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Impact damage and compression behaviours of three-dimensional angle-interlock woven composites after thermo-oxidation degradation

This paper reports impact and compression behaviours of three-dimensional angle interlock woven composites after the thermal ageing degradation in both experimental and finite element analyses. The composite coupons have been aged in atmospheric environment for 4, 8, 16 and 32 days at 180℃. Barely visible impact damage was induced by low velocity impact test and the residual strength was evaluated by following compression test. The results show a substantial decline in compression after impact properties after thermal ageing. After aging at 180℃ for 32 days, the compression after impact stress and modulus retention rates of three-dimensional woven composites are 59% and 82.2%, respectively. Such degradation is attributed to interface damage and matrix degradation. The fracture morphologies observed by microscopy revealed that the failure of the original specimen was dominated by matrix crack, while for long time aged specimens interface degradation became main damage mechanism. The numerical study was used to unveil the influence of matrix crack and interface degradation on failure developments of composites. The results indicate a variation from a brittle failure mode to a progressive failure model after long time ageing.