Continuum mechanics and thermodynamics (Chapter 2) constitute the basic theoretical tools for the formulation of the physical phenomena of deformation and fracture. For fundamental and practical reasons, we model each broad class of phenomena separately. The aim of this chapter is to differentiate from a qualitative point of view and identify the most common types of material behaviour. The phenomenological method used is based on observed experimental results. We, therefore, present some basic elements on the types of tests, the machines and the modern measurement techniques likely to be used. Progress in electronics, automatic controls, digital measurements, and more recently in microprocessors has resulted in a radical transformation, especially during the 1970s, of the laboratories engaged in characterization of materials. We no longer have to be content with approximate measurements of a few quantities; we are now in a position to measure the evolution of any mathematically well defined variable precisely. The identification of complex models has thus become possible, but it requires numerical methods for the identification of nonlinear processes which still belong to the domain of ‘heuristic’ techniques.

The resulting schematic classification allows us to associate, a priori, to each material, a theory of only the dominant phenomena in a limited domain of state variables. Beyond its fundamental interest, this offers a guide for the choice of material in the design stage and helps to simplify the estimation of the resistance of a structure under service loads.