Investigating the Thin-Film Versus Bulk Material Properties of Structural Adhesives

Abstract

A combined experimental and computational investigation was performed to determine whether the material properties of structural adhesives differ between their thin-film “in-situ” and bulk forms. Shear testing focused on the use of the V-notched Iosipescu shear specimen whereas tensile testing focused on adhesively bonded butt-joint specimens as well as bulk adhesive bar specimens. The apparent shear strength was found to be independent of bondline thickness. Further, shear strengths obtained from bulk adhesive testing were comparable with those from in-situ testing. Results from butt-tensile testing and analysis suggest that the apparent variation in tensile strength as a function of bondline thickness is a result of variations in the adhesive stress state, rather than the actual tensile strength of the adhesive. These results suggest that the adhesive properties obtained from bulk adhesive specimens are valid for use in structural analysis of in-situ thin-film adhesives.