Predicting mechanical performance of adhesively bonded joints based on acousto-ultrasonic evaluation and geometric weighting

Abstract

Prediction of the performance of adhesively bonded joints is essential to the acceptance of this mode of fastening. In ideal situations where the bonding is uniform throughout the joint the stress distribution depends on the material properties and the joint geometry. Knowledge of the bond properties and the stress distribution and magnitude can then be used to determine failure initiation, damage growth, subsequent stress distributions, and final failure. However, few bonds can be characterized as "ideal", as the bonding is generally not uniform throughout the joint and even the properties of the adhesive may vary. This paper describes work that addresses this situation. Acoustic microscopy has been used to provide a detailed image of the bonded joint, while acousto-ultrasonic measurements have been used to evaluate the stress transfer capability of modified lap shear joints. Knowledge of the stress distribution in the joint has provided a means of identifying critical areas of interest in the joint. The adhesively bonded composite specimens were mechanically tested and performance correlated with NDE results. Wave mode filtering is offered as a phenomena describing the basis for the correlation.