Dislocation wall structures near a stress concentration in fatigued copper polycrystals

Abstract

The fatigue failure of metals is one of the most difficult failure mechanisms to understand. Since the 1950s it has been recognized that the microcracks that ultimately lead to failure are often associated with persistent slip bands. The two-phase model of active persistent slip bands in a relatively inactive matrix provided a basis for the development of models relating cyclic deformation, the development of dislocation microstructures and crack initiation. A large amount of work on dislocation structures in a variety of systems, e.g. Cu, Al, steels, Ti and ionic systems, has led to a better understanding of the fundamental physical processes involved. A gap, however, exists in progressing from such studies to real engineering situations due to the differences between laboratory experiments and real applications. The two key differences between laboratory and engineering applications are the complex stress states and/or the existence of stress concentrations due to component shape or in-service damage. This preliminary study examines the effect of a relatively simple stress concentration on dislocation microstructure formation in fatigued polycrystalline copper.