Damage evolution during high-temperature oxidative aging of composites

The service life of the High Temperature Polymer Matrix Composites (HTPMCs) is limited by thermo-oxidative degradation. Oxidation weakens the material and drives crack formation and propagation. Newly formed crack surfaces allow oxygen to permeate deeper into the structure and accelerate the oxidative degradation. A high-resolution chemo-mechanics model has been developed to study the thermo-oxidative degradation of polymer resins and composites subjected to long-term (thousands of hours) exposure to oxidative environments. This approach entails simulating the time-dependent growth of the surface oxidation layer and analyzing the stress and damage in the material using an oxidation-state dependent constitutive model. This paper describes the effect of fibers on the oxidation and damage growth in a lamina. Since both the oxygen diffusivity and the strength of the lamina are orthotropic, the acceleration of oxidation growth after damage initiation is controlled by the transverse strength and toughness of the oxidized zones in the lamina. We show the long-term oxidation and damage growth in a Carbon/Polyimide composite system subjected to high-temperture isothermal aging.