Seawater immersion ageing of glass-fibre reinforced polymer laminates for marine applications

Four glass-fibre reinforced polymer (GRP) materials along with castings of their matrix resins have been aged in seawater in the laboratory, some loaded under set-strain. Water uptake behaviour has been compared for the polyester, phenolic and vinylester GRPs and neat resin castings, and losses in mechanical properties determined for the GRPs. The phenolic GRP displayed anomalous uptake behaviour considered to relate to both interface and matrix absorption. Water uptake by the polyester and vinylester laminates appeared to be affected initially by suppression from fibre barrier effects then later by enhancement from interface effects. Flexural strength fell by 15–21% for the water saturated polyester and vinylester GRPs, and by 25% for the phenolic GRP. Loading at 20% of ultimate strain while under immersion exacerbated only the phenolic laminate degradation, advancing the loss in strength to 36%. Interlaminar shear strengths fell by between 12 and 21% for the GRPs at close to saturation.