Polycrystalline FE Modeling of Deformation and Fatigue Cracking Using Experimental 3D Microstructures
Résumé
Growing experimental capabilities (through both serial sectioning and X-ray tomography) to asses the 3D grain microstructure of structural metallic materials allows microstructure sensitive finite element calculations at the grain level. Grain to grain comparison of strain tensors, as well as crack initiation and propagation behavior in 3D becomes possible. Several difficulties are to be overcome before such comparison can be carried out. Both experimental and modeling difficulties will be presented. Regarding the experiments, the destructive nature of serial sectioning technique prevent to probe the material in situ, whereas X-ray tomography has some limitation in terms of specimen size and spatial resolution. Specific technical developments to improve those aspects will be discussed. On the modeling side, suitable meshing of the grain microstructure remain cumbersome. The search for a purely automated method is still under work but several algorithms can be used to deal with this problem. Second the material behavior at the grain scale has to be considered including elastic anisotropy and crystal plasticity. Finally microstructure sensitive calculations often lead to very large calculations. A review of recent work in several materials will be presented such as (i) fatigue crack initiation in stainless steel studied by serial sectioning (ii) deformation of pure titanium studied by diffraction contrast tomography and (iii) short fatigue crack propagation in a beta-titanium alloy studied both by diffraction contrast tomography and phase contrast tomography. In all three cases, the 3D microstructure has been meshed and calculated by finite element using the experimental grain orientations allowing a direct comparison with the measurements.