ASTM_B_771_-_11_2017.pdf

Designation:B77111(Reapproved 2017)Standard Test Method forShort Rod Fracture Toughness of Cemented Carbides1This standard is issued under the fixed designation B771;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.1.Scope1.1 This test method covers the determination of the fracturetoughness of cemented carbides(KIcSR)by testing slotted shortrod or short bar specimens.1.2 The values stated in SI units are to be regarded asstandard.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.1.4 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards,Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade(TBT)Committee.2.Referenced Documents2.1 ASTM Standards:2E399 Test Method for Linear-Elastic Plane-Strain FractureToughness KIcof Metallic Materials3.Terminology Definitions3.1 stress intensity factor,Kl,(dimensional units FL3/2)the magnitude of the ideal-crack-tip stress field for mode 1 ina linear-elastic body.NOTE1Values of K for mode l are given by:Kl5 limity=2r#(1)r0where:r=distance directly forward from the crack tip to alocation where the significant stress yis calculated,andy=principal stress normal to the crack plane.3.2 Abbreviations:fracture toughness of cemented carbide,KIcSR,(dimensional units FL3/2)the material-toughnessproperty measured in terms of the stress-intensity factor Klbythe operational procedure specified in this test method.4.Summary of Test Method4.1 This test method involves the application of an openingload to the mouth of the short rod or short bar specimen whichcontains a chevron-shaped slot.Load versus displacementacross the slot at the specimen mouth is recorded autographi-cally.As the load is increased,a crack initiates at the point ofthe chevron slot and slowly advances longitudinally,tending tosplit the specimen in half.The load goes through a smoothmaximum when the width of the crack front is about one thirdof the specimen diameter(short rod)or breadth(short bar).Thereafter,the load decreases with further crack growth.Twounloading-reloading cycles are performed during the test tomeasure the effects of any macroscopic residual stresses in thespecimen.The fracture toughness is calculated from themaximum load in the test and a residual stress parameter whichis evaluated from the unloading-reloading cycles on the testrecord.5.Significance and Use5.1 The property KIcSRdetermined by this test method isbelieved to characterize the resistance of a cemented carbide tofracture in a neutral environment in the presence of a sharpcrack under severe tensile constraint,such that the state ofstress near the crack front approaches tri-tensile plane strain,and the crack-tip plastic region is small compared with thecrack size and specimen dimensions in the constraint direction.A KIcSRvalue is believed to represent a lower limiting value offracture toughness.This value may be used to estimate therelation between failure stress and defect size when theconditions of high constraint described above would be ex-pected.Background information concerning the basis for1This test method is under the jurisdiction of ASTM Committee B09 on MetalPowders and Metal Powder Products and is the direct responsibility of Subcom-mittee B09.06 on Cemented Carbides.Current edition approved April 1,2017.Published April 2017.Originallyapproved in 1987.Last previous edition approved in 2011 as B771 111.DOI:10.1520/B0771-11E01R17.2For 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 StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards,Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade(TBT)Committee.1 development of this test method in terms of linear elasticfracture mechanics may be found in Refs(1-7).35.2 This test method can serve the following purposes:5.2.1 To establish,in quantitative terms significant to ser-vice performance,the effects of