Prediction of Delamination in Wind Turbine Blade Structural Details

Delamination between plies is the root cause of many failures of composite materials structures such as wind turbine blades. Design methodologies to prevent such failures have not been widely available for the materials and processes used in blades. This paper presents simplified methodologies for the prediction of delamination under both static and fatigue loading at typical structural details in blades. The methodology is based on fracture mechanics. The critical strain energy release rate, G_IC and G_IIC, are determined for opening mode (I) and shearing mode (II) delamination cracks; fatigue crack growth in each mode is also characterized. These data can be used directly for matrix selection, and as properties for the prediction of delamination in structural details. The strain energy release rates are then determined for an assumed interlaminar flaw in the structural detail. The flaw is positioned based on finite element analysis (FEA), and the strain energy release rates are calculated using the virtual crack closure feature available in codes like ANSYS. The methodology has been validated for a skin-stiffener intersection. Two prediction methods differing in complexity and data requirements have been explored. Results for both methods show good agreement between predicted and experimental delamination loads under both static and fatigue loading.