A comparison of oven-cured and induction-cured adhesively bonded composite joints

The advantages of using adhesives for joining composite structures are now well accepted. Adhesive joints may offer, over bolted joints, advantages such as a lower assembly weight, a superior stress transfer and an improved fatigue resistance. However, in some applications the above advantages may be offset by the processing conditions required to cure the adhesive. Indeed, in the conventional oven curing process the thermal energy must diffuse through the composite layers to heat the joint interfaces, resulting in long and expensive processing time as well as wasted energy. A novel method of achieving adhesive bonds is addressed in the present study. The method of electromagnetic heating is well suited for rapid and efficient localized heating of adhesive bond lines, provided suitable susceptors are used at the interfaces. This paper presents the results of a study on the use of induction heating for bonding composite adherends. Single-lap shear tests and double-cantilever beam fracture experiments were performed on oven-cured and induction-cured adhesively bonded joints made from woven-fabric composites. The feasibility of using the induction-heating technique for the hardening of adhesives in composite bonded joints was demonstrated. It was found that the strength of single-lap shear joints was not significantly affected by the choice of the hardening method of the adhesive. Furthermore, the critical fracture energy of the oven-cured and induction-cured double-cantilever beams was found to be only dependent on the adhesive type. Induction-cured specimens were found to be as tough as corresponding oven-cured specimens.