Additive Manufacturing of Glass Fiber‐Reinforced Polypropylene and Its Behavior Under Controlled Hydrogen Exposure

ABSTRACT Glass fiber‐reinforced polypropylene (GFRPP) composites are increasingly explored for hydrogen transport and storage due to their lightweight nature and corrosion resistance. However, the hydrogen response of additively manufactured (AM) GFRPP under laboratory‐scale exposure remains poorly understood. In this study, GFRPP composites were fabricated using extrusion‐based additive manufacturing through systematic optimization of key printing parameters and exposed to hydrogen partial pressures of 3.5 and 7 bars. Mechanical behavior was evaluated using post‐exposure tensile testing. The results revealed a pressure‐dependent response, whereas under the lower experimental hydrogen pressure (3.5 bar), mean UTS increased by 3.73% after 3 days and 9.79% after 5 days, while fracture strain decreased by 3.09% and 1.00%, respectively, although these differences were not statistically significant. In contrast, higher experimental hydrogen pressure reduced UTS by up to 33.68% and ε f by 27.32%, indicating a transition toward brittle fracture behavior. The initial improvement in mechanical properties at the lower experimental hydrogen pressure (3.5 bar) is suggested to arise from localized stiffening and enhanced fiber–matrix stress transfer, whereas the degradation observed at the higher experimental hydrogen pressure (7 bar) is attributed primarily to hydrogen‐induced plasticization, micro‐void formation, fiber–matrix interfacial weakening, and accelerated crack initiation and propagation. These findings provide insight into AM–structure–hydrogen interactions and highlight the importance of processing optimization and controlled hydrogen exposure testing.