Fatigue life analysis of hybrid E-glass/carbon fibre powder epoxy materials for wind turbine blades

A medium scale demonstrator of a hybrid glass/carbon fibre composite wind turbine blade spar cap/root joint was designed, manufactured and tested statically and dynamically. The current study describes a the step-wise pattern of the demonstrator, its manufacturing and mechanical testing. The glass-carbon fibre transition and ply drop-off strengths are critical to the design of the blade. The design of the glass-carbon transition demonstrator aims to provide a constant stiffness over the specimen length whilst concurrently aiming to keep stress concentrations at a minimum. The specific composite structure combines triaxial and biaxial E-glass and carbon fibres embedded in a powder epoxy matrix. One of the most important aspects of this work relates to the damage response of the coupons. The fatigue analysis of the coupons and the failure mechanisms, such as interfacial delamination and debonding within the transition are presented for all examined coupons. The results provide sufficient evidence to describe the mechanical behavior of the demonstrator over time, and they indicate that the demonstrator has structural integrity over a fatigue life of >1M cycles at 50% of the ultimate tensile strength.