ASTM_D_813_-_07_2014.pdf

Designation:D81307(Reapproved 2014)Standard Test Method forRubber DeteriorationCrack Growth1This standard is issued under the fixed designation D813;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.This standard has been approved for use by agencies of the U.S.Department of Defense.1.Scope1.1 This test method covers the determination of crackgrowth of vulcanized 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 D430.Cracking initiated in these materials by smallcuts or tears in service,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 artificially 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 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:2D430 Test Methods for Rubber DeteriorationDynamicFatigueD1349 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 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 frequent 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 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 MachineThe 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 other 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 movingmember shall be adjustable and shall be obtained 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.).1This test method is under the jurisdiction of ASTM Committee D11 on Rubberand is the direct responsibility of Subcommittee D11.15 on Degradation Tests.Current edition approved May 1,2014.Published May 2014.Originallyapproved in 1944.Last previous edition approved in 2007 as D813 07.DOI:10.1520/D0813-07R14.2For 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 6.1.4 The 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 smoothness 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