Dynamic Behavior of Composite Subjected to Maritime Environments

Material degradation of composite materials is a major concern in maritime applications. In this experimental investigation, effects of moisture-induced degradation, using two different salt solutions with concentrations of 1.8% and 3.7%, on reinforced epoxy composites were studied by means of designed experiments. The objective of this study is to find the change of dynamic behavior of the composite material exposed to marine environments for different time spans of weathering. Two different layups were compared, namely the simple cross ply construction [0°|90°]2s and a balanced symmetric bi-axial construction [±45°]2s. The composite laminate specimens manufactured by vacuum infusion process under laboratory conditions were immersed in the two salt solutions, representing salinity levels of oceans and seas, e.g. Atlantic and Pacific Ocean, Baltic Sea and Black Sea, at accelerated weathering conditions of 65°C. The comparative study comprised three weathering stages, specimens in the non-weathered stage in a desiccated condition, specimens subject to weathering for 15 days and 30 days, respectively. Drop-weight impact tests were performed on all specimens to obtain the maximum load of this sensitive out-of-plane impact stress state. A diffusion study was performed for all layups and solutions at two temperatures, 65°C and 25°C. Thus, the diffusion was described quantitatively to derive damage state predictions. Diffusion curves and diffusion coefficients of both layups [0°|90°]2s and [±45°]2s did not differ significantly. This is, seemingly, because both laminate constructions possessed the same fiber volume fraction f=55%. Different salt concentrations did not penetrate the composite material with different rates. Peak loads through drop-weight testing were significantly decreased by means of the weathering treatment. Once, the composite material was saturated, no significant change of properties occurred for the 30 days period at the accelerated diffusion rate. Comparing both layups, the angle ply laminate significantly bore a higher amount of out-of-plane load in both cases, the non-weathered and weathered specimens in the lower salt concentration. Exceeding certain salinity, in this study reached through the higher salt concentration of 3.7%, the peak loads through impact testing became alike for both layups