Effect of vacuum thermal cyclic exposures on unidirectional carbon fiber/epoxy composites for low earth orbit space applications

The effects of the low earth orbit environment on three types of unidirectional high-modulus carbon fiber (M40 J, M55 J and M60 J)-reinforced composites were determined in detail. The synergistic environmental factors were the vacuum environment and thermal cycling. Cyclic thermal loading was performed in the temperature range between 120 °C and −175 °C for up to 2000 cycles under the high-vacuum state of 1.3−3 Pa. The material responses were characterized through an assessment of the physical, thermal and mechanical property changes. It follows from the experimental results presented that the synergistic actions of the vacuum and the thermal cycling on the composite property degradation can be attributed to the formation of microvoids and interfacial sliding at the fiber–matrix interface in the early stages of cycling. The implications of these degradation processes based on the dependence of composite properties on vacuum thermal cycling are also discussed.