Delamination between plies is the root cause of many failures of composite material 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 in typical structural details in blades under both static and fatigue loading. The methodologies are based on fracture mechanics. The critical strain-energy release rate, GIC and GIIC, 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 a 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 methodologies have 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.

Issue Section:
Technical Papers
Keywords:
wind turbines, delamination, fatigue, fracture mechanics, finite element analysis
Topics:
Delamination, Fatigue, Fracture (Materials), Stress, Skin
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