Fatigue failure model including both initiation and propagation of the crack

Abstract

It is assumed that after N i(a th) cycles of loading, a crack with length a th is initiated. a th is the ultimate value of length, for which equation N i(a)∼-N i(0) is valid. N i(a) stands for life until failure in the point with distance a from the point of the maximal stress, under the condition that no crack appears at any other point, the stress value neglected. Taking into account that the main crack propagates into the damaged material, a multiplier 1/(1-N i(a th)/N i(a)) is introduced into the classical approach to the crack propagation speed. The model is actually independent of the crack growth rate at low values of Δ K. The present paper shows a reasonable correlation between the theoretically assumed and experimentally achieved results. For small holes, the suggested model provides results which are close to those calculated by means of a model with a given initial crack. The present communication provides an explanation of the above phenomenon.