Marine environment induced failure of FRP composites used in maritime transport

•Real sea environment effects on marine composites for prolonged periods.•Marine organisms create voids in the matrix influencing mechanical properties.•The research indicates the importance of biofouling for marine composites.•Future development of a stochastic predictive mechanical behavior numerical model. Fiber reinforced polymer (FRP) composites are being extensively considered for construction of ships and marine structures. Due to harsh environmental operational conditions, failure prediction of such structures is an imperative in this industry sector. This paper presents the final results of a 2-year research of real marine environment induced changes of mechanical properties in FRP composites. Realistic environmental input parameters for structural modeling of marine structures are crucial and can be obtained by conducting tests in real sea environment for prolonged periods, as opposed to usual accelerated laboratory experiments. In this research, samples of epoxy/glass and polyester/glass with various fiber layout configurations have been submerged under the sea for periods of 6, 12 and 24 months. An analysis of mass changes, marine microbiology growth, tensile strength and morphological structures of the coupons was performed and compared with samples exposed to room environment. All samples exhibited an increase in mass due to seawater absorption and microorganism growth in the organic resins (matrix). The tensile strength loss variation through the periods of submersion showed a correlation with the fiber layout configuration. The results of optical and scanning electron microscopical investigation indicated significant matrix morphological changes primarily due to salt crystal formation and the impact of sea microorganisms embedding in and attaching to the resin. The outcome of this research will be the basis for a set of realistic input parameters for a failure analysis numerical tool currently in development that can be applied for life-time behavior predictions of marine structures.