Experimental evidence and physical models of fatigue crack initiation

• Relevant experimental evidence on the fatigue crack initiation is presented.
• The initiation of fatigue cracks from intrusions is demonstrated.
• Relation between surface relief and internal structure is shown and discussed.
• Physically based model of fatigue crack initiation are critically exposed.
• Predictions of the models are discussed in relation with experimental data.

Results of the study of the early fatigue damage in a number of model and structural crystalline materials using modern experimental techniques are presented. The dislocation structure of the persistent slip bands and the evolution of the surface relief resulting in the formation of persistent slip markings during cyclic loading are documented. The dislocation mechanisms leading to production of point defects in cyclic loading are described and point defect production and annihilation rates are derived. The kinetics of point defect migration is characterized. The physically based models of the surface relief formation describing the formation of extrusions and intrusions are presented. The models are confronted with experimental evidence. It is concluded that intrusions representing sharp surface crack-like defects play the principal role in the initiation of fatigue cracks.

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