Long-term service performance of polymeric materials from short-term tests: prediction of the stress shift factor from a minimum of data

We use the time–stress correspondence (TSC) principle and consider creep compliance D data for a polymer liquid crystal (PLC). A master compliance plot is created from two stress σ levels only; the lower stress level is the reference while the other set is shifted on the logarithmic time axis. The master plot so created is quite close to that constructed after a significant amount of experimentation at several σ levels. A formula for stress shift factor aσ obtained by one of us is applied for the prediction of aσ values for the other σ levels. Again, a low σ level is used as the reference while D values for two higher σ levels are used in calculations. The predicted aσ values agree with the experimental ones within the limits of the experimental accuracy. Very close values of the Doolittle constant B are obtained from different subsets of minimum amounts of results and also from the full set of experiments for nine stress levels. The accuracy of the results is affected by the stress range covered (a wider range gives better results) but not by the amount of data used.