Plasticity

Abstract

With elastic loading, atomic structures are not affected, which is typical of processes in which there is no internal energy dissipation. Then, once the load has been removed, the solid returns to its initial state. In certain types of materials, if we keep loading, a level will be reached in which the atoms begins to restructure (dislocation at the atomic level), so, in this way, we have internal energy dissipation (an irreversible process). Most of the dissipated energy will be used to increase the temperature (heat release), and as a result there will be an increase in system disorder, i.e. a rise in entropy. A rise in temperature also involves the dilation phenomenon. At the macroscopic level, in ductile materials, this atomic restructuring is characterized by permanent deformation (plastic strain). That is, if the material which has been internally restructured is completely unloaded, it can be observed that part of the total deformation is regained. This recoverable part is characterized by the elastic strain, and the permanent deformation by the plastic strain, (see Figure 9.1), and the constitutive models devised to represent this phenomenon are called “plasticity models” or “elastoplastic models”.