Biaxial Creep Deformation of Softened Celluloid under Variable Stresses

Abstract

Applying constant axial stress and variable torsional stress to a thin-walled tubular specimen of softened celluloid, creep deformation of the material was investigated. The main features obtained may be summarized as follows : (1) In tests with a variation in torsional stress, the axial creep strain shows transient softening just after the torsional stress change, and the rate of hardening of the material is continuous in the same stress state. (2) In cyclic torsional stress test, the torsional creep strain shows softening at the first reversal of torsional stress, while hardening of the material appears at the cyclic stress reversal and is saturated. (3) The viscous-viscoelastic theory may be applicable to creep deformation of the material under reversal and removal of stress by using the modification for the ratio of recoverable strain.