Experimental and numerical analyses of matrix shrinkage and compressive behavior of 3-D braided composite under thermo-oxidative ageing conditions

Matrix shrinkage induced in thermo-oxidative ageing process of composites may lead to interfacial damage and thus significantly affect their mechanical properties. This work aims to characterize the oxidation-induced matrix shrinkage in three-dimensional (3-D) braided composite. Specimens were exposed at hot air (180 °C) for 4, 8, and 16 days respectively. Interferometric microscope was employed to determine the matrix shrinkage in composite surface under different ageing conditions. The resulting interfacial damage was observed by optical microscopic examination. Based on the experimental results, we propose a two-step numerical methodology to investigate the effect of thermo-oxidative ageing on compressive properties of braided composite. The established finite element model can effectively capture the deformed and degraded configuration of the aged material. Further simulation results reveal that the shrinkage-induced interfacial damage leads to a lower stress distribution in the exposed ends of braiding yarns. The ultimate deterioration in compressive properties of braided composite is attributed to both resin degradation and yarn-matrix interfacial damage.