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In order to help understand matrix-dominated behavior in laminated polymer matrix composites, an elastic/viscoplastic constitutive model was developed and used to predict stress/strain behavior of both off-axis and angle-ply symmetric laminates under in-plane, isothermal, axial tensile loading.
The model was validated for short duration tests on graphite-reinforced thermoplastic and bismaleimide composites at elevated temperatures. It accurately accounted for short-term stress relaxation and short-term creep, strain rate sensitivity, and material nonlinearity. For long-term behavior, the short-term testing times were extended by approximately 20 times. Periods of creep and stress relaxation were used to investigate the ability of the model to account for the extended time behavior. The model generally underestimated the total change in strain and stress for both the extended creep and extended relaxation, respectively.
aging, material nonlinearity, constitutive model, elevated temperature, stress relaxation, creep, viscoplasticity
NASA Langley Research Center, Hampton, VA