Elasto-plastic strain field measurement at micro-scale on 316L stainless steel

Abstract

This study deals with the characterisation of the mechanical behaviour of an austenitic stainless steel (316L) at the micrometric scale in its elasto-plastic domain. For that, the full-field “grid method”, adapted to this scale, is implemented. The direct interferometric photolithography is used here to produce gratings (the pitch is approximately 5 μm) on specimen surface. The gratings are digitized at every step of the tensile loading thanks to a white-light interferometric microscope. The in-plan strain fields are then deduced from these grating images (resolution is closed to 2×10-3 for a spatial resolution of bout 20 μm). The results show that the strain localisation is in accordance with the microstructure. Some considerations about the average strain within different grains of the steel sample are made to show how the plastic deformation begins locally before the global yield point σY. It was then observed that these local σY values thus determined may vary by +/-20 MPa around the macroscopic value (180 MPa).