# Durability of polymeric composites after elevated temperature aging

 Title: Durability of polymeric composites after elevated temperature aging Author: Poole, Eric L Abstract: The Compression After Impact (CAI) strength of polymeric composites after long term elevated temperature aging is studied. Aging temperatures range from 149$\sp\circ$C to 204$\sp\circ$C (300$\sp\circ$F to 400$\sp\circ$F). Two types of matrix material are studied, a thermoset bismaleimide (5260) and a thermoplastic polyimide (K3B). Glass transition temperature (T$\rm\sb{g})$ and fracture toughness are measured after aging. Microscopy and Secondary Ion Mass Spectroscopy (SIMS) are used to evaluate the aged composites. Out-of-plane bending of the CAI specimens during compression is measured by shadow moire. Moire interferometry is used to determine in-plane displacement and strain fields around the impact damage.Results show that the CAI strength degrades with aging for both K3B and 5260. The 5260 matrix suffers from thermo-oxidative degradation at higher temperatures. Surface decomposition causes weight loss and reduces mechanical properties. The CAI strength of the K3B matrix composite also decreases after aging. Evidence of an oxidation reaction is found in the K3B polymer by SIMS, but no weight loss is associated with this chemical reaction. Measured changes in fracture toughness and T$\rm\sb{g}$ do not correlate with CAI strength degradation. Stiffness changes due to aging are insignificant in this study.The degradation region is measured by microscopy near the surface of composites after long aging times. The depth of the degradation zone is dependent on aging time. Degradation growth is modeled with finite elements using diffusion/reaction governing equations. Finite element results agree well with the experimental data. Description: Thesis (Ph. D.)--University of Washington, 1997 URI: http://hdl.handle.net/1773/9963

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