Local elastodynamic stresses in the unit cell of a woven fabric composite

Summary A theoretical study of the local elastodynamic stresses of woven fabric composites under dynamic loadings is presented in this article. The analysis focuses on the unit cell of an orthogonal woven fabric composite, which is composed of two sets of mutually orthogonal yarns of either the same fiber (nonhybrid fabric) or different fibers (hybrid fabric) in a matrix material. Using the mosaic model for simplifying woven fabric composites and a shear lag approach to account for the inter-yarn deformation, a one-dimensional analysis has been developed to predict the local elastodynamic and elastostatic behavior. The initial and boundary value problems are formulated and then solved using Laplace transforms. Closed form solutions of the dynamic displacements and stresses in each yarn and the bond shearing stresses at the interfaces between adjacent yarns are obtained in the time domain for any type of in-plane impact loadings. When time tends to infinity, the dynamic solutions approach to their corresponding static solutions, which are also developed in this article. Solutions of certain special cases are identical to those reported in the literature. Lastly, the dynamic stresses and bond shearing stresses of plain weave composites subjected to step uniform impacts are presented and discussed as an example of the general analytical model. Received 3 May 1999; accepted for publication 22 September 1999     

耐热梯度功能材料的热应力研究进展

介绍了梯度功能材料的概念和开发背景：回顾了近些年来在梯度功能材料热应力研究方面所取得的研究成果,并对梯度功能材料的发展趋势作一展望．着重论述了梯度功能材料在热应力分析领域的研究现状及其应用前景     

A Model of Arterial Adaptation to Alterations in Blood Flow

Mechanisms of arterial adaptation to changes in blood flow rates were tested by comparing the predictions of a proposed theoretical model with available experimental data. The artery was modeled as an elastic membrane made of a nonlinear, incompressible, elastic material. Stimulation of the vascular smooth muscle was modeled through the generation of an active component of circumferential stress. The muscular tone was modulated by flow-induced shear stress sensed by the arterial endothelium, and is responsible for the vasomotor adjustment of the deformed arterial diameter in response to changes in blood flow. This study addresses the hypothesis that the synthetic and proliferative activity of smooth muscle cells, leading to a change in arterial dimensions, is shear stress dependent and is associated with changes in the contractile state of the smooth muscle cells and changes in the circumferential wall stress. Remodeling to a step change in flow was formulated as an initial-value problem for a system of first order autonomous differential equations for the evolution of muscular tone and evolution of arterial geometry. The governing equations were solved numerically for model parameters identified from experimental data available in the literature. The model predictions for the time variation of the geometrical dimensions and their asymptotic values were found to be in qualitative agreement with available experimental data. Experiments for validating the introduced hypotheses and further generalizations of the model were discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

疲劳寿命估算的能量法及其实验研究

根据疲劳损伤滞后能等效原理,导出了缺口件与光滑件的当量应力关系,通过Ｎｅｕｂｅｒ公式和饱和应力应变关系,可确定当量应力取值;采用定量方程随机化方程,建立了γ－ｐ－ε－Ｎ曲线（置信度－可靠度－应变－寿命曲线）公式及其实验测试方式;根据疲劳累积损伤理论和γ－ｐ－ε－Ｎ曲线公式,得到了随机载荷谱作用下构件疲劳寿命估算公式;最后,实验验证了复杂实测载荷谱作用下,ＬＹ１２ＣＺ铝合金含孔试样的疲劳寿命估算结果     

Effect of microstructure on the hardening and softening behaviors of polycrystalline shape memory alloys Part II: Numerical simulation under axisymmetrical loading

Based on the microstructure-based constitutive model established in Part I, a detailed numerical investigation on the role of each microstructure parameter in the kinematical and kinetic evolution of polycrystalline SMA under axisymmetrical tension loading is performed. Some macroscopic constitutive features of stress-induced martensite transformation are discussed. The subject supported by the Research Grant Committee (RGC) of Hong Kong SAR, the National Natural Science Foundation of China and the Provincial Natural Science Foundation of Jiangxi Province of China     

Experimental study on crack curving propagation in bending beams under impulsive load

Dynamic fracture behaviour of crack curving in bent beams has been investigated. In order to understand the propagation mechanism of such cracks under impact, an experimental method is used that combines dynamic photoelasticity with dynamic caustics to study the interaction of the flexural waves and the crack. From the state change of the transient stresses in polymer specimen, the curving fracture in the impulsively loaded beams is analyzed. The dynamic responses of crack tips are evaluated by the stress intensity factors for the cracks running in varying curvature paths under bending stress wave. The project supported by the National Natural Science Foundation of China and the Scientific Commission of Yunnan Province of China     

抗压桩与抗拔桩侧阻的研究

对抗压桩和抗拔桩的桩侧摩阻力进行了理论探讨 ,从定量上考虑了桩周土的剪胀性及主应力方向旋转对侧阻的影响 ,得到了相应的影响系数和侧阻的预测公式.     

钢构件应力集中区低周疲劳分析及实验研究

针对两个具有应力集中区的特定钢构件的低周疲劳问题进行理论分析和实验研究。文中提出了一套低周疲劳分析的相关近似方法 :由材料静力参数估算其疲劳参数 ,并利用实验数据加以修正 ,获得了循环应力 -应变曲线和应变 -疲劳寿命曲线 ;进而把非线性有限元法和局部应力应变分析结合在一起计算疲劳寿命。理论结果和实验结果作了比较 ,从而证明本文提出的分析方法是行之有效的。     

参数激励的幅值不是很小时Mathieu方程的一种解法

用改进的变形参数法求得了激励的幅值不是小量时Mathieu方程的周期解及过渡曲线。     

材料交界面上连续应力分析的改进拉氏乘子法

引进材料界面的节理单元,以其刚度参数为罚参数,利用代表界面接触应力的拉氏乘子,通过迭代求解得到界面上的应力,为计算粘结在一起的不同材料交界面上的应力提供了一种非常有效的方法。