The aim of this thesis is to understand and model the ratcheting phenomenon by implementing a full-field numerical simulation approach, using the finite element method, of the mechanical response of polycrystalline aggregates under cyclic loading. In this context, the description of local behavior, at the grain scale, will be based on constitutive equations of crystal plasticity (or visco-plasticity) type, including non- linear isotropic and/or kinematic hardening formulated in terms of dislocation density. Particular attention will be paid to the description of latent hardening.
This work will involve, among other things, implementing the numerical integration scheme of the local behavior law within the finite element solver used (Abaqus, Zset or Foxtrot – Academic code developed in- house, etc.) by developing user subroutines or using suitable free libraries (M-Front, https://tfel.sourceforge.net). The implementation of full-field calculations will require the use of parallel computing, performed on a regional cluster.
The model material chosen for this study is an austenitic stainless steel, whose cyclic behavior is well documented. To define the simulated configurations (loading, material parameters) and analyze the results, the PhD student will have the possibility of drawing on data from tests carried out in the laboratory, notably through regular collaborations with industrial partners in the nuclear power sector. (EDF, Framatome). If necessary, additional targeted mechanical tests can be carried out during this thesis. These may be accompanied by microstructural characterization at the grain and sliding system scale (Scanning Electron Microscopy, EBSD, in-situ tests).
Practical framework: This thesis will be carried out at the Pprime Institute –Unit of CNRS UPR3346, more specifically within the Physics and Mechanics of Materials Department, and the “Damage and Durability” team (ENDO), hosted by ISAE-ENSMA. It will make intensive use of the supercomputer facilities of the regional MesoCentre, and, if necessary, of national calculation resources (GENCI).
