ASTM C849-88(2006)
(Test Method)Standard Test Method for Knoop Indentation Hardness of Ceramic Whitewares
Standard Test Method for Knoop Indentation Hardness of Ceramic Whitewares
SIGNIFICANCE AND USE
The Knoop indentation hardness is one of many properties that is used to characterize ceramic whitewares. Attempts have been made to relate Knoop indentation hardness to tensile strength, grinding speeds, and other hardness scales, but no generally accepted methods are available. Such conversions are limited in scope and should be used with caution, except for special cases where a reliable basis for the conversion has been obtained by comparison tests.
SCOPE
1.1 This test method covers the determination of the Knoop indentation hardness of ceramic whitewares and the verification of Knoop indentation hardness testing machines using standard glasses.
1.2 This standard may involve hazardous materials, operations, and equipment. This standard does not purport to address all of the safety problems associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
General Information
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Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation:C849–88(Reapproved 2006)
Standard Test Method for
Knoop Indentation Hardness of Ceramic Whitewares
This standard is issued under the fixed designation C849; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
is given in Test Method E384. The present method differs from this
1. Scope
description only in areas required by the special nature of ceramic
1.1 This test method covers the determination of the Knoop
whitewares.
indentation hardness of ceramic whitewares and the verifica-
tion of Knoop indentation hardness testing machines using
5. Significance and Use
standard glasses.
5.1 The Knoop indentation hardness is one of many prop-
1.2 This standard does not purport to address all of the
ertiesthatisusedtocharacterizeceramicwhitewares.Attempts
safety concerns, if any, associated with its use. It is the
have been made to relate Knoop indentation hardness to tensile
responsibility of the user of this standard to establish appro-
strength, grinding speeds, and other hardness scales, but no
priate safety and health practices and determine the applica-
generally accepted methods are available. Such conversions
bility of regulatory limitations prior to use.
arelimitedinscopeandshouldbeusedwithcaution,exceptfor
special cases where a reliable basis for the conversion has been
2. Referenced Documents
obtained by comparison tests.
2.1 ASTM Standards:
E4 Practices for Force Verification of Testing Machines 6. Apparatus
E384 Test Method for Microindentation Hardness of Mate-
6.1 Testing Machines:
rials
6.1.1 There are two general types of machines available for
making this test. One type is a self-contained unit built for this
3. Terminology
purpose,andtheothertypeisanaccessoryavailabletoexisting
3.1 Definitions:
microscopes. Usually, this second type is fitted on an inverted-
3.1.1 Knoop hardness number ( KHN)—a number obtained
stage microscope. Good descriptions of the various machines
,
by dividing the applied load in kilograms-force by the pro- 3 4
are available.
jected area of the indentation in square millimetres, computed
6.1.2 Design of the machine should be such that the loading
from the measured long diagonal of the indentation and the
rate, dwell time, and applied load can be standardized within
included edge angles of the diamond. It is assumed that the
the limits set forth in 3.1.1. It is an advantage to eliminate the
indentation is an imprint of the undeformed indenter.
human element whenever possible by appropriate machine
design. The machine should be designed so that vibrations
4. Summary of Test Method
induced at the beginning of a test will be damped out by the
4.1 This test method describes an indentation hardness test
time the indenter touches the sample.
using a calibrated machine to force a pointed, rhombic-base,
6.1.3 Thecalibrationofthebalancebeamshouldbechecked
pyramidal diamond indenter having specified face angles,
monthly or as needed. Indentations in standard glasses are also
under a predetermined load, into the surface of the material
used to check calibration when needed.
under test and to measure the long diagonal of the resulting
6.2 Indenter:
impression after removal of the load.
6.2.1 The indenter shall meet the specifications for Knoop
NOTE 1—A general description of the Knoop indentation hardness test indenters. See Test Method E384.
6.2.2 Fig. 1 shows the indenter and its maximum usable
dimensions. The diagonals have an approximate ratio of 7:1,
and the depth of the indentation is about ⁄30 the length of the
ThistestmethodisunderthejurisdictionofASTMCommitteeC21onCeramic
long diagonal. A perfect Knoop indenter has the following
Whitewares and Related Products and is the direct responsibility of Subcommittee
C21.03 on Methods for Whitewares and Environmental Concerns.
angles:
Current edition approved Feb. 15, 2006. Published February 2006. Originally
approved in 1976. Last previous edition approved in 1999 as C849 – 88 (1999).
DOI: 10.1520/C0849-88R06. Specifications for Knoop indenters can be found in Small, L., Hardness Theory
For referenced ASTM standards, visit the ASTM website, www.astm.org, or and Practice (Part I: Practice) pp. 241–243, Service Diamond Tool Co.,AnnArbor,
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM MI, 1960.
Standards volume information, refer to the standard’s Document Summary page on Mott, B. W., Micro-Indentation Hardness Testing, Butterworth’s Scientific
the ASTM website. Publications, London, 1956.
Copyright ©ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA19428-2959, United States.
C849–88 (2006)
FIG. 1 Knoop Indenter Showing Maximum Usable Dimension
6.2.2.1 Included longitudinal angle 172° 30 min 00 s. 7.1.3 Radius of Curvature—The KHN obtained will be
6.2.2.2 Included transverse angle 130° 00 min 00 s. affected even when the curvature is only in the direction of the
6.2.3 The constant C for a perfect indenter is 0.070 28, and short diagonal. Care should be used when relating KHN values
p
thespecificationsrequireavariationofnotmorethan1 %from obtained on curved surfaces to those obtained on polished flat
this value. surfaces.
6.3 Measuring Microscope—Themeasurementsystemshall
8. Preparation of Apparatus
be so constructed that the length of the diagonals can be
determined with errors not exceeding 60.0005 mm. The 8.1 Verification of Load—Most of the machines available
apparent length of the diagonal is corrected in the calculations for Knoop hardness testing use a loaded beam. This beam
for the limit of resolution of the objective being used in the should be tested for zero load. An indentation should not be
microscope. visible with zero load, but the indenter should contact the
sample.Avisible indentation should be obtained with a load of
7. Test Specimens
0.1 gf. Other methods of verifying the load application are
7.1 The Knoop indentation hardness test is adaptable to a given in Practice E4.
wide variety of ceramic whiteware specimens. In general, the 8.2 Verification by Standard Glasses—Table 1 gives the
accuracy of the test will depend on the smoothness of the Knoop hardness of several National Institute of Standards and
surface and, whenever possible, ground and polished speci- Technology (NIST) standard glasses. Knoop hardness mea-
mens should be used. The back of the specimen shall be fixed surement on a piece of one of these glasses that has been
so that the specimen cannot rock or shift during the test. ground and polished within the last 24 h should agree with the
7.1.1 Thickness—As long as the specimen is over ten times value in the table 65 %. Tests should be made using 100 gf.
as thick as the indentation depth, this will not affect the test. In
9. Procedure
general, if specimens are at least 0.10 mm thick, the hardness
will not be affected by variations in the thickness. 9.1 Specimen Placement—Place the specimen on the stage
7.1.2 Surface Finish—As pointed out above, the accuracy of the machine in such a way so that the specimen will not be
of the test depends on the surface finish. However, if one is able to rock or shift during the measurement.
investigating a surface coating or treatment, he cannot grind 9.2 Specimen Leveling:
and polish the sample. Experience has shown that six inden- 9.2.1 The surface of the specimen being tested must lie in a
tations on a ground and polished surface of glass will repro- plane normal to the axis of the indenter. Fig. 2 shows an
duce within 61 %. Six indentations on an “as-received” indentation as it will appear through the microscope with five
surfacemaybeasbadas 610 %.Groundandpolishedsurfaces points labe
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