Une modélisation de la genèse des contraintes résiduelles lors d'un traitement superficiel par une source laser mobile

Abstract

The numerical simulation of the internal stresses genesis in processes of heat treatment holds, indeed, to the formulation of the coupled thermomechanics–metallurgic problem taking into account several and severe physical non linearities. This study aims to develop at least, a multipurpose model for prediction of the residual stresses state generated by a superficial heat treatment in solid phase without diffusion. For the generality of the models set up, to the sense of the thermomechanical history and other coupling terms importance, we consider the case of the treatment by a moving laser source and self quenching. Thus, the solution of this evolution problem, will lie in both the thermal and thermomechanical aspects as well as in the phase transformation effects. For the thermal analysis, we propose a non linear transient model allowing the simulation of the whole thermal history during the treatment process until the return to the thermal balance. The thermomechanical analysis is dealt with a non linear incremental model whereby we simulate the mechanical history since the beginning of the treatment until the residual stress state establishing. In the numeric scheme developed within a FEM code, the mechanical features are described in space–time evolutions depending on the temperature and the local instantaneous phases which are present throughout the domain. We introduce a global dilatometric coefficient to take into account the simultaneous and cumulated thermal and phase transformation strains. The comparison of numeric and experiment results reveals on the one hand a better qualitative consistency of the model, and tends on the other hand towards a new description of the structural transformations to reach a truly quantitative model.