Investigation of the effect of wrinkle features on wind turbine blade sub-structure strength

Wrinkles are known to have a strong knock-down on the mechanical performance of structures made from composite materials. Here, static tensile tests were conducted to investigate the effect of wrinkle features on the strength of a wind turbine blade sub-structure, representative of a blade root feature. A pultruded tapered insert is embedded in each sub-structure and the wrinkle is in close vicinity to the termination of the tapered insert. Each of the tested sub-structures was then numerically modelled using finite element simulations. The numerical representations of the wrinkle geometries were constructed based on measurements of the actual structures, and an automatic fitting of the four chosen wrinkle features; angle, depth, wash out, and location. There is less than 5% deviation between the simulation and experimental results for all tested sub-structures. The numerical model was able to predict when the failure mode changed from a delamination at the tapered insert to a delamination in the wrinkle area. The average wrinkle angle was found to be a better metric than the maximum wrinkle angle to characterise the severity of the wrinkles in the vicinity of a tapered insert.