DEFORMATION AND RUPTURE OF ELASTOMERS IN EQUAL BIAXIAL AND SIMPLE TENSION.

Stress-strain and rupture data were obtained on unfilled styrene-butadiene vulcanizate SBR-IV in equal biaxial tension at extension rates from about 0.15 to 4 min-1 and from -43C to 90C. The tests involved inflating a rubber sheet into a bubble. A time- and temperature-independent strain function was derived from the stress-strain data and compared with results derived from data obtained previously in pure shear. In biaxial tension, the elongation at break was roughly 400, nearly independent of extension rate and temperature, in contrast to the marked rate and temperature dependence in simple uniaxial tension. The rupture stress was manyfold greater than in simple tension, except at the lower test temperatures. These observations, along with the temperature dependence of the rupture pattern, are considered in terms of the orientation of molecular chains and implicitly, of the stress in the longitudinal and latitudinal directions. Stress-strain and rupture data were obtained on three specially prepared noncrystallizable polyurethane elastomers that presumably had somewhat different network topologies, although nearly the same crosslink densities. No significant difference in their viscoelastic and ultimate properties was observed. Author