A micromechanical model for small fatigue crack growth: an approach based on two threshold conditions

This paper presents a micromechanical description of small fatigue crack growth based on the successive blocking of the monotonic plastic zone (MPZ) and cyclic plastic zone (CPZ) of a crack at microstructural barriers such as grain boundaries and phase limits. This allows two different fatigue crack growth thresholds to be established, one of which, the maximum-controlled fatigue threshold, is dependent on the ability of MPZ to overcome successive material barriers and the other, the range-controlled fatigue threshold, is associated with the ability of CPZ to overcome such barriers as well. The proposed model connects in a natural manner with recent advances in fatigue mechanics relying on the use of two parameters, K-max and Delta K, approaches to describe crack propagation process.