Energy absorption characteristics of expanded graphite-reinforced carbon/Elium and carbon/epoxy composites exposed to cryogenic conditions for hydrogen storage application

This study investigates, for the first time, the combined effects of expanded graphite (EG) nano-reinforcement, matrix type (epoxy vs. Elium), laminate curvature, and cryogenic conditioning on the low-velocity impact (LVI) behavior of carbon-fiber (CF) composites engineered for hydrogen storage applications. Unlike prior work limited to flat laminates and ambient conditions, this study uniquely integrates nanofiller effects, structural geometry, and cryogenic exposure. Incorporating worm-like EG into both matrices simultaneous enhances stiffness, peak load, and elastic energy recovery at ultra-low filler content. An optimal EG loading of 0.1 wt.% is identified, forming an effective stress-bridging network, as confirmed by Raman mapping and interlaminar shear strength improvements of ∼22% (CF/epoxy) and ∼23% (CF/Elium). Distinct reinforcement mechanisms are revealed, chemical stiffening in CF/epoxy and plasticity-driven energy dissipation in CF/Elium leading to fundamentally different impact responses. Notably, EG-reinforced CF/Elium laminates achieve a 11% higher absorbed energy than neat one and retain significant elastic energy after cryogenic conditioning, demonstrating exceptional low-temperature resistance. Curved laminates, representative of tank geometries, further reveal matrix-dependent transitions between elastic and plastic dissipation modes, with EG-reinforced CF/Elium showing superior stiffness recovery and delayed instability. Overall, this work establishes a novel framework linking nanofiller, matrix, and geometry for designing damage-tolerant composites for cryogenic hydrogen storage.