ON STABLE DEFORMATION OF UNSTABLE MATERIALS IN A RIGID TRIAXIAL TESTING MACHINE

REALIZABILITY of the process of uniform supercritical deformation of s pecimens under testing is examined. Realizability is identified with s tability of the process in the sense of Drucker's postulate. Specimen configuration and the boundary conditions adopted are idealizations of those that apply to actual rigid triaxial testing machines. The analy sis is based on a theorem, proved here, of Van Hove's type. It is show n that a process of uniform supercritical deformation of homogeneous o rthotropic specimens with symmetric moduli tensors in the ideal machin e of the type considered is stable in Drucker's sense and unique up to violation of Hadamard's condition (i.e. up to the absolute bound for theoretically admissible material states).