Transient response of a finite crack in an orthotropic strip under the in-plane shear impact

The transient response of a central crack in an orthotropic strip under the in-plane shear impact loading is studied by using the dual integral equation method proposed by Copson and Sih. The general formula for the shear stress intensity factor near the crack tip is derived. Numerical results of with in various cases are obtained by solving the second kind Fredholm integral equation and by performing the inverse Laplace transform.     

三相介质饱和土自由场中爆炸波的传播规律

饱和土是由固体上颗粒、水和少量封闭的空气组成的三相介质。介绍了爆炸波作用下三相介质饱和土有限元基本方程的建立过程，推导了引进人工粘性项的动力有限元方程，得到在饱和土自由场中爆炸波的传播规律；不同空气含量饱和土中爆炸波随深度的衰减规律。文中还给出了有限元与有限差分间断分解结果的比较，以说明本文理论方法的有效性。     

An optimal control approach to the analysis of inelastic structures under cyclic loading

Optimal control theory is used to study the asymptotic behaviour of elasto-viscoplastic structures under cyclic loading. With this approach, the asymptotic state is found as the solution of a minimization problem. General properties of this method are established. A simple thermomechanical problem is studied to illustrate and validate this approach. An interest of the proposed method lies in its capacity to handle other nonlinearities than plasticity. To illustrate this point, the approach is extended to the coupled viscoplasticity/frictionless contact problem. Some numerical results are given for an elasto-viscoplastic half-plane under cyclic frictionless indentation.     

复杂载荷作用下圆柱壳的弹塑性动力屈曲研究

对复杂载荷作用下圆柱壳的弹塑性动力屈曲问题进行了研究。基于Hamilton变分原理导出圆柱壳的运动方程 ,本构关系采用增量理论 ,借助增量数值算法求解动力方程组。结果表明 ,均匀径向外压对圆柱壳的轴向冲击的过程或冲击性态有较大的影响 ,并讨论了径向压力与轴向冲击载荷的幅值对结构临界动力屈曲载荷和临界动力失效载荷的影响。     

基于概率密度演化方法的随机结构可靠度分析

随机结构反应的概率密度演化方法能够给出随机荷载作用下随机结构反应的概率密度函数。在此基础上，根据给定的正常使用位移限值要求，直接进行积分给出了随机结构的正常使用可靠度及其失效概率。在实例分析中，与一类情况下的精确解答及基于反应正态分布假定的二阶矩方法分析结果进行了比较。研究表明：基于密度演化方法的随机结构可靠度分析具有很高的精度，而二阶矩方法的可靠度分析结果则往往具有一定的偏差，在失效概率较低时可能给出虚假的失效概率。     

Plastic-strain evolution for cyclic loading based on the equations of the field theory of defects

A relation governing the plastic-strain evolution under applied stresses is obtained within the field theory of defects to analyze the specific features of deformation under sign-varying cyclic loading. The effect of the applied stress amplitude, loading frequency, and cycle skewness on the deformation process under uniaxial loading conditions is studied. Specific features of the plastic-strain evolution in a stable deformation process are considered, and the time to failure of the system in an unstable process is determined. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 47, No. 3, pp. 112–118, May–June, 2006.     

Interlaminar hygrothermal stresses in laminated plates

Within the elasticity formulation the most general displacement field for hygrothermal problems of long laminated composite plates is presented. The equivalent single-layer theories are then employed to determine the global deformation parameters appearing in the displacement fields of general cross-ply, symmetric, and antisymmetric angle-ply laminates under thermal and hygroscopic loadings. Reddy’s layerwise theory is subsequently used to determine the local deformation parameters of various displacement fields. An elasticity solution is also developed in order to validate the efficiency and accuracy of the layerwise theory in predicting the interlaminar normal and shear stress distributions. Finally, various numerical results are presented for edge-effect problems of several cross-ply, symmetric, and antisymmetric angle-ply laminates subjected to uniform hygrothermal loads. All results indicate high stress gradients of interlaminar normal and shear stresses near the edges of laminates.     

坚硬岩石在强冲击荷载作用近区的性状研究

根据坚硬岩石的性质,利用力学模型分析了在冲击荷载作用下的岩石破坏过程,经由弹性状态向内摩擦状态的转变,最终达到流体力学状态。通过对内摩擦状态的分析,认为在强冲击荷载区域的变形近似为一维变形状态。冲击荷载作用在岩石中产生的应力波可以看作类似于冲击波的短波,在波阵面附近的某个狭窄区域内将发生参数的急剧变化。根据近区变形状态与质量守恒导出了侵彻近区的速度场表达式。根据短波的研究,给出了近区应力波的衰减规律。     

大长细比弹体斜侵彻混凝土靶的动力学响应

基于刚塑性自由梁在横向冲击载荷下的动力学响应研究方法,结合空腔膨胀理论给出的弹体载荷分析,给出了弹体作为自由梁在塑性铰出现之前的响应行为,得到了梁内任一截面在横向载荷下剪力和弯矩分布规律以及轴向载荷下的轴力分布规律。计算结果表明,大长细比结构弹体的危险截面在承受较大轴向惯性压力载荷后,对由非正侵彻导致的横向载荷极为敏感。最后基于压弯联合作用载荷分析,给出了动能弹设计的抗弯极限壁厚要求。     

Development of the large increment method for elastic perfectly plastic analysis of plane frame structures under monotonic loading

The displacement-based finite element method dominates current practice for material nonlinear analysis of structures. However, there are several characteristics that may limit the effectiveness of this approach. In particular, for elastoplastic analysis, the displacement method relies upon a step-by-step incremental approach stemming from flow theory and also requires significant mesh refinement to resolve behavior in plastic zones. This leads to computational inefficiencies that, in turn, encourage the reconsideration of force-based approaches for elastoplastic problems.One of these force algorithms that has been recently developed is the large increment method. The main advantage of the flexibility-based large increment method (LIM) over the displacement method is that it separates the global equilibrium and compatibility equations from the local constitutive relations. Consequently, LIM can reach the solution in one large increment or in a few large steps, thus, avoiding the development of cumulative errors. This paper discusses the extension of the large increment methodology for the nonlinear analysis of plane frame structures controlled by an elastic, perfectly plastic material model. The discussion focuses on the power of LIM to handle these nonlinear problems, especially when plastic hinges form in the frame and ultimately as the structure approaches the collapse stage. Illustrative planar frame examples are presented and the results are compared with those obtained from a standard displacement method.