Real-time damage monitoring in trailing edge bondlines of wind turbine blades with triboluminescent sensors

Abstract

Adhesively bonded joints in wind turbine blades, particularly trailing edge joints, are prone to damage due to high-intensity stress concentrations, missing adhesive, or deficient bonds at the bonding surfaces. If not detected early, cracks or disbonds in the trailing edge might propagate rapidly resulting in catastrophic failure of the whole blade. No dedicated in situ sensor system is, as of now, available for real-time damage monitoring in the critical adhesively bonded joints. This article discusses the use of in situ triboluminescent optical fiber sensors for damage monitoring in adhesively bonded composite joints. Double cantilever beam and three-point bend end-notched flexure samples were fabricated from a thick glass fiber/vinyl ester composite and glued with a two-part methacrylate-based structural adhesive. The in situ triboluminescent optical fiber sensors were embedded into the adhesive layer. Double cantilever beam and three-point bend end-notched flexure tests were performed to determine the mode I and mode II fracture toughness of the adhesive joints, respectively. The results show that the triboluminescent emissions occur at the onset of damage when performing double cantilever beam and three-point bend end-notched flexure fracture tests on adhesively bonded composite panels of different adhesive thicknesses. The triboluminescent response increases with the fracture toughness of adhesive joints. The double cantilever beam and three-point bend end-notched flexure specimens undergo cohesive failure in the adherend thickness. Optical microscopy was utilized to obtain better insights of fracture lines. Results indicate that in situ triboluminescent optical fiber sensors can monitor damage in adhesive in real-time without generating false alarms.