Hygrothermal Aging and Failure Mechanism of Glass Fiber Reinforced Polyurethane Composite Frames for Offshore Applications

The durability of glass fiber reinforced polyurethane (GFRPU) composites under harsh marine environments is critical for offshore photovoltaic applications. This paper investigates the hygrothermal aging behavior and failure mechanisms of GFRPU composites by pressure cooking test (PCT) at 121°C and 100% RH for up to 240 h. Moisture absorption increases linearly to 2.42% after 240 h without reaching saturation, deviating from Fickian behavior due to diffusion‐damage coupling. Mechanical properties show a two‐stage evolution: tensile strength and modulus initially increase (106% and 103% at 48 h) due to post‐curing of residual reactive groups, then decline to 59% and 87% at 240 h, while flexural strength and ILSS drop to 44% and 38%, revealing an interface‐dominated damage hierarchy (ILSS > flexural > tensile). Microstructural analysis confirms a four‐stage causal chain (swelling, hydrolysis, debonding, and crystallization‐induced failure) driven by progressive urethane hydrolysis. The Arrhenius model predicts a service life of 10 ~ 13 years in tropical humid climates. These findings establish interface‐controlled failure as the root cause of long‐term degradation, offering a mechanistic framework for durability design of offshore composite.