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The adhesion performance of a sealant is often assessed by conducting a peel adhesion test using the 180° peel test, ASTM C 794-80 adhesion in peel. The ASTM C 784-80 test method is difficult to interpret for the following reasons: 1) only one peel speed is used to measure peel force, 2) the failure mode is predominately cohesive and 3) the peeling energy is dominated by the viscoelastic properties of the joint. Consequently, the 180° peel test is not an optimal peel test for surface sensitive measurement. A 45° peel test devise is described and compared to the 180° peel test. The 45° peel test measures the peeling speed as a function of applied fracture energy. Peel speed is measured using a displacement transducer. The applied fracture energy is provided by a known mass and the force of gravity. The peeling measurement is conducted at very slow peeling speeds, less than 107 m/s in order to reduce the effect of viscose dissipation. Using model sealant formulations, the authors demonstrate the ability of the 45° peel test to distinguish between the two sealant formulations. Conversely, the 180° peel test is unable to measure a difference in adhesion between the two different sealants.
peel test, sealant, failure mode, silicone, viscoelastic, modulus, aluminum
Research Specialist, Dow Corning Corporation, Midland, MI
Professor, Virginia Polytechnic Institute and State University, Blacksburg, VA