Measuring the interlaminar fracture toughness of thin carbon fiber/ polyamide6 composites using adhesively bonded stiffeners

The present work investigates the interlaminar fracture toughness of a thin unidirectional carbon fiber-reinforced/polyamide6 (CF/PA6) composite laminate. Aluminum (Al) stiffening beams are adhesively bonded on both sides of the thin laminate to avoid undesirable large deformations during the subsequent double cantilever beam tests. Experimentation with various surface treatment techniques and different adhesives is presented, from which it is concluded that the mode I fracture toughness of the CF/PA6 laminate is always higher than the fracture toughness of the adhesives used. Consequently, the crack initiates at the Al-composite interface. A finite element (FE) model is proposed, and quantitative results for the fracture toughness of the laminate are provided (e.g., GIc,ini = 2.1 N/mm). Overall, the study highlights the challenges in the adhesive joining of stiff-ening beams to CF/PA6 surfaces, ways to improve adhesion, and the FE simulation as an alternative to deter-mining the interlaminar fracture toughness of such thin laminates.