A Microstructure-Based Model for Simulation of Short Fatigue Crack Growth in 3-D

This paper presents a microstructure-based model to quantify short fatigue crack growth in 3 dimensions in planar slip alloys, such as high strength Al alloys and Ni-base superalloys. The model defines the resistance of a gran boundary to short fatigue crack growth as a Weibull-type function of the twist angle of the crack plane deflection at the boundary. The total resistance at a grain boundary is also contributed by all its neighboring grain boundaries as a normal distribution function of distance. The driving force for crack growth is the delta K at the furthest point along the crack. The effective driving force is then this driving force minus the total resistance at each grain boundary along the crack front, and used in the modified Paris equation to quantify the growth behavior of the crack in 3 dimensions. This model has been verified by the surface growth rate of a short crack, measured experimentally, in an Al-Li alloy. The model could incorporate the effects of grain structure and texture in simulating the short fatigue crack growth. It shows that texture could significantly affect the life of a short fatigue crack. This model presents the potentials for more accurate prediction of the life of an engineering alloy and advancement of alloy design technology.