Buckling Driven Disbond Growth in Sandwich Structures Exposed to Cyclic Loading

Composite sandwich structures in the aerospace and wind energy sectors are subjected to cyclic loading which can foster propagation of pre-existing defects or service induced damages such as face/core disbonds. These disbonds may end up reaching critical sizes, where local buckling of the face sheet is triggered, endangering the structure and deteriorating its aerodynamic efficiency. This work presents a numerical model combining finite element analysis and linear elastic fracture mechanics, aimed at predicting the propagation of face/core disbonds under fatigue loading. The model is compared with experiments performed on GFRP/PVC foam sandwich beams and panels with a pre-existing mid-span disbond exposed to four-point bending. A sensitivity study of the accuracy of the face/core interface fatigue fracture characterization parameters is also presented in order to assess the suitability of the linear elastic fracture mechanics approach in combination with experimental fracture mechanical input data generated using the DCB-UBM experimental fixture. The need for a standardized testing methodology for the fracture characterization of interface fatigue properties for sandwich composites is also discussed.