A Microcrack Description of Multiaxial Low Cycle Fatigue Damage

Abstract

A continuum damage mechanics modelfor the low cycle fatigue behaviour of initially isotropic materials with two families ofparallel microcracks is presented. The expression for the equivalent strain in the fatigue damage evolution equation contains the three material parameters as well as the strain intensity for the amplitudes, and joint invariants for the strain amplitudes and for the two unit vectors associated with the directions of microcracks. It is shown how these material parameters can be determined from a series of basic experiments outlined in this paper. Specific expressions for the equivalent strain with a smaller number of material parameters and invariants are obtained. Theoretical results are found to be in good agreement with the experimental data under multiaxial loading obtained on cruciform specimens.