Some New Aspects of the Nonlinear Characterization of Creep and Stress Relaxation of Polymers

Summary

Based on the well-known mechanical models made of springs and dashpots, the linear viscoelastic behavior of materials can be described by exponential series with a limited number of terms. Since the models for creep (increasing function) and stress relaxation (decreasing function) are different, the series are also of different type. The approach can be extended to the nonlinear viscoelastic range by introducing some load dependent nonlinearity functions. In the present paper it is shown that both, creep and stress relaxation can be represented by the same type of exponential series. Further, based on experimental data, it is shown that the instantaneous response of the nonlinear polymeric material to the sudden loading step is always linear elastic. Finally, a way to reduce considerably the experimental efforts needed for the material characterization is shown.