Measurement of plastic strains by 3D image correlation photogrammetry at the grain scale

Polycrystals with columnar coarse grains are plastically compressed in a channel die for imposing an external plane-strain state. The spatial distribution of the accumulated plastic surface strains in the deformed polycrystals is determined by measuring the displacement fields using 3D quantitative image correlation photogrammetry. For this purpose digital stereological image pairs of the sample surface are taken at the beginning and after each deformation step. The displacement field is derived from them by applying an image analysis method based on pattern recognition to the data before and after straining. The three components of the plastic displacement vector field are used to derive the surface portion of the plastic strain tensor field. The microtexture of the specimens is determined by analysis of electron back scattering patterns obtained in a scanning electron microscope. The experiments are interpreted by comparing them to corresponding crystal plasticity finite element simulations