Theory of Plasticity studies the distribution of stresses and particle velocities (or displacements) in a plastically (irreversible) deformed body, when are known the external factors which have acted upon him and the history of variation of these factors. The theory was applied to metals to describe working processes both at cold (drawing, rolling, etc.) and warm (extrusion, forging, etc.), to describe term behavior (high and law) involving also temperatures, to short term behavior, to describe impact, shocks, perforation, etc. It was applied to geomaterials, as soils, rocks, sands, clays, etc., with the description of civil engineering applications as tunnels, wells, excavations of all sorts, etc. It was applied to other materials as concrete, asphalt, ceramics, ice, powder-like materials, various pastes, slurries, etc.

In the classical sense the Plasticity Theory is time independent. However a time dependent theory was also developed and called Viscoplasticity. Besides Rheology deals with any flow or deformation in which time is the main parameter.

From the point of view of formulation of problems, in plasticity one considers in some of the problems, as in elasticity, that the strains are small; whoever in some other problems the consideration of the problems are as in nonlinear fluid mechanics when the strain are finite.

1 Diagnostic Tests

These are the slow tests in compression or in tension ( ?10 ^?2 s ^?1, say) so as the strain is uniform along the specimen. We denote by

the Piola-Kirchhoff and the Cauchy s stresses. Here F is the...