Damnification And Mechanism Of Carbon Fiber/BMI Composites In Vacuum Thermal-Cycling

Due to its outstanding performance, composite materials has been widely used in aerospace and become the fourth type of aerospace structural materials. Many factors, which include atomic oxygen, ultraviolet radiation, particle radiation, high vacuum, plasma, thermal cycling, micro-meteoroids and space debris and so on in space environment, affect the performance of the materials. And due to the complexities of composites itself, it is of great importance to explore space environment effects to composites.In this paper, carbon fiber/bismaleimide (BMI) resin matrix composites were exposed to a simulated low-Earth orbit environment of±140℃and 10-3Pa. The influences of vacuum thermal-cycling on physical and thermal properties of carbon fiber/bismaleimide resin matrix composites were investigated. The surface and fracture morphologies were observed by AFM and SEM, respectively. The results show that the vacuum thermal-cycling of carbon fiber/bismaleimide resin matrix composites increases the mass loss ratio and the surface roughness of composites, the tensile strength decreases firstly, tends to be smooth after 48 cycles, flexural strength and ILSS increase at first and then decrease, reach the maximum after 48 cycles, it is found in DMA test thatαrelaxation peak decreases with increasing vacuum thermal cycles, the temperature corresponding to the peak shifts to a higher one and tanδpeak broadens, indicating the enhanced Tg by increasing vacuum thermal cycles. It can be seen that the thermal expansion coefficient increases with increasing vacuum thermal cycles through the thermal expansion coefficient curves. Simulated test implies that outgassing of composites, a certain degree of damage the interface and post curing of the resin matrix are attributed to vacuum thermal-cycling.