High Temperature Polymer Matrix Composites (HTPMCs) are widely used by the aerospace industry today because of their high specific strengths, light weight, and the ability to custom tailor their mechanical properties to individual applications. Because of the harsh environmental conditions these materials experience during service use, these composite structures are susceptible to a high rate of thermo-oxidative degradation that ultimately causes premature failure in service. The current knowledge base is lacking in the fundamental spatial variability of the constituent materials upon aging, which precludes composite developers from predicting lifetime mechanical properties of the composites in use. The current study summarizes state of the art techniques in characterizing the thermally oxidized matrix resin system (PMR-15 polyimide), and develops novel techniques in direct mechanical measurement of the spatial variability of mechanical properties. Works to date and future advances in the field with respect to in situ testing are presented.

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