Multiaxial Stress Based High Cycle Fatigue Model for Adhesive Joint Interfaces

Large utility wind turbine rotor blades (WTBs) comprise of adhesive joints with typically thick bond lines. The dynamic aero-elastic interaction of the WTB with the airflow generates multiaxial non-proportional, variable amplitude stress histories in the adhesive joints. Structural optimization of WTBs employed at an early design stage sets high demands on computationally efficient interface fatigue models capable of accurately predicting the critical locations prone for interface failure. The numerical stress-based interface fatigue model presented in this work uses the Drucker-Prager (DP) criterion to compute three different damage indices corresponding to the two interface shear tractions and the outward normal traction. The DP model was chosen because of its ability to consider shear strength enhancement under compression and shear strength reduction under tension. The model was implemented as Python plug-in for the commercially available finite element code Abaqus. The model was used to predict the interface damage of an adhesively bonded, tapered glass-epoxy composite cantilever I-beam tested by LM Wind Power under constant amplitude compression-compression tip load in the high cycle fatigue regime. Results show that the model was able to predict the location of debonding in the adhesive interface between the webfoot and the cap.