ASTM_C_730_-_98_2013.pdf

Designation:C73098(Reapproved 2013)Standard Test Method forKnoop Indentation Hardness of Glass1This standard is issued under the fixed designation C730;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 Knoopindentation hardness of glass and the verification of Knoopindentation hardness testing machines using standard glasses.1.2 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:2E4 Practices for Force Verification of Testing MachinesE384 Test Method for Knoop and Vickers Hardness ofMaterials3.Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 Knoop hardness number(KHN)a number obtainedby dividing the applied load in kilograms-force by the pro-jected area of the indentation in square millimetres,computedfrom the measured long diagonal of the indentation and theincluded edge angles of the diamond.It is assumed that theindentation is an imprint of the undeformed indenter.3.1.2 The Knoop hardness number(KHN)is computed asfollows:KHN5P/Ap!5P/d2Cp!(1)P=load,kgf,Ap=projected area of the indentation,mm2,d=length of the long diagonal of the indentation,mm,Cp=12(cot A/2 tan B/2),A=included longitudinal edge angle(see Fig.1),andB=included transverse edge angle(see Fig.1).3.1.3 Knoop indentation hardness tests in glass are made ata test load of 100 gf(0.1 kgf).3.1.4 The rate of indenter motion prior to contact with thespecimen shall be 0.20 6 0.05 mm/min.This low rate of loadapplication tends to alleviate the effect of the magnitude of theload on Knoop hardness number.3.1.5 The indenter should remain in contact with the speci-men between 20 and 30 s.Most of the calibrated machines thatare used for making Knoop hardness tests are dash-potcontrolled and this dwell time is consistent with the adjustmentof the dash-pot to meet the loading rate standard.3.1.6 Table 1 gives the Knoop hardness of several glasses asa function of load when the loading rate and dwell time areheld at the values recommended above.3.1.7 Knoop indentation hardness testan indentation hard-ness test using a calibrated machine to force a pointed,rhombic-base,pyramidal diamond indenter having specifiedface angles,under a predetermined load,into the surface of thematerial under test and to measure the long diagonal of theresulting impression after removal of the load.NOTE1A general description of the Knoop indentation hardness testis given in Test Method E384.The present method differs from thisdescription only in areas required by the special nature of glasses.4.Significance and Use4.1 The Knoop indentation hardness is one of many prop-erties that is used to characterize glasses.Attempts have beenmade to relate Knoop indentation hardness to tensile strength,grinding speeds,and other hardness scales,but no generallyaccepted methods are available.Such conversions are limitedin scope and should be used with caution,except for specialcases where a reliable basis for the conversion has beenobtained by comparison tests.5.Apparatus5.1 Testing Machines:5.1.1 There are two general types of machines available formaking this test.One type is a self-contained unit built for this1This test method is under the jurisdiction of ASTM Committee C14 on Glassand Glass Products and is the direct responsibility of Subcommittee C14.04 onPhysical and Mechanical Properties.Current edition approved Oct.1,2013.Published October 2013.Originallyapproved in 1972.Last previous edition approved in 2008 as C730 98(2008).DOI:10.1520/C0730-98R13.2For 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 purpose,and the other type is an accessory available to existingmicroscopes.Usually,this second type is fitted on an inverted-stage microscope.Good descriptions of the various machinesare available.3,45.1.2 Design of the machine should be such that the loadingrate,dwell time,and applied load can be standardized withinthe limits set forth in 3.1.3 3.1.5.It is an advantage toeliminate the human element whenever possible by appropriatemachine design.The machine should be designed so that3Specifications for Knoop indenters can be found in the book Small,L.,Hardness Theory and Practice(Part I:Practice),Service Diamond Tool Co.,AnnArbor,