The Nonlinear Viscoelastic-Viscoplastic Behavior of IM7/5260 Composites Subjected to Cyclic Loading

A constitutive model consisting of a combination of the Schapery nonlinear viscoelastic heredity integral and a nonlinear viscoplastic functional employed by Zapas and Crissman is described. Material constants associated with the constitutive models are measured for graphite-bismaleimide (IM7/5260) composites at elevated temperatures and stress levels. These results are then combined with classical lamination theory, so as to predict the response of a multi-angle laminate to cyclic thermomechanical loadings. Predictions are favorably compared with measurements obtained during a 50-hr test involving ten 5-hr loading cycles.