He then (1972-90) developed a mechanistic approach to crystal plasticity: characterization and representation of latent strain-hardening for different classes of single crystals, prediction of its role in the strain-hardening of polycrystals, the formation of crystallographic textures and the initiation of plastic instabilities in large deformations (shear bands...); analysis of the mechanical influence of grain boundaries , triple junctions and intergranular sliding on the plasticity of multicrystals and polycrystals.