Discreteness and self-similarity of failure in stable fatigue crack growth

Abstract

1. On the basis of the approaches of linear fracture mechanics and the theory of self-similarity developed by Sedov it has been shown that the effect of the external factors on the cracking resistance criteria can be reduced to a single factor, i.e., the degree of constraint of plastic deformation characterized by parameter Q = (σ11)max/σT. 2. As the criterion controlling the transition from quasielastic self-similar to elasto-plastic self-similar crack propagation, it is proposed to use the Huber-Mises criterion, i.e., the critical value of octahedral tangential stress τo = τo* = √2/3σT for the local stress field at the crack front. This makes it possible to determine the range of variation of the σnσT ratio (0.47 ⩽σn/σT ⩽ 0.82) within which self-similar elastoplastic crack growth takes place in the steel with the formation of a single striation per cycle at the minimum elastoplastic constraint Q = 3. 3. The KI*-m diagram linking the threshold values of KI* with coefficient m which characterizes the crack growth retardation capability has been proposed. The regions of the KI* values and of the corresponding values of m which correspond to self-similar elastoplastic crack growth have been defined. The boundaries of self-similarity have been verified by means of experiments, and the experimental results were found to be in agreement with theory.