Influence of local crystallography on the mechanisms of fatigue crack nucleation and propagation in metallic materials

The cyclic deformation mechanisms leading to crack nucleation in metallic materials are reviewed along with those responsible for fatigue crack growth, placing emphasis on local crystallography effects elucidated through experiments on bicrystals and multicrystals of FCC materials. Models for the kinematics of fatigue crack growth are discussed with respect to local slip geometry and the kinetics of crack propagation as well as Prof. Knott's fundamental contributions to the field. It is found that fatigue crack growth can be strongly affected by the local slip geometry and anisotropy. Furthermore, recent studies using Orientation Imaging Microscopy (OIM) reveal that the path followed by a fatigue crack in a multicrystal can be correlated to slip geometry inside a grain for transgranular fracture and the grain boundary misorientation for intergranular crack growth. The factors affecting the preference of one path over the other are discussed in terms of current models for fatigue crack growth.