Fatigue delaminations in composites for wind turbine blades with artificial wrinkle defects

Out-of-plane wrinkles are manufacturing defects that affect the structural performance of wind turbine blades under fatigue. Glass Fiber Reinforced Polymer (GFRP) laminated specimens embedded with artificial wrinkle defects at two severity ratios (amplitude/half-wavelength) show different resistance to cyclic loading when tested under tension-compression fatigue. This work presents the validation of a fatigue formulation for the prediction of fatigue damage from wrinkles characteristic of wind turbine blades. The validation is performed through numerical models combined with experimental tests in which the fracture framework aims at predicting crack initiation and delamination propagation. The experimental fatigue program loaded the specimens with R = −1 to assess damage growth. The fatigue damage mechanism is quantified as a stiffness degradation, and the damage level is classified into five phases. Comparing the two severity types of wrinkles, the fatigue lifetime for equal external loading differs by approximately two decades. This difference is also captured by the numerical predictions. The lower the aspect ratio (AR), the higher the defect resistance to reversed fatigue loading. The numerical models captured the qualitative behavior of the SN curves and delamination fracture path and location observed in the experiments.