Assessment of Integrity for Three Dimensional Cracked Members by an Influence Function Method

本文提出了一种用影响函数法计算任意分布表面应力作用下表面裂纹的应力强度因子K的方法。为了使上述方法有效，必须事先通过三维有限元分析计算一系列的影响系数K_&lt；ij&gt；在本研究中，作者获得了K&lt；ij&gt；对于(1)平板中的半椭圆表面裂纹，(2)平板中的四分之一椭圆表面裂纹，(3)圆棒中的半椭圆表面裂纹，(4)管道中的半椭圆表面裂纹，已将数据库存储在个人计算机的软盘上，并开发了表面裂纹在任意分布的应力(如残余应力、热应力和/或缺口根部应力)下的K计算软件系统。此外，还开发了表面裂纹构件疲劳寿命的模拟程序。该算法基于巴黎定律的积分，可以用影响函数法计算应力强度因子的瞬时范围&lt；通过考虑表面裂纹尺寸和形状的随机性以及控制疲劳裂纹扩展速率的材料参数，采用概率方法估算疲劳寿命。

An influence function method has been developed by which the stress intensity factors, K, of surface cracks subjected to arbitrarily distributed surface stresses can be calculated easily by a personal computer. In order for the abouvemethod to be effective, a series of influence coefficients, K_<ij>, have to be calculated previously by three dimensional finite element analysis. In this study the author has obtained a data base of K_<ij> for cracks such as (1) semielliptical surface crack in flat plate(2) quarter-elliptical surface crack in a flat plate(3) semielliptical surface crack in a round bar(4) semielliptical surface crack in a pipe.The data base has been stored on a floppy disc of a personal computer, and a software system has been developed to calculate K for surface cracks under arbitrarily distributed stresses such as residual stress, thermal stress, and/or stress at the notch root.Further, a simulation program to estimate the fatigue life of the surface-cracked members has been developed. The algorithm is based on the integration of the Paris' law, in which the instantaneous range of the stress intensity factor, <delta>K, can be calculated by the influence function method. A probabilistic approach has been adopted in estimating the fatigue lives by taking account of the stochastic nature about the size and shape of the surface crack and material parameters dominating the rate of fatigue crack propagation.