Static and Fatigue Characterization of Large Composite T-Bolt Connections in Marine Hygrothermal Environments

• Published in: Journal of marine science and engineering Vol. 11; no. 12; p. 2309
• Main Authors: Murdy, Paul, Hughes, Scott, Miller, David A., Presuel-Moreno, Francisco J., Bonheyo, George T., Gunawan, Budi, Hernandez-Sanchez, Bernadette A.
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 01.12.2023; MDPI
• Subjects: Ageing; Aging; bolted connections; Composite materials; Composite structures; Degradation; Energy; ENGINEERING; Environmental degradation; Epoxy compounds; Epoxy matrix composites; Fasteners; Fatigue life; Fiber composites; Fiber reinforced polymers; Glass fiber reinforced plastics; Glass-epoxy composites; hygrothermal aging; Laboratories; Laminates; Layers; Marine energy; Marine environment; marine renewable energy; Materials fatigue; Moisture absorption; Offshore structures; Polymer matrix composites; Polymers; Renewable energy; Renewable resources; structural validation; Temperature; Tension; Test methods; TIDAL AND WAVE POWER; Turbines; Wave energy; Wave power; Wave power devices; United States > US
• ISSN: 2077-1312; 2077-1312
• DOI: 10.3390/jmse11122309

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 research has investigated how this translates into larger-scale composite structures. This paper presents a subcomponent-scale study which investigates the effects of hygrothermal aging and subsequent static and fatigue characterization of 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, even though the composite specimens were only partially saturated with water. 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 ultimate strengths and fatigue lives of even partially saturated thick composite T-bolt connections, indicating that degradation of the outer plies on thick composite laminates can have pronounced effects on the whole structure. It discusses the challenges of building an understanding of the effects of harsh marine environments in large-scale composite structures.