ABSTRACT
Our relatively recent understanding of the nature and role of dislocations in solids is based on the meeting of two distinct approaches.
The first approach, which is both theoretical and fundamental (although the rubber manufacturer Pirelli showed interest in it at a very early stage) involved studying the lines of elastic singularity in continuous media from a mathematical point of view, by solving Navier's equation for various boundary conditions (Italian school: Volterra, 1907).
The second experimental and intuitive approach aimed to discover the mechanisms for the deformation of solids. Despite considerable work1, few useful data were available until around the beginning of this century. It was at least known that, in many cases, the deformation of crystals involved glides along planes, much as the sheets in a ream of paper glide on top of one another. This led to the idea (Yamaguchi, 1929) that these planes might well be nothing other than the support of elementary linear distortions propagating2 from one edge of the sample to the other during the deformation. These distortions were called dislocations. The idea was refined in the 1930s (Taylor, Orowan, Polanyi).
