Methodology to predict stiffness knock-down in laminates for wind turbine blades with artificial wrinkles

This work presents a methodology to evaluate the effect of wrinkle defects in the stiffness response of laminate characteristic of wind turbine blades. The assessment is carried out through numerical models and experimental tests with coupon specimens embedded with artificial wrinkles. Specimens are manufactured with two types of defects, prone to arising along the manufacturing process of wind turbine blades. Image-based numerical models were built to enclose the actual features of the cross-sectional wrinkling of each defect type. Experimental quasi-static tension and compression tests were performed, where extensometers collect the strain distribution about the wrinkle section as around the flat section of the test specimens. Two-dimensional finite element simulations carried out in Abaqus/Standard captured the stiffness behaviour of the two types of wrinkles. The numerical approach is validated against the quasi-static tests retrieving a fair agreement with experimental data. A significant knock-down in the stiffness response was found due to the wrinkle with larger aspect ratio of amplitude / half-wavelength.</p