Short fatigue crack propagation and effect of notch plastic field

Abstract

In engineering application, almost all structures and components contain notches or holes. They often experience severe fatigue loading, and have been recognized as a potential site for small fatigue crack initiation and propagation. In this paper, the effects of notch plastic field on small fatigue crack initiation and propagation from notch member, under cyclic tensile loading control, are investigated. Experiment shows that small crack initiates from notch specimen at far higher rate than that of smooth specimen; small crack propagation is still faster than that of smooth specimen within notch plastic field, though this difference is progressively lessening; beyond notch plastic zone, small crack growth rate is approaching long crack growth rate. Analysis via finite element and analytical method reveals that notch plasticity has key influence on small crack initiation, crack tip generated plasticity has critical impact on small crack propagation within notch plastic field, while plasticity induced crack closure has dominant effect on crack propagation out of notch plastic field. A comparison between experimental and analytical results is made to identify the mechanisms of small fatigue crack initiation and propagation within notch plastic field.