Deformation Behaviour of Softened Celluloid under Complex Loading : Along Orthogonal Bi-linear Stress Trajectory

Deformation behaviour of softened celluloid is observed by applying combined loadings of tension after torsion along orthogonal bi-linear stress trajectories of a thin-walled tubular specimen. The experiment is performed under two conditions : creep test and continuous loading test. From the experimental decreases just after the corner of stress trajectory, and this trend decreases with the development of a deformation after the corner. The trend appears more remarkably for higher level of pre-stress. In order to formulate a stress-strain relation from the experimental results, the relation having a principal term of the third order in the non-linear viscoelastic theory is extended to application for the above-mentioned trajectories. The influence function contained in the relation is determined by using experimental results. The stress-strain relation obtained is confirmed to approximate precisely the experimental results.