Fatigue resistant fiberglass laminates for wind turbine blades

Recent test results show that fiberglass laminates composed of unidirectional (0{degree}) and {+-}45 stranded fabric layers, typical blade materials, vary significantly in tensile fatigue resistance depending on the overall fiber content and the relative amounts of reinforcement in each direction. S-N fatigue data are presented for a range of laminates under both tensile and compressive fatigue loading. The results show poorer than expected fatigue performance for laminates composed of stranded fabrics at (a) high fiber contents and (b) high relative amounts of {+-}45{degree} reinforcement. Optimum fatigue resistant materials appropriate for both flange areas and webs of blades are identified. Laminates which fall into the poor fatigue resistance category (similar to woven fabrics and triax stitched fabrics) do not behave in a fiber-dominated manner which is required for application of the high cycle DOE/MSU database to lifetime prediction as described in Sutherland and Mandell (1996).