Non-linear viscoelastic response of polycarbonate in torsion

Viscoelastic behavior of polycarbonate at room temperature and non-linear constitutive law description of the sub yield behavior are determined using pseudotime or material clock concepts of non-linear viscoelasticity. The energy clock model was tested using the single-step and two-step stress relaxation experiment and was compared to the original BKZ and a modified Boltzman equation. Results showed that the clock model described the second step torque response in which the deformation returns fully to zero; however, the model over estimated the magnitude of the negative torque obtained upon reaching the zero deformation.