Detection of degradation or potential degradation of an adhesive bond before bond failure would be a significant improvement over current technology that generally requires separation or, at least, a kissing unbond (a bond in which the two surfaces are in intimate contact, but which can-not transfer any stress). Because the primary cause of environmentally induced degradation of a bonded joint is moisture intrusion into the bondline [25-27], detection of moisture is one way to achieve this goal. For high-performance surface treatments that provide a high density of physical bonds (mechanical interlocks) and are resistant to hydration, bondline moisture requires a long time before hydration of the adherend surface causes joint failure . Thus use of the electrochemical sensor or other moisture-detecting device could provide ample warning before irreversible structure damage occurs to the joint.
In-Situ Sensor to Detect Moisture Intrusion and Degradation of Coatings, Composites, and Adhesive Bonds, G.D. Davis, C.M. Dacres, and L.A. Krebs, DACCO SCI Inc.