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Significance and Use
When a constant strain is imposed on rubber, the force necessary to maintain that strain is not constant but decreases with time; this phenomenon is called force decay (stress relaxation). Conversely, when rubber is subjected to a constant stress, an increase in the deformation takes place in time; this behavior is called creep. These phenomena are of practical significance in rubber articles, such as seals and gaskets.
The processes responsible for force decay may be either physical or chemical in nature, and under all normal conditions both processes will occur simultaneously. However, at ambient or low temperatures and/or short times, force decay is dominated by physical processes, while at elevated temperatures and/or long times, chemical processes are dominant. Hence, it is neither safe to extrapolate time/force decay curves in order to predict force decay after periods considerably longer than those covered by the test, nor to use tests at higher temperatures as accelerated tests to give information on force decay at lower temperatures.
In addition to the need to specify the temperature and time-intervals in a force decay test, it is also necessary to specify the initial stress and the previous mechanical history of the test specimen, since these may also influence the measured force decay, particularly in rubbers containing fillers.
1.1 This standard specifies two methods for determining the decrease in counterforce exerted by a test specimen of vulcanized rubber or thermoplastic elastomer which has been compressed at a constant deformation under specified conditions of time and temperature.
1.2 This document was developed based on testing in air and liquids.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
2. Referenced Documents (purchase separately) The documents listed below are referenced within the subject standard but are not provided as part of the standard.
D573 Test Method for Rubber--Deterioration in an Air Oven
D1349 Practice for Rubber--Standard Temperatures for Testing
D3182 Practice for Rubber--Materials, Equipment, and Procedures for Mixing Standard Compounds and Preparing Standard Vulcanized Sheets
D3767 Practice for Rubber--Measurement of Dimensions
D4483 Practice for Evaluating Precision for Test Method Standards in the Rubber and Carbon Black Manufacturing Industries
E145 Specification for Gravity-Convection and Forced-Ventilation Ovens
ICS Number Code 83.140.99 (Other rubber and plastic products)
UNSPSC Code 13101606(Thermplastic rubber); 13101601(Vulcanized rubber)