1、Designation: C849 88 (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 la
2、st 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 o
3、f 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 a
4、pplica-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 divid
5、ing 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 Tes
6、t 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 result
7、ingimpression after removal of the load.NOTE 1A 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 h
8、ardness 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 shou
9、ld 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 t
10、he 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 standard
11、ized 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 calib
12、ration 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 usab
13、ledimensions. 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
14、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
15、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,
16、 Butterworths ScientificPublications, London, 1956.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1and the depth of the indentation is about130 the length of thelong diagonal. A perfect Knoop indenter has the followingangles:6.2.2.1 I
17、ncluded 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 shallbe so constructed th
18、at the length of the diagonals can bedetermined with errors not exceeding 60.0005 mm. Theapparent length of the diagonal is corrected in the calculationsfor the limit of resolution of the objective being used in themicroscope.7. Test Specimens7.1 The Knoop indentation hardness test is adaptable to a
19、wide variety of ceramic whiteware specimens. In general, theaccuracy of the test will depend on the smoothness of thesurface and, whenever possible, ground and polished speci-mens should be used. The back of the specimen shall be fixedso that the specimen cannot rock or shift during the test.7.1.1 T
20、hicknessAs long as the specimen is over ten timesas thick as the indentation depth, this will not affect the test. Ingeneral, if specimens are at least 0.10 mm thick, the hardnesswill not be affected by variations in the thickness.7.1.2 Surface FinishAs pointed out above, the accuracy ofthe test dep
21、ends on the surface finish. However, if one isinvestigating a surface coating or treatment, he cannot grindand polish the sample. Experience has shown that six inden-tations on a ground and polished surface of glass will repro-duce within 61 %. Six indentations on an “as-received”surface may be as b
22、ad as 610 %. Ground and polished surfacesshould be used. If this is not possible, the number of indenta-tions should be increased.7.1.3 Radius of CurvatureThe KHN obtained will beaffected even when the curvature is only in the direction of theshort diagonal. Care should be used when relating KHN val
23、uesobtained on curved surfaces to those obtained on polished flatsurfaces.8. Preparation of Apparatus8.1 Verification of LoadMost of the machines availablefor Knoop hardness testing use a loaded beam. This beamshould be tested for zero load. An indentation should not bevisible with zero load, but th
24、e indenter should contact thesample.Avisible indentation should be obtained with a load of0.1 gf. Other methods of verifying the load application aregiven in Practice E4.8.2 Verification by Standard GlassesTable 1 gives theKnoop hardness of several National Institute of Standards andTechnology (NIST
25、) standard glasses. Knoop hardness mea-surement on a piece of one of these glasses that has beenground and polished within the last 24 h should agree with thevalue in the table 65 %. Tests should be made using 100 gf.9. Procedure9.1 Specimen PlacementPlace the specimen on the stageof the machine in
26、such a way so that the specimen will not beable to rock or shift during the measurement.9.2 Specimen Leveling:FIG. 1 Knoop Indenter Showing Maximum Usable DimensionC849 88 (2016)29.2.1 The surface of the specimen being tested must lie in aplane normal to the axis of the indenter. Fig. 2 shows aninde
27、ntation as it will appear through the microscope with fivepoints labeled. To level the specimen, make a test indentationusing a 100-gf load.9.2.2 The following minimum specifications must be met:OA 5 OB65% (1)OC 5 OD65%9.2.3 Leveling the specimen to meet these specifications isfacilitated if one has
28、 a leveling device.9.3 Magnitude of Test LoadA test load of 1000 gf (9.8 N)is specified. If cracks develop at this load, measurementswithin 500- or 250-gf (4.9- or 2.45-N) loads may be madealthough the Knoop indentation hardness does vary with load.Table 1 gives an indication of the magnitude of thi
29、s variation tobe expected. In all cases, the load actually used should bereported.9.4 Application of Test Load:9.4.1 Start the machine smoothly. The rate of indentermotion before contact with the specimen shall be 0.20 6 0.05mm/min. If the machine is loaded by an electrical system or adash-pot lever
30、 system, it should be mounted on shock absorb-ers which damp out all vibrations by the time the indentertouches the specimen. If the specimen is handloaded, takeextreme care to see that the loading rate never goes higher than0.25 mm/min.9.4.2 The indenter should remain in contact with the speci-men
31、between 20 and 30 s. After the indenter has been incontact with the specimen for the required dwell time, carefullyraise it off the sample to avoid a vibration impact at this time.9.5 Spacing of IndentationsAllow a distance of at leastthree times the short diagonal between indentations.9.6 Number of
32、 IndentationsThe number of indentationswill vary with the type of specimen. For example, if one isinvestigating the hardness gradient in a sample, he will make aseries of indentations and plot the KHN as a function ofdistance. In the usual test, one has a piece of ceramicTABLE 1 Knoop Hardness of NI
33、ST Standard GlassesA, BLaboratoryNIST710NIST711NIST715GEFusedQuartzNIST710NIST711NIST715GEFusedQuartz25-gf Load 50-gf LoadA 486 411 589 614 497 394 575 559C 594 450 537 415D 479 426 505 541 478 380 538 501E 521 415 608 620 497 392 574 586F 498 414 568 643 484 403 567 577GAv 516 423 567.5 609.5 499 3
34、97 563.5 556Departure, max, % 15 6 11 11 8 5 5 10Range, max, % 22 9 18 17 12 9 7 15100-gf Load 200-gf LoadA 475 387 558 554 468 380 550 523C 478 387 554 593 468 371 544 530D 452 368 521 473 433 360 529 474E 490 396 544 530 488 372 546 510F 467 381 538 524 457 367 524 502G 481 388 550 558Av 474 384.5
35、 544 539 463 370 539 508Departure, max, % 5 4 4 12 6 3 3 7Range, max, % 8 7 7 22 12 5 5 11ANIST 710NIST standard soda-lime-silica glass. NIST 711NIST standard lead-silica glass. NIST 715NIST standard alkali-free aluminosilicate glass.BThese data were obtained from ASTM round-robin testing.FIG. 2 Sam
36、pling Leveling MeasurementsC849 88 (2016)3whiteware that is fairly homogeneous and he is trying to obtaina mean KHN for that specimen. In this case, it is recommendedthat at least ten indentations be made and that both the meanKHN and the standard deviation be reported. The standarddeviation is:s 5
37、=(KHN 2 KHNn!2/n 2 1! (2)where:s = standard deviation of a single observation,KHN = mean KHN,KHNn= KHN obtained from nth indentation, andn = number of indentations.10. Measurement of Indentation10.1 The accuracy of the test method depends to a verylarge extent on this measurement, as follows:10.1.1
38、If the measuring system contains a light source, takecare to use the system only after it has reached equilibriumtemperature. This is because the magnification of a microscopedepends on the tube length.10.1.2 Carefully calibrate the measuring system with a stagemicrometer or, better, with a grating.
39、10.1.3 If either a measuring microscope or a filar microm-eter is used, always rotate the drum in the same direction toeliminate backlash errors.10.1.4 Check each reading twice. They should reproduce to60.0002 mm. One filar unit is equal to about 0.0002 mm whena 50 objective is used in conjunction w
40、ith a filar micrometerthat has a millimetre scale and a 100-division drum.10.1.5 Use the same filters in the light system at all times.Usually a green filter is used.11. Calculation11.1 The Knoop hardness number (KHN) is computed asfollows:KHN 5 P/Ap! 5 P/d2Cp! (3)where:P = load, kgf;Ap= projected a
41、rea 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).However, in the microscope only part of this diagonal is seendue to the finite resolving pow
42、er of the light microscope.4d 5 do17 /2 NA (4)where:do= apparent length of the long diagonal as measuredwith light microscope, mm; = wavelength of light, mm; andNA = numerical aperture of objective used in microscope.11.2 If we combine Eq 1 and 2, we get:KHN 5 P/do17/2 NA!#2Cp(5)11.3 It is often con
43、venient to include the conversion fromfilar units to millimetres in the table. In this case, the equationbecomes:KHN 5 P/LK17/2 NA!#2Cp(6)where:L = apparent length of the long diagonal in filar units asmeasured with the light microscope andK = calibration constant, which tells what fraction of amill
44、imetre is represented by a filar unit.12. Report12.1 The report shall include the following:12.1.1 Mean KHN,12.1.2 Test load,12.1.3 Surface conditions and surface preparation,12.1.4 Thermal history of the sample,12.1.5 Number of indentations, and12.1.6 Standard deviation.13. Precision and Bias13.1 P
45、recisionBased on experience with one instrumentand several operators, the coefficient of variation using stan-dard metal block calibrations is consistently within 1 %. Forsintered high-alumina ceramic materials, the coefficient ofvariation ranges from 5 to 8 %.13.2 BiasEach ceramic material tested h
46、as its own intrin-sic hardness. There are no absolute terms against which tomeasure hardness on ceramic whitewares products.14. Keywords14.1 ceramic whitewares; Knoop indentation hardnessC849 88 (2016)4APPENDIX(Nonmandatory Information)X1. ASTM ROUND ROBIN ON STANDARD GLASSESX1.1 The data presented
47、in Table 1 are the results of anASTM round robin on NIST standard glasses using theprocedure given in this test method.5X1.2 The 100-gf numbers can be used for verification inaccordance with the instructions in 8.2.ASTM International takes no position respecting the validity of any patent rights ass
48、erted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time b
49、y the responsible technical committee and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address s
