Relationship of fatigue crack propagation to dislocation structure and slip geometry

The mechanisms of fatigue crack propagation are breifly reviewed in relation to Professor McClintock's contributions to the early development of the field. The most securely established understanding has been obtained for those mechanisms of propagation involving plasticity-induced geometrical changes to the crack tip during tensile and compressive straining (the plastic blunting process). The roles of more complex factors in controlling the kinetics of crack propagation, which cause the magnitude of the Paris exponent to exceed 2, remain to be elucidated. Recently obtained results revealing the interconnection between the slip behaviour at the crack tip, the plastic blunting process and the dislocation structures present in the material before the crack encounters them are reported.