Multi-scale analysis of compressive behavior of 3D five-directional braided composites after thermal oxygen aging: Experimentally validated theoretical and numerical models

Three-dimensional (3D) braided composites have been widely used in the aeronautics and astronautics industries, especially as components in hot-pressing conditions. However, its mechanical performances are specially affected under high temperatures. This work proposes to detect the influence of thermal oxygen aging on residual mechanical behaviors and failure mechanisms of 3D five-directional braided composites with different braiding parameters using the multi-scale method. Firstly, a micro-scale theoretical mass loss model was developed to predict the mass loss, and the effective mechanical properties of the fiber bundle were calculated using the Mori-Tanaka model. Moreover, meso-scale parameterized model was established to capture the damage evolution and predict residual mechanical responses. Finally, the compressive experiments of aged composites were conducted to verify theoretical and numerical models. The results concluded that as the aging days increased, the compressive performance continuously decreased, and the degradation of performance retention rate slowed down. The resin plasticization and interface debonding were primary factors to result in the decline of mechanical performances of composites. The effect of thermal oxygen aging on composites with small braiding angle was more significant. The theoretical and simulation strategies could effectively predict aging behaviors of component structures and residual mechanical properties.