Contribution a la modélisation du dommage en fatigue multiaxiale d’un acier C36 : confrontation à l’expérience

The basic objective of this thesis is the experimental characterization of deterioration mechanisms for simple (tension and torsion) loading cycles as well as for complex sequential loading programmes. The study of cumulative damage development for corresponding (tension and torsion) loadings blocks is put forward. This experimental investigation is a basis for coupled damage-plasticity mesomechanical modelling of the multiaxial fatigue phenoma. Established within a thermodynamic framework, there are in fact three modular and ascending damage models proposed. The gradual increase in their respective complexity is a consequence of accounting for increasing number of phenomena : nucleation, propagation in mode II, bifurcation, propagation in mode I, combination of the both and finally ruin of the crystalline aggregate. Moreover, by using an approach considering privileged slip direction within the activated system, it is possible to establish a description of damage intensity accounting for multitude of orientations in physical space of the material. A statistical approach is also proposed within the above approach.