Application of Digital Image Correlation to the Thick Adherend Shear Test

The purpose of this study was to develop and validate a novel method for measuring shear deformation during the Thick Adherend Shear Test (TAST), to determine in situ mechanical properties of an adhesive under tensile shear loading, using two-dimensional (2D) Digital Image Correlation (DIC). Shear strains were optically measured using DIC from the bond line and also from adherend deformations; both were compared against measurements made using the ASTM D5656 standard (KGR-1 extensometers). The results from 17 TAST specimens showed that all techniques were in good agreement, however, both DIC techniques had significantly lower variance on measured mechanical properties compared to the KGR-1 extensometers. The use of correlated adherend deformations was the preferred technique for deriving plastic shear strains, and overall produced the lowest scatter on mechanical properties. This study demonstrates the potential for the use of 2D DIC as a more precise, and time-efficient alternative to the KGR-1 extensometers for room temperature in situ characterization of adhesives in shear.