The tensile stress-at-break σ b (based on the initial cross-sectional area) and the corresponding ultimate extension ratio λ b of unfilled vulcanizates of silicone, hydrofluorocarbon (Viton B), butyl (both sulfur-cured and resin-cured), and natural rubber were determined at many strain rates and temperatures; the latter ranged from slightly above the glass transition temperature T g , up to a temperature somewhat below that at which chemical degradation affected the results. For each vulcanizate except natural rubber, data obtained over an extended temperature range superposed to give a time- and temperature-independent failure envelope on a plot of log (σ b 273/T) vs log (λ b −1) , where T is the test temperature in °K; for natural rubber, data obtained between 90° and 120° C superposed, but those at lower temperatures did not because of strain-induced crystallization. For each vulcanizate, data at elevated temperatures gave, or tended toward, a line of unit slope on a plot of log (λ b σ b 273/T) vs log (λ b −1) , where λ b σ b is the breaking stress based on the cross-sectional area at the moment of rupture. The position of each line corresponded to the equilibrium modulus E e derived from stress-strain curves. Failure envelopes previously obtained for two styrene—butadiene vulcanizates, which had different crosslink densities, superposed to give a master failure envelope on a plot of log (λ b σ b 273/T) vs logE e (λ b −1) . On this type of plot, failure envelopes for all the vulcanizates except silicone and natural rubber were found to be essentially identical. At a given value of λ b σ b , silicone had a smaller λ b λ b and natural rubber a somewhat larger λ b λ b than the vulcanizates of the three other rubbery polymers.
No takes yet. Share an insight, caveat, or question.
Thor L. Smith (1964) studied this question.