THE NONLINEAR VISCOELASTIC-VISCOPLASTIC BEHAVIOR OF IM7 5260 COMPOSITES SUBJECTED TO CYCLIC LOADING/

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