Effect of Moisture on Mechanical and Fracture Response of Rotorcraft Composites

Environmental durability of composite structures is extremely important for design and certification for rotorcraft, which are typically operated in extreme temperature/humidity environments. Extensive empirical evaluations of environmental effects on the structural integrity of laminated composites are therefore performed so that the effects of long-term exposure on the mechanical response can be fully understood. This paper presents the latest observations obtained from a multi-year test program performed by Bell Helicopter Textron Inc. The environmental effects on mechanical and delamination responses of several carbon- and fiberglass-reinforced composite materials are investigated. The study focuses on the resin-dominated material properties and mode I delamination behavior by exposing the specimens to a variety of moisture-laden environments. The results quantify the effects of moisture on mechanical and fracture response for various composite laminates and thus should be extremely useful for future design efforts where such environmental factors must be taken into consideration.