Microscale and mesoscale modeling of seawater diffusion and its degradation in composites materials

Abstract This study investigates the effect of seawater ageing on composite materials through finite element modeling at multiple scales. A microscale Representative Volume Element (RVE) with random fiber distribution was developed to simulate moisture diffusion as a function of fiber volume fraction and interface properties. At the mesoscale, Double Cantilever Beam (DCB) cohesive-zone simulations were performed to evaluate changes in interlaminar fracture toughness under different ageing levels. Results show that moisture uptake follows Fickian diffusion and occurs predominantly in the polymer matrix, while higher fiber fractions reduce diffusivity by limiting available pathways. Moderate ageing produced a temporary increase in fracture toughness, attributed to post-curing effects, whereas prolonged exposure led to a significant reduction in mechanical properties. These findings highlight the dual role of seawater exposure: limited absorption may enhance performance, but long-term immersion results in deterioration. The FEM framework provides a predictive basis for assessing durability of composites in marine environments.