Influence of mixed-mode loading on fatigue-crack propagation

The subject of fatigue which comprises crack nucleation, crack propagation and final failure or fracture has, over the years, been the subject of numerous theoretical and experimental studies. These studies have highlighted the extrinsic influence of mixed-mode loading in governing the fatigue behavior of a wide spectrum of engineering materials and structures. In this paper we review the basic criteria and models that have been proposed and used to predict crack behavior and response for structures containing large cracks and subject to mixed-mode loading. Since the aspect of crack growth is the focus of this review, the effects or contributions from intrinsic microstructural effects are largely excluded. Specific criteria discussed are the maximum tangential stress, minimum strain-energy density and the maximum energy-release rate criteria. The use of these criteria to predict the behavior of structures is examined based on results published in the open literature. The characteristics and implications of each criterion are examined and discussed with particular relevance to threshold conditions on crack growth, direction of crack growth and crack-growth rate. The limitations of each criterion are highlighted.