A PLASTICITY MODEL OF FATIGUE CRACK GROWTH

A model of fatigue crack growth is presented in this paper involving the advance of the crack tip in steps accompanied by plasticity and necking. The model accounts for the shape of Regions II and III and it proposes that Region I arises as da/dN approaches the atomic scale. The model also accounts for the observed influences of Youngs modulus E and the stress ratio R, and the lack of influence of the yield stress on the Paris curve. In the model the parameter n, the strain preceding the onset of necking, has a strong influence. It is suggested that teachers of fatigue may find the model useful because it involves physical processes and yields results which are consistent with the empirical facts.