Analysis of Plasticity-induced Crack Closure of Fatigue Crack Interacting with Microstructure.

Abstract

The propagation behavior of small fatigue cracks was numerically simulated to evaluate the development of crack closure with crack growth. The effect of the interaction between crack-tip slip band and grain boundaries on plasticity-induced crack closure was analyzed under plane stress condition. The crack and slip bands were assumed to be coplanar. When the slip band crosses the grain boundary, the larger resistance of slip motion in the next grain induces a reduction in the crack opening displacement range and an increase in the crack opening stress. The distribution of the residual stretch was geometrically similar to the change of the maximum crack tip opening displacement with crack extension. The relation between the crack opening displacement range and the effective stress intensity range was nearly unique. When the slip band extends over many grains, the irregularity of crack opening displacement range and crack opening stress diminishes. The crack propagation life can be calculated as a function of the crack length and the stress level on the basis of the crack-tip opening displacement range.