Dynamic Effective Young's Modulus of Thin Adhesive Layers in Bonded Joints

Abstract

Abstract In recent years, adhesive bonding has shown promise in replacing or supplementing conventional methods of joining such as riveting, welding, mechanical fastening, and so forth. To evaluate the dynamic characteristics of bonded structures, it is necessary to know the dynamic characteristics of bonded joints. This paper presents the development of an experimental technique to evaluate the dynamic effective Young's modulus (DEYM) of a thin adhesive layer sandwiched between metallic adherends. Considering the difficulties in measuring the strain across the adhesive layer, it was decided to avoid the measurement of strain in this technique. The joint is introduced in a cantilever beam, which causes its resonant frequency to drop because of the lower modulus of the adhesive layer. An analytical technique has been developed to evaluate its modulus from the drop in resonant frequency. Experiments were conducted on two types of adhesives. It was observed that the DEYM is significantly influenced by the thickness of the adhesive layer. A thin adhesive layer has a higher modulus, which is less sensitive to change in the frequency. A thick adhesive layer, on the other hand, permits wider tolerances on the joint surfaces and makes fabrication easier. An optimum adhesive layer thickness has to be chosen as a compromise depending on the various joint parameters. The technique described in this paper can be used for such studies.