Degradation Due to Oxidation Around Voids, Cracks and Holes

High Temperature Polymer Matrix Composites (HTPMCs) exposed to oxidizing environments are subject to mechanical property degradation due to chemical changes in the resin. Long-term degradation rates due to oxidation in a composite structure are controlled by the damage evolution rates in the oxidized zones, which in turn are determined by the composite’s strength and toughness in these regions. The presence of voids, cracks, and holes in the structure alters the local oxidation zone morphologies. In this paper, we describe a methodology for prediction of Open Hole Tensile (OHT) residual strength of isothermally-aged IM7/(bis) maleimide quasi-isotropic composites under static loading. The composite oxidation profiles around holes are explained by monitoring the development and growth of damage through fluorescence imaging in conjunction with optical microscopy and X-ray computed tomography (CT) techniques. Preferred damage initiation directions are investigated for several combinations of the fiber orientations with respect to the mechanical loading direction and its influence on OHT. The paper presents comparisons of observed and simulated microstructure changes and correlations of damage states and strength predictions with experimental observations.