A technique, which allows characterizing the local strain field over a domain representative of the microstructure of a heterogeneous material, is described. It is based on scanning electron microscopy, microelectrolithography, image analysis and in situ mechanical tests. On one hand, in relation with a microstructure analysis, it allows characterizing the different mechanisms responsible for the plasticity or the damage of materials. On the other hand, a quantitative analysis allows comparing and validating from a local to a global scale, the different models used for the prediction of materials constitutive laws. Finally, the knowledge of the experimental displacement improves seriously the results of finite element computations, by a better determination of the boundary conditions.