Rapid adhesive bonding of thermoplastic composites and titanium withthermoplastic adhesives

Abstract

ADHESIVE bonding processes are often used in the aerospace industry for joining structural elements. Fiber-reinforced polymeric composite materials are particularly amenable to adhesive bonding because of load transfer uniformity. However, certain drawbacks in current adhesive bonding technology, including relatively long heating and bonding cycles, have limited its application. Advanced thermoplastic adhesives are candidates for adhesive bonding of titanium or composite structures. These thermoplastics do not require long processing times, but usually require processing temperatures above 600 °F to achieve strong bonds. However, because of the thermal inertia of fixtures and equipment, at least several hours in presses or autoclaves are required. Rapid adhesive bonding (RAB) concepts have been developed at NASA Langley Research Center (LARC) to utilize a toroid induction technique to provide heat directly to the bondline and/or adherends, without heating the entire structure, tooling, and support fixtures of a bonding assembly. Bonding times for specimens can be decreased by a factor of 10 to 100 compared to standard press or autoclave bonding.1 This paper focuses on rapid adhesive bonding of titanium and an advanced composite material (graphite-fiber-reinforced PEEK) using advanced thermoplastic adhesives. Bonding parameters, bond strengths at room and elevated temperatures, and the effect of thermal cycling or water boil exposures on bond strength are described. A promising nondestructive technique for evaluation of bond strength is also described.