Investigation of failure mechanisms in GFRP sandwich structures with face sheet wrinkle defects used for wind turbine blades

Wrinkle defects can be formed during the production of wind turbine blades consisting of composite monolithic and sandwich laminates. Earlier studies have shown that the in-plane compressive strength of a sandwich panel with wrinkle defects may decrease dramatically. This study focuses on the failure modes of sandwich specimens consisting of thick GFRP face sheets with a wrinkle defect and a balsa wood core subjected to in-plane compression loading. Three distinct modes of failure were found, and the strain distributions leading up to these failures were established by use of digital image correlation (DIC). Finite element analyses were subsequently conducted to model the response of the test specimens prior to failure, and generally a very good agreement was found with the DIC measurements, although slight differences between the predicted and measured strain fields were observed in the local strain values around the wrinkle defect. The Northwestern University (NU) failure criterion was applied to predict failure initiation, and a good correlation with the experimental observations was achieved.