Mechanism of matrix influencing the cryogenic mechanical property of carbon fibre reinforced epoxy resin composite

This study focuses on the cryogenic mechanical property of carbon fibre reinforced epoxy resin composite (CFRP) unidirectional laminate, and the cryogenic evolution mechanism is discussed from the microstructural perspective of resin free volume and intermolecular forces. The primary transition temperature (147 degrees C) and the secondary transition temperature (-25 degrees C) is identified through dynamic mechanical analysis. As the cryogenic condition (-196 degrees C) is significantly lower than the temperature of main-chain segmental and micro-structure unit motion, the resin molecular segments are frozen, free volume fraction and resin toughness are reduced, thus the brittleness increases. These effects reduce the cryogenic failure strain of CFRP at break by 43.7% compared to room temperature, resulting in a smoother fracture surface morphology. Resin molecules under cryogenic condition have higher packing density, stronger intermolecular forces, which increase the strength and modulus of both resin and CFRP.