Influence of compressive plastic zone at the crack tip upon fatigue crack propagation

In this paper, based on physical meanings of hysteresis loops denoting a relationship between loads and strains near the fatigue crack tip, variations of the tensile plastic zone in loading and the compressive plastic zone in unloading as well as the effects on acceleration, retardation and non-propagation in fatigue crack propagation are studied under different amplitude loadings. To the two closure types obtained from tests, the influence of each zone of a hysteresis loop upon fatigue crack propagation is evaluated and the effects of the compressive plastic zone at the crack tip on fatigue crack propagation are ascertained.