Interfacial Damage Evolution in Hygrothermally Aged CF/PPA Composites used in Type V Hydrogen Tanks: A Multi-scale Approach

This paper presents a multi-scale experimental investigation into the damage mechanisms in carbon fiberreinforced polyphthalamide (CF/PPA) composites subjected to hygrothermal aging. The study specifically targets their suitability for structural components in advanced hydrogen storage systems, such as Type V pressure vessels. Polyphthalamides (PPAs), as semi-aromatic polyamides, offer superior thermal stability, chemical resistance, and mechanical performance compared to conventional aliphatic polyamides, making them promising candidates for structural components exposed to harsh environments. In order to simulate more severe environmental exposure, accelerated hygrothermal aging tests were conducted at 50 ◦C in immersion. A range of microscopic to macroscopic characterization techniques were used to assess changes in mechanical performance and microstructural integrity. The analysis revealed that the CF/PPA composites retained good matrix ductility even after aging, indicating the resilience of the semi-aromatic polyamide matrix under hygrothermal stress. Multi-scale damage analysis has been performed on both unaged and aged samples at 50 ◦C for various aging times. The dominant damage mechanism identified was decohesion at the fiber/matrix interface, rather than bulk matrix degradation. This interfacial debonding has a significant impact on mechanical performance and is attributed to moisture-induced weakening of interfacial interactions. These findings emphasize the potential of CF/PPA composites for use in high-performance hydrogen storage applications, while highlighting the critical need for interface-tailored designs to enhance environmental durability.