(A) study on the damage monitoring of adhesive joints by piezoelectricity

Abstract

Adhesive joints have been widely used for fastening thin adherends because they can distribute the load over a larger area than mechanical joints, require no hole, add very little weight to the structure and have superior fatigue resistance. Since the reliability of adhesive joints is dependent on many parameters such as the shape of joints, type of applied load, and environment, an accurate estimation of the fatigue life of adhesive joints is seldom possible, which necessitates in-situ damage monitoring of the joints during the operation of structures. Recently, a piezoelectric method using piezoelectric characteristics of epoxy adhesives has been successfully developed for the adhesive joints because it can monitor continuously the damage of adhesively bonded structures without producing any defects. Therefore, in this study, the fatigue characteristics of adhesive joints were investigated with respect to the volume fraction of adhesive filler, curing conditions and environmental temperature. During the fatigue tests, damage monitoring of adhesive joints by the piezoelectric method was performed with respect to the mean and alternating stress, and volume fraction of adhesive filler. A crack propagation model was developed and verified in order to explain the change of damage monitoring signals. Using the analysis results of the measured damage monitoring signals, the diagnosis criterion and system for the reliability assessment of adhesive joints have been constructed.