MECHANISMS OF REVERSIBLE AND IRREVERSIBLE LOSS OF MECHANICAL PROPERTIES OF ELASTOMERIC VULCANIZATES WHICH OCCUR AT ELEVATED TEMPERATURES
Technical documentary rept. 1 May 1961-30 Apr 1962
STANFORD RESEARCH INST MENLO PARK CA
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Strength characteristics of five elastomeric gum vulcanizates were investigated over a wide range of conditions. Results from continuous and intermittent stress-relaxation evaluations made between 100 and 200 deg C showed that the thermal stabilities of the vulcanizates decrease in the following order hydrofluorocarbon, resin-cured butyl, silicone, sulfur-cured butyl, and natural rubber. Tensile properties of each vulcanizate in the absence of thermal degradation were determined with an Instron tester at about 10 strain rates and 10 temperatures. Except for natural rubber, the ultimate tensile properties of each vulcanizate could be characterized by a time- and temperature-independent failure envelope which results from a plot of log sigma sub b 273T vs. log epsilon sub b where sigma sub b is the tensile strength and epsilon sub b is the ultimate strains. No fundamental differences seem to exist in the strength characteristics of the various vulcanizates provided they are compared in corresponding temperature and physical states. Stress-strain curves for natural rubber were analyzed to separate time and finite- strain effects. Between -20 and 100 deg C, the stress-strain data were time independent although they are temperature dependent.
- Physical Chemistry
- Elastomers and Rubber