The Development of the System that Analyzes Surface Cracks by the Influence Function Method

本文利用影响函数法，在工程工作站上开发了一套有效的三维表面裂纹应力强度因子K的计算系统，该系统可以方便地计算三维表面裂纹在裂纹表面受任意分布的应力作用下的应力强度因子K。通过对平板半椭圆形表面裂纹、平板四分之一椭圆形表面裂纹、圆棒半椭圆表面裂纹、空心圆筒内表面半椭圆轴向裂纹、空心圆筒环向表面裂纹、法兰式接管拐角半椭圆表面裂纹等构件的一系列有限元分析，得到了影响系数Kij的数据库。此外，为了方便地计算K值和表面裂纹在复杂应力场中的扩展，通过将KIJ数据库存储在计算机磁盘中，在PC机上开发了疲劳裂纹扩展模拟系统。结果表明，所开发的影响函数方法和模拟系统对估算表面裂纹在残馀应力、热应力等复杂应力作用下的应力强度因子K和表面裂纹扩展是非常有用的，并表明该模拟系统对评估含裂纹构件的剩余寿命、泄漏和/或失效概率是有用的。该系统给出的结果已在ASME和JSME的一些标准中得到应用。

In this study an effective evaluating system, by which the stress intensity factor, K,can be calculated easily for the 3-dimensional surface cracks subjected to arbitrarily distributed surface stresses on the cracked surface, was developed on the engineering work-station (EWS) by using the influence function method. The data base of the influence coefficients, Kij, has been obtained by a series of finite element analysis for various cracked members, such as, semi elliptical surface crack in a flat plate, quarter-elliptical surface crack in a flat plate, semi elliptical surface crack in a round bar, semi elliptical axial crack on the inner surface of hollow cylinder, circumferential surface crack in a hollow cylinder, semi elliptical surface crack in a flange type nozzle corner, and so on. Further more, in order to evaluate the K-value and the surface crack propagating in a complex stress field easily, a simulation system of fatigue crack propagation was developed on a personal computer by storing the Kij data base in the disc of the computer. It has been shown that the developed influence function method and the simulation systems are very useful to evaluate the stress intensity factor, K,and the surface crack propagating, for the surface cracks subjected to such complicated stress as residual stress, thermal stress, and it has been shown that the simulation system is useful to assess the residual life of the cracked structural components, and leak and/or failure probabilities. The results given by the system has been used in some standard of ASME and JSME.