Effect of long-term gaseous hydrogen exposure on the static and fatigue behaviour of T700/VTC401 unidirectional laminates

The long-term effects of gaseous hydrogen exposure on the mechanical performance of carbon-fibre-reinforced polymers (CFRPs) remain poorly understood. This study investigates the static and fatigue behaviour of T700/VTC401 [0]2S carbon-fibre-reinforced epoxy laminates after exposure to hydrogen at 6 bar and room temperature for 10 months. Static tensile tests showed no statistically significant changes in elastic modulus or ultimate tensile strength. In contrast, tension–tension fatigue tests (R = 0.1, 10 Hz) revealed a reduction in fatigue resistance, with an approximately 10% decrease in the fatigue strength corresponding to 2x10^6 cycles and a flatter S-N response. Optical microscopy, Raman spectroscopy, and secondary electron microscopy did not identify hydrogen-specific damage features, suggesting that the observed fatigue degradation resulted from subtle changes in matrix and fibre–matrix interfacial behaviour. The results demonstrate that prolonged exposure to low-pressure gaseous hydrogen can reduce fatigue performance while leaving static tensile properties largely unaffected.