ASTM_C_849_-_88_2016.pdf

Designation:C84988(Reapproved 2016)Standard Test Method forKnoop Indentation Hardness of Ceramic Whitewares1This standard is issued under the fixed designation C849;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 ceramic whitewares and the verifica-tion of Knoop indentation hardness testing machines usingstandard 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 Microindentation Hardness of Mate-rials3.Terminology3.1 Definitions: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.4.Summary of Test Method4.1 This test method describes an indentation hardness testusing a calibrated machine to force a pointed,rhombic-base,pyramidal diamond indenter having specified face angles,under a predetermined load,into the surface of the materialunder test and to measure the long diagonal of the resultingimpression 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 ceramicwhitewares.5.Significance and Use5.1 The Knoop indentation hardness is one of many prop-erties that is used to characterize ceramic whitewares.Attemptshave been made to relate Knoop indentation hardness to tensilestrength,grinding speeds,and other hardness scales,but nogenerally accepted methods are available.Such conversionsare limited in scope and should be used with caution,except forspecial cases where a reliable basis for the conversion has beenobtained by comparison tests.6.Apparatus6.1 Testing Machines:6.1.1 There are two general types of machines available formaking this test.One type is a self-contained unit built for thispurpose,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.3,46.1.2 Design of the machine should be such that the loadingrate,dwell time,and applied load can be standardized withinthe limits set forth in 3.1.1.It is an advantage to eliminate thehuman element whenever possible by appropriate machinedesign.The machine should be designed so that vibrationsinduced at the beginning of a test will be damped out by thetime the indenter touches the sample.6.1.3 The calibration of the balance beam should be checkedmonthly or as needed.Indentations in standard glasses are alsoused to check calibration when needed.6.2 Indenter:6.2.1 The indenter shall meet the specifications for Knoopindenters.3See Test Method E384.6.2.2 Fig.1 shows the indenter and its maximum usabledimensions.The diagonals have an approximate ratio of 7:1,1This test method is under the jurisdiction ofASTM Committee C21 on CeramicWhitewares and Related Productsand is the direct responsibility of SubcommitteeC21.03 on Methods for Whitewares and Environmental Concerns.Current edition approved July 1,2016.Published July 2016.Originally approvedin 1976.Last previous edition approved in 2011 as C849 88(2011).DOI:10.1520/C0849-88R16.2For 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.3Specifications for Knoop indenters can be found in Small,L.,Hardness Theoryand Practice(Part I:Practice)pp.241243,Service Diamond Tool Co.,Ann Arbor,MI,1960.4Mott,B.W.,Micro-Indentation Hardness Testing,Butterworths ScientificPublications,London,1956.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 and the depth of the indentation is about130the length of thelong diagonal.A perfect Knoop indenter has the followingangles:6.2.2.1 Included longitudinal angle 172 30 min 00 s.6.2.2.2 Included transverse angle 130 00 min 00 s.6.2.3 The constant Cpfor a perfect indenter is 0.070 28,andthe specifications require a variation of not more than 1%fromthis value.6.3 Measuring MicroscopeThe measurement system shal