1、Designation: D 4482 07Standard Test Method forRubber PropertyExtension Cycling Fatigue1This standard is issued under the fixed designation D 4482; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number
2、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 test method covers the determination of fatigue lifeof rubber compounds undergoing a tensile-strain cycle. Duringpart of the cycle, the
3、strain is relaxed to a zero value. Thespecimens are tested without intentionally initiated flaws, cuts,or cracks. Failure is indicated by a complete rupture of the testspecimen.1.2 No exact correlation between these test results andservice is given or implied. This is due to the varied nature ofserv
4、ice conditions. These test procedures do yield data that canbe used for the comparative evaluation of rubber compoundsfor their ability to resist (dynamic) extension cycling fatigue.1.3 The values stated in SI units are to be regarded as thestandard. The values given in parentheses are for informati
5、ononly.1.4 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. Refer
6、enced Documents2.1 ASTM Standards:2D 3182 Practice for RubberMaterials, Equipment, andProcedures for Mixing Standard Compounds and Prepar-ing Standard Vulcanized SheetsD 3767 Practice for RubberMeasurement of DimensionsD 4483 Practice for Evaluating Precision for Test MethodStandards in the Rubber a
7、nd Carbon Black ManufacturingIndustries2.2 British Standard:BS5324 Guide to Application of Statistics to Rubber Test-ing33. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 extension ratiothe ratio of the extended length of aspecimen, L, to the unextended length, Lo, calculated as
8、follows:l5LLo(1)3.1.2 fatigue life (sample)the mean value of the numberof cycles required to cause failure for a number of specimensof the sample.3.1.3 fatigue life (specimen)the total number of cyclesrequired to cause failure of a specimen, defined as a completerupture or separation of the specimen
9、.3.1.4 strain energythe energy per unit of volume requiredto deform the specimen to the specified strain. It is measuredby the area under a stress-strain curve and expressed in kJ/m3(see Annex A1).4. Summary of Test Method4.1 The dumbbell test specimens are cyclically strained at afixed frequency an
10、d a series of fixed maximum extension ratiossuch that little or no temperature rise is induced. This cyclicalstraining action is called flexing. As a result of the flexing,cracks usually initiated by a naturally occurring flaw, grow andultimately cause failure which is defined as complete rupture of
11、the test specimen. The number of cycles to failure (fatigue life)is recorded.4.2 Fatigue, as used in this test method, implies a rupturefailure mechanism that results from the growth of flaws in thespecimen. Fatigue does not refer to the drastic alteration of thephysical-chemical rubber structure ch
12、aracteristic of high fre-quency flexing tests that give rise to a substantial temperatureincrease.4.3 Fatigue life may be determined at each of a number ofdifferent extension ratios and the log (fatigue life) plotted as a1This test method is under the jurisdiction of ASTM Committee D11 on Rubberand
13、is the direct responsibility of Subcommittee D11.15 on Degradation Tests.Current edition approved July 1, 2007. Published August 2007. Originallyapproved in 1985. Last previous edition approved in 2006 as D 4482 06.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM
14、Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from British Standards Institute, 2 Park St., London W1A 2BF,United Kingdom.1Copyright ASTM International, 100 Barr Harbor Drive, PO Bo
15、x C700, West Conshohocken, PA 19428-2959, United States.function of either extension-ratio or log (strain energy). Asingle extension-ratio or log (strain energy) may be used forlimited comparisons of rubber vulcanizates having similarstress-strain properties and the same polymer system (seeAnnex A1)
16、.5. Significance and Use5.1 This test method covers one procedure for determiningfatigue life at various extension-ratios. The strain cycle ischaracteristic of the type of test apparatus specified. Experi-ence in fatigue testing shows that fatigue life may have a wide,non-normal distribution and, th
17、erefore, a large standard devia-tion that is compound dependent. Natural rubber, for example,has shown a narrower distribution than many synthetic rubbers.A large number of specimens may, therefore, be required toyield the desired precision. Comparison of different rubbercompounds should be made wit
18、h due consideration to thestandard deviation for each (see 7.1).5.2 Fatigue data, as generated in this test method, giveprimarily an estimate of the crack initation behavior of a rubbervulcanizate and only a very approximate measure of the crackpropagation rate. The information obtained may be usefu
19、l inpredicting the flex-life performance of a compound in activeservice; however, the user should be aware that in actual use,products are subjected to many other fatigue factors notmeasured in this test method.6. Apparatus6.1 Fatigue Tester, consisting of framework capable ofcontaining two or more
20、sets of multi-place specimen racks orcrossheads that hold specimens in a vertical position, side-by-side, in suitable grips. A crosshead or rack set is comprised ofone stationary bar to which grips are attached and onemoveable bar that is cycled by a cam at 1.7 6 0.17 Hz (100 610 cpm). Specimens are
21、 mounted in the grips, one specimen ineach set of upper and lower grips.6.1.1 The fatigue tester shall be capable of nominal speci-men extension ratios of 1.6 to 2.4. The extension ratio iscontrolled by the use of a cam attached to a rotating drive shaft.The eccentricity of the cam imports the chara
22、cteristic straincycle to the specimen. Each cycle consists of:6.1.1.1 Increasing strain for one quarter of the cycle time,6.1.1.2 Decreasing strain for one quarter of the cycle time,and6.1.1.3 Zero imposed strain for one half of the cycle time.6.1.2 The specimen grips shall not cause premature failu
23、reoutside the restricted portion of the test specimen. This isachieved by using a dumbbell test specimen with a thickbeaded edge molded at each end of the specimen. Thisspecimen is placed into grips that loosely hold it at the bead butimpose no compressive stress on it (see Fig. 1).6.2 Mold, sheets,
24、 to be used to cut specimens, can bevulcanized in a single cavity compression mold of two piececonstruction with a hard chrome finish (see Fig. 1). The cavityis 254 mm (10 in.) by 78.54 mm, and has a 6.35-mm (0.25-in.)diameter bead along each lengthwise edge. Cutting guidesshould be included at 14.3
25、 mm (0.56 in.) intervals along thebeaded edges.6.3 Press, as described in accordance with Practice D 3182.6.4 Specimen CutterThe cutting die shall conform to Fig.2. The inside faces of the reduced section shall be polished andperpendicular to the plane formed by the cutting edges for adepth of at le
26、ast 5 mm (0.2 in.).6.5 Vernier CalipersCalipers capable of making measure-ments in accordance with Practice D 3767, with a minimumrange of 15 mm (0.6 in.), and precision of 0.05 mm (0.002 in.).6.6 Stress-Strain Measuring ApparatusEither of twotypes may be used:6.6.1 A machine in which the actual ext
27、ension is measuredat a given dead-weight force. A stand enables masses to besuspended from the specimen. A set of masses that includes atleast one 50, one 100, two 200, two 500, and one 1000-g massshall be available.6.6.2 Alternatively, a tensile testing machine may be usedthat is capable of extendi
28、ng the specimen at a rate of 50.0 mm/min (2.0 in./min). It should automatically measure elongationto an accuracy of 65 % of the specimens original length.6.7 MicrometerThe micrometer or thickness gauge shallconform to the specifications in Practice D 3767.6.8 Bench Marker, with two parallel straight
29、 marking sur-faces ground smooth in the same plane. The surfaces shall bebetween 0.05 and 0.08-mm (0.002 and 0.003-in.) wide and23-mm (0.9-in.) long. The angle between the marking surfacesand sides shall be at least 75. The distance between themarking centers shall be 25 6 0.50 mm (0.984 6 0.020 in.
30、).7. Sampling7.1 Sampling shall be done in a way that justifies theconclusions drawn from any particular test program in declar-ing one compound to be superior to another. In fatigue-lifemeasurement, a sampling variance that includes mix andcuring variance components shall be used.8. Specimen Prepar
31、ation8.1 Compounds shall be prepared in accordance with Prac-tice D 3182 and vulcanized in the specified mold with themilling-grain direction parallel to the beaded edge.8.2 The molded sheet shall be conditioned in an unstrainedstate for at least 24 h at test temperature before testing.8.3 Specimens
32、 shall be cut with the die cutter at right anglesto the beaded edge. The die cutter shall be sharp and free fromnicks and oil prior to cutting. Support the sheets on a suitablecutting surface (cardboard, linoleum, etc.) covered with a thinplastic film to prevent inclusions. Cut the sheets with a sin
33、gle,smooth stroke.8.4 Discard specimens having obvious flaws. Before testing,physically randomize the specimens from all sheets of the samecompound.9. Conditioning9.1 Test TemperatureIt is suggested that the test tempera-ture be 23 6 2C.NOTE 1It is recommended that the laboratory room housing thefat
34、igue tester be free of any ozone-generating equipment.10. Procedure10.1 Fatigue Tester:D448207210.1.1 Install the proper cam that will give the desiredextension ratio.NOTE 2If previous knowledge about fatigue life of a particularcompound is not available, an initial extension-ratio of 2.0 is often u
35、sed.10.1.2 Adjust the distance between the flat, inner surface ofthe grips to 6 cm. A gauge block 6 cm long is convenient forthis adjustment.FIG. 1 Single-Cavity Compression MoldD448207310.1.3 If permanent set and extension-ratio measurementsare desired, place two bench marks approximately 25 mm apa
36、rton the reduced section of two specimens of each sample. Placethe marks perpendicular to the longitudinal axis and equidistantfrom the center of the specimen. This distance is designated Li.10.1.4 Manually set the cam position to the minimumcrosshead separation. Mount the specimens randomly in theg
37、rips.10.1.5 Start the fatigue tester.10.1.6 At 1000 cycles stop the tester and manually adjustthe drive mechanism to produce minimum crosshead separa-tion.NOTE 3If the tester is using two sets of crossheads, follow theinstructions starting with 10.1.6 for one bank of specimens at a time.10.1.7 For e
38、ach specimen, one at a time, use the gripadjustment to increase the distance between the grips until thespecimen is under a slight tension, then relieve the tension untila slight bow is just perceptable in the specimen. The specimenhas now been adjusted for permanent set.10.1.8 For specimens requiri
39、ng permanent set measure-ments, measure the distance between the bench marks andrecord as Loto the closest 61 mm. Calculate the permanent setusing the Li measurement from 10.1.3.Permanent set, % 5SLo2 LiLiD100! (2)NOTE 4Repeatability may be improved if the specimen is notadjusted for permanent set.1
40、0.1.9 For those specimens requiring a strain ratio measure-ment: After the specimens have rested at zero strain for at least3 min, manually adjust the drive mechanism until the speci-mens are at maximum extension. Measure the distance be-tween the bench marks and record as L to the closest 61.0 mm.C
41、ompute the extension ratio, l .l5LLo(3)10.1.10 Restart the tester, readjust the permanent set at10 000 additional cycles, and then each 24 h, thereafter.10.1.11 At the end of the test, record the total cycles foreach specimen, note and record the number of failures.Terminate the test when all specim
42、ens have failed or anarbitrary number of cycles have been obtained, or an arbitrarynumber of specimens remain intact.10.1.12 Repeat steps 10.1.1 through 10.1.11 for each de-sired extension ratio.10.2 Strain Energy Determination:10.2.1 If strain energy comparisons are necessary, deter-mine stress-str
43、ain properties using either the method in 10.2.2,the Manual Machine Method, or 10.2.3, the Tensile TestingMachine Method. This is optional for single extension ratiotests.10.2.2 Manual Machine MethodMeasure the specimenwidth and thickness with the micrometer. Stretch the specimen30 times to the maxi
44、mum extension used in testing. Placebench marks just short of the end of the straight, reducedsection of the specimen at maximum strain and then release tozero strain. Measure the unextended length with verniercalipers. Place sufficient force on the specimen to obtain anextension ratio of approximat
45、ely 1.2 within 1 min. Increase theforce at 1 min intervals to achieve a maximum extension ratioof 2.5. Measure the extended length 0.5 min after each force isapplied.10.2.3 Tensile Machine MethodMeasure the specimenwidth and thickness with the micrometer. Stretch the specimen30 times to the maximum
46、extension used in testing. Elongatethe specimen at 50 mm/min (2 in./min), automatically record-ing the force at every 10 % elongation increment until anextension ratio of 2.5 (150 % elongation) is obtained. Aconstant rate of extension tensile machine may be used.11. Calculations11.1 Determine the ge
47、ometric mean fatigue life for eachrubber vulcanizate at each extension. When the logarithmictransformation is applied, the mean fatigue life is determinedas follows:G 5 n=N13 N23 . 3 Nn(4)whereG = geometic mean,Ni= fatigue life of theith specimen, andn = total number of specimens.11.1.1 On a log bas
48、is:log G 5( log Ni!n(5)11.2 The use of log (fatigue life) has been found toapproximately normalize the distribution and reduce the stan-dard deviation of a single compound at multiple extensionratios.A 12.50 6 1.00 mm (0.492 6 0.039 in.)B 12.50 6 0.030 R (0.492 6 0.012 R)C 8.00 6 0.030 R (0.315 6 0.
49、012 R)D 78.74 6 0.013 mm (3.100 6 0.005 in.)E 39.37 6 0.064 mm (1.550 6 0.0025 in.)F 12.50 6 0.25 mm (0.492 6 0.010 in.)G 25.00 6 0.050 mm (0.984 6 0.020 in.)NOTECutter to be used for cutting samples from molded rubber sheets.Matl: A2 tool steel.FIG. 2 Specimen CutterD448207411.3 The variability of fatigue testing leads to difficulties indetermining “average” fatigue lives. In addition to the use ofthe geometric mean, the median value of the tests has also beenused. Annex A2 is taken from the British Standard BS5324,and may provide useful information for the
