Elevated Temperature Creep of Polyurethane under Nonlinear Torsional Stress with Step Changes in Torque

Constant stress experiments, recovery, and multi-step creep tests in torsion in the nonlinear range were performed at different temperatures up to 160 °F. It was found that the results could be described by a power function of time whose exponent was independent of stress and temperature. Most of the temperature effect and most of the nonlinearity were found in the coefficient of the time-dependent term. The nonlinearity was described by the multiple integral representation, and the changes in stress were adequately predicted by the modified superposition method, except at the highest temperatures.