1、Designation: D 813 07Standard Test Method forRubber DeteriorationCrack Growth1This standard is issued under the fixed designation D 813; 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 parenth
2、eses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the Department of Defense.1. Scope1.1 This test method covers the determination of crackgrowth of vulcanized
3、 rubber when subjected to repeatedbending strain or flexing. It is particularly applicable to tests ofsynthetic rubber compounds which resist the initiation ofcracking due to flexing when tested by Method B of TestMethods D 430. Cracking initiated in these materials by smallcuts or tears in service,
4、 may rapidly increase in size andprogress to complete failure even though the material isextremely resistant to the original flexing-fatigue cracking.Because of this characteristic of synthetic compounds, particu-larly those of the SBR type, this test method in which thespecimens are first artificia
5、lly punctured in the flex area shouldbe used in evaluating the fatigue-cracking properties of thisclass of material.1.2 The values stated in SI units are to be regarded as thestandard. The values given in parentheses are for informationonly.1.3 This standard does not purport to address all of thesaf
6、ety 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:2D 430 Test Methods for Rubber D
7、eteriorationDynamicFatigueD 1349 Practice for RubberStandard Temperatures forTestingD 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 P
8、recision for Test MethodStandards in the Rubber and Carbon Black ManufacturingIndustries3. Summary of Test Method3.1 A molded test specimen with a pierced groove isrepeatedly flexed on a DeMattia type machine with the flexing(bending) axis parallel to the groove. The cut length ismeasured at frequen
9、t intervals to determine the cut growth rate.The cut is initiated by a specially shaped piercing tool.4. Significance and Use4.1 The test gives an estimate of the ability of a rubbervulcanizate to resist crack growth of a pierced specimen whensubjected to bending or flexing.4.2 No exact correlation
10、between these test results andservice is implied due to the varied nature of service condi-tions.5. Interference5.1 Presence of significant concentrations of ozone willaffect test results. Care should be taken that ambient ozoneconcentrations do not exceed 1 pphm.6. Apparatus6.1 DeMattia Flexing Mac
11、hineThe essential features ofthe apparatus, one design of which is shown in Fig. 1, are asfollows:6.1.1 The machine has an adjustable stationary head ormember provided with suitable grips for holding one end of thetest specimens in a fixed position and a similar reciprocatingmember for holding the o
12、ther end of each of the specimens.6.1.2 The reciprocating member is so mounted that itsmotion is straight in the direction of and in the same plane asthe center line between the grips. The travel of the moving1This test method is under the jurisdiction of ASTM Committee D11 on Rubberand is the direc
13、t responsibility of Subcommittee D11.15 on Degradation Tests.Current edition approved Feb. 1, 2007. Published March 2007. Originallyapproved in 1944. Last previous edition approved in 2006 as D 813 06.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Servi
14、ce at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.member shall be adjustable and shall be obtai
15、ned by means ofa connecting rod and eccentric having a minimum length ratioof 10 to 1.6.1.3 The eccentric shall be driven by a motor operating atconstant speed under load and giving 5 6 0.1 Hz (300 610 cpm). Provision shall be made for a maximum travel of themoving grips of 100 mm (4 in.).6.1.4 The
16、machine may be designed so that all the speci-mens are mounted on a single bar and all are flexed at the sametime. A double bar may also be used in which case thosespecimens mounted on one bar are being flexed while those onthe other bar are being straightened. Such an arrangementimproves the smooth
17、ness of operation.6.2 MoldA mold for curing individual test specimens isrequired, preferably of a multiple cavity design and havingadequate overflow cavities. The cavity plate shall have aminimum thickness of about 20 mm (0.750 in.) and the coverplate a minimum thickness of 14.5 mm (0.575 in.). Refe
18、r toPractice D 3182.NOTE 1The curing of wide samples from which specimens may becut may be provided for by increasing the width of the cavity andmaintaining all other dimensions.6.3 Measuring Scale of suitable length, graduated in milli-metres (or 0.01 in.) for measuring the length of cut growth.6.4
19、 Micrometer, to measure the thickness of the test speci-men as specified in Practice D 3767, Procedure A2.7. Test Specimens7.1 The test specimens shall consist of molded or cut strips,conforming to the shape and dimensions given in Fig. 2. Theyshall have a smooth surface and be free of surface irreg
20、ularitiesand defects in the groove and adjacent area. The thickness shallbe measured in the area adjacent to the groove and results shallbe compared only between specimens having a thickness of 6.46 0.1 mm (0.250 6 0.005 in.).7.2 Test specimens shall be conditioned in accordance withSection 13.NOTE
21、2The thickness of a test specimen cured from a tread typeFIG. 1 DeMattia Tester with a Double Row of Specimens Mounted for Flex-Cracking TestD813072compound consisting of 100 parts rubber and 50 parts of IRB Number 6black, and the necessary curative materials and using the mold shown inFig. 3, will
22、conform to the thickness of 6.4 mm (0.250 in.) specified in Fig.2. Preparation of the uncured specimens, on the basis of a constant volumeplus an approximate overflow of 10 %, provides assurance of well-moldedspecimens of uniform thickness.7.3 Compounds differing in stiffness may be expected todevia
23、te from the thickness of 6.4 mm (0.250 in.) as obtainedwith the standard compound referred to above. Extreme casesresulting in thickness outside the tolerances may requireadditional study. It is recommended that a new averagethickness be determined for such compounds, based on aminimum of ten specim
24、ens, and the allowable tolerance thenbe applied to this revised thickness measurement. The report ofthe data should then include such deviations from the control.8. Number of Test Specimens8.1 At least three specimens of each sample or compoundshall be tested and the median value reported. It is des
25、irable,when possible, to test a set of control specimens of knowncrack-growth resistance with each set of test specimens.9. Preparation of Specimens9.1 Each test specimen shall be prepared by piercing thebottom of the groove at a point equidistant from the sides. Thetool shall be maintained perpendi
26、cular to both the traverse andlongitudinal axes and the cut accomplished by a single inser-tion and withdrawal of the tool. The dimension H (of Fig. 4)ofthe tool shall be parallel and centered with the longitudinal axisof the groove. The leading cutting edge of the tool shallcompletely penetrate the
27、 specimen and project through thespecimen a minimum of 3.2 mm (0.125 in.). Lubrication withwater containing a suitable wetting agent may be used. Thepiercing tool shall be a spear-type instrument conforming to thedimensions given in Fig. 4. It is imperative that the tool is sharpand maintained to th
28、e correct dimensions, or test results will beaffected. It is recommended that the piercing tool be held in asuitable apparatus3that will maintain the tip in a perpendicularplane to the specimen and allow it to be pierced in onecontinuous motion.3The sole source of supply of the piercing tool and app
29、aratus known to thecommittee at this time is CCSI, 221 Beaver St.,Akron, OH 44304. If you are awareof alternative suppliers, please provide this information to ASTM InternationalHeadquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee,1which y
30、ou may attend.AB C D Emmin.15067532.39 6 0.030.094 6 0.0016.35 6 0.130.250 6 0.005251FIG. 2 Test Specimen with Circular GrooveABCmmin.6.45 6 0.030.254 6 0.0014.78 6 0.0510.188 6 0.0022.39 6 0.030.094 6 0.001FIG. 3 Test Specimen Moldmm (in.)A 2.62 (0.103)B 44.5 6 04 (1.75 6 0.015)C3.86 0.4 (0.150 6 0
31、.015)D 10.3 6 0.1 (0.400 6 0.005)E 0.38 + 0.05 0.00 (0.015 + 0.002 0.000)F 1.00 + 0.05 0.00 (0.041 + 0.002 0.000)G 0.3 + 0.05 0.00 (0.015 + 0.002 0.000)H 2.03 + 0.05 0.00 (0.080 + 0.002 0.000)I 25 rad (1.0 rad)J 58.42 (2.300)FIG. 4 Piercing ToolD81307310. Clamping Specimens in Machine10.1 One end of
32、 the specimen shall be clamped in thestationary grip and the other in the movable grip, care beingtaken to see that the longitudinal axis of the specimen isparallel to the direction of motion.10.2 The circular groove of the clamped specimens shall belocated symmetrically, midway between the clamps.
33、The speci-mens may be mounted on the machine most conveniently byholding them properly spaced in parallel positions in a specialrack. The distance between the outer edges of the side bars ofthe rack shall be equal to the space between the jaws of thetesting machine when positioned for holding the sp
34、ecimenswithout tension. The specimens can be mounted on the testingmachine by bringing the jaws into contact with the mountingrack and tightening the clamps on the projecting ends of thespecimens.10.3 The specimens shall not be closer than 3 mm(0.125 in.) when mounted in the machine. The free length
35、 (notin tension) of the specimen between the clamps shall be75.9 + 0.3 or 0.0 mm (2.99 + 0.01 or 0.00 in.).10.4 The circular groove shall be so restrained that it willbecome the outer surface of the bent specimen.11. Adjustment of Machine11.1 The positions of the stationary and movable gripsrelative
36、 to each other and the length of the eccentric arm andconnecting rod shall be adjusted so that during each stroke ofthe machine the grips approach each other to a distance of 19.06 0.1 mm (0.750 6 0.005 in.) and separate to a distance of75.9 + 0.3 or 0.0 mm (2.99 + 0.01 or 0.00 in.).11.2 Parallelism
37、 of the grips must be maintained at all timesand can only be assured by periodic checks.11.3 Machines operating within enclosures may be subjectto conditions resulting in different rates of cracking fordifferent positions in the grips. Correlation between all posi-tions should be determined for each
38、 machine, using a standardcontrol compound, and corrections made when necessary.12. Procedure12.1 After adjustments of the apparatus and specimens havebeen completed, start the machine and record the time. At theend of any period of operation, calculate the number of flexingcycles by multiplying the
39、 observed time in minutes by themachine rate of 5 Hz (300 cpm). This shall also be checked bymeans of a counter on the machine.12.2 Since the rate of crack growth is important, takefrequent readings early in the test. Stop the machine after 1000,3000, and 5000 cycle periods, observe the specimens, a
40、ndmeasure the length of the developed crack to the nearest0.3 mm (0.01 in.) with an accurate scale, preferably metric.12.3 For improved precision, make the observation with theaid of a low-powered reticulated magnifying glass while thegrips are separated 65.0 mm (2.56 in.).12.4 Continue the test wit
41、h readings at regular intervalsuntil a crack at least 12.5 mm (0.5 in.) in length is developed.Continuation to break may be desirable when testing agedspecimens or when operating at elevated temperatures. Theinitial cut produced by the puncturing spear shown in Fig. 4 is2 6 0.1 mm (0.08 + 0.002 0.00
42、0 in.) in width.13. Temperature of Test13.1 The standard temperature for testing shall be 23 6 2C(73.4 6 3.6F). Specimens shall be conditioned for at least12 h prior to testing. Controlled temperatures outside thestandard range are acceptable and often desirable. Special noteof such temperatures sha
43、ll appear in the report.NOTE 3The standard test temperature herein specified is that pre-scribed for the Standard Laboratory Atmosphere in Practice D 1349. Anychanges or revisions hereafter in Practice D 1349 relating to the standardtest temperature shall be considered effective at once for this pro
44、cedure.14. Report14.1 The molded dimensionsA, C, D, and E (as specified inFig. 2) of the test specimen shall be reported.14.1.1 The dimensions shall be obtained in accordance withPractice D 3767 except that the dimensions shall be obtainedusinga2mmspherical radius contact foot.14.2 The crack growth
45、data may be reported in any one ofthree ways, as follows:14.2.1 As the number of cycles required to reach a specifiedcrack length; for example, from 2 mm to 20 mm (0.080 to0.80 in.);14.2.2 As the average rate of crack growth over the entiretest period;14.2.3 As the rate of cracking in millimetres pe
46、r kilocycleduring a portion of the test, for example:(a)2to4mm,(b)4to8mm,or(c)8to12mm.15. Precision and Bias415.1 This precision and bias section has been prepared inaccordance with Practice D 4483. Please refer to this practicefor terminology and other statistical calculation details.15.2 Two preci
47、sion evaluation programs have been con-ducted for this test method.15.2.1 Program 1 was conducted in 1985 with five differentlaboratories testing four different compounds on two separatedays. The measured parameter is the flexlife in kilocycles to acrack length of 12.5 mm. A test result is defined a
48、s the mean(average) of the flexlife for two different test specimens.15.2.2 Program 2 was conducted in 1993 using a revisedprocedure as stipulated in the latest edition of this test method.In this program five different laboratories tested three com-pounds on two separate days. Two measured paramete
49、rs wereevaluated for this program:(1) the flexlife in kilocycles to 300 % crack growth, and(2) the flexlife (in kc) to 600 % crack growth.A test result for either parameter is the mean (average) ofthree specimens.15.3 The precision results in this precision and bias sectiongive an estimate of the precision of this test method with thematerials (rubbers, etc.) used in the particular interlaboratoryprograms as described below. The precision parameters shouldnot be used for acceptance or rejection testing of any group of4Supporting data have been fi
