INVESTIGATION OF NONDESTRUCTIVE MONITORING OF THE ENVIRONMENTAL DEGRADATION OF STRUCTURAL ADHESIVE JOINTS

Structural adhesive joints exposed to harsh environmental conditions exhibit a permanent degradation in their performance until a complete failure occurs. The rate of the degradation is affected by the adhesive type and the quality of the surface treatment to the adherends prior to bonding. In this study, four aluminum adhesive joints representing two thicknesses and two adhesive/cohesive properties were immersed in hot water. The joint specimens were subjected to x-ray and neutron radiographic inspections at the beginning of the experiment and upon its termination, and to periodic ultrasonic scanning. The results of these three nondestructive techniques are discussed. A consistent and comprehensive pattern in the values of features derived from the ultrasonic echo signals as a function of the amount of water absorbed by the joints allows for a practical method for tracing water degradation of in-service structural adhesive joints.