Fractographic analysis of sandwich panels in a composite wind turbine blade using optical microscopy and X-ray computed tomography

This study provides a new perspective on the failure of sandwich panels in a composite wind turbine blade. Fractographic characteristics of fracture regions are examined thoroughly using optical microscopy and X-ray computed tomography. The detailed fractographic analysis leads to the identification of the failure modes and failure sequence. This study addresses an important but rarely studied failure process in the sandwich panels cored with grooved foams. The partially resin-filled grooves lead to large voids in the foams that cause crack migration of skin/core debonding from one side of sandwich panels to the other. In this study, the adverse effects of the partially resin-filled foams are addressed and the associated challenges in the blade design are highlighted. It is found that the fracture of skin laminates under biaxial compression is characterized by a shear-dominated failure mode in the form of kink bands in two directions. The whitening of skin laminates under tension is caused by micro-cracks in the matrix and the fiber/matrix interface. Moreover, fiber breakage also occurs in the whitening region although it is not visually apparent. These fractographic characteristics could help the identification of the root causes of blade failure if similar observations are found.