On the prediction of stress relaxation from known creep of nonlinear materials

A method to predict the nonlinear relaxation behavior from creep experiments of nonlinear viscoelastic materials is presented. It is shown that for given nonlinear creep properties, and creep compliance represented by the Prony series, the Schapery creep model can be transformed into a set of first, order nonlinear equations. The solution of these equations enables the obtaining of the nonlinear stress relaxation curves. The strain-dependent constitutive equation can then be constructed for a given nonlinear viscoelastic model, as needed for engineering applications. A comparison example of the calculated stress relaxation curves, with test data for polyurethane demonstrates the very good accuracy of the proposed method.