1、Designation: D 6147 97 (Reapproved 2002)Test Method forVulcanized Rubber and Thermoplastic ElastomerDetermination of Force Decay (Stress Relaxation) inCompression1This standard is issued under the fixed designation D 6147; the number immediately following the designation indicates the year oforigina
2、l adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This standard specifies two methods for determining thedecrease i
3、n 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 a
4、ddress 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:D 573 Standa
5、rd Test Method for RubberDeterioration inan Air Oven2D 1349 Standard Practice for RubberStandard Tempera-tures for Testing2D 3182 Standard Practice for RubberMaterials, Equip-ment, and Procedures for Mixing Standard Compoundsand Preparing Standard Vulcanized Sheets2D 3767 Standard Practice for Rubbe
6、rMeasurement ofDimensions2D 4483 Standard Practice for Determining Precision forTest Method Standards in the Rubber and Carbon BlackIndustries2E 145 Specification for GravityConvection and Forced-Ventilation Ovens33. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 Compressive Str
7、ess, 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, e
8、xpressed 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 b
9、eing 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 forc
10、e measurements, whichare made at 23 6 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, fo
11、r 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 impo
12、sed 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. Thes
13、e phenomena are of practicalsignificance in rubber articles, such as seals and gaskets.1This practice is under the jurisdiction of ASTM Committee D11 on Rubber andis the direct responsibility of Subcommittee D11.14 on Time and Temperature-Dependent Physical Properties.Current edition approvedDec. 10
14、, 2002. Published January 2003. Originallyapproved in 1997. Last previous edition approved in 1997 as D 6147 97.2Annual Book of ASTM Standards, Vol 09.01.3Annual Book of ASTM Standards, Vol 14.04.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, Uni
15、ted States.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
16、 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 infor
17、mation 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 stress and the previous mechanical history ofthe test specimen, since these may also influence the measuredforce decay
18、, particularly in rubbers containing fillers.6. Apparatus6.1 Compression Device, consisting of two parallel, flatplates, between the faces of which the test specimens arecompressed. The two devices shown schematically in Fig. 1and Fig. 2 were found to be acceptable through interlaboratorytesting. Ma
19、terial 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 exceed 0.6 m (24 micro inches) arithmetical meandeviation from the mean line of the profile. The plates shall besufficie
20、ntly 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 compression device shall be connected with suit-able equipment for compressing the test specimen to thespecified compression with
21、in 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 temperature. Care shall be taken to ensure thatthere is no loss of heat from the test specimen, for example byconduction throu
22、gh 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 %. The device may be such as to contain the test specimensduring the whole duration of the test, in which case continuou
23、smeasurements are possible. Alternatively, a testing machinemay be used in which the counterforce is measured afterprescribed time-intervals on test specimens, compressed in asuitable jig, by applying a slight increase in the compression ofthe test specimen. This additional compression shall be assm
24、all as possible and in no case more than a force of 1N or halfpercent (12 %) of original load for balance type machine and0.1 mm (0.004 in) or 2 % of original deflection for stress-straintype machines, in a time not greater than 30 s after commenc-ing the additional compression.6.5 Oven, with temper
25、ature 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 D 573 or Specification E 145).6.6 Temperature reading device (optional), with for ex-ample a thermocouple as the sensing ele
26、ment, 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 mm (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 (
27、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 with 2.0 6 0.2 mm (0.080 6 0.008 in) thickness.Within the sample test specimens, thickness variation shall bewithin 0.0
28、25 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 washer type testspecimen (7.1.3) is preferred.7.3 Preparation of Test SpecimensTest specimens may beprepared by taking a
29、 sample of the compound or material ofinterest. If this is a compound it shall be cured and molded inaccordance with Practice D 3182, or prepared by cutting frommolded sheets. Cutting is carried out by means of a sharp,rotating, circular die or revolving knife, lubricated with soapywater, and brough
30、t 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 cutting pressure is kept small enough to avoid“cupping” of the cut surface.7.4 Due to shape factor effect, equivalen
31、t 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-Interval Between Vulcanization and TestingThetime-interval between vulcanization and testing shall be at least24 h at amb
32、ient 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 Measure the thickness of each test specimen at thecentral portion with an accuracy of 0.01 mm (0.0004 in). Thethickn
33、ess shall be determined according to Practice D 3767.8.3 Method A8.3.1 Preheat the compression device to the test tempera-ture.8.3.2 Preheat the test specimen to the test temperature inaccordance with Practice D 1349. A preheating period of 30012min. is recommended.8.3.3 Compress the preheated test
34、piece by 25 6 1 % in thecompression device (6.1) at the test temperature; use a com-pression of 15 6 1 % if a compression of 25 % cannot beobtained. Apply the compression within 30 s. When reached,the final compression shall be fixed and maintained during theD 6147 97 (2002)2FIG.1Shawbury-WallaceStr
35、essRelaxationFixtureD 6147 97 (2002)3entire 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 compression has been applied for 30012min.,measure the counterforce with an accuracy of 61 %, still at thetest temper
36、ature.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 counterforce measure-ments shall be performed three (3) times for each specimen andthe median value used.8.4 Method B8.4
37、.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 reached, the final compression shall befixed and maintained during the entire test period (apart fromthe further sm
38、all compression which may be used for measure-ment of counterforce, mentioned in 6.4).8.4.2 After the compression has been applied for 30012min.measure the counterforce with an accuracy of 61 %, still at thestandard laboratory temperature.8.4.3 Store the compressed test specimen in the oven (6.5)at
39、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 temperature for 2 0.210h, determinethe counterforce and then return to the test environment for afurther time. It is i
40、mportant 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 standard laboratory temperature,shall be included in the duration of test.8.4.5 Repeat the measurement of the counter
41、force 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) times for each test specimenand the median value used.9. Liquid Immersions Testing Procedure9.1 In some applicatio
42、ns force decay testing under liquidimmersion conditions is necessary. Under these conditions thefollowing additional preparation of the jig is necessary.9.2 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 o
43、n the rubber.9.3 The test specimen/test fixture shall be completely im-mersed in liquid under consideration. The immersed testFIG. 2 Wykeham Farrance Stress Relaxation FixtureD 6147 97 (2002)4specimen shall be in the compressed condition, similar totesting in air as discussed in Section 8. Care shal
44、l 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 whileperforming liquid immersion testing. If the effect of liquid oninside and outside surfaces of rubber is des
45、ired, 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 flow of liquidtowards inside diameter of the sample.9.4 Follow test procedures in 8.3 for Method A or 8.4 forMethod
46、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 16820h has been found suitable for many elastomers.The test period begins after the initial compression. If longertesting times are neede
47、d, 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 Temperature of TestThe temperature of test shall bechosen from Practice D 1349. Unless for technical reasonsanother
48、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 duration of test, t, expressed as a percentage ofthe initial counterforce, is calculated by Eq 1.Rt! 5Fo FtFo3 100 (1
49、)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. This may be calculated by Eq 2:FRt! 5 100 Rt! (2)where:FR(t) = force retention expressed as a percent, after
