Mathematical framework for the plastic flow of fine-grained solids, from yield to fracture

A newly proposed mathematical approach to plastic flow, holding from yield to fracture, of a fine-grained polycrystal with no voids or cracks is reviewed and applied to commercial steels. The formalism models the polycrystal by a continuum array of random deformable polyhedra leaving no voids between them, which can slide past each other along the shared faces when the shear stress resolved in the face plane exceeds a finite threshold. Grain reshaping for preserving matter continuity induces local forces assumed much weaker than those causing sliding. The relative velocity of adjacent sliding grains is taken as proportional to the local shear stress resolved in the common boundary plane. Explicit equations are derived for the plastic deformation, from yield to fracture. The analysis of mechanical tests of two commercial stainless steels is shown to illustrate how well the theory agrees with practice.