Nonlinear Viscoelastic Behavior of Rigid Polyvinylchloride Resin

Abstract

Nonlinear viscoelastic behavior of rigid poly-vinylchloride (PVC) resin under time dependent extension was investigated at 20°C and 65% R. H. In log modulus-log time plots, the initial modulus decreases and the rate of relaxation increases as the strain increases, and a master curve can be obtained by shifting each of the curves along the log time axis. The master curve.and the shift factors are used as the basic data for constructing singleintegral type constitutive equation of the time-strain reduced model. This equation is applied to predict stress responses under the following tests: (1) two step stress relaxation, (2) loading and unloading at constant strain-rate, and (3) stress relaxation after loading of constant strain-rate.
In the two-step stress relaxation, the predicted values are in good agreement with the observed values when the additive strain Δε is positive, while the former are greater than the latter values when Δε is negative. The discrepancy between predicted and observed values of stress becomes more marked as the ratio of |Δε|de to the first strain ε₁, increases. In the loading tests at a wide range of constant strain-rates, the ranges of strain where the linear theory is applicable are found to be independent of strain rate. All the results of constant strain-rate experiments can be described by the simple constitutive equation adopted in this study. The applicability of the theory to the results of PVC is better than that to polyethylene studied in our previous papers.