ASTM_D_6147_-_97_2014.pdf

Designation:D614797(Reapproved 2014)Standard Test Method forVulcanized Rubber and Thermoplastic ElastomerDetermination of Force Decay(Stress Relaxation)inCompression1This standard is issued under the fixed designation D6147;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.1.Scope1.1 This standard specifies two methods for determining thedecrease in counterforce exerted by a test specimen of vulca-nized rubber or thermoplastic elastomer which has beencompressed at a constant deformation under specified condi-tions of time and temperature.1.2 This document was developed based on testing in airand liquids.1.3 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2.Referenced Documents2.1 ASTM Standards:2D573 Test Method for RubberDeterioration in an AirOvenD1349 Practice for RubberStandard Conditions for Test-ingD3182 Practice for RubberMaterials,Equipment,and Pro-cedures for Mixing Standard Compounds and PreparingStandard Vulcanized SheetsD3767 Practice for RubberMeasurement of DimensionsD4483 Practice for Evaluating Precision for Test MethodStandards in the Rubber and Carbon Black ManufacturingIndustriesE145 Specification for Gravity-Convection and Forced-Ventilation Ovens3.Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 Compressive Stress,nthe time-dependent force nec-essary to maintain a constant compressive strain,divided bythe original cross-sectional area over which the force isapplied.3.1.2 Force Decay,nthe decrease in stress which hasoccurred after a specified time-interval,during application of aconstant deformation,expressed as a percentage of the stress atthe commencement of that time-interval.(Stress relaxation is asynonym.)4.Summary of Test Method4.1 Method AThe test specimen is compressed at the testtemperature,and it is maintained at this temperature through-out the test period,all force measurements being made at thetest temperature.4.2 Method BThe test specimen compression and theinitial measurement of the counterforce take place at 23 6 2C(73 6 4F);the test specimen is then stored in a chambercontrolled at the test temperature,but it is removed from thechamber for each of the subsequent force measurements,whichare made at 23 6 2C(73 6 4F).4.3 The two methods,Aand B,of carrying out the measure-ment do not give the same values of force decay and compari-son of values obtained from the two methods must be avoided.The method selected for use depends on the purpose of the test.Thus,for fundamental studies and in applications wheresealing at elevated temperatures is a problem,method A maybe preferred,and in applications where temperature cyclingfrom normal to an elevated temperature is a problem,methodB may be preferred.5.Significance and Use5.1 When a constant strain is imposed on rubber,the forcenecessary to maintain that strain is not constant but decreaseswith time;this phenomenon is called force decay(stressrelaxation).Conversely,when rubber is subjected to a constantstress,an increase in the deformation takes place in time;thisbehavior is called creep.These phenomena are of practicalsignificance in rubber articles,such as seals and gaskets.1This test method is under the jurisdiction of ASTM Committee D11 on Rubberand is the direct responsibility of Subcommittee D11.10 on Physical Testing.Current edition approved Nov.1,2014.Published December 2014.Originallyapproved in 1997.Last previous edition approved in 2008 as D6147 97(2008)1.DOI:10.1520/D6147-97R14.2For referenced ASTM standards,visit the ASTM website,www.astm.org,orcontact ASTM Customer Service at serviceastm.org.For Annual Book of ASTMStandards volume information,refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 5.2 The processes responsible for force decay may be eitherphysical or chemical in nature,and under all normal conditionsboth processes will occur simultaneously.However,at ambientor low temperatures and/or short times,force decay is domi-nated by physical processes,while at elevated temperaturesand/or long times,chemical processes are dominant.Hence,itis neither safe to extrapolate time/force decay curves in orderto predict force decay after periods considerably longer thanthose covered by the test,nor to use tests at higher tempera-tures as accelerated tests to give information on force decay atlower temperatures.5.3 In addition to the need to specify the temperature andtime-intervals in a force decay test,it is also necessa