PNNL

Abstract

Fiber-reinforced polymer composites have been highlighted as ideal candidates for structural applications in marine renewable energy devices, such as tidal turbines and wave energy converters. It is well understood that harsh marine environments can cause strength degradation of composite laminates, which has been extensively researched at the coupon scale; however, no re- search has investigated how this translates to larger-scale composite structures. This paper presents a subcomponent-scale study, which investigates the effects of hygrothermal aging and subsequent static and fatigue testing on thick composite T-bolt connections, as part of a large, multilaboratory materials research effort. Of the glass-reinforced epoxy and vinylester-epoxy matrix composites tested, both showed measurable static strength degradation (4%–36 %) after being hygrothermally aged. Under tension-tension fatigue loading, the epoxy specimens performed very well in their dry states but exhibited significant degradation after hygrothermal aging. In comparison, the vinylester- epoxy specimens had much shorter fatigue lives in their dry states but exhibited no degradation after hygrothermal aging. Overall, this research demonstrates that hygrothermal aging can have significant effects on the static and fatigue strengths of even partially saturated thick composite T- bolt connections and discusses the challenges of building an understanding of the effects of harsh marine environments in large-scale composite structures.