Hydrogen effects on the plasticity of model fcc and bcc alloys: Experiments on model engineering materials and modelling in the framework of the elastic theory of discrete crystal defects

International audienceBecause crack propagation in engineering materials – even ‘brittle’ ones - is always associated to the development of a plastic zone, the understanding and prediction of hydrogen-assisted damage has to consider both aspects: hydrogen effects on the microscopic fracture process on the one hand ; and on the dynamics and extent of plastic activity on the other. In this communication, we will report on a 12-years effort conducted at Ecole des Mines de Saint-Etienne to address the later. Because of the localized character of hydrogen-plasticity interactions and the existence of steep gradients close to notches and crack tips, we chose to investigate these effects by looking at the stress-strain response of uniformly charged smooth tensile specimens, assuming that modern simulation methods such as gradient / crystal plasticity or discrete dislocation dynamics will be able to transpose the results in the vicinity of cracks and defects. For modelling, we rely on the framework of ‘hydrogen elasticity’ – as laid out by P. Sofronis in the mid 90s by elaborating on Larché and Kahn theory of chemo-elasticity - to revisit the classical theory of dislocation plasticity, introducing hydrogen effects on elementary dislocation properties, such as elastic pair interactions, line energy, line tension, and (in bcc crystals) activation enthalpy of double-kink formation. Despite the experimental difficulties raised by such an approach, quantitative results were obtained and cross-checked, which are now ready to be incorporated in mesoscopic-scale simulations of crack-tip plasticity