A model of fatigue crack nucleation in single crystal iron and copper

Over the years, many theories and models have been proposed to explain how fatigue cracks nucleate over many thousands of cycles of applied load (strain). In the model originally proposed by Mura and co-workers, fatigue crack initiation is considered a nucleation process in that an energy barrier due to the formation of new surfaces must be overcome. Therefore, by minimizing Gibbs free energy change, the critical number of cycles required to nucleate fatigue cracks can be estimated. In a previous contribution, the present authors demonstrated the validity of this model with data from commercial purity iron and a high-strength–low-alloy steel. The present paper extends these concepts, in particular with respect to strain localization sites responsible for crack nucleation. Experimental data for single crystal iron and copper are utilized to support these theoretical concepts.