Thermal,rheological,and mechanical properties of a polymer composite cured at different isothermal cure temperatures

Thermal, rheological, and mechanical properties of a commercial carbon fiber epoxy prepreg, Cycom 977-2 UD, were obtained for isothermal cure temperatures ranging from 149°C to 182°C. For each cure profile, an encapsulated-sample rheometer (ESR) was used to measure the storage modulus. Each ESR cure profile was followed by the glass transition temperature (T_g) test. The degree of cure (α) during cure and the heat of reaction of the prepreg were obtained using a differential scanning calorimeter (DSC). Combined loading compression (CLC) and short-beam shear (SBS) tests were performed to obtain compressive properties and SBS strength, respectively. It was observed that the compressive properties did not vary significantly for the studied isothermal cure temperatures; likewise, the compressive failure mode was the same for all the CLC specimens. However, the SBS strength for the specimens cured at 149°C was approximately 10% less than that of those cured at isothermal cure temperatures ranging from 160°C to 182°C. Further, the failure mode of the SBS specimens cured at 149°C was also different from other specimens. The storage modulus of the ESR sample cured at 149°C also showed a 10% decrease compared to other ESR samples. The SBS strength exhibited a good correlation with the storage modulus and a weak correlation with T_g and α.