Viscoelastic effects in cutting and tearing rubber

Measurements of cutting resistance have been made for a crosslinked styrene-butadiene copolymer over a wide range of cutting speeds and temperatures. A characteristic fracture energy was determined using the procedure of Lake and Yeoh. A lower limit, about 150 J/m², was obtained at low cutting speeds. This value is significantly higher than the threshold tear strength, about 30 J/m², due to roughness of the blade tip. The tear resistance increased dramatically as the test temperature was lowered, by a factor of over 1000X, whereas the cutting resistance remained largely unchanged over a considerable temperature range. Much of the enhanced tear resistance at low temperatures is therefore attributed to increasing roughness of the tear tip, the intrinsic strength remaining approximately constant. As the tear strength followed a WLF temperature dependence closely, roughening of the tear tip is associated with viscoelastic effects. Higher cutting resistance was shown by a sulfur vulcanizate, but carbon black had no additional effect. Variations in tensile strength with rate of elongation and temperature are discussed in terms of tearing from an initial edge flaw.