(Received 20 November 2013; accepted 1 April 2014)
Published Online: 2014
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Part 1 (Bafna, S. S., “The Effect of Temperature on the Tear Behavior of Various Elastomers,” J. Test. Eval., Vol. 42, No. 3, 2014, pp. 1–10) of this series discussed the tear behavior per ASTM D624-00 Type B (propagation) and Type C (initiation) for commercial sealing grade butyl, ethylene propylene diamine (EPDM), fluorosilicone (FS), and two fluorocarbon elastomers. Part 2 provides additional insight based on application considerations. The behavior of polychloroprene intended for shock and vibration isolation applications is compared to that of silicone and other elastomers intended for sealing applications (such as O-rings). The trend of tear strength for propagation being higher than or equal to (within measurement error) that for initiation is confirmed. This is shown to be an artifact of the difference in the ASTM D624-00 test specimen geometries. Propagation tear strength/energy values reported in literature are from the “trouser” tear (ASTM D624 Type-T or modification thereof) test, which leads to lower values than Type B. While Type-T is closer in deformation mode to pure tear, Types B and C more closely simulate tear damage in actual hardware. The polychloroprene grade tested is processed using transfer molding and has a much lower viscosity in the uncured state. After cure, its tensile strength is lower than that of all compression molding grades and its tensile elongation is the highest. However, its tear strength is higher than that of the silicone or FS grades tested, consistent with its application requirements. At the higher temperatures, the polychloroprene tear strength is higher than that of all the compression molding grades. A higher level of filler (as manifested by a high specific gravity), along with strain induced crystallization, helps explain this retention of tear properties with temperature. The tear strain at break generally increases with temperature but, if temperature is sufficiently above the glass transition temperature, then the tear strain actually decreases with temperature and thus non-monotonic behavior is observed. The poor tear properties of silicones and FS are confirmed.
Materials, Processes, and Producibility Department, Raytheon Missile Systems, Tucson, AZ
Stock #: JTE20130302