球形塑性薄壳在平头圆柱体冲击下贯穿过程的研究

对球形塑性壳在平头圆柱体冲击下的动力贯穿行为进行了分析．通过引入等度量变换,给出了壳体的变形模态．在此基础上对球壳在平头圆柱体撞击下的贯穿机制进行了分析研究,给出了贯穿模型,由此结合Hamilton原理,导出了运动方程组．采用Runge-Kutta方法求解了该方程组,最后分别给出了贯穿时间-弹体初速度;残余窝陷半径-弹体初速度;贯穿后弹体剩余速度-弹体初速度的关系曲线．     

柔性头颅模型撞击弹性板的动态响应分析

将柔性接触撞击过程处理为一个振动系统响应,采用机械网络图和求机械阻抗的方法解决了这一动态响应问题。柔性接触撞击模型考虑了头部的实际结构,把头部简化成撞击部位的头皮和头骨的质量、头部其它部分的头骨和脑液的质量、头部的刚度、头皮和脑液的阻尼系数组成的振动模型,弹性板也同样简化成由质量、刚度和阻尼构成的振动模型。采用求激振点速度阻抗的方法,得到了系统的动态撞击力、头部所受到的撞击加速度值,以及板的弹性变形、系统的固有频率等动态响应。实验数据与计算数据符合较好,证明方法是计算撞击作用下系统动态响应的实用方法,从而为头部撞击保护设计提供参考。     

柱形弹体撞击塑性变形的G.I.泰勒理论的分析解及其改进

柱形弹体对刚性靶体的纵向撞击塑性变形理论是G.I.泰勒[1]首先提出的.这个理论的重要性在于通过这个理论可以从实验数据计算动力屈服强度,而且从实验结果[2]中看到,动力屈服强度和撞击速度无关,动力屈服强度高于静力屈服强度,对某些材料而言,可以超出好几倍.这样就为弹塑性撞击研究提供了一个重要的根据.但是,泰勒理论由于微分方程的复杂性,求解过程都是数值计算,这样对使用其结果时深感不便.本文提供了全部分析解,并对其结果进行了讨论.本文对冲量计算进行了修正,修正理论的分析解指出,其结果比泰勒理论的解更加符合实验[2].     

承受斜撞击的悬臂梁的力学分析模型

结构受到飞射物的斜撞击,是工程中经常遇到的重要问题.作为理论分析的第一步,本文对刚-线性强化悬臂梁端部承受刚性块斜撞击的问题建立了力学分析模型.这是一个将Parkes模型与Taylor模型结合起来的“双铰模型”,其运动受控于4个非线性代数方程的联立方程组.给出的算例显示了双铰运动的规律和杆端速度变化的历吏.     

反冲塞效应的热弹性理论分析（Ⅱ）——反鼓包运动

本文对我们新近发现的长脉冲激光束对金属薄片材料的一种新的破坏方式──“反冲塞”效成（ＲＰＥ）的反鼓包运动进行了热弹性理论分忻．在不考虑膜力和弯矩相互耦合的小变形热弹性板理论情形下，将挠度ω分解为准静态部分ωｓ和动态部分ωｄ，得到了挠度ω的精确解．同时还分析了等效热载荷以及对早期运动状态进行了无量纲分析．这些分析能较好地定性解释反冲塞效应的早期运动状态即反鼓包运动特征．     

夹层圆柱壳在移动内压作用下的临界速度研究

基于夹层壳理论和三维弹性动力学理论,研究了无限长夹层圆柱壳在移动内压作用下的临界速度．首先,基于夹层壳理论,考虑夹芯的压缩和剪切变形以及面板的剪切变形,研究了轴对称简谐波在无限长夹层圆柱壳中的传播问题;其次,基于三维弹性动力学理论,将位移变量用Legendre正交多项式系表示,同时引入位置相关函数,将求解导波问题化为简单的特征值问题．利用这两种方法得到了最低模态的频散曲线,最小相速便是内压移动的临界速度．最后,用算例和数值模拟来验证方法的有效性．结果表明,两种理论得到临界速度吻合得较好;当波数较小时,两种理论得到的频散曲线吻合得很好,当k→∞时,夹层壳理论和弹性动力学理论得到的极限相速分别趋于面板和夹芯的剪切波波速．波数较小时,两种理论分析夹层圆柱壳的导波问题是有效的．数值模拟预测的临界速度与理论分析的结果吻合得很好．     

运动热源产生的温度场的有限元分析

本文采用运动元法,考虑了热辐射、热交换和变热传导系数,在较宽的速度范围内研究了运动热源所产生的温度场.给出了在运动坐标和静止坐标系中,不同速度情况下温度场随时间变化的情形,给出了在运动坐标系中不同速度情况下温度场的(定常)等温线分布图.本文还讨论了动态裂纹扩展中裂纹端部过程区的塑性变形所引起的温度场,结果表明,结构钢中过程区的温度一般不会超过1000℃,或1832℉.     

纤维增强复合材料靶板抗钢球贯穿的工程分析方法研究

介绍了钢球贯穿纤维增强复合材料靶板的一维工程近似分析方法.钢球被假定为刚体,复合材料靶被近似为横观各向同性弹埋性材料.通过将球腔膨胀模型和柱腔贯穿相结合的方法,提出了一种改进的复合材料靶抗贯穿的工程近似分析方法.利用该方法,对三维芳纶纤维编织(3DKw)复合材料靶板开展了抗钢球贯穿的工程近似分析,计算结果与实验结果一致性较好;并进一步讨论了计算中材料主要参数对靶板抗贯穿规律的影响.     

激光状态方程测量中飞片增压技术的实验研究

利用高功率激光作为驱动源,对飞片空腔靶增压技术的可行性及其增压效果进行了研究.实验获得了激光烧蚀加速的飞片撞击靶产生的平面性良好的靶背面冲击加热发光信号,测量了靶中的冲击波速度,给出了铝、铜靶中的冲击压力.结果表明,飞片空腔靶的增压效果是非常明显的,对于两种不同空腔长度的增压效果,也进行了初步的研究.     

弹塑性杆在刚性块轴向撞击下的动力屈曲

基于能量原理,对弹塑性杆在刚性块轴向撞击下的动力屈曲问题进行了讨论．用特征线法分析了刚性块轴向撞击弹塑性直杆时应力波传播的过程．考虑了弹塑性应力波传播对屈曲的影响,建立了该问题横向扰动方程．用幂级数解法,理论上给出了该问题的级数解．分析解的性质,得到了发生屈曲时的临界条件．通过理论分析和数值计算,得到了临界速度与冲击质量、临界长度及线性强化模量间的关系．     

Numerical and experimental simulation of wave formation during explosion welding

The results of numerical and experimental simulation of wave formation under an oblique impact of metal plates during explosion welding are presented. The numerical simulation was carried out on the basis of the Maxwell relaxation model and by a molecular dynamics method. In the experiments, the impact of metal plates was investigated with X-ray radiography of phenomena in front of and behind the point of contact, and the preserved samples were studied metallographically. It is shown that the numerical simulation correctly reproduces the formation and evolution of waves on the contact boundary. Simultaneously, constraints are pointed out that prohibit the use of the elastoplastic model in the impact zone of the plates starting from the moment when the material of the plate in this zone is decomposed into thin jets. In this zone, the dependence of the specific deformation energy E on the tensor C _j ⁱ is no longer described by a convex function. It is this fact that motivated the transition to the molecular dynamics model.     

Solution to projectile motion with quadratic drag and graphing the trajectory in spreadsheets

This note gives the analytical solution to projectile motion with quadratic drag by decomposing the velocity vector to x, y coordinate directions. The solution is given by definite integrals. First, the impact angle is estimated from above, then the projectile coordinates are computed, and the trajectory is graphed at various launch angles and speed using an interactive Excel application.     

Problème de Cauchy sur un conoïde caractéristique pour des équations quasi-linéaires

Summary Cauchy problem for system of quasilinear differential equations of order two on a characteristic conoid is solved. It is proved that, given a conoid with the values of the unknown functions on it such that it is a characteristic conoid, there is a unique solution, which is smooth at the apex of the conoid. This result is obtained under smoothness conditions on the data and some supplementary conditions on the data at the apex of the conoid, and by use of Leray's theory [6].     

Finite-element modeling of the particle clustering effect in a powder-metallurgy-processed ceramic-particle-reinforced metal matrix composite on its mechanical properties

A new numerical method is proposed to predict the effect of particle clustering on grain boundaries in a ceramic- particle-reinforced metal matrix composite on its mechanical properties, and micromechanical finite-element simulation of stress–strain responses in composites with random and clustered arrangements of ceramic particles are carried out. A particular material modeled and analyzed is a TiC-particle-reinforced Al matrix composite processed by powder metallurgy. A representative volume element of a composite microstructure with 5 vol.% TiC is reconstructed based on the tetrakaidecahedral grain boundary structure by using a modified random sequential adsorption. The model proposed in this study accurately represents the stress concentrations and particle-particle interactions during deformation of the powder-metallurgy-processed composite. A comparison with the random-arrangement model shows that the present numerical approach is more accurate in simulating the behavior of the composite material.     

研究金属中激波构造与衰减的一个物理模型

本文给出了研究金属中激波构造与衰减的一个物理模型.为了建立高速形变下材料的本构方程和研究激波过渡带的构造,需要考虑二个独立的理论方面.首先,将比内能分解成弹性压缩能和弹性形变能,而将形变能作为弹性应变和熵的函数展开到三阶项,其中考虑了热与机械能的耦合效应.其次,从位错动力学角度建议了一个塑性松弛函数以便描述高温、高压下塑性流动的特性.另外,本文给出了一个常微分方程组用以计算定态激波过渡带中各状态变量的分布以及激波的厚度.倘若假定在激波上熵的跳跃可以忽略,并用Hugoniot压缩模量代替等熵压缩摸量,可以获得一个分析解.最后,本文还提出了求解平板对称碰撞中激波波头衰减的一个近似方法。     

截锥形弹低中速贯穿薄靶板时的动力分析与计算

本文根据引信设计的需要,结合引信的结构特点,对截锥形弹以低速(200～500米/秒)和中速(500～1000米/秒)贯穿薄靶板(包括金属铝板和非金属的木质胶合板)时的动态特性进行了分析和计算。在建立模型过程中,由于考虑了靶板强度效应的影响,解决了原来一些模型对低速冲击不适用的问题。并通过惯性效应和强度效应的比较,从理论上证明了Zaid和Paul的试验结论:即当冲击速度高于500米/秒时,可忽略强度的影响,而当冲击速度低于500米/秒时,不能忽略强度效应的影响。     

Motion of a circular viscoplastic plate subject to projectile impact

A method is presented for the solution of problems involving the impact on circular plates of projectiles moving with velocities high enough to produce plastic deformations. The plate material is assumed to obey the Mises-Huber yield condition and its associated flow rule for static deformations and behave as a viscoplastic solid for dynamic deformations. The nonlinear constitutive equations of the material are partially linearized in such a way as to allow the required result to be obtained by superposition of the static rigid perfectly-plastic solution and the dynamical elastic solution of equivalent problems. The method is illustrated by application to the case of a clamped plate struck at the center by a projectile of negligible radius.In addition a method for the rapid estimation of the motion of the projectile after impact is given and the result for the time required to bring the projectile to rest and the consequent central deflection of the plate are obtained.

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Zusammenfassung Es wird eine Methode zur Lösung von Problemen beschrieben, die sich im Zusammenhang mit dem Aufschlag von Geschossen auf kreisförmige Platten ergeben; dabei soll die Geschossgeschwindigkeit so hoch sein, dass plastische Deformationen auftreten. Das Plattenmaterial soll der Mises-Huberschen Fliessbedingung und dem zugehörigen Fliessgesetz für statische Deformationen genügen und sich für dynamische Deformation wie ein viskoplastischer Festkörper verhalten. Die nicht linearen Stoffgleichungen des Materials werden teilweise linearisiert, so dass das gesuchte Resultat als Superposition der statischen starr-ideal-plastischen Lösung und der dynamisch-elastischen Lösung erhalten werden kann. Die Methode wird durch Anwendung auf den Fall einer eingespannten Platte veranschaulicht, auf deren Mittelpunkt ein Geschoss von vernachlässigbarem Radius auftrifft.Ausserdem wird eine Methode zur Abschätzung der Geschossbewegung nach dem Einschlag gegeben und die Zeit vom Aufprall bis zum Stillstand des Geschosses sowie die resultierende Auslenkung des Scheibenmittelpunktes berechnet.

     

Prediction of hypervelocity orbital debris impact damage to the space station by neural networks

Prediction of damage to orbiting space craft due to collisions with hypervelocity space debris is an important issue in the design of Space Station Freedom. Space station wall structures are designed to absorb impact energy during a collision. A proposed wall structure consists of a multilayer insulation (MLI) directly covering the pressure wall, and a bumper layer placed 100mm from the pressure wall. In experiments at The Marshall Space Flight Center, 2.5–12.7 mm projectiles have been fired at this wall structure at speeds of 2–8 km/s. In this paper, three-layer backpropagation networks are trained with two sets of impact damage data. The input parameters for training are pressure wall thickness, bumper plate thickness, projectile diameter, impact angle, and the projectile velocity. Output from the network consists of hole dimensions for the bumper and the pressure wall in the minor and major axis directions, and damage to the MLI. To evaluate network generalization, networks are tested with experimental data points that are not used for training. Network performance is compared with that of other damage prediction methods. Network determination of qualitative damage estimation is suggested as a new direction for research. Preliminary testing of qualitative prediction of pressure wall damage is presented. The results are promising, and suggest several areas for further study.