Thermal oxidation growth and damage evolution are highly coupled as oxidative reactions produce thermal stress and weaker materials leading to crack growth, which in turn accelerates the penetration of oxide layers deeper into the structure. Oxygen diffusion-reaction model can predict the time-dependent oxidation state and evolution of oxide layers in unidirectional composites. With given oxidation state and presumed initial cracks, extend finite element method (XFEM) can be used to calculate the damage evolution due to oxidation-induced stress in the composites. These two models run iteratively to predict the oxidation degradation of polymer composites serving at high temperature.

A probabilistic strength distribution model is formulated in this research to represent the scatter of mechanical properties of composite materials and initiate discrete cracks with Hashin failure criteria. With initiated discrete cracks, damage evolution due to high-temperature thermal oxidation can be calculated. The oxidation growth and damage evolution predicted correlate well with experimental observations. The probabilistic strength distribution model enables crack initiation and damage evolution prediction of use-life and durability of composites structures operating at high temperatures.

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