Materials with elastic range and plastic change of volume

Following the lines of [1, 2, 3, 4), we sketch a theory of materials with elastic range that, at variance with the treatm ent in those papers, does not incorporate the assumption of no plastic change of volume (or any other assumption of a sirnilar kind). We then describe with some detail the constitutive behavior of two important classes of materials with elastic range that, by analogy with the terminology used in classical plasticity, we call v. Mises materials and ideally plastic materials. Finally, for a specific ideal1y plastic v. Mises material, we present a numerical computation that shows how, when plastic change of volume is allowed, the shear stress maintaining a pure shear flow needs not have constant value.