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Systematic improvements in the fatigue crack propagation (FCP) properties of metal alloys through combinations of heat treatment, processing, and composition control depend on identifying the basic processes and parameters that are involved. Towards that end, numerous models have been developed. These models generally fall into three classes: (1) macroscopic, in which bulk properties are used to fit a modified Paris equation; (2) microscopic, in which dislocation deformation processes are incorporated into a criterion for crack advance; and (3) low-cycle fatigue (LCF) based, in which crack propagation is assumed to result from failure of a microscopic LCF ligament defining a process zone directly ahead of the propagating crack. This paper reviews the basic assumptions underlying these models. Their implications are discussed and compared with experimental data, both numerical and microstructural. Various experimental procedures are reviewed and some suggestions are made for research that could be used to verify the validity of these models.
fatigue crack propagation, low-cycle fatigue, fatigue models, microstructure, fatigue damage dislocations, nickel-base superalloys, copper alloys, aluminum alloys, steels
Ecole Polytechnique, Montreal, Quebec
Director and Professor of Metallurgy, Fracture and Fatigue Research Laboratory, Georgia Institute of Technology, Atlanta, Ga.