Mechanical Characterization of Flexible Adhesives

Abstract

In this paper, the performances of two different adhesive types—a polyurethane and a high temperature thixotropic adhesive sealant, room temperature vulcanizing (RTV) silicone rubber—were studied through adhesive joint tests. The standard Thick Adherend Shear Test (TAST) was performed in order to measure the shear properties of the adhesives. Single lap joints (SLJs) were fabricated and tested to assess the adhesive performance in a joint. The influence of temperature on the lap shear strength of the adhesives was investigated. It is shown that the lap shear strength of both adhesives is affected by variation of temperature. The effect of bondline thickness and overlap length on the lap shear strength of the adhesives was studied. The reduction of failure load with increasing the bondline thickness is a very common situation when dealing with structural adhesives. For the low strength flexible adhesive Sikaflex® 552 the failure load as well as the overall stiffness of the SLJs decreases as the bondline gets thicker, whereas for AS1805 RTV adhesive the failure loads increase as the bondline gets thicker. Also, in contrast to joints with brittle adhesives, the failure loads of joints with flexible adhesives increase almost proportionally with increasing overlap length. Fatigue tests were also performed and show a low variability in the results.

Keywords:

• Fatigue
• Lap shear strength
• Polyurethane adhesive
• RTV adhesive
• Temperature tests

ACKNOWLEDGMENTS

The authors would like to thank the Portuguese Foundation for Science and Technology for supporting the work presented here through the research project PTDC/EME-PME/67022/2006, Sika Portugal for supplying the polyurethane adhesive, and ACC Silicones Ltd. for supplying the RTV adhesive.

Notes

Presented in part at the 2nd International Conference on Advanced Computational Engineering and Experimenting (ACE-X 2008), Barcelona, Spain, 14–15 July, 2008