Improved Surface Treatment of SMA Foils and Damage Suppression of SMA-Foil Embedded CFRP Laminates

The authors have been conducting research and development studies on some applications of embedded SMA foil actuators in CFRP laminates for weight reduction and improvement of reliability for next generation aircraft. The goal of this research is to develop a method for the suppression of damage growth in CFRP laminates. It is certified that one of the key technologies is bonding properties between SMA foils and CFRP laminates. In this paper, improvement of bonding properties between SMA foils and CFRP and confirmation of suppression effects of damage growth are described. Some surface treatments (sol-gel method, anodic-oxidation method and spattering method) were performed on SMA foils. Then, peel resistance and single lap shear strength tests were performed using surface treated SMA foils. It was found that treatment by 10%NaOH is the most effective treatment for improvement of bonding properties. The treated surface was found porous and rough, which is supposed to provide anchoring effects of SMA/CFRP interfaces. Then, quasi-static load-unload tests were performed using the optimum treatment as mentioned above to investigate the damage behavior of quasi-isotropic CFRP laminates with embedded SMA foils. Micromechanisms of fracture behavior and the correlation between the crack density and the residual strain were discussed. The recovery stress of the SMA foil generated at over Af temperature showed capability of suppression for onset of transverse cracks in quasi-isotropic CFRP laminates with embedded SMA foils.