ASTM_D_7779_-_20.pdf

Designation:D777920Standard Test Method forDetermination of Fracture Toughness of Graphite atAmbient Temperature1This standard is issued under the fixed designation D7779;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.Scope*1.1 This test method covers and provides a measure of theresistance of a graphite to crack extension at ambient tempera-ture and atmosphere expressed in terms of stress-intensityfactor,K,and strain energy release rate,G.These crack growthresistance properties are determined using beam test specimenswith a straight-through sharp machined V-notch.1.2 This test method determines the stress intensity factor,K,from applied force and gross specimen deflection measuredaway from the crack tip.The stress intensity factor calculatedat the maximum applied load is denoted as fracture toughness,KIc,and is known as the critical stress intensity factor.If theresolution of the deflection gauge is sensitive to fracturebehavior in the test specimen and can provide a measure of thespecimen compliance,strain energy release rate,G,can bedetermined as a function of crack extension.1.3 This test method is applicable to a variety of grades ofgraphite which exhibit different types of resistance to crackgrowth,such as growth at constant stress intensity(strainenergy release rate),or growth with increasing stress intensity(strain energy release rate),or growth with decreasing stressintensity(strain energy release rate).It is generally recognizedthat because of the inhomogeneous microstructure of graphite,the general behavior will exhibit a mixture of all three duringthe test.The crack resistance behavior exhibited in the test isusually referred to as an“R-curve.”NOTE1One difference between the procedure in this test method andtest methods such as Test Method E399,which measure fracturetoughness,KIc,by one set of specific operational procedures,is that TestMethod E399 focuses on the start of crack extension from a fatigueprecrack for metallic materials.This test method for graphite makes use ofa machined notch with sharp cracking at the root of the notch because ofthe nature of graphite.Therefore,fracture toughness values determinedwith this method may not be interchanged with KIcas defined in TestMethod E399.1.4 This test method gives fracture toughness values,KIcand critical strain energy release rate,GIcfor specific condi-tions of environment,deformation rate,and temperature.Frac-ture toughness values for a graphite grade can be functions ofenvironment,deformation rate,and temperature.1.5 This test method is divided into two major parts.Thefirst major part is the main body of the standard,whichprovides general information on the test method,the applica-bility to materials comparison and qualification,and require-ments and recommendations for fracture toughness testing.The second major part is composed of annexes,which provideinformation related to test apparatus and test specimen geom-etry.Main BodySectionScope1Referenced Documents2Terminology3Summary of Test Method4Significance and Use5Apparatus6Test Specimen7Procedure8Specimen Dryness9Calculation of Results10Report11Precision and Bias12Keywords13AnnexAnnex A11.6 The values stated in SI units are to be regarded asstandard.No other units of measurement are included in thisstandard.1.6.1 Measurement units expressed in these test methods arein accordance with IEEE/ASTM SI 10.1.7 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,health,and environmental practices and deter-mine the applicability of regulatory limitations prior to use.1.8 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.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 Oct.1,2020.Published December 2020.Originallyapproved in 2011.Last previous edition approved in 2015 as D7779 11(2015).DOI:10.1520/D7779-20.*A Summary of Changes section appears at the end of this standardCopyright 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 Standar