Metal alloys used in industrial applications can form oxide layers in the presence of a corrosive environment. These oxides may be distributed on the surface and/or localized at the grain boundaries. In the latter case, the oxidized grain boundaries may experience brittle fracture under mechanical loading, potentially leading to intergranular cracking of the material. This mechanism is, for example, a possible scenario for the failure of austenitic stainless steel bolts used in the internals structure of Pressurized Water Reactors (PWRs). Under the effect of mechanical loading, neutron irradiation and the presence of a corrosive environment, these bolts fail through a phenomenon known as irradiation-assisted stress corrosion cracking. To model this phenomenon, we need to determine the fracture properties of intergranular oxides, and to take into account the coupling between cracking, oxidation and irradiation. In this thesis, experimental and numerical work will be combined. Firstly numerical simulations based on the variational approach to fracture approach will be assessed in order to design micro-beam micromechanics experiments aimed at reliably determining the fracture properties of oxides, and also to study the couplings between cracking, oxidation and irradiation. In particular, the cracking-oxidation coupling that prefigures the transition between initiation and propagation will be investigated in detail. These experiments will then be carried out on model and industry-relevant steels, and interpreted using numerical simulations. Finally, all the results obtained in this work will be incorporated into simulations of polycrystalline aggregates, in order to assess the possibility of quantitatively predicting intergranular cracking in the context of irradiation-assisted stress corrosion.
By the end of the PHD, the doctoral student will have acquired both experimental skills - micromechanical tests - and numerical skills - numerical simulations of fracture - at the cutting edge of the state of the art and applicable to a large number of problems in the mechanics of materials.
A Master's 2 / end-of-studies internship preparatory to the PHD is available in 2024.