Creep crack propagation by cavitation near crack tips

Abstract

A model in which cracks propagate by nucleation, growth, and coalescence with cavities in front of the crack tip is analysed in detail. The applied stress field is assumed to be elastic or elastic–plastic, and the relaxation of stresses from the growth of cavitation damage is included in the analysis. The spacing of the cavities, the threshold stress for the nucleation of cavities, and the self-diffusion coefficients are the important material parameters. The model results in a threshold stress intensity and a K _I ⁿ dependence of steady-state crack propagation rate when K _I > K _th. The stress distribution in front of the crack during the transient and the steady states is calculated. The size of the ‘damage zone’ varies from about 10 to 100 cavity spacings. Since the typical cavity spacing in engineering materials is about 1 μm, the damage zone is expected to be a few grain diameters in length.