ASTM_D_7972_-_14.pdf

Designation:D797214Standard Test Method forFlexural Strength of Manufactured Carbon and GraphiteArticles Using Three-Point Loading at Room Temperature1This standard is issued under the fixed designation D7972;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 determination of the flexuralstrength of manufactured carbon and graphite articles using asquare,rectangular or cylindrical beam in three-point loadingat room temperature.1.2 The values stated in SI units are to be regarded asstandard.No other units of measurement are included in thisstandard.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:2C78 Test Method for Flexural Strength of Concrete(UsingSimple Beam with Third-Point Loading)C559 Test Method for Bulk Density by Physical Measure-ments of Manufactured Carbon and Graphite ArticlesC1161 Test Method for Flexural Strength of AdvancedCeramics at Ambient TemperatureC1239 Practice for Reporting Uniaxial Strength Data andEstimating Weibull Distribution Parameters for AdvancedCeramicsC1322 Practice for Fractography and Characterization ofFracture Origins in Advanced CeramicsD7775 Guide for Measurements on Small Graphite Speci-mensE4 Practices for Force Verification of Testing MachinesE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method3.Terminology3.1 Definitions:3.1.1 flexural strengtha measure of the ultimate loadcarrying capacity of a specified beam in bending.3.1.2 grainin manufactured(synthetic)carbon andgraphite,particle of filler material(usually coke or graphite)inthe starting mix formulation.Also referred to as granularmaterial,filler particle,or aggregate material.4.Significance and Use4.1 This test method provides a framework for materialdevelopment,quality control,characterization,and design datageneration purposes.The user needs to assess the applicabilityof the method on the specific material and for the intended use,as shown by the interlaboratory study.4.2 This test method determines the maximum loading on agraphite specimen with simple beam geometry in threepointbending,and it provides a means for the calculation of flexuralstrength at ambient temperature and environmental conditions.4.3 The flexure stress is computed based on simple beamtheory with assumptions that the material is isotropic andhomogeneous,the moduli of elasticity in tension and compres-sion are identical,and the material is linearly elastic.Formaterials with large grains,the minimum specimen dimensionshould be significantly larger than the maximum grain size(seeGuide D7775).4.4 Flexural strength of a group of test specimens isinfluenced by several parameters associated with the testprocedure.Such factors include the loading rate,testenvironment,specimen size,specimen preparation,and testfixtures.Specimen sizes and fixtures should be chosen toreduce errors due to material variability or testing parameters,such as friction and non-parallelism of specimen surfaces.4.5 The flexural strength of a manufactured graphite orcarbon material is dependent on both its inherent resistance tofracture and the size and severity of flaws.Variations in thesecause a natural scatter in test results for a sample of testspecimens.Fractographic analysis of fracture surfaces,al-though beyond the scope of this standard,is highly recom-mended for all purposes,especially if the data will be used fordesign as discussed in Practices C1239 and C1322.1This test method is under the jurisdiction of ASTM Committee D02 onPetroleum Products,Liquid Fuels,and Lubricants and is the direct responsibility ofSubcommittee D02.F0 on Manufactured Carbon and Graphite Products.Current edition approved Dec.1,2014.Published February 2015.DOI:10.1520/D7972-14.2For 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 4.6 The three-point test configuration exposes only a verysmall portion of the specimen to the maximum stress.Therefore,three-point flexural strengths are likely to be muchgreater than four-point flexural strengths.Three-point flexurehas some advantages.It uses simpler test fixtures,allowingsmall specimen testing and fracture toughness measurements.However,four-point flexure is preferred and reco