A new tool for the experimental characterization of micro-plasticity

The aim of this study is to provide a tool, which is capable of studying, at a sub-grain level, the formation and evolution of strain inhomogeneities at the surface of polycrystalline materials. The capabilities of the tool are demonstrated on an oxygen free high conductivity copper (OFHC) specimen which is plastically deformed in an in-situ tensile test in the scanning electron microscope (SEM). At different deformation stages, SEM micrographs are captured which are processed by a new system for local deformation analysis. The key part of the system is a matching procedure for the determination of homologue points in two deformation micrographs. The homologue points form a deformation field, which can be numerically derived to evaluate the local in-plane strains. Due to the high matching accuracy and the high density of the homologue points, it is possible to determine the in-plane strain fields with an accuracy and lateral resolution that has not been possible so far. The system allows us to conduct local deformation analyses in a wide range of magnifications. As an example, a region of about 180×130 μm is analyzed on the copper specimen in deformation steps of about 1% global strain. The in-plane components of the local strain field are characterized by incremental or cumulative strain maps. The exact distribution of the local strains near grain and twin boundaries is obtained by means of local displacement and strain profiles.