Fatigue of marine laminates in aqueous environments

Abstract

The effect of pre-exposure in sea water on the fatigue of glass fibre composites has been investigated in fully reversed bending at constant amplitude. Stiffness monitoring during fatigue showed the usual gradual decline caused by increasing microcrack density, followed by a rapid fall due to the onset of delamination. This transition has been characterised for three resin systems and both wet and dry. Glass–polyester was the only system adversely affected by pre-exposure, which significantly reduced the number of cycles to the transition point, presumably by affecting the fibre/matrix interface. In contrast, both glass–vinyl ester and glass–phenolic resin were largely unaffected by pre-exposure. This was attributed to a superior hydrolysis resistant interface in the vinyl ester case and to a relatively poor initial interface in the case of the phenolic resin. When exposed to water over time, glass–phenolic resin and glass–polyester display rather similar fatigue performances. For polyester there was a significantly higher level of acoustic emission events in the wet samples, especially at higher numbers of cycles, indicating a greater level of ongoing damage.