Viscoelastic Assessment of Fibre-Reinforced Sandwich Structures in Marine Environment

This study investigates the viscoelastic behaviour of fibre-reinforced composite sandwich structures (FRPSSs) for marine applications, with an emphasis on the impact of seawater exposure on their damping properties. FRPSSs composed of E glass-fibre/epoxy facesheets and various PVC foam core configurations were evaluated using tensile and dynamic mechanical analysis tests. Moisture uptake during seawater exposure was tracked using gravimetric methods. All samples followed Fickian moisture absorption patterns, which led to reductions in load-bearing capacity, with tensile strength and elastic modulus declining by 35.4% and 8.4%, respectively. Type B specimens showed a 38% greater reduction in storage modulus compared to Type A, while Tan delta increased by 10% for Type A and 5.7% for Type B, indicating higher strain energy dissipation. Type A specimens exhibited superior stiffness and energy dissipation post-exposure. The higher Tan delta indicated greater strain-energy dissipation and a transition toward more viscous behaviour, implying accelerated degradation over time. Prony-series parameters were extracted to support the development of numerical viscoelastic models for optimizing FRPSS designs, enhancing their resistance to out-of-plane damage in marine environments.