In-Situ Observation in Adhesive Layer of Adhesively Bonded Butt Joints with a Thin Adherend under Cyclic Loading.

Recently, damage to the adhesive layer has been investigated by in-situ observation under several load conditions.However, these observation have been limited to the surface of the adhesive layer.If an adhesively bonded butt joint with a very thin adhesive layer could be tested, damage to the interior of the adhesive layer could be observed under transmitted light, which would facilitate clarification of the fracture mechanism of adhesively bonded joints.In this study, to observe the damage interior to the adhesive layer, adhesively bonded butt joint specimens were made using 0.3mm-thick steel plates with plasticizer and rubber modified epoxy adhesives.Then, cyclic tensile fatigue tests were conducted using these joints, where damage to the adhesive layer was observed by a microscopic videocamera under transmitted light.The main results were as follows: In the case of a butt joint with plasticizer-modified adhesive, an initial crack appeared at the end of the adhesive/adherend interface.On the other hand, in the case of a butt joint with rubber-modified adhesive, the damage zone appeared in the middle of the adhesive layer.These observations were discussed from the viewpoint of stress and strain distributions of the adhesive layer.