Epoxy/Polystyrene Blend as a Model for Simulating Void Expansion and Crack Initiation After High‐Pressure Hydrogen Exposure

ABSTRACT Epoxy (EP)/polystyrene (PS) blends are used to model crack initiation from voids formed after high‐pressure hydrogen exposure. The blends contain spherical PS domains as well‐defined sparse structures within the EP matrix, as origins of internal fracture. SEM analyses show domain sizes followed a lognormal distribution and expand after 90 MPa hydrogen exposure. In EP with 5 wt% PS(EP/PS5), matrix cracks are observed originating from the spherical PS domains. Matrix cracking after hydrogen exposure occurred in EP/PS5 with spherical PS domains about 3 μm in diameter, indicating that larger PS domains correlate with crack initiation in the epoxy matrix. The cracks exhibit a disk‐like morphology. In all samples, originating from the sparse region in EP, voids with diameters of approximately 100 nm are observed. Density changes predicted from domain expansion agree with measurements, except EP/PS5 where matrix cracking caused further reduction. Elastic moduli decrease with PS content. Elastic moduli of EP with 4 wt% PS and EP/PS5 drop significantly after exposure due to domain expansion and matrix cracking, respectively. EP/PS blends with well‐defined sparse/dense structure demonstrate the fracture process by internal pressure, which simulates void formation and void growth in the polymeric material by penetrated hydrogen.