On buckling of cantilever rectangular plates under symmetrical edge loading

The stability of cantilever rectangular plates under the symmetrical edge loading will be studied in this paper by lite varialional calculus. We are going to find out the minimum critical loading for cantilever rectangular plates subjected to various edge loadings symmetrically on a pair of opposite free edges. We’ll discuss the least critical loadings when the buckling of rectangular plates acted on bv a pair of concentrated forces, uniformly distributed loads, locally uniform distributed loads, distributed loads in the form of triangle and a pair of concentrated couples occur respectively.     

Ratchetting under tension–torsion loadings: experiments and modelling

This paper is concerned with the mechanical behaviour of 316 austenitic stainless steel under multiaxial loadings and particular attention is paid to ratchetting under tension–torsion non-proportional loadings. First, a series of uniaxial tests and biaxial tests has been carried out in order to calibrate five different cyclic plasticity models based on an isotropic hardening rule and a non-linear kinematic hardening rule. It is shown that this class of models gives quite good agreement between the experimental and numerical results. Second, another series of ratchetting tests has been carried out under tension–torsion loadings in order to test the prediction capacities of the previous models. It is shown that whereas the models have been calibrated with similar loading paths, four of the five selected models give poor predictions.     

城市建设地质极限问题分析

从地质学与力学的角度看 ,城市的不断扩展等同于城市建设对地质环境施加规模和强度不断增大的荷载 ,而城市下伏岩土体承受荷载的能力是有限的。本文由此侧面切入城市地质环境与地质灾害问题。注重潜在的、缓慢的城市地质作用。     

Strain-rate effect on initial crush stress of irregular honeycomb under dynamic loading and its deformation mechanism

The seemingly contradictory understandings of the initial crush stress of cellular materials under dynamic loadings exist in the literature, and a comprehensive analysis of this issue is carried out with using direct information of local stress and strain. Local stress/strain calculation methods are applied to determine the initial crush stresses and the strain rates at initial crush from a cell-based finite element model of irregular honeycomb under dynamic loadings. The initial crush stress under constant-velocity compression is identical to the quasi-static one, but less than the one under direct impact, i.e. the initial crush stresses under different dynamic loadings could be very different even though there is no strain-rate effect of matrix material. A power-law relation between the initial crush stress and the strain rate is explored to describe the strain-rate effect on the initial crush stress of irregular honeycomb when the local strain rate exceeds a critical value, below which there is no strain-rate effect of irregular honeycomb. Deformation mechanisms of the initial crush behavior under dynamic loadings are also explored. The deformation modes of the initial crush region in the front of plastic compaction wave are different under different dynamic loadings.     

爆破地震效应若干问题的探讨

对爆破地震效应的若干问题进行了研究，提出了一些新的观点。内容包括:微差爆破问题；焊破地震动转动分量的推算；地震荷载的计算；基于多维反应谱方法的内力组合。     

Nonlinear Combination of Load Processes

An important problem in structural reliability is the combination of time-variant stochastic loadings. The failure probability in the case of nonlinear combinations of stochastic processes can be approximated by the mean crossing rates of time-variant loadings out of the safe domain of structural states. Except for linearly bounded safe domains, these rates are difficult to compute; therefore, the quality of veirious linearization points is investigated. Comparisons are made of some examples showing that for time-variant problems the Hasofer-Lind point is often suboptimal. A linearization at the point of maximum local outcrossing density might generally produce non-degenerate, sufficiently accurate results.     

Micromechanical model of the high temperature cyclic behavior of 9–12%Cr martensitic steels

9–12%Cr quenched and tempered martensitic steels are known to soften under cyclic loadings at high temperature. The present article proposes a model based on physical mechanisms described at the scale of slip systems. This model describes explicitly the microstructural recovery (corresponding to a decrease of the dislocation density and subgrain coarsening) observed experimentally. The scale transition is carried out in the framework of self-consistent homogenization schemes. The model assumptions and its physical basis are explicitly discussed. The parameters are identified on a very limited amount of experimental data. The model turns out to give very good predictions and extrapolations for the cyclic softening effect observed in uniaxial tension–compression loadings for strain ranges larger than 0.3%. Stress–relaxation and creep behavior can also be simulated for high stresses. In addition the cyclic softening effect is reproduced for multiaxial tension–torsion loadings.     

动载下复合材料基体裂纹与夹杂相互作用的数值模拟

采用ABAQUS软件及粘聚裂纹模型对动态拉伸载荷下复合材料中垂直于基体-夹杂界面的基体裂纹与夹杂的相互作用进行了数值模拟.结果表明:在给定的界面强度下,当加载率(或应变率)低于某一临界值(临界应变率)时裂纹将沿基体-夹杂界面扩展,当高于该临界值时裂纹可以穿过界面在夹杂中扩展.此外,随着界面强度的提高,临界应变率降低;当界面强度超过一定值后,裂纹扩展方向将不受外部载荷影响,裂纹将沿自相似方向扩展;当界面强度低于该临界值时,裂纹将沿界面扩展;并且临界应变率随夹杂尺寸的增大而降低,即小夹杂更难于破坏.上述结果可为前人的混凝土动态实验数据提供合理的细观理论解释.     

Analytical solution of bending-compression column using different tension-compression modulus

Based on elastic theory of different tension-compression modulus, the analyttcal solution was deduced for bending-compression column subject to combined loadings by the flowing coordinate systemaxis, stress, strain andand phased integration methoddisplacement were developed,The formulations for the neutralthe finite element program was compiled for calculation, and the comparison between the result of finite element and analytical solution were given too. Finally, compare and analyze the result of different modulus and the same modulus, obtain the difference of two theories in result, and propose the reasonable suggestion for the calculation of this structure.     

Singular loadings in elasticity problems and singular solutions of the corresponding integral equations

The method of singular integral equations is an efficient method for the formulation and numerical solution of plane and antiplane, static and dynamic, isotropic and anisotropic elasticity problems. Here we consider three cases of singular loadings of the elastic medium: by a force, by a moment and by a loading distribution with a simple pole. These loadings cause corresponding singularities in the right-hand side function and in the unknown function of the integral equation. A method for the numerical solution of the singular integral equation under the above singular loadings is proposed and the validity of this equation at the singular points is investigated.     

The stability of growth of a through-wall circumferential crack in a pipe subject to combined bending and tensile loadings

The stability of growth of a through-wall circumferential crack in a pipe is analysed for the case where the material has a high crack growth resistance, the analysis being based on the tearing modulus procedure. Rotations and lateral displacements are applied at the ends of the pipe, and this allows the combined effects of bending and tensile loadings on the stability of crack growth to be assessed. The general conclusion is that tensile loadings can have an adverse effect on crack stability, in accord with the conclusion reached in the author's earlier studies of plane strain crack growth in a beam. The stability results are compared with those obtained by Tada, Paris and Gamble, who allowed the tensile loadings to affect the position of the neutral axis, but did not consider instability in terms of the deformations produced by these loadings.     

密闭空间内不同炸药爆源的能量输出结构及与目标作用研究

对钝化黑索今（RDX）、含铝炸药（RDX/Al）、一次引爆型燃料空气炸药（SEFAE）在爆炸容器和爆炸水池中爆炸波的能量输出结构进行了实验研究。用TVD格式数值模拟了带平板封头爆炸容器的内部爆炸载荷的分布规律。并对在不同爆炸载荷作用下,容器典型位置的应变进行了测量。结果表明:（1）密闭空间内,RDX/Al（90/10）和SEFAE体系具有后燃效应;（2）在本实验条件下,平板封头与罐体结合处的载荷最大;（3）SEFAE产生的爆炸载荷对容器的作用最小,钝化RDX和RDX/Al（90/10）两者相当。3种炸药产生应变的频谱相似,强度略有差别;（4）在本实验的条件下,爆炸载荷的结构不是应变增长的主要原因。     

Nonlinear stability and dynamics of composite skew plates under nonuniform loadings using differential quadrature method

The buckling, postbuckling and postbuckled vibration behaviour of composite skew plates subjected to nonuniform inplane loadings are presented here. The skew plate is modelled using first order shear deformation theory accounting for von-Kármán geometric nonlinearity and initial geometric imperfections. The different types of nonuniform loads that have been considered in this study are concentrated load, partial load and parabolic load. The explicit analytical expressions for prebuckling stress distributions within composite skew plate subjected to three different types of nonuniform inplane loadings are developed by solving plane elasticity problem using Airy's stress function approach. It is observed that the inplane normal stress distributions within the skew plate due to above nonuniform loadings do not become uniform even at mid-section. The generalized differential quadrature (GDQ) method is used to solve the nonlinear governing partial differential equations. It is observed that the postbuckled load carrying capacity of skew plate under concentrated loading is the lowest compared to other nonuniform and uniform loadings.     

Optical response and yield behavior of a polyester model material

A mixture of flexible and rigid polyester resins is one of the materials that has been used in the past to model elasto-plastic prototype behavior. As a result of recent curtailments in plastic production, one of the constituents of the mixture is no longer available. A different flexible resin of the same family is available, however, and has been shown in this program to be suitable for optical-model studies involving deformations into the plastic range of material response. In this paper, complete mechanical and optical properties for the new model material are presented for both uniaxial tensile and compressive loadings. Results from a series of thin-walled cylinder tests under internal-pressure loadings are also presented which provide some information on the optical and yield characteristics of the polyester model material under a biaxial state of stress. Results of the study indicate that stress-strain curves for the material can be modified significantly by changing the mixture ratio or the test temperature. Optical data from the study indicate that the fringe order in the material is a function of the instantaneous principal-strain difference. Data from the uniaxial tension and compression tests, together with limited data from the cylinder tests, indicate that the polyester material may follow a modified von Mises yield criterion which accommodates differences in tensile and compressive yield strengths of a material.     

Shearing properties of sand under a repeated loading representing the ground pressure distribution of a tracked vehicle

This paper deals with experiments concerning the shearing properties of sand under repeated loading simulating the ground pressure distribution of a tracked vehicle. Shearing tests were carried out in sand by using a direct shear apparatus. It was confirmed that the shear strength of sand under repeated loading decreases with an increase in the number of loadings. This influences the soil thrust exerted by a highspeed tracked vehicle.     

Localisation de la déformation sous sollicitations lentes : une approche dynamique

For materials exhibiting a non-linear behaviour (instantaneous elasticity and viscid non-linearities), strain-localization is associated with the occurrence of dynamic effects, even at slow loadings. A criterion is proposed for testing the relevance of the usual equilibrium hypothesis associated with slow loadings; at its fulfilment, the boundary problem is treated as dynamic, leading, by combination of inertia and viscosity terms, to localization. A 1D example of this approach is eventually given.     

泊松方程中域积分化为边界积分的方法

本文讨论了二维和三维泊松方程中域积分化为边界积分的方法。对于形如x~ig_x(y,z)、y~ig_x(x,z)和z~ig_z(x,y)的荷载给出了域积分转化为边界积分的正确公式。而对于复杂荷载,利用泰勒展开将域积分近似地转化为边界积分并给出了误差估计。计算结果表明利用本文方法可大大节省计算时间。因此,本文方法是一种十分有效的方法。     

A new technique for large deflection analysis of non-prismatic cantilever beams

This paper studies the very large deflection behavior of prismatic and non-prismatic cantilever beams subjected to various types of loadings. The formulation is based on representing the angle of rotation of the beam by a polynomial on the position variable along the deflected beam axis. The coefficients of the polynomial are obtained by minimizing the integral of the residual error of the governing differential equation and by applying the beam’s boundary conditions. Several numerical examples are presented covering prismatic and non-prismatic cantilever beams subjected to uniform, non-uniform distributed loads and tip concentrated loadings in vertical and horizontal directions. The loads considered in this study are restricted to the non-follower type loads. Cases with different loadings and geometries are compared with MSC/NASTRAN computer package. However, for some very large deflection case, the MSC/NASTRAN failed to predict the deflected shape due to divergence problems.     

高孔隙率闭孔泡沫铝的低应变率压缩行为

通过落锤冲击实验研究高孔隙率闭孔泡沫铝的动态压缩性能及抗低速冲击特性, 同时通过高速摄影仪观察试件的动态压缩行为, 并记录落锤冲击速度的衰减过程. 结果表明, 高孔隙率闭孔泡沫铝的抗冲击缓冲效果明显, 且在低速冲击条件下其变形特征与准静态变形类似. 采用有限元方法分析了落锤和泡沫中应力的分布特点以及表面摩擦系数对应力分布的影响. 由于摩擦力阻碍了接触面处泡沫的横向位移, 致使其压缩外形呈``鼓形'; 在低速冲击时, 应力在泡沫铝试件内部的传播周期远小于冲击的缓冲时间, 应力波现象并不明显, 应力的变化与准静态压缩时相似. 在考虑接触面上摩擦力的基础上, 通过第2类Lagrange方程建立了落锤-泡沫材料的碰撞解析模型, 将预测的落锤冲击速度的衰减过程分别与实验和有限元结果进行比较, 取得了较为一致的结论, 并进一步讨论了不同冲击速度和材料参数对冲击过程的影响.