裂尖超钝化:实验、理论与数值模拟

本文报道了在改性聚丙烯裂尖平面应变段发生超钝化的实验发现。利用环向冷拉模型,可说明裂尖超钝化的形成取决于冷拉传播速率与加载率之比。裂尖超钝化可使材料韧性,尤其是冲击韧性的改善,达到一个新的水平。本文在超弹性-粘塑性各向异性损伤的有限变形本构模型下进行了详尽的数值计算。模拟结果成功地再现了裂尖超钝化的基本特征。     

试验确定自增强圆筒的表面裂纹K1因子和疲劳扩展规律

本文提供了一种可以进行自增强处理的圆筒试样,通过实验用柔度法确定了该试样的表面裂纹的应力强度因子,介绍了含表面裂纹试样的柔度测试技术,导出了柔度与表面裂纹尖端前缘各点的应力强度因子的关系式,该式可作为各种含表面裂纹试样柔度法测表面裂纹 K_1因子的参考,本文还测定了不同自增强程度下,自增强圆筒的表面裂纹疲劳扩展规律。     

压电材料平面应力状态的直线裂纹问题一般解

研究了含直线裂纹系的压电材料平面应力问题单个裂纹和双裂纹问题的封闭解答表明，在裂纹尖端，应力、电场强度和电位移有１／２阶的奇异性并与前人结果比较了产生电场奇异性的物理因素     

非均匀弹性材料中反平面的运动裂纹

用解析方法研究了非均匀弹性材料中反平面运动裂纹问题。首先采用余弦变换求解非均匀材料的基本方程，然后根据混合边值条件建立裂纹运动的对偶积分方程，再把对偶积分方程化为第二类Fredholm积分方程。给出了数值算例，计算结果表明材料的非均匀性对动应力强度因子有较大的影响。     

条形平板中裂纹识别的遗传算法

研究条形平板中平行于上下边界的单一裂纹的识别问题。给出了当一声波入射这一条形平板时，裂纹参数与反射、透射系数之间的关系式，并应用遗传算法对裂纹进行了定量识别。计算结果表明本文给出的方法具有较好的识别精度。     

T-STRESS IN PIEZOELECTRIC SOLID

The non-singular and bounded terms for stresses near the crack tip were investigated. The crack problem in a transversely isotropic piezoelectric solid for the plane problem was dealt with. The principle of superposition and the Plemelj formulation were introduced. The non-singular terms are given by solving Rieman-Hilbert problem. It is shown that the non-singular terms are influenced by the elastic and electric constants.     

Influence of cyclic loading on crack growth kinetics in a viscoelastic orthotropic plate made of a composite material

The kinetics of crack growth in a viscoelastic orthotropic plate made of a composite material is analyzed. The external load is the superposition of a cyclic load and a constant tensile load. The level of the tensile load is assumed to exceed the amplitude of the cyclic load. The kinetic curves are compared with the constant tension curves. The effect of the cyclic component is studied.Translated from Prikladnaya Mekhanika, Vol. 40, No. 9, pp. 116–122, September 2004.     

INTERACTION OF ELECTRIC CHARGES IN A PIEZOELECTRIC WITH RIGID EXTERNAL CRACKS

IntroductionRecently much attention has been paid to Green’s functions[1 -7]for anisotropic mediabecause of their important applications in boundary element methods used widely inengineering analysis. Generally speaking, it is relatively easy to obtain G…     

Invariant Integrals in the Problem of a Crack on the Interface between Two Media

The equilibrium problem for an elastic body containing a crack on the interface between two media is considered. It is proved that there exist invariant (independent of the integration surface) integrals in this problem. The existence of invariant integrals is also established in the problem of a contact between an elastic body and a rigid stamp. Nonlinear boundary conditions of mutual non-penetration are prescribed on the contact boundaries. The physical meaning of invariant integrals is established.__________Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 46, No. 5, pp. 123–137, September–October, 2005.     

Experimental and numerical investigation of concrete properties effects on fracture toughness under complex loading

Abstract

This article is presenting the common experimental specimen for determining the fracture toughness of the first pure mode and second pure mode. The Notched beam is chosen from a presented common specimen in the form of three-point flexure beam and four-point flexure beam that were built in the concrete laboratory. For prevention of cracks growth, a critical load of first pure mode and the second pure mode of each specimen computed. Obtained results are used for computing the fracture toughness. For the purpose of investigating the effective fracture parameters in the suggested specimen, finite element analysis on the mentioned geometry is performed. Obtained results show that different parameters are effective on the fracture toughness including crack length, cement percentage, water and the thickness of biggest used aggregate in the sand. Also with changing each of these parameters, the fracture mechanic properties are changed. Each of these effects is examined separately in this article and the conclusions presented in tables and figures.

Communicated by Dumitru Caruntu.