Fatigue life evaluation and crack detection of the adhesive joint with carbon nanotubes

For a composite material having a high specific strength and specific stiffness with excellent damping and good impact properties, joint design is a very important consideration because an improper design may lead to overweight or defective structures. Adhesive bonding does not require holes and distributes the load over a larger area than mechanical joints. As the use of adhesively bonded joints subjected to cyclic loading has increased in recent years, it is important to measure and improve the fatigue cracking and the lifetime of these adhesive joints. In this paper, the static and dynamic strengths of adhesive joints incorporating carbon nanotubes were compared to those of adhesive joints without carbon nanotubes. Composite to aluminum single-lap joints were fabricated and their strengths were evaluated. From the tests, fatigue strengths of the adhesive joints increased when the adhesive of the adhesive joint had carbon nanotubes although their static strengths decreased. Also, crack initiation and propagation can be effectively detected by measuring the variation of equivalent resistance when carbon nanotubes are dispersed into the adhesive in the adhesive joint.