Study of the Metal Sphere Explosion Driven by Pulsed Discharge for Separating Adherends

A metal sphere's state by pulsed discharge in air was characterized for the application of an explosion of a metal sphere inserted in the bonding adhesive caused by the pulsed discharge to separate bonded structures. Although the adhesive is widely used in composite materials for automobiles and aircraft, dismantling bonded structures has been challenging. Therefore, facile and selective separation of bonded structures is required for easy disassembly. In this study, a metal sphere set in the adhesive in place of an alumina sphere that adjusted the thickness of the adhesive layer was exploded by the Joule heating caused by the discharge current flow to fracture the adhesive and separate the adherend. High-speed images of the metal sphere's state in air, as the behavior in the adhesive is not observable, showed that an explosion occurred at the contact point between the metal sphere and the electrode. An electrothermal simulation using the measured current flow to consider the contact conditions indicated that the Joule heating at the contact point increased the sphere's temperature above the boiling point of iron at the time of the explosion observed in the experiment. A test model of the bonded structure containing the adhesive with the sphere also showed that the sphere allowed control of the discharge path in the adhesive, separating 25-mm2 adhesive surfaces with a charging energy of 30 J. These results indicated that adding a metal sphere to adhesive is effective for selectively separating the adherend from the bonded structure using pulsed discharge to generate the explosion of the sphere at the contact point.