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Testing and computer modeling of adhesives in bulk and bonded states

One of the objectives of structural adhesive characterization is to provide material property data for analytical design purposes. However, the adhesive properties obtained from bulk testing may often prove unrealistic when transferred to a bonded joint in the presence of interfaces between the adhesive and the adherends. As a result, researchers are developing novel experimental procedures that can measure the in situ adhesive properties. A three-point bend test of a bonded beam to measure the in-situ adhesive shear modulus is a case in point. The adhesive shear modulus obtained from the three-point bend test was found to be up to an order of magnitude lower than that obtained from tensile test on bulk adhesive. In order to resolve this issue, a finite element analysis was performed to numerically simulate the test results and to conduct a sensitivity study to determine the dependence of beam deflection on various material parameters. The objective of this paper is to demonstrate that an approach that combines the use of a computational procedure such as the finite element method with a new test methodology leads to a better understanding of the test results while providing a consistency check. The finite element code used for this purpose, called NOVA-3D, is specifically designed for the analysis of adhesively bonded joints. Some of the unique capabilities of the code with regard to stress analysis and life-prediction of a bonded joint are described in this paper. An application of this special purpose finite element code to study the influence of environmental effect on adhesive response is also discussed.