Investigating the microcracking behaviour of a commercial epoxy matrix under cryogenic conditions

Carbon fibre-reinforced polymers (CFRPs) are increasingly being adopted in cryogenic applications, particularly in zero-emission aviation and lightweight liquid hydrogen storage. This study examines the susceptibility of a commercial epoxy infusion matrix to cracking under cryogenic conditions using in-situ characterisation techniques. At cryogenic temperatures, the CFRP exhibits a 76% reduction in stress at first crack, while, in contrast, the fracture toughness of the neat epoxy increases considerably. To investigate this, we report for the first time the use of cryo-scanning electron microscopy (cryo-SEM) to visualise in-situ microscale damage evolution in an epoxy CFRP under controlled temperature change. Differences in microstructural damage development between slow and rapid cooling provide new insight into cryogenic damage processes. The findings underscore the critical role of thermally induced local stresses in driving microcracking in CFRPs.