Effect of physical aging and variable stress history on the strain response of polymeric composite

A constitutive equation capable of modeling the effect of physical aging on the non-linear creep response for frequently changing stress levels is presented. Schapery's non-linear theory is used to model the non-linear viscoelastic behavior and the effect of physical aging is incorporated through the use of Struik's effective time theory. The constitutive model is then combined with classical laminate theory to predict the response of multi-angle laminates subjected to cyclic loading. Predictions on the basis of this constitutive model are compared with data from the literature. These comparisons confirm that preditions without including the effect of physical aging grossly overpredict the measured creep status. (C) 1997 Elsevier Science Limited.