柔性头部模型与大挠度板接触撞击力的预报方法

针对被撞击板是大挠度的特点,提出了模拟函数预报撞击力的方法,根据撞击系统的动量守恒原理推导出了撞击力的预报方程,用恢复系数考虑头皮对撞击缓冲的影响．得到了头部与发动机罩板大变形、非线性、瞬态撞击过程的响应函数．分析结果与鸿巢敦宏、石川博敏的试验数据进行了对比,结果显示有较好的一致性,表明该方法能够较好地描述柔性球体模型与大挠度板接触撞击的响应过程．同时还利用该预报方程分析了各种因素对接触撞击力的影响．     

多胞材料的动态应力应变状态及其一致近似关系

多胞材料在高速冲击下呈现出逐层压溃的变形模式,塑性冲击波模型可以用来表征这种集中变形带的传播行为。本文中采用截面应力计算方法得到了随机蜂窝在恒速冲击下的一维应力分布,进而对冲击波的传播规律进行了分析。比较了高速冲击下由不同方法得到的冲击波速度与冲击速度的关系,结果表明R-PP-L（率无关,刚性-理想塑性-锁定）模型高估了冲击波速度,但R-PH（率无关,刚性-塑性硬化）模型以及一维冲击波理论得到的冲击波速度与有限元结果比较接近。冲击波速度与冲击速度在高速情形下趋于线性关系,但随着冲击速度的减小,冲击波速度不断减少并趋于常数。根据这一特征和塑性冲击波模型,发展了可以表征冲击波速度与冲击速度的关系、动态应力应变关系的一致近似模型。     

柔性梁刚柔耦合碰撞动力学及变形传播研究

运用柔性多体系统刚柔耦合动力学理论,研究了作大范围回转运动柔性梁的碰撞动力学问题.考虑柔性梁的横向变形,以及横向变形引起的纵向缩短项即非线性耦合变形项.采用基于Hertz接触理论及非线性阻尼理论的非线性弹簧阻尼模型来求解碰撞过程中产生的碰撞力,运用第二类拉格朗日方程建立了系统的刚柔耦合碰撞动力学方程.编制仿真软件进行动力学仿真计算,得到了碰撞力和系统动力学响应,对比分析了不同动力学模型对系统动力学响应的影响.同时研究了碰撞导致的柔性梁横向变形传播的波动特性.     

单层5A06铝合金板高速撞击实验研究

采用非火药驱动二级轻气炮发射球形弹丸,对单层5A06铝合金板进行高速撞击实验研究,从而模拟空间碎片对航天器防护结构的高速撞击作用。实验得到了该铝合金板在不同的速度区间的损伤模式。结果表明,弹丸撞击速度一定时,弹坑深度和弹坑直径均与弹丸直径呈线性关系。当撞击速度在4km/s至5km/s时,靶板上的弹坑深度和弹坑直径随撞击速度的增大而减小,在其它速度范围内,弹坑深度和弹坑直径随撞击速度的增大而增大。通过固定弹丸直径,变化撞击速度,寻找临界撞击速度的方法获得了该铝合金板在弹丸撞击速度为1.0km/s至4.2km/s时的撞击极限曲线,并将实验弹坑深度与由Cour-Palais方程得到的预测弹坑深度进行了比较,实验弹坑深度大于预测值。     

杆式弹对厚壁壳体装药冲击起爆机制模拟分析

为研究高速杆式弹冲击厚壁壳体装药的起爆机制,运用冲击物理显式欧拉型动力学SPEED软件,开展了不同弹径和弹长的钨合金杆式弹与厚壁壳体Comp-B装药相互作用过程的数值模拟,采用升降法获得弹体起爆装药临界着速及装药起爆位置变化。研究结果表明:弹体起爆装药临界着速随弹径增大而显著降低,随弹长增大呈先降低后平缓变化的规律;弹体以临界着速起爆装药时,存在2种装药起爆机制,即弹体贯穿壳体后的宏观剪切起爆和未贯穿壳体的低速冲击起爆,且其机制随弹体着速在临界着速以上继续提高会发生转变,最终均会转变为高速冲击起爆机制;装药起爆位置均发生在炸药壳体交界面后一定距离处,相同机制下此距离随弹体着速提高而减小。     

Crack formation and fracture under repeated tension-impact loads

To study the fracture behaviour under repeated impact loads, a series of tests are conducted by using commercial aluminium as an experimental material. The size and shape of cracks in repeated impact are obtained from fractographic observation. A crack growth model is proposed which is based on the assumption of Irwin type plastic zone. A relation between crack length and number of impacts is obtained which is found to be in good agreement with the experimental results.     

Determination of impact parameters by optical measurement of the impactor displacement

In dynamic materials research, high precision impact displacement, velocity and force measurements are often required. In lower velocity testing apparatus, impact force histories are most often obtained through strain gage, piezoelectric force transducer or accelerometer signals. Velocity and displacement histories are then obtained by integration. Non-contact measurement systems have a number of advantages over these more common mechanical contact methods, and can generally be used at higher impact speeds. In this paper a relatively simple optical technique is presented for recording the impactor displacement history, from which the impact velocity and force histories can be readily obtained for a (quasi-) rigid impactor. The technique is based on the relative displacement of two moiré line gratings: one grating attached to the impacting body and the other serving as stationary reference grating. The technique has proven to be useful for impact speeds of a few m/s to well over 200 m/s. Results of transverse impact experiments on composite laminates are presented.     

Analysis of dynamic stress intensity factors of three-point bend specimen containing crack

A new formula is obtained to calculate dynamic stress intensity factors of the three-point bending specimen containing a single edge crack in this study. Firstly, the weight function for three-point bending specimen containing a single edge crack is derived from a general weight function form and two reference stress intensity factors, the coefficients of the weight function are given. Secondly, the history and distribution of dynamic stresses in uncracked three-point bending specimen are derived based on the vibration theory. Finally, the dynamic stress intensity factors equations for three-pointing specimen with a single edge crack subjected to impact loadings are obtained by the weight function method. The obtained formula is verified by the comparison with the numerical results of the finite element method (FEM). Good agreements have been achieved. The law of dynamic stress intensity factors of the three-point bending specimen under impact loadings varing with crack depths and loading rates is studied.     

基于分形统计强度理论的煤颗粒冲击破碎概率研究

基于分形统计强度理论对煤颗粒的冲击破碎概率进行研究。以Hertz接触假设为基础,得到煤颗粒冲击破碎概率与最大接触压应力之间的函数关系,并结合碰撞动力学理论,建立了冲击破碎概率的分形模型。对不同矿区工作面的煤颗粒进行冲击破碎试验,统计分析表明：分形模型可以对煤颗粒的冲击破碎概率进行很好的描述,冲击破碎概率与冲击速度在对数坐标中为线性关系。通过试验确定分形模型的分形维数和破碎常数,可以得到不同冲击速度下煤颗粒的冲击破碎概率以及煤颗粒全部破碎需要的冲击速度,为冲击破碎效果评价以及冲击速度的确定提供了理论指导。     

THE DYNAMIC BUCKLING OF ELASTIC-PLASTIC COLUMN SUBJECTED TO AXIAL IMPACT BY A RIGID BODY

I. INTRODUCTIONSince the 1960s the investigation on the dynamic buckling of elastic-plastic structures under impactload has been a very active subject of study in solid mechanics. In this respect the research advanceswere summarized and reviewed from di?erent aspects by some famous scholars[1??4]. The column is themost important structural element in practical engineering. So the dynamic buckling of the column hasattracted much more attention of many researchers. Lindberg H.E. carried ou…     

Analysis of dynamic stress intensity factors of three-point bend specimen containing crack

A new formula is obtained to calculate dynamic stress intensity factors of the three-point bending specimen containing a single edge crack in this study. Firstly, the weight function for three-point bending specimen containing a single edge crack is derived from a general weight function form and two reference stress intensity factors, the coefficients of the weight function are given. Secondly, the history and distribution of dynamic stresses in uncracked three-point bending specimen are derived based on the vibration theory. Finally, the dynamic stress intensity factors equations for three-pointing specimen with a single edge crack subjected to impact loadings are obtained by the weight function method. The obtained formula is verified by the comparison with the numerical results of the finite element method (FEM). Good agreements have been achieved. The law of dynamic stress intensity factors of the three-point bending specimen under impact loadings varing with crack depths and loading rates is studied.     

薄膜式锰铜压阻计的动态标定

介绍了以飞片平面撞击标定某新型锰铜压阻计的过程及方法. 标定在Phi 130 mm轻气炮上进行, 采用有机玻璃, Cu和W 3种材料为飞片和靶板材料, 实现不同速度下的 同种材料平面正撞击, 获得0.66$\sim$25.4\,GPa范围的入射压力, 并利用几何修 正和$D$-$u$关系修正两种方法对结果进行了修正, 给出了标定结果以及拟合曲线.     

有限长Timoshenko梁弹性碰撞接触瞬间的动态特性

给出了质点与有限长Timoshenko梁横向弹性碰撞接触问题的半解析解,分析了该碰撞问题在碰撞接触瞬间的动态响应特性：揭示了其中的波传播现象．     

冲击载荷下镁铝合金裂纹动态扩展过程的数值模拟

采用基于黏聚裂纹模型的扩展有限元方法,开展了镁铝合金结构冲击破坏过程的数值模拟研究。通过镁铝合金三点弯曲试样冲击实验,获得了不同子弹撞击速度下试样的冲击破坏模式。在此基础上,建立了实验结构的扩展有限元模型,并采用最大主应力准则,以及含损伤型的本构关系模拟材料的冲击断裂行为。对于裂纹尖端附近区域,采用黏聚裂纹模型模拟裂纹的断裂过程。对子弹速度分别为12.2、15.1、26.3 m/s的3种工况下镁铝合金试样的动态破坏过程进行了数值模拟研究,获得了与实验相一致的断裂模式。计算结果表明,试样以Ⅰ型断裂模式为主,裂纹沿初始预制裂纹方向扩展。当裂纹扩展到一定程度后,在试样韧带区域被撞击端附近,由于应力波及边界效应导致该区域处于复杂应力状态,试样出现复合型断裂模式,裂纹偏离原扩展路径,与本文实验结果相吻合。     

New method for oblique impact dynamics research of a flexible beam with large overall motion considering impact friction force

A flexible beam with large overall rotating motion impacting with a rigid slope is studied in this paper. The tangential friction force caused by the oblique impact is analyzed. The tangential motion of the system is divided into a stick state and a slip state. The contact constraint model and Coulomb friction model are used respectively to deal with the two states. Based on this hybrid mod-eling method, dynamic equations of the system, which include all states (before, during, and after the collision) are obtained. Simulation results of a concrete example are compared with the results obtained from two other models: a nontangential friction model and a modified Coulomb model. Differences in the results from the three models are discussed. The tangential friction force cannot be ignored when an oblique impact occurs. In addition, the results obtained from the model proposed in this paper are more consistent with real movement.     

Experimental investigation of longitudinal wave propagation in an elastic rod with coulomb friction

This paper presents the experimental results obtained from the propagation of a compression stress wave generated by the longitudinal impact of two cylindrical elastic rods. One of these rods is subjected to a uniformly distributed coulomb-friction force. In order to determine the stress-wave shape and the decay rate, the rod is subjected to longitudinal impact for different values of coulomb friction. As the stress wave propagates along the rod, it is measured at strain-gage stations located on the stationary rod.In order to correlate the experimental results, the solution of the modified wave equation with coulomb friction is obtained for the longitudinal impact of two semi-infinite rods.     

强脉冲电磁力驱动的冲击载荷

冲击载荷在材料科学与工程领域具有一定的应用。随着研究的深入, 对冲击速度、冲击能量提出了更高的需求, 是落锤所无法达到的。强脉冲磁场可由脉冲大电流产生, 通过合适的装置可产生强脉冲电磁力, 进而可转换为冲击载荷。通过数值模拟, 给出了强脉冲磁场、电磁力及冲头运动过程的数值模拟结果。采用高速摄像对该压缩冲击装置的运动过程进行记录, 通过对影像数据处理获得了冲击速度及冲击能量, 验证了模拟结果。     

APPROXIMATE FORMULASOF IMPACT FORCE FOR NORMAL IMPACT OF A FINITE ELASTIC BEAM OF ELASTIC FOUNDATION BY A FINITE ROD

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Determination of Dynamic History of Impact Loadings Using Polyvinylidene Fluoride (PVDF) Films

We propose a simple experimental method for determining dynamic history of impact loadings on flexible structures using polyvinylidene fluoride (PVDF) films. The dynamic impact history obtained from the proposed method is verified with impact hammers with inbuilt force sensors. The performance of the proposed method is demonstrated with FEM computations based on the acquired impact history to predict the transient responses of a flexible cantilever beam.     

Impact of a strip of compressible liquid on a barrier

The exact solution of the plane problem of the impact of a finite liquid strip on a rigid barrier is obtained in the linearized formulation. The velocity components, the pressure and other elements of the flow are determined by means of a velocity potential that satisfies a two-dimensional wave equation. The final expressions for them are given in terms of elementary functions that clearly reflect the wave nature of the motion. The exact solution has been thoroughly analyzed in numerous particular cases. It is shown directly that in the limit the solution of the wave problem tends to the solution of the analogous problem of the impact of an incompressible strip obtained in [1]. A logarithmic singularity of the velocity parallel to the barrier in the corner of the strip is identified. A one-dimensional model of the motion, which describes the behavior of the compressible liquid in a thin layer on impact and makes it possible to obtain a simple solution averaging the exact wave solution, is proposed. Inefficient series solutions are refined and certain numerical data on the impact characteristics for a semi-infinite compressible liquid strip, previously considered in [2–4] in connection with the study of the earthquake resistance of a dam retaining water in a semi-infinite basin, are improved. The solution obtained can be used to estimate the forces involved in the collision of solids and liquids. It would appear to be useful for developing correct and reliable numerical methods of solving the nonlinear problems of fluid impact on solids often examined in the literature [5].Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 6, pp. 138–145, November–December, 1990.The results were obtained by the author under the scientific supervision of B. M. Malyshev (deceased).