Synergistic enhancement of dynamic energy absorption of CF/epoxy composites via expanded graphite: Effect of laminate geometry and cryogenic conditioning

This study investigates the synergistic effects of expanded graphite (EG) reinforcement (0 - 1 wt%), structural geometry, and cryogenic conditioning on the low-velocity impact (LVI) performance of carbon fiber/epoxy (CF/epoxy) composite laminates. Flat and curved CF/epoxy laminates were fabricated with varying EG loadings using in-house engineered worm-like EGs synthesized via microwave expansion of intercalated Ceylon vein graphite. Flat laminates served as baseline structures, while curved panels, manufactured using a custom mold, representing a composite pressure vessel segment, were cryogenically conditioned in liquid nitrogen at −196 °C and tested at 50 J impact energy using a customized curved fixture. Initial LVI tests to evaluate the optimal EG concentration revealed that 0.1 wt% EG loading exhibited the best performance, increasing peak contact force and energy absorption by 20.5% and 38%, respectively, relative to neat composites, due to enhanced particle dispersion and improved interfacial adhesion. This optimized system was then used to investigate the effects of structural geometry and cryogenic conditioning. While flat laminates showed a greater initial stiffness, the EG-reinforced curved panels surpassed their neat flat equivalents, both in terms of the peak contact force and energy absorption, by over 11% in both cases, highlighting the toughening role of EGs. Cryogenic conditioning further improved performance, with the EG-modified curved laminates absorbing 26% more energy than their ambient-tested counterparts. These results demonstrate the potential of EGs for enhancing the impact resistance of composite structures for use in extreme environments.