Evaluation of Fatigue Strength of Cracked Components Based on Analysis of Plasticity-Induced Crack Closure.

Abstract

The propagation behavior of fatigue cracks emanating from pre-cracks was numerically simulated to evaluate the development of crack closure with crack growth. Plasticity-induced crack closure was analyzed for two dimensional through cracks and penny-shaped cracks in plane stress, plane strain and Tresca's yield condition. The plastic constraint factor of penny-shaped cracks in Tresca's yield condition decreases with increasing applied stress. When compared at the same amount of crack extension, the development of crack opening stress with crack extension for through cracks and penny-shaped cracks in plane strain condition was nearly close. The crack opening stress intensity factor at the threshold can be simply approximated as a function of the applied stress and the amount of crack extension. The cyclic resistance-curve method was used to predict the fatigue thresholds of pre-cracked components. When compared at the same initial crack length, the fatigue limit for fracture of penny-shaped cracks in plane strain condition is larger than that of through cracks. On the other hand, the relation between the initial crack length and the fatigue limits for fracture is nearly independent of the defect type.