1、Designation: D6147 97 (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 of
2、original 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 thedecr
3、ease 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 purpor
4、t 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
5、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 Practi
6、ce 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-es
7、sary 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 stres
8、s 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
9、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
10、 2C (73 6 4F).4.3 The two methods, A and 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 applicat
11、ions 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
12、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 practicalsignifica
13、nce 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 pr
14、evious 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 ont
15、he ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States15.2 The processes responsible for force decay may be eitherphysical or chemical in nature, and under all normal conditionsboth processes will occur simultaneously. Howeve
16、r, 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 conside
17、rably 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 necessary tospecify the initial
18、 stress and the previous mechanical history ofthe test specimen, since these may also influence the measuredforce decay, particularly in rubbers containing fillers.6. Apparatus6.1 Compression Device, consisting of two parallel, flatplates, between the faces of which the test specimens arecompressed.
19、 The two devices shown schematically in Fig. 1and Fig. 2 were found to be acceptable through interlaboratorytesting. Material of construction of the jig shall not be subjectto attack from the test environment (for example acidic oil).6.2 The finish of the surface of the compression plates shallnot e
20、xceed 0.6 m (24 micro inches) arithmetical meandeviation from the mean line of the profile. The plates shall besufficiently rigid to withstand the stress without bending, andof sufficient size to ensure that the whole of the compressed testspecimen is within the area of the plates.6.3 The compressio
21、n device shall be connected with suit-able equipment for compressing the test specimen to thespecified compression within 30 s. It shall be capable of settingand maintaining the compression during the whole duration oftest and shall be such that it can be kept in an oven at thespecified test tempera
22、ture. Care shall be taken to ensure thatthere is no loss of heat from the test specimen, for example byconduction through metal parts which are connected with theoutside of the oven.6.4 Counterforce measuring device, capable of measuringcompression forces in the desired range with an accuracy of61 %
23、. The device may be such as to contain the test specimensduring the whole duration of the test, in which case continuousmeasurements are possible. Alternatively, a testing machinemay be used in which the counterforce is measured afterprescribed time-intervals on test specimens, compressed in asuitab
24、le jig, by applying a slight increase in the compression ofthe test specimen. This additional compression shall be assmall as possible and in no case more than a force of 1N or halfpercent (12%) of original load for balance type machine and 0.1mm (0.004 in) or 2 % of original deflection for stress-s
25、traintype machines, in a time not greater than 30 s after commenc-ing the additional compression.6.5 Oven, with temperature control to maintain the specifiedtemperature within the prescribed tolerances. Satisfactory cir-culation of the air shall be maintained by means of a fan (seeTest Method D573 o
26、r Specification E145).6.6 Temperature reading device (optional), with for ex-ample a thermocouple as the sensing element, mounted in acentral position in the oven.7. Test Specimen7.1 Type of Test SpecimenThe test specimen shall be oneof the following:7.1.1 A cylindrical disc of diameter 13.0 6 0.5 m
27、m (0.5126 0.020 in) and thickness 6.3 6 0.3 mm (0.248 6 0.012 in).7.1.2 Cylindrical disc of diameter 29.0 6 0.5 mm (1.142 60.020 in) and thickness 12.5 6 0.5 mm (0.492 6 0.020 in).7.1.3 Washer of 12.5 6 0.5 mm (0.492 6 0.020 in) insidediameter and 19.0 6 0.5 mm (0.748 6 0.020 in) outsidediameter wit
28、h 2.0 6 0.2 mm (0.080 6 0.008 in) thickness.Within the sample test specimens, thickness variation shall bewithin 0.025 mm (0.001 in).7.1.4 Other test specimen sizes may be used as dictated byend use.7.2 The first three test specimens described above wereevaluated in interlaboratory testing. The wash
29、er type testspecimen (7.1.3) is preferred.7.3 Preparation of Test SpecimensTest specimens may beprepared by taking a sample of the compound or material ofinterest. If this is a compound it shall be cured and molded inaccordance with Practice D3182, or prepared by cutting frommolded sheets. Cutting i
30、s carried out by means of a sharp,rotating, circular die or revolving knife, lubricated with soapywater, and brought carefully into contact with the rubber.Alternatively, the die or knife is kept stationary and the rubberrotated against it. The rubber is mounted on suitable backingmaterial and the c
31、utting pressure is kept small enough to avoid“cupping” of the cut surface.7.4 Due to shape factor effect, equivalent results may not beobtained for the different test specimen shapes describedabove.7.5 Number of Test SpecimensAt least three test speci-mens shall be used for each test.7.6 Time-Interv
32、al Between Vulcanization and TestingThetime-interval between vulcanization and testing shall be at least24 h at ambient conditions.8. Procedure8.1 Carefully clean the operating surfaces of the compres-sion device. The test specimen surface shall be free from moldrelease agent or dusting powder.8.2 M
33、easure the thickness of each test specimen at thecentral portion with an accuracy of 0.01 mm (0.0004 in). Thethickness shall be determined according to Practice D3767.8.3 Method A8.3.1 Preheat the compression device to the test tempera-ture.8.3.2 Preheat the test specimen to the test temperature ina
34、ccordance with Practice D1349. A preheating period of 302012min. is recommended.D6147 97 (2014)2FIG.1Shawbury-WallaceStressRelaxationFixtureD6147 97 (2014)38.3.3 Compress the preheated test piece by 25 6 1 % in thecompression device (6.1) at the test temperature; use a com-pression of 15 6 1 % if a
35、compression of 25 % cannot beobtained. Apply the compression within 30 s. When reached,the final compression shall be fixed and maintained during theentire test period (apart from the further small compressionwhich may be used for measurement of counterforce, men-tioned in 6.4).8.3.4 After the compr
36、ession has been applied for 302012min.,measure the counterforce with an accuracy of 61 %, still at thetest temperature.8.3.5 Repeat the measurement of the counterforce afterdifferent times, according to 10.1. Take all measurements at thetest temperature.8.3.6 Due to operator variability, all counter
37、force measure-ments shall be performed three (3) times for each specimen andthe median value used.8.4 Method B8.4.1 Compress the test piece by 25 6 1 % at 23 6 2C (736 4F); a compression of 15 6 1 % may be used when acompression of 25 % cannot be obtained. Apply the compres-sion within 30 s. When re
38、ached, the final compression shall befixed and maintained during the entire test period (apart fromthe further small compression which may be used for measure-ment of counterforce, mentioned in 6.4).8.4.2 After the compression has been applied for 302012min.measure the counterforce with an accuracy
39、of 61 %, still at thestandard laboratory temperature.8.4.3 Store the compressed test specimen in the oven (6.5)at the specified elevated temperature.8.4.4 When making measurements of counterforce after thetimes specified, remove the apparatus from the oven, maintainit at the standard laboratory temp
40、erature for 220.210h, determinethe counterforce and then return to the test environment for afurther time. It is important that the apparatus and testspecimen reach thermal equilibrium within 2 h, and forcecooling may be necessary. In method B, the 2 h required aftereach time-interval, to attain sta
41、ndard laboratory temperature,shall be included in the duration of test.8.4.5 Repeat the measurement of the counterforce afterdifferent times, according to 10.1. Take all measurements atambient temperature.8.4.6 Due to operator variability, all counterforce measure-ments shall be performed three (3)
42、times for each test specimenand the median value used.9. Liquid Immersions Testing Procedure9.1 In some applications force decay testing under liquidimmersion conditions is necessary. Under these conditions thefollowing additional preparation of the jig is necessary.FIG. 2 Wykeham Farrance Stress Re
43、laxation FixtureD6147 97 (2014)49.2 Apply a lubricant to the top and bottom surface of thejig. It shall consist of a thin coating of the test fluid havingsubstantially no action on the rubber.9.3 The test specimen/test fixture shall be completely im-mersed in liquid under consideration. The immersed
44、 testspecimen shall be in the compressed condition, similar totesting in air as discussed in Section 8. Care shall be takenwhile performing force decay under liquid immersions (espe-cially at elevated temperatures) to avoid hazardous test condi-tions. Environmentally safe practices shall be followed
45、 whileperforming liquid immersion testing. If the effect of liquid oninside and outside surfaces of rubber is desired, the washertype test specimen (7.1.3), is recommended. In this case thefixture used shall have an inlet and vent hole of at least 3.2 60.3 mm (0.125 6 0.012 in) diameter to allow flo
46、w of liquidtowards inside diameter of the sample.9.4 Follow test procedures in 8.3 for Method A or 8.4 forMethod B.10. Duration and Temperature of Test10.1 Duration of TestThe duration of the test shall bemutually agreed upon by the customer and the supplier. A testperiod of 168220h has been found s
47、uitable for many elastomers.The test period begins after the initial compression. If longertesting times are needed, a logarithmic time-scale may be used.In method B, the 2 h required after each time-interval, to attainstandard laboratory temperature, shall be included in theduration of test.10.2 Te
48、mperature of TestThe temperature of test shall bechosen from Practice D1349. Unless for technical reasonsanother temperature is required, the ambient temperature shallbe 23 6 2C (73 6 4F).11. Calculation of Test Results11.1 The compression force decay (stress relaxation), R(t),after a specified dura
49、tion of test, t, expressed as a percentage ofthe initial counterforce, is calculated by Eq 1.Rt! 5Fo 2 FtFo3100 (1)where:Fo = initial counterforce measured 30 min. after compres-sion of the test specimen, andFt = counterforce measured after the specified duration oftest.11.2 The median value of the calculated results for com-pression force decay shall be used.11.3 For some applications, it may be more useful tocalculate compressive force retention values, that is, FR(t) atvarious times after the compression is applied, rather than forcedecay values. Thi
