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.

Keywords:

• Bulk adhesive properties
• In-situ properties
• Mechanical properties
• Shear testing
• Structural adhesive
• Tensile testing
• Test methods
• Thin-film properties

ACKNOWLEDGMENTS

The authors gratefully acknowledge the support of the Federal Aviation Administration through the Airworthiness Assurance Center of Excellence, Cooperative Agreement No. 01-C-AW-UU. Special thanks are extended to Mr. Peter Shyprykevich, Technical Monitor, FAA Technical Center, for his technical guidance and support. In addition, the authors acknowledge the guidance of Dr. Larry DeVries of the University of Utah.

Notes

One of a Collection of papers honoring David A. Dillard, the recipient in February, 2010 of The Adhesion Society Award for Excellence in Adhesion Science, Sponsored by 3M.