Perforation of metallic plates struck by a blunt projectile with a soft nose

The present paper constructs a rigid–plastic model to assess the effect of a soft nose on the perforation of metallic plates struck by a stubby projectile. A low-density nose-cabin-column, i.e., an assembly of seeker and guidance/control unit, is installed in the front of a real missile. It usually acts as an energy absorber and buffer in the perforation of metallic plates and notably affects the terminal results of projectile. The problem is equivalent to a blunt rigid projectile with a soft nose perforating a circular metallic plate. Effects of transverse shear, bending and membrane deformations on the perforation process are included in a rigid–plastic analysis. Especially the effect of an ahead structural response, induced by the soft nose impacting the target plate, is considered in the model. Analytical formulae for the ballistic performance are obtained for a range of plate thicknesses, which agree well with available experimental results.     

Dynamic failure by adiabatic shear banding

This paper addresses adiabatic shear localization from a different point of view. New results are reviewed which indicate that the process can be viewed as triggered by dynamic recrystallization instead of being the result of thermal softening as universally assumed. A simple dislocation dynamics model (modified ETMB) is used to reproduce the salient features of the physical observations, namely dynamic recrystallization in the strain-hardening phase with a minor temperature rise. The main parameters of the model are discussed from an experimental identification point of view.     

Experimental investigation of clamped beams struck transversely by a mass

A series of experimental tests on clamped metal beams struck by a mass is reported in this paper. The impact point varies from the mid-span of the beam to the immediate vicinity of a support. Good agreement is found between the permanent transverse deformations of the beams, which were recorded in the experimental tests, and the theoretical rigid-plastic predictions which are reported in Liu and Jones (Int. J. Solids Struct. In press). Two types of beam failure were observed and classified as tensile tearing and shear failure. The onset of these failure modes depends on the uniaxial rupture strain ε_m of the materials, the location of the impact point l₁ and the clamping condition.     

Shear and adiabatic shear failures in an impulsively loaded fully clamped beam

An analytical model is proposed for studying the material failure in shear hinges which develop during the dynamic plastic response of beams under impulsive pressure loadings. The structural response outside a shear hinge is modelled using a rigid, perfectly plastic theory. However, within the shear hinge, strain hardening, strain rate and temperature effects are considered in order to obtain the conditions for an adiabatic shearing failure. A critical impulsive velocity is obtained for Menkes and Opat’s beam problem, which describes a transition from a transverse shear failure mode (Mode III) to an adiabatic shear banding mode with increase of impulse. A similar procedure is used to examine circular plates and cylindrical shells, as well as mass impact problems.     

带有边缘径向裂纹的固支圆板湿模态分析

基于Rayleigh-Ritz法,分析了置于无限大障板中、单面临水、带有边缘径向裂纹的固支圆板的固有频率和振型.引入角函数对裂纹的影响进行描述,采用薄板假设计算裂纹深度等于板半径的边缘径向裂纹圆板振动的最大动能和最大势能;在无旋、无粘、不可压和板微幅振动的假设条件下,采用速度势描述水体运动并获得了由位移基函数表达的附加动能,并通过Rayleigh-Ritz过程获得流固耦合振动系统的特征矩阵,进而求得湿模态对应的固有频率和振型.结果表明,固有频率降低率整体上随模态阶数的增大而减小,而干、湿模态振型的差别则整体上随模态阶数的增大而增大;水体对对称模态和反对称模态的影响有明显的区别.计算结果与ANSYS数值仿真的结果符合的较好.     

Optimization of a circular thin-film piezoelectric actuator lying on a clamped multilayered elastic plate

A system consisting of a circular multilayered thin-film elastic plate and a piezoelectric actuator, which is generally used for ultrasound generation in air, is studied in this paper. Effects of the electrode dimension of a circular thinfilm piezoelectric actuator lying on a clamped multilayered elastic plate are discussed theoretically, while the first-order theory of asymmetrically laminated piezoelectric plates with consideration of coupled extension and flexure of the reference plane is used. Numerical results show that the deflection of the elastic plate can be optimized by adjusting the radius of the top electrode.     

Transverse deflection of a clamped mild-steel plate

The theory of plastic flow by extended slip (Acta Mech 223:655–668, 2012; Philos Mag A 91:3343–3357, 2011; Z Angew Math Mech 84:266–279, 2004; Q J Mech Appl Math 52:645–662, 1999) is applied to a problem of bi-axial strain: the transverse plastic deflection, by means of a flat-ended punch, of a clamped plate of mild-steel. Two new theorems concerned with the Mechanics of Plates are presented. It is shown that, if the static shear yield stress of the plate material remains independent of strain, then the load–deflection relation for the punch, in the case of quasi-static punching of a plate clamped along a closed arbitrary contour, obeys an exactly linear theoretical relation. This prediction is then confirmed by experiments carried out at quasi-static rates of loading with thin plates of hot-rolled mild-steel. It is demonstrated by experiment, in the case of concentric circular punch and clamp contours, that the load–deflection relation for the punch remains linear to within <1 % provided that the maximum principal strain within the free domain of the plate does not exceed the yield-point elongation strain of the mild-steel concerned.     

Deformation and failure of clamped shallow sandwich arches with foam core subjected to projectile impact

The dynamic response of clamped shallow sandwich arches with core of aluminum foam has been experimentally studied by impacting the arches at mid-span with metal foam projectiles. The resistance to shock loading is measured by the permanent transverse deflection at mid-span of the arches. The deformation mechanisms of shallow sandwich arches were investigated. In addition, the deformation/failure modes of the shallow sandwich arch were classified and analyzed systematically. The effects of initial projectile momentum, face sheet thickness, core thickness and radius of curvature on the structural response were obtained. The results indicated that permanent deflection at mid-span can be efficiently controlled by increasing face sheet thickness, core thickness or appropriately increasing curvature. Meanwhile, shock resistance of the shallow sandwich arch can also be improved. The experimental results are useful in the optimum design of cellular metallic sandwich structures.     

A study on the failure of circular plates struck by masses. Part 1: experimental results

In the present study experimental results recorded from a series of tests are presented, which examine the dynamic response and petalling failure of thin circular plates struck transversely at the centre by masses having conical heads and spherical noses. The circular plates are cut from mild steel plates with five different thicknesses of 1.17, 1.5, 2, 3 and 4 mm and three different diameters of 250, 300 and 350 mm, to make a ratio of thickness to diameter ranging from 3.34×10⁻³ to 11.43×10⁻³. The impact velocity ranges from 3 to 11 m/s, corresponding to an impact energy varying from 100 to 1700 J. The radius of the sphere on the tip of conical head of the drop mass is chosen as 6, 8 and 10 mm. It has been observed that a necking circle is initiated approximately in the central part of plates along a small circle, which is directly under the transition circle from the spherical surface to conical surface of the drop mass. This is due to the excessive in-plane tensile strain. A through-thickness crack, then, is formed at one point on the circle, which is recognised as in-plane tearing failure. The crack is opened further and ends with a petalling pattern tearing failure around the crack for severe impact cases. It has been found that the critical impact energy required for the onset of failure varies significantly with the thickness of plates and the radius of spherical nose of the drop mass.     

The influence of a steel rear barrier on the detonation response of a steel covered explosive struck by a steel projectile

Experiments by Weickert showed that the critical impact velocity of a shaped charge jet, required to cause detonation of a steel/explosive/steel laminate, reduced when the explosive thickness reduced. This paper examines the cause of this change using hydrocode simulations with and without a temperature based burn model. The simulations show that the change in critical impact velocity is caused by the reflected shock from the rear plate exceeding the shock at the cover plate. At this point the site of the detonation moves from the cover plate to the rear plate. Further reduction in explosive thickness causes further reduction in critical impact velocity due to the reduced dissipation of the shock reaching the back plate. The change in critical velocity for hemispherical-nosed projectiles is predicted to be not as sharply defined as for flat-nosed projectiles. This is due to a later, third stage reflection from the bulge of the advancing cover plate.     

Perforation of rigid-plastic plate by blunt missile

Three rigid plastic models are presented to treat circular plate deformation during perforation by a rigid missile; these models are based on different assumptions for yield. The analysis considers plate bending, stretching and also shear around the periphery of a central plug. An equivalent strain failure criterion is developed that includes the influence of both shear and radial tensile strain on localized failure of the plate. Both this and a pure shear failure criterion of Shadbolt et al. [1] are used together with three structural deformation models to calculate the ballistic limit and final deformed profiles of plates. These calculations are compared with some experimental results for plates of different materials.     

The influence of microstructural anisotropy on the mode of plate failure during projectile impact

Changes in the failure mode of rolled steel plate during projectile impact were examined in terms of the angle between the planes of microstructural inhomogenieties in the steel and the plane of the target. Two failure modes were identified: (1) discing failure involving multiple shear band formation in the rolling plane with separation along the shear bands to form a disc segment, and (2) tensile star cracking with the propagation of a tensile tear through the rear surface of the plate. Both the ballistic resistance and the predominant mode of failure were critically dependent on the orientation of the microstructural banding in the plate.     

分层对TC4钛合金板抗平头弹撞击失效特性的影响

使用Abaqus/Explicit有限元分析软件,开展平头弹撞击不同厚度双层TC4钛合金板数值模拟,研究双层TC4钛合金板撞击失效特性与失效模式随厚度变化规律及机理.通过对比撞击试验与仿真结果,验证数值模型和参数的有效性.在此基础上与等厚度单层TC4钛合金板的抗侵彻性能进行对比,结果表明,对于12.68 mm直径的平头...     

Effectiveness of gas-film cooling in a circular tube with adiabatic walls

The effectiveness of gas-film cooling in the presence of a turbulent air flow in an adiabatic circular tube with an initial porous section is discussed in relation to the experimental results.     

Microstructure in adiabatic shear bands in a pearlitic ultrahigh carbon steel

Abstract

Adiabatic shear bands, obtained in compression deformation at a strain rate of 4000 s^?1, in a pearlitic 1·3%C steel, were investigated. Shear bands initiated at 55% compression deformation with the width of the band equal to 14 μm. Nano-indentor hardness of the shear band was 11·5 GPa in contrast to the initial matrix hardness of 3·5 GPa. The high strength of the shear band is attributed to its creation from two sequential events. First, large strain deformation, at a high strain rate, accompanied by adiabatic heating, led to phase transformation to austenite. Second, retransformation upon rapid cooling occurred by a divorced eutectoid transformation (DET). The result is a predicted microstructure consisting of nano size carbide particles within a matrix of fine ferrite grains. It is proposed that the DET occurs in iron–carbon steels during high rate deformation in ball milling, ball drop tests and in commercial wire drawing.     

Development of adiabatic shear band in cold-rolled titanium

The evolution of adiabatic shear localization in commercial titanium subjected to heavy cold rolling was investigated. The evolution of the morphology, microhardness, local shear strain, and local temperature increments were systematically studied and estimated. A shear band with about 25 μm in width was formed and fine nanograins with a range of dimensions varying from 20 to 160 nm and had a mean size of about 70 nm were observed inside the centre of shear band after 83% cold-rolling. Microhardness test shows that hardness within the shear band is markedly higher than that of the surrounding matrix. The calculated shear strain and maximum temperature increase within the shear band are much higher than that of the overall deformed sample. The initiation of shear localization may depend on geometric perturbation instead of thermal ones.     

四边固支功能梯度板中波的传播

摘要：考虑剪切变形和转动惯性的影响,采用一阶剪切变形板理论和小应变的应变－位移关系,利用Hamilton原理推得运动控制方程,并应用特征值方程得到频散方程。给出了波在功能梯度板中传播的频散,相速度和群速度随波数变化的曲线,分析了不同的功能梯度材料指数对波传播的影响规律。