DETERMINATION OF FATIGUE CRACK INITIATION LIFE

Abstract

Abstract— A reanalysis has been carried out on the results of Zachariah. An elastic‐plastic analysis based on S‐N data indicates that the mechanism of growth of very small cracks is similar to that expressed by linear elastic fracture mechanics, i.e. crack growth in mild steel is given by image where Δγ p is the plastic shear strain range and a is the crack length. Crack initiation occurs within a single grain and crack propagation is given by the above equation for cracks which can be smaller than a few microns. The size of an initiated crack is a function of stress level varying from 0·1–1·0 μm in the high strain fatigue regime to 2·3 μm close to the fatigue limit. The period of crack initiation is negligible in the HSF regime whilst the initiation period can dominate lifetime at low stress levels.