1、Designation: C 730 98 (Reapproved 2008)Standard Test Method forKnoop Indentation Hardness of Glass1This standard is issued under the fixed designation C 730; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision
2、. 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 hardne
3、ss 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 regulato
4、ry limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E4 Practices for Force Verification of Testing MachinesE 384 Test Method for Microindentation Hardness of Ma-terials3. Terminology3.1 Descriptions of Terms Specific to This Standard:3.1.1 Knoop hardness number (KHN)a number obtai
5、nedby 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.3.1.1.
6、1 The Knoop hardness number (KHN) is computed asfollows:KHN 5 P/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 3 tan B/2),A = included longitudinal edge angle (see Fig. 1), andB = included transverse edge
7、angle (see Fig. 1).3.1.1.2 Knoop indentation hardness tests in glass are madeat a test load of 100 gf (0.1 kgf).3.1.1.3 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 theloa
8、d on Knoop hardness number.3.1.1.4 The indenter should remain in contact with thespecimen between 20 and 30 s. Most of the calibratedmachines that are used for making Knoop hardness tests aredash-pot controlled and this dwell time is consistent with theadjustment of the dash-pot to meet the loading
9、rate standard.3.1.1.5 Table 1 gives the Knoop hardness of several glassesas a function of load when the loading rate and dwell time areheld at the values recommended above.3.1.2 Knoop indentation hardness testan indentationhardness test using a calibrated machine to force a pointed,rhombic-base, pyr
10、amidal 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.NOTE 1A general description of the Knoop indentation hardness testis given in Test Method
11、E 384. 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 ten
12、sile 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.1This test method is
13、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 April 1, 2008. Published December 2008. Originallyapproved in 1972. Last previous edition approved in 2003 as
14、C 730 98 (2003).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.1Copyright ASTM International, 100 Barr Harbo
15、r Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.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 thispurpose, and the other type is an accessory available to existingFIG. 1
16、Knoop Indenter Showing Maximum Usable DimensionTABLE 1 Knoop Hardness of NIST Standard and Other GlassesA,BLaboratory NIST 710 NIST 711 NIST 715GEFusedQuartzNIST 710 NIST 711 NIST 715 GE Fused Quartz25-gf Load 50-gf LoadA 486 411 589 614 497 394 575 559C 594 450 537 415D 479 426 505 541 478 380 538
17、501E 521 415 608 620 497 392 574 586F 498 414 568 643 484 403 567 577GAvg 516 423 567.5 609.5 499 397 563.5 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 4
18、74E 490 396 544 530 488 372 546 510F 467 381 538 524 457 367 524 502G 481 388 550 558Avg 474 384.5 544 539 463 370 539 508Departure, max,%544126337Range, max, % 8 7 7 22 12 5 5 11ANIST 710NIST standard soda-lime-silica glass (no longer available; NIST 710a may be substituted), NIST 711NIST standard
19、lead-silica glass. NIST 715NISTstandard alkali-free aluminosilicate glass.BThese data were obtained from ASTM round-robin testing.C 730 98 (2008)2microscopes. Usually, this second type is fitted on an inverted-stage microscope. Good descriptions of the various machinesare available.3,45.1.2 Design o
20、f the machine should be such that the loadingrate, dwell time, and applied load can be standardized withinthe limits set forth in 3.1.1.2-3.1.1.4. It is an advantage toeliminate the human element whenever possible by appropriatemachine design. The machine should be designed so thatvibrations induced
21、 at the beginning of a test will be damped outby the time the indenter touches the sample.5.1.3 The calibration of the balance beam should be checkedmonthly or as needed. Indentations in standard glasses are alsoused to check calibration when needed.5.2 Indenter:5.2.1 The indenter shall meet the spe
22、cifications for Knoopindenters.4See Test Method E 384.5.2.2 Fig. 1 shows the indenter and its maximum usabledimensions. The diagonals have an approximate ratio of 7:1,and the depth of the indentation is about130 the length of thelong diagonal. A perfect Knoop indenter has the followingangles:5.2.2.1
23、 Included longitudinal angle 172 308 009.5.2.2.2 Included transverse angle 130 008 009.5.2.3 The constant Cpfor a perfect indenter is 0.07028 andthe specifications require a variation of not more than 1 percentfrom this value.5.3 Measuring MicroscopeThe measurement system shallbe so constructed that
24、 the length of the diagonals can bedetermined with errors not exceeding 60.0005 mm. Theapparent length of the diagonal should be corrected for thelimit of resolution of the objective being used in the micro-scope (see Appendix X1).6. Test Specimen6.1 The Knoop indentation hardness test is adaptable
25、to awide variety of glass specimens, ranging from tubing totelevision faceplates to polished plate glass. 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 t
26、hat the specimen cannot rock or shift during the test.6.1.1 ThicknessAs 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.6.1.2 Su
27、rface FinishAs pointed out above, the accuracyof the test depends 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
28、61 %. Six indentations on an “as-received”surface may be as bad as 610 %. Ground and polished surfacesshould be used. If this is not possible, the number of indenta-tions should be increased.6.1.3 Radius of CurvatureThe KHN obtained will beaffected even when the curvature is only in the direction of
29、 theshort diagonal. Care should be used when relating KHN valuesobtained on curved surfaces to those obtained on polished flatsurfaces.7. Verification of Apparatus7.1 Verification of LoadMost of the machines availablefor Knoop hardness testing use a loaded beam. This beamshould be tested for zero lo
30、ad. An indentation should not bevisible with zero load, but the indenter should contact thesample. A visible indentation should be obtained with a load of0.1 gf. Other methods of verifying the load application aregiven in Practices E4.7.2 Verification by Standard GlassesTable 1 gives theKnoop hardne
31、ss of several standard glasses. Knoop hardnessmeasurement 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.8. Procedure8.1 Specimen PlacementPlace the specimen on the stageof the m
32、achine in such a way so that the specimen will not beable to rock or shift during the measurement.8.2 Specimen Leveling:8.2.1 The surface of the specimen being tested must lie in aplane normal to the axis of the indenter. Fig. 2 shows an3Specifications for Knoop indenters can be found in the book Sm
33、all, L.,Hardness Theory and Practice (Part I: Practice), Service Diamond Tool Co., AnnArbor, MI, 1960, pp. 241243.4Mott, B. W., Micro-Indentation Hardness Testing, Butterworths ScientificPublications, London, 1956. FIG. 2 Sampling Leveling MeasurementsC 730 98 (2008)3indentation as it will appear th
34、rough the microscope with fivepoints labeled. To level the specimen, make a test indentationusing a 100-gf load.8.2.2 The following minimum specifications must be met:OA5OB65%OC5OD65%8.2.3 Leveling the specimen to meet these specifications isfacilitated if one has a leveling device.8.3 Magnitude of
35、Test LoadA test load of 100 gf isspecified. If cracks develop at this load, measurements within50 or 25-gf loads may be made although the Knoop indentationhardness does vary with load. Table 1 gives an indication of themagnitude of this variation to be expected. In all cases, the loadactually used s
36、hould be reported.8.4 Application of Test Load:8.4.1 Start the machine smoothly. If the machine is loadedby an electrical system or a dash-pot lever system, it should bemounted on shock absorbers which damp out all vibrations bythe time the indenter touches the specimen. If the specimen ishand-loade
37、d, take extreme care to see that the loading ratenever goes higher than 0.25 mm/min.8.4.2 After the indenter has been in contact with thespecimen for the required dwell time, carefully raise it off thesample to avoid a vibration impact at this time.8.5 Spacing of IndentationsAllow a distance of at l
38、eastthree times the short diagonal between indentations.8.6 Number of IndentationsThe number of indentationswill vary with the type of specimen. For example, if one isinvestigating the hardness gradient in an ion-exchangedsample, he will make a series on indentations and plot the KHNas a function of
39、 distance. In the usual test, one has a piece ofglass that is fairly homogeneous and he is trying to obtain amean 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:s5
40、=SKHN2KHNn!2/n2! (2)s = standard deviation of a single observation,KHN = mean KHN,KHNn= KHN obtained from nth indentation, andn = number of indentations.9. Measurement of Indentation9.1 The accuracy of the test method depends to a very largeextent on this measurement, as follows:9.1.1 If the measuri
41、ng 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.9.1.2 Carefully calibrate the measuring system with a stagemicrometer or, better, with a grating.9.1.3 If either
42、 a measuring microscope or a filar micrometeris used, always rotate the drum in the same direction toeliminate backlash errors.9.1.4 Check each reading twice. They should reproduce to60.0002 mm. One filar unit is equal to about 0.0002 mm whena503 objective is used in conjunction with a filar microme
43、terthat has a millimetre scale and a 100-division drum.9.1.5 Use the same filters in the light system at all times.Usually a green filter is used.10. Conversion of Diagonal Measurement to KHN10.1 Convert the diagonal measurement KHN by usingeither Eq X1.2 or Eq X1.3 of Appendix X1, or prepare tables
44、using these equations.11. Report11.1 Report the following:11.1.1 Mean KHN,11.1.2 Test load,11.1.3 Surface conditions and surface preparation,11.1.4 Thermal history of the sample,11.1.5 Number of indentations, and11.1.6 Standard deviation.12. Precision and Bias12.1 PrecisionOne operator on one testin
45、g machine isgenerally 62 % (coefficient of variation) for 100 to 200-gmlevels. Lower load statistics increase the coefficient of variationto 66%.12.2 BiasThe scientific community has avoided norms forthis property. The data in Table 1 may be referenced forcomparison. These data lend some measure for
46、 bias determi-nation, but by no means are intended for absolute reference.13. Keywords13.1 glass; hardness; indentation; KnoopC 730 98 (2008)4APPENDIXES(Nonmandatory Information)X1. CALCULATION OF TABLES TO CONVERT DIAGONAL LENGTHS TO KNOOP HARDNESS NUMBERSX1.1 Equation one given in 3.1.1.1 was:KHN5
47、Pd2Cp(X1.1)where d is the length of the long diagonal of the indentation, inmm. However, in the microscope only part of this diagonal isseen due to the finite resolving power of the light microscope.5d5do17l2NA(X1.2)where:do= apparent length of the long diagonal as measuredwith light microscope, mm,
48、l = wavelength of light, mm, andNA = numerical aperture of objective used in microscope.X1.2 Combining Eq X1.1 and Eq X1.2:KHN5PSdo17l2NAD2Cp(X1.3)X1.3 It is often convenient to include the conversion fromfilar units to millimetres in the table. In this case, the equationbecomes:KHN5PSLK17l2NAD2Cp(X
49、1.4)where:L = apparent length of the long diagonal in filar units asmeasured with the light microscope, andK = calibration constant, which tells what fraction of amillimetre is represented by a filar unit.X2. ASTM ROUND ROBIN ON STANDARD GLASSESX2.1 The data presented in Table 1 are the results of anASTM round robin on NIST standard and other glasses usingthe procedure given in this test method.5X2.2 The 100 gf numbers can be used for verification inaccordance with 7.2.ASTM International takes no position respecting the validity of any patent rights a
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