| High performance polymeric composites have achieved a wide acceptance as primary structural materials, and their application is expanding to more aggressive temperature conditions. In this work, polymer matrix degradation is studied not only to identify the service conditions but also to utilize it as a manufacturing process. Providing the fundamental understanding of heterogeneous and anisotropic composite degradation, several model composite systems were collectively investigated to understand various aspects of composite degradation processes. Volatile-induced thermoset-based composite processing was first investigated in order to manufacture a void-free phenolic/carbon composites, which were utilized as carbon/carbon precursors. High temperature processing of this model composite system was also investigated up to 1000{dollar}spcirc{dollar}C using various thermal-chemical-mechanical characterization techniques. Furthermore, carbonization-process modelling was performed to study pressure build-up, temperature distribution, and degree of degradation within degrading composites, which were considered to affect the final performance of carbon/carbon composites. In order to quantitatively indicate the degree of degradation in the time-temperature coordinate, weight-loss kinetics of polymers were thoroughly investigated, providing a composite degradation methodology. As an important property of degrading composites, viscoelastic properties were measured by dynamic mechanical time-temperature multiplexing techniques, and characterized by both the empirical superposition principles and the expanded Dillman-Seferis viscoelastic model. Finally, the consistency of thermo-oxidative weight-loss measurements was examined by isothermal aging experiments, and the effect of composite size and anisotropy on the weight loss was identified. Overall, these seemingly diverse studies are integrated into a basic theme of processing-structure-property relations for high temperature composite characterization and utilization. |
