A micromechanical theory of fatigue crack initiation of an aluminum single crystal

A micromechanic theory of extrusions and intrusions in an aluminum single crystal with multiple fatigue bands under stresscontrolled loading is presented. The micro-stress and strain fields of this crystal were analyzed as a three dimensional elastic– plastic solid using Boundary Element Method. From these microfields, the macroscopic stress and strain of the crystal at different stages of loading were calculated. The numerical analyses give the changes in hysteresis loop shapes and sizes with loading cycles. The incremental plastic strain distribution in each cycle depends on the initial shear stress. Two sets of initial shear stress are taken to show the dependence of the shape and size of the hysteresis loop on the initial stress. The details of the occurrence of the second slip system are shown. They compare well with the experimental results of the single crystal tests performed in Oxford.