Postbuckling of non-linear viscoelastic imperfect laminated plates part I: Material considerations

A method of predicting the non-linear relaxation behavior from creep experiments done on non-linear viscoelastic orthotropic materials is presented. Such a method is desirable since creep experiments are those mainly performed for these materials. It is shown that for given non-linear creep properties, and creep compliance represented by the Prony series, the Schapery creep model for non-linear viscoelastic orthotropic material can be transformed into a set of first-order non-linear equations. The solution of these equations makes it possible to obtain the non-linear stress relaxation curves, from which the strain-dependent constitutive equation of any non-linear viscoelastic model can be constructed, as needed for engineering applications.