On the role of point defects in fatigue crack initiation

Abstract

Analysis of inhomogeneous cyclic straining, observation of surface relief at emerging persistent slip bands (PSBs) and data on point defect generation and migration in fatigued metal single cyrstals and polycrystals are the origin of a new model for fatigue crack initiation in PSBs. Because of the high plastic strain amplitude, non-equilibrium point defects are generated in PSBs. They are distributed inhomogeneously according to the inhomogeneous sink distribution. Point defect migration over short distances causes mass transport and results in the formation of extrusions and intrusions on the metal surface. The distribution of extrusions and intrusions is related to the dislocation substructure of the PSB. Cyclic straining under stress together with the strain concentration at sharp intrusions result in environment-assisted formation of new surfaces and therefore in crack initiation.