TWO SCALE DAMAGE MODEL

On the idea that fatigue damage is localized at the microscopic scale, a scale smaller than the mesoscopic one of the Representative Volume Element (RVE), a three-dimensional two scale damage model has been proposed for High Cycle Fatigue applications and extended to anisothermal cases and to thermo-mechanical fatigue. Mean stress effect was first introduced by the modelling of microdefects (or microcracks) closure by means of a microdefects closure parameter h in the expression of the energy density release rate. This parameter is not sufficient to represent realistic behavior at high stress ratio. The consideration of the first stress invariant in the microscale plasticity criterion makes now the two scale damage model and the associated fatigue post-processor DAMAGE able to take properly into account the mean stress effect in calculations. Haigh and Goodman diagrams are gained by the time integration of the constitutive equations over the whole loading thanks to this post-processor