Quantitative prediction of environmentally assisted cracking based on a theoretical model and computer simulation

Abstract

This paper describes a comparison between quantitative prediction of environmentally assisted cracking by theoretical modelling and that by finite element method (FEM) computer simulation in terms of film rupture strain at a crack tip. The crack growth rate was simulated on a 1T-CT (one inch-thick compact tension) specimen, which met American Society for Testing and Materials (ASTM) E813, under the slow strain rate test (SSRT) condition by an FEM simulation code, Finite Element Environmentally Assisted Cracking Simulator (FEEACS) for film rupture strain ε f=10 −2, 10 −3, and 10 −4. As the theoretical model includes unknown parameters which cannot be determined theoretically, they were evaluated by chi-square fitting method so that the crack growth rates of the theoretical model fit those of FEM computer simulation. In this method the film rupture strain ε f and the position r where crack tip strain is defined are evaluated. The calculation was carried out for two cases. One is for irradiation-assisted stress corrosion cracking (IASCC), and the other is without irradiation. Parameters for irradiated material are the yield strength σ y=980 MN/m 3/2, the slope of the current decay m=0.5, and the strain hardening exponent n=3. In the irradiated case the crack growth rates obtained by the theory agree well with those obtained by FEM using the relation ε f Theory=3.1 ε f FEM, while they do not agree in the case without irradiation.