Damage Effect Of Vacuum Thermal Cycling On T700/3234 Composites

In order to reveal the damage effects of vacuum thermal-cycling on space flight parts, the changes in mass loss rate, coefficient of thermal expansion and mechanical properties of T700/3234 composites were investigated under vacuum thermal-cycling at the interval of -140~140℃and 10-3Pa. AFM, SEM, FTIR-ATR and DMA were used to characterize the surface morphology, fracture surface morphology and the microscopic structure of composites and storage modulus before and after vacuum thermal-cycling.The experimental results show that the mass loss ratio of the composites firstly increases with increasing vacuum thermal cycles and begins to increase gradually after 48 cycles. Mass loss is due to the gradual evaporation of the water absorbed in the composites and the residual organic solvent retained during preparation in vacuum. With increasing thermal cycles, the 90°tensile strength of the composites was seen to decrease at the initial stage of thermal cycling, increase after 48 cycles, which tends to level off after about 95 cycles. The bend strength and bend modulus were both found to increase at the initial stage of thermal-cycling, decrease after 14 cycles, which tends to be smooth after approximate 100 cycles. The interlaminar shear strength of the composites decreases with increasing thermal cycles and then begins to increase after 14 cycles, which finally becomes flat after 48 cycles. It can be found in AFM, DMA and FTIR-ATR test that the crosslinking degree of polymer matrix is found to increase after 48 vacuum thermal cycles and interfacial bedonding within the composites appears. The interfacial debonding region gradually becomes saturated after 198 cycles. With decreasing the temperature, the longitudinal coefficient of thermal expansion,ΔL/L, of the composites is found to rise at initial stage. After vacuum thermal-cycling, it decreases firstly and then increases with decreasing temperature. However the transverse coefficient of thermal expansion of the composites is nearly not affected by vacuum thermal-cycling.