Co-authors​ :

 Dharun VADUGAPPATTY SRINIVASAN (SWITZERLAND), Anastasios P. VASSILOPOULOS (SWITZERLAND) 

Wind turbine rotor blades are predominantly assembled using structural epoxy paste adhesives, wherein the adhesive bond line thickness can vary from 2 mm up to 30 mm to accommodate assembly tolerances. Imperfect bonding, voids, residual stresses induced during adhesive curing, and complex loading conditions can initiate cracks in the bond line, compromising the structural integrity of blades. Addressing this challenge necessitates the development of crack-arresting features for thick adhesive joints to improve damage tolerance. This research investigates the quasi-static mode-I fracture behavior of thick glass fiber-reinforced polymeric (GFRP) composite-epoxy adhesive joints, specifically with a nominal bond line thickness of 10 mm. The thick adhesive bond line is toughened by incorporating thermoplastic layers (polyetherimide, perforated polyetherimide, and architected polylactic acid), and their impact on fracture performance is analyzed. The polyetherimide layers are 1.5 mm thick and placed on the GFRP and adhesive interfaces whereas the architected polylactic acid layers are additively manufactured via fused deposition modelling. In pristine joints, the crack propagates in a slip-stick nature. It tends to kink from the adhesive bond line into the adherend, causing severe composite damage and preventing the full potential of the epoxy adhesive from being realized. However, strategic design of the thermoplastic layers at the interface or bond line can control the crack path within the adhesive, minimizing or eliminating damage to the composite adherend. Furthermore, the study evaluates the influence of the presence of thermoplastic layers on both crack initiation and propagation toughness. Figure 1 shows the load versus displacement response of the adhesively bonded GFRP double cantilever beams under mode-I loading.