The use of fiber-reinforced composites in marine applications such as components of tidal turbines and wave energy converters is becoming attractive because of their reduced weight and improved corrosion resistance. However, when these polymer matrix composite structures are exposed to seawater environment, degradation of material properties is produced affecting reliability. A deep understating of seawater ageing effect on composite structures is essential to ensure long-term performance and durability. A systematic investigation was conducted in this work to evaluate the effect of seawater ageing on mechanical properties of five different composites manufactured with two types of fiber fabrics (unidirectional glass and carbon) and three types of resin systems (epoxy, vinylester and polyester). The behavior of samples with and without accelerated seawater ageing and subjected to tensile, compressive, flexural and shear loading was evaluated. A significant strength reduction due to seawater ageing was observed on composites with epoxy and polyester matrices. Low strength and stiffness values of composites with vinylester matrix are in general observed; however, seawater ageing makes these properties increase slightly. Fracture surface examination by scanning electron microscopy revealed delamination, fiber debonding and resin crumbling due to seawater effect.

During their service life, composite marine structures made up of glass fiber reinforced polymers are susceptible to be affected by environmental and loading conditions such as seawater and low velocity impacts which can cause them severe structural damage. Based on this fact and concern, the present work investigates the influence of seawater aging on impact behavior of glass fiber/epoxy composite laminates with and without drilled holes. To achieve this goal, glass fiber/epoxy laminates were manufactured by resin transfer molding and then cut into specimens for low velocity impact testing. Before impact tests, specimens were immersed in artificial seawater at 70°C for 1464 h. After that time, dry (before seawater aging) and wet (after seawater aging) specimens were tested at 10 and 15 J impact energies using a drop-weight impact tower. The results of accelerated seawater aging confirmed that the presence of drilled holes in composites does not influence on their moisture absorption content and diffusion coefficient. The impact test results showed that the impact properties of wet specimens are significantly lower respect to dry specimens. It was found that the peak force of wet specimens displays a reduction of approximately 40% with respect to the dry specimens as a consequence of moisture absorption which causes plasticization of the polymeric matrix. Ultrasonic C-scan inspection showed that damage area of wet specimen increased up to 250% compared to that of dry specimen. Fractographic analyses by scanning electron microscopy and X-ray computerized tomography revealed that low velocity impact in composite laminates produced damage mechanisms associated to matrix cracking, fiber/matrix debonding, fiber breakage, and delamination, which were more prominent in laminates with drilled holes and subjected to a previous seawater exposition.