In the 1950s the direct observation of dislocations became possible, stimulat- ing the interest of many research workers in the dynamics of dislocations. This led to major contributions to the understanding of the plasticity of various crys- talline materials. During this time the study of metals and alloys of fcc and hcp structures developed remarkably. In particular, the discovery of the so-called in- ertial effect caused by the electron and phonon frictional forces greatly influenced the quantitative understanding of the strength of these metallic materials. Statis- tical studies of...