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The ultimate properties of amorphous rubbers at temperatures above Tg are considered in terms of stress-strain curves to rupture measured at different strain rates and temperatures. The consideration indicates that a specimen held at a fixed elongation should break eventually, provided the elongation exceeds a critical value. This expected behavior was found by studying an SBR rubber. For samples maintained at different elongations for up to seven days, both the time to break and the stress at break were measured at eight temperatures from 1.7° to 60°C. For comparison, the ultimate properties were also measured at different strain rates and temperatures. The comparison indicates that for a given ultimate elongation and stress at break, the time to break under conditions of constant elongation is less than under conditions of constant strain rate.
Smith et al. (Tue,) studied this question.