Testing to evaluate water effects in composites: a critical regard

Abstract

Polymer matrix composites are already widely used in marine applications, but many of these are overdesigned (glass/polyester pleasure boat hulls for example) and rarely heavily loaded. These structures can last for 30 years or more and the main issue is how to dispose of them at the end of their useful life. However, composite materials are increasingly being proposed for more highly loaded structural components such as propellers and tidal turbine blades. For these structures, the effects of seawater aging combined with mechanical loads are critical, as the commercial success of such components depends on minimal intervention and high reliability. For this type of composite the tests performed to evaluate degradation due to long term immersion are therefore critical. It is also essential to have a robust approach in order to evaluate potential alternative materials, some of which (natural fibre composite for example) show quite specific behaviour when wet. This paper will describe the current approach to account for wet aging, its limitations and some proposals for an improved testing methodology