     

Numerical modelling of foam-cored sandwich plates under high-velocity impact

This paper studies the high-velocity impact response of sandwich plates, with E-glass fibre/polyester face-sheets and foam core, using finite-element models developed in ABAQUS/explicit code. The failure of the face-sheets was predicted by implementing Hou failure criteria and a procedure to degrade material properties in a user subroutine (VUMAT). The foam core was modelled as a crushable foam material. The numerical models were validated with experimental data obtained from scientific literature. The contribution of the foam core on the impact behaviour was evaluated by the analysis of the residual velocity, ballistic limit, and damaged area.     

高速撞击下无氧铜破坏机理实验研究

采用φ100mm一级轻气炮开展了无氧铜飞片撞击氧化铝陶瓷的一维应变冲击压缩实验,利用VISAR测试了样品的自由面质点速度历程.实验发现,在OFHC与陶瓷撞击时,OFHC飞片也可发生层裂,SEM分析表明其层裂方式为准解理断裂,在撞击区域OFHC的晶粒长大,并伴随孪晶生成,而且OF-HC在高速撞击下不会产生绝热剪切带和析出相,其原因是透射稀疏波在飞片中与飞片后界面反射的稀疏波迎面相遇形成拉伸波区所造成的.     

Modelling of composite sandwich structures with honeycomb core subjected to high-velocity impact

In this study the perforation of composite sandwich structures subjected to high-velocity impact was analysed. Sandwich panels with carbon/epoxy skins and an aluminium honeycomb core were modelled by a three-dimensional finite element model implemented in ABAQUS/Explicit. The model was validated with experimental tests by comparing numerical and experimental residual velocity, ballistic limit, and contact time. By this model the influence of the components on the behaviour of the sandwich panel under impact load was evaluated; also, the contribution of the failure mechanisms to the energy-absorption of the projectile kinetic energy was determined.     

弹体高速侵彻陶瓷复合厚靶的计算模型研究

针对平头弹高速撞击陶瓷复合厚靶的问题,以集中质量法为基础并考虑靶体的内摩擦效应对Fellows模型加以改进,建立侵彻过程的理论计算模型并利用Matlab编程求得不同撞击速度下弹体侵彻复合靶体的侵彻深度,模型得到了试验结果和数值计算结果的验证。参数分析的结果表明,陶瓷厚度的增加可提高复合靶体的抗侵彻能力,但随着初始撞击速度的提高,弹体的侵彻深度增长曲线趋于平缓。     

Experimental analysis of perforation of glass/polyester structures subjected to high-velocity impact

In this paper the ballistic behaviour of several glass/polyester laminate structures was studied, evaluating the residual velocity of the projectile and the damage area. Three monolithic laminates of different thicknesses and two multiplate laminate structures were analyzed: one of a sandwich type with face-sheets of glass/polyester and a foam core, and another made with the same face-sheet, which were separated by a distance equal to the thickness of the core. It was found that laminates of greater thickness show a larger damage area and a greater ballistic limit. The influence of the core on the ballistic limit of multiplate laminate structures is negligible but, nevertheless, the extension of the damage area in the back face-sheet is increased.     

Composite structures under ballistic impact

In the present study, investigations on the ballistic impact behaviour of two-dimensional woven fabric composites has been presented. Ballistic impact behaviour of plain weave E-glass/epoxy and twill weave T300 carbon/epoxy composites has been compared. The analytical method presented is based on our earlier work. Different damage and energy absorbing mechanisms during ballistic impact have been identified. These are: cone formation on the back face of the target, tensile failure of primary yarns, deformation of secondary yarns, delamination, matrix cracking, shear plugging and friction during penetration. Analytical formulation has been presented for each energy absorbing mechanism. Energy absorbed during each time interval and the corresponding reduction in velocity of the projectile has been determined. The solution is based on the target material properties at high strain rate and the geometry and the projectile parameters. Using the analytical formulation, ballistic limit, contact duration at ballistic limit, surface radius of the cone formed and the radius of the damaged zone have been predicted for typical woven fabric composites.     

Shock-spall asymmetry in high-velocity impact of solids

A new, previously unreported physical phenomenon has been observed in experiments with high-velocity impact of various strikers on metal targets of finite thickness. According to this, sufficiently strong and tough structural materials (armor steel, titanium alloys, etc.) exhibit fractionation of the spall plate formed upon dynamic contact with the striker or its deformed part. This always results in an odd number of fragments (three, five, seven, etc.) of similar configuration. Systematic experiments on retained samples revealed progressive fractionation of the spall plates, with the number of fragments increasing up to eleven. Further evolution was difficult to follow because trapping of the fragments was hindered by their high velocities, which led to unavoidable additional fragmentation of the spall plates in the course of their interaction with a gradient package of trapping material (ranging from felting to sand).     

An oblique impact anomaly in high-velocity liquid impact on glass

The residual strength of glass discs after impact by high-velocity water jets has been found as a function of impact angle. An unexpected result is that under certain conditions the damage suffered is a maximum for non-normal impact. This effect is shown to be caused by radial cracks forming during the oblique impact. These cracks are not observed for normal impact and their formation is dependent upon specimen geometry. The result is of practical significance to the rain erosion situation where aircraft and missile components may suffer damage by encounters with rain drops.     

Evolution and calibration of a numerical model for modelling of hybrid-fibre ECC panels under high-velocity impact

A material model for hybrid-fibre engineered cementitious composites (ECC) under impact loading is developed and calibrated in this paper, and size effect, appropriate erosion criteria and strain rate effect are investigated and accounted for in the model. Employing the new material model, a numerical model and modelling technique are developed to model the impact behaviour and impact process of hybrid-fibre ECC panels using LS-DYNA commercial software. The material model and the numerical model developed in this paper are validated against the experimental results.     

Influence of high-velocity impact on metals

The work is devoted to investigation of metals’ behavior under shock loading. The materials under investigation were copper, aluminum, lead, titanium, titanium alloys and different steels. Microstructure investigations have been carried out using optical microscopy. The strength behavior was investigated with the help of a microhardness device. Comparison of the spherical action of waves and uniaxial shock loading for the aforementioned metals has been done.     

Vortex structure in high-T c ceramic superconductors

We consider penetration of magnetic flux in the rare earth ceramic superconductors within the framework of a generalized Ginzburg-Landau theory, based on the coexistence of antiferromagnetism and superconductivity. We study vortex structure produced for a magnetic field close to . We make a new prediction that may serve to test the theory experimentally.     

Crack resistance of materials with high-velocity impact

A procedure is suggested for determining critical dynamic stress intensity factors with normal separation and transverse shear from crack stopping under rear spalling conditions for specimens. Results obtained by the method suggested for three grades of steel are compared with those calculated by the Panasyuk-Andreikiv procedure. Good agreement is noted for critical stress intensity factors with normal separation.Translated from Problemy Prochnosti, No. 12, pp. 19–23, December, 1990.     

Vortex structures in rotating3He-A

In the hydrodynamic approximation, the free energy of high-field Seppälä-Volovik vortices in rotating³He-A is minimized with respect to an additional textural rotation angle. The transition from singular, singly quantized vortices to nonsingular, doubly quantized vortices is predicted to occur at a temperature-dependent angular velocity of order 1 rad / sec, in rough agreement with experimental observations.     

Edge cracked piezoelectric ceramic block under electromechanical impact loading

The dynamic field intensity factors and energy release rates in a piezoelectric ceramic block containing an edge crack with the condition of continuous electric crack faces under electromechanical impact loading are obtained. Integral transform method is used to reduce the problem to two pairs of dual integral equations, which are then expressed to an Fredholm integral equation of the second kind. Numerical values on the dynamic stress intensity factor and dynamic energy release rate are obtained to show the influence of the geometry and electric field.     

Another approach to a hybrid particle-finite element algorithm for high-velocity impact

This article presents a hybrid particle-finite element algorithm for high-velocity impact. In the hybrid approach, both finite elements and meshless particles represent the same material simultaneously. The initial hybrid concept was introduced and developed by Fahrenthold and others. It is based on a Hamiltonian formulation for both the particles and elements, and it has used a structured arrangement for the finite elements. The work presented here is based on the Generalized Particle Algorithm, and it can be used with a variety of element types and arrangements. A finite element mesh is generated as it would be for a traditional finite element computation (except that contact surfaces do not need to be defined), and the hybrid algorithm simply becomes another option for the user. The hybrid algorithm of Fahrenthold computes the compressive pressure at the nodes (particles), with the strength and tensile pressure computed in the elements. This approach allows large distortions and fragmentation to be represented, it eliminates tensile instabilities in the particles, and it allows the contact to be performed within the particle algorithm. There are additional advantages and disadvantages of the hybrid approach when compared to other techniques, such as the automatic conversion of distorted finite elements into meshless particles, and these are discussed. The new hybrid algorithm is demonstrated in both 2D and 3D geometries with a range of example computations. Comparisons to computations performed with a conversion (of elements into particles) algorithm are also presented.     

Response of boron carbide subjected to high-velocity impact

This article presents an evaluation of the response of boron carbide (B₄C) subjected to impact loading under three different conditions. Condition A is produced by plate-impact experiments where the loading condition is uniaxial strain and the stresses and pressures are high. Under plate-impact loading the material fails at the Hugoniot Elastic Limit (HEL) and the failed material undergoes high confining pressures and relatively small inelastic strains. Condition B is produced by projectile impact onto thick targets where the stresses and pressures are dependent on impact velocity, but they are generally lower than those from plate impact. Under thick-target impact/penetration most of the material fails under compression, the inelastic strains are large and the material appears to exhibit more ductility than under condition A. Lastly, condition C is produced by projectile impact and perforation of thin targets where the stresses and pressures are a combination of compression and tension. Under thin-target perforation the material fails in both tension and compression. The Johnson–Holmquist–Beissel (JHB) constitutive model is used to evaluate the material behavior for each of the three conditions, but it is not possible to accurately reproduce the experimental results of the three conditions with a single set of constants. Instead, three different sets of constants are required to accurately model the three impact conditions. These three models/constants are used to provide insight into the complex response of B₄C, and to identify possible mechanisms that are not included in the JHB model.     

Damage evaluation of concrete plates by high-velocity impact

This paper describes the evaluation of the local damage of concrete plates by the impact of high-velocity rigid projectiles. A new launching system of mushroom-shaped projectiles has been developed. Impact tests for concrete plates have been conducted by using the system to examine failure modes of the local damage of concrete plates. The damage or failure behavior has been discussed on the basis of the failure process captured by a high speed video camera and the strain histories obtained by strain gauges on the concrete plate. Numerical simulations have been also carried out in order to explain the mechanism of the local damage observed by the experiment. A reasonable numerical model has been discussed in terms of a constitutive model and strain rate effect of concrete material. Mechanism of the local damage of concrete plates has been illustrated schematically.