Deformation of a Thin-walled Tube of Softened Celluloid under Cyclic Torsional Stress with Superimposed Constant Axial Stress

An experiment was performed by applying combined loadings of a constant axial stress and a torsional stress cycle to a thin-walled tube of softened celluloid. The results obtained are summarized as follows: (1) When the torsional stress is applied after the axial stress, the deformation resistance of the material decreases due to an abrupt change in the deformation state, and the ratchet strain and the range of cyclic torsional strains increase markedly in the first few cycles. Such an effect of pre-stress declines thereafter as a hardening trend appears with an increase in the number of cycles N. (2) The hardening trend of both strains may be expressed by an exponential function of N. (3) Fluctuations showing an alternate softening and hardening every few cycles appear in both strains. (4) The softening and hardening characteristics and fluctuations in both strains may be interpreted as indicating variations in the micro-structure of the material which may be assumed the cause of the residual strain.