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A Methodology for the Analysis of the Initiation of Inter-Fiber Failure and Local Delamination in Wind Turbine Blade Shell Sandwich Structures

Sandwich structures are extensively used in wind turbine blade shell structures design to reduce total blade weight while providing buckling resistance. In this paper, a novel methodology to analyze the initiation of inter-fiber failure (IFF) and IFF induced local delamination in sandwich face-sheet laminate under full blade fatigue test is proposed. The detrimental influence of in-plane shear stress on IFF initiation under multiaxial fatigue loading was accounted for using a strength-based knockdown factor approach. The initiation of the local delamination was analyzed by a Fracture Mechanics model, where energy release rate (ERR) was studied as the delamination driving force. It is found that the critical ERR for local delamination depends on face-sheet laminate layup as well as resultant forces. The proposed methodology provides a very simple but useful method for evaluating the potential associated damage of blade structure during fatigue testing and it can also be extended to analyze the static loading scenario.