Problems in creep testing under biaxial stress systems

Abstract

Two types of creep testing machine, one to apply bi-axial tension to cruciform specimens and the other, torsion to disc-shaped specimens, have been constructed in the course of an investigaton of the behaviour of copper subject to multi-axial stress systems. Problems of bending in biaxial tension and buckling in torsion were encountered subsequent to construction of the machines. In the former case the deficiency was accepted and eccentric loading used to control the bending within acceptable limits. In the latter case microscopic examination was found necessary in order to define creep failure.