(Received 1 July 2013; accepted 8 October 2013)
Published Online: 2013
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The tear behavior of commercial butyl, EPDM, fluorosilicone, and two fluorocarbon elastomers, used for sealing applications, was studied at −40°C and +49°C. Measurements were made to study initiation and propagation behavior, using Die-C and Die-B, respectively, per ASTM D624. The behavior of tear strength, engineering strain, and energy per unit volume was studied. Tear strength for propagation was always higher than or equal to (within measurement error) that for initiation. Butyl showed the highest tear strength as well as elongation at break; hence, it also had the highest tear energy. The effect of post-cure on butyl is studied. Butyl which had not been post-cured showed unusually high elongation; this translates to the highest tear energy. Temperature is shown to have a major effect on the tear behavior but the magnitude of this effect is significantly different for different elastomers. The two fluorocarbons studied showed markedly different relative behavior at −40°C as compared to +49°C due to the difference in their glass transition temperatures. All torn surfaces of the test specimens after tear showed smooth and uniform surfaces, consistent with steady shearing; this was also consistent with the absence of “chatter” in the force signal. However, the tear direction (perpendicular to or at an angle to the displacement direction) did not show any simple correlation with other tear properties. The difference in behavior between EPDM and butyl rubbers (both with saturated aliphatic hydrocarbon backbones and both with carbon black filler) is elucidated.
Materials, Processes and Producibility Department, Raytheon Missile Systems, Tucson, AZ
Stock #: JTE20130160