Computational and experimental investigations of the local strain field in elastoplastic two-phase materials

A two-phase elastoplastic Ni/Ag model material has been tested under uniaxial compression in the chamber of a scanning electron microscope. The local strain field could be measured by means of high resolution images of 5 mum-step microgrids marked at the surface of the sample and their processing by digital image correlation techniques. Strong local strain heterogeneities can be observed with the formation of long-range deformation bands that spread out over distances about 3 times longer than the characteristic length of the phase domains, even at small overall strain levels (0.8% for the first investigated load step). The predictions of these heterogeneities with a 2D finite element model based on the real microstructure are satisfying, but only under the condition that experimental displacements are applied at the boundaries of the model. Accurate calculations with homogeneous boundary conditions would probably require larger and computationally more intensive models. A simpler model based on a geometric detection of "soft paths" for the deformation in the microstructure by means of image analysis is a computationally less demanding alternative solution for a first analysis.