Influence of strain rate and strain cycling on fatigue crack-tip plasticity

Abstract

A general relationship for the calculation of strain rates at the fatigue crack tip was derived. This relationship is applied to predict the effect of strain rate and strain cycling on the dimensions of the monotonic and cyclic plastic zones. Strain rates are independent of the applied DELTA K or K//m//a//x, but depend on frequency and stress ratio R. The experimental values of the alpha ** theta / alpha ** theta //c - ratios of the plastic zone size, obtained in plane strain conditions and quoted in the literature are predicted by this relationship, taking into account the high strain rates and also the strain cycling usually occurring within the plastic zones at the fatigue crack tip.