This work aims to investigate the quasi-static mode-I fracture behavior of thick glass fiber-reinforced polymeric composite-epoxy adhesive joints having a nominal bond line thickness of 10 mm, focused on wind turbine rotor blade applications. The thick adhesive joint was modified with PEI interlayers and architected crack-arresting features and their effect on mode-I strain energy release rate (SERR) was experimentally investigated. By having PEI layers at the joint interface, the crack path is controlled within the adhesive-PEI interface leaving no or minimal damage to the composite adherend. Architected crack-arresting features can significantly increase the SERR during crack initiation and exhibit stable failure as compared to the pristine joints.