Full‐Scale Cohesive Zone Modeling and Experimental Investigation of Debonding Behaviors in Root Joints for Wind Turbine Blades

ABSTRACT This study investigates the failure behavior of wind turbine blade root joints, employing a full‐scale nonlinear progressive model validated through the building block approach. The model integrates two principal failure mechanisms: A cohesive zone model (CZM) for interface failures between steel‐to‐composite and composite‐to‐composite components; a progressive damage model for the failure of composite structures. At the lowest level of the test pyramid for the building block approach are the sandwich double cantilever beam (DCB) and end notch flexure (ENF) tests, which are used to obtain the interface material properties for the glass fiber–reinforced plastics (GFRP)‐to‐steel interfaces and to validate the CZM parameters. Composite failure was simulated using a progressive damage approach based on material property degradation rules. The failure behaviors for the root joint component were experimentally tested and analyzed with simulations. The results show that the failure modes predicted by the numerical simulations are consistent with the experimental observations, with a deviation of 3% in the maximum failure load. Debonding at the GFRP‐to‐steel interface is the precursor to root joint failure, leading to the damage of wrap yarn. Furthermore, it is demonstrated that the longitudinal stiffness of the UD block in the root joint significantly influences the maximum load‐bearing capacity. The validated model offers valuable insights for optimizing root joint design to improve wind turbine blade performance and durability.