Cyclic tensile creep behaviour of cellulose nitrate and evaluation of constitutive equations

The cyclic creep behaviour under axial tension was quantitatively investigated using non-linear viscoelastic cellulose nitrate heated at 65°C. The instantaneous strains at the instants of loading and unloading for three creep cycles and the creep strain rates during the three creep cycles were found to be influenced by the cycle numbers. However, the effect of the cycle number on the loading process was quite different from that on the unloading process in the cyclic creep deformation. The evaluation of the creep constitutive equations for the loading and unloading processes at one loading cycle deduced in the previous papers is discussed for the cyclic creep deformation. The deduced creep equations give good agreement with the actual observations for the three creep cycles independent of the cycle numbers and of the creep stress levels.