ASTM C849-88(2020)

Standard Test Method for Knoop Indentation Hardness of Ceramic Whitewares

SIGNIFICANCE AND USE
5.1 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 does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.3 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 31-Oct-2020
• ICS: 81.060.20 - Ceramic products
• Technical Committee: C21 - Ceramic Whitewares and Related Products
• Drafting Committee: C21.03 - Methods for Whitewares and Environmental Concerns

Relations

• Refers: ASTM E4-14 - Standard Practices for Force Verification of Testing Machines
• Effective Date: 01-Jun-2014
• Refers: ASTM E4-10 - Standard Practices for Force Verification of Testing Machines
• Effective Date: 01-Jun-2010
• Refers: ASTM E384-10e1 - Standard Test Method for Knoop and Vickers Hardness of Materials
• Effective Date: 01-Feb-2010
• Refers: ASTM E384-10 - Standard Test Method for Microindentation Hardness of Materials
• Effective Date: 01-Feb-2010
• Refers: ASTM E4-09a - Standard Practices for Force Verification of Testing Machines
• Effective Date: 01-Nov-2009
• Refers: ASTM E384-09 - Standard Test Method for Microindentation Hardness of Materials
• Effective Date: 01-May-2009
• Refers: ASTM E4-09 - Standard Practices for Force Verification of Testing Machines
• Effective Date: 01-Apr-2009
• Refers: ASTM E4-08 - Standard Practices for Force Verification of Testing Machines
• Effective Date: 01-Dec-2008
• Refers: ASTM E384-08a - Standard Test Method for Microindentation Hardness of Materials
• Effective Date: 15-Mar-2008
• Refers: ASTM E384-08ae1 - Standard Test Method for Microindentation Hardness of Materials
• Effective Date: 15-Mar-2008
• Refers: ASTM E384-08 - Standard Test Method for Microindentation Hardness of Materials
• Effective Date: 01-Jan-2008
• Refers: ASTM E384-07a - Standard Test Method for Microindentation Hardness of Materials
• Effective Date: 15-Dec-2007
• Refers: ASTM E384-07 - Standard Test Method for Microindentation Hardness of Materials
• Effective Date: 01-Jul-2007
• Refers: ASTM E4-07 - Standard Practices for Force Verification of Testing Machines
• Effective Date: 01-Jan-2007
• Refers: ASTM E384-06 - Standard Test Method for Microindentation Hardness of Materials
• Effective Date: 15-Nov-2006

Overview

ASTM C849-88(2020): Standard Test Method for Knoop Indentation Hardness of Ceramic Whitewares defines a reliable procedure to measure the Knoop indentation hardness of ceramic whitewares. Issued by ASTM International, this standard is essential for laboratories and quality control departments working with ceramic products. The method is specifically tailored for the ceramic whiteware industry and provides guidance on equipment verification using standard reference glasses, enhancing the accuracy and repeatability of hardness tests.

Key Topics

• Knoop Indentation Hardness: The standard details the use of a pyramidal diamond indenter under specific loading to create an indentation on a ceramic specimen, measuring the long diagonal of this impression using precision microscopy.
• Testing Equipment: Guidance is provided on the selection and calibration of Knoop indentation hardness testing machines, including apparatus specifications for consistent results.
• Specimen Preparation: Recommendations on surface finish, thickness, and mounting techniques to ensure reliable test outcomes.
• Measurement and Calculation: Instructions on load application, leveling, indentation measurement, and calculation of the Knoop Hardness Number (KHN).
• Reporting Requirements: Details on what data to include in test reports for traceability and quality assurance.

Applications

The test method outlined by ASTM C849-88(2020) has significant practical value for a range of ceramic materials and products. Typical applications include:

• Quality Control in Manufacturing: Assessing the mechanical integrity and consistency of ceramic whitewares such as tiles, insulators, and sanitaryware.
• Material Characterization: Comparing hardness properties among batches, formulations, or after processing treatments.
• Research and Development: Evaluating new ceramic compositions, coatings, or treatments for improved hardness and durability.
• Verification of Testing Instruments: Using NIST standard reference glasses for checking and calibrating Knoop hardness testing machines, ensuring the reliability of test data.

While the Knoop indentation hardness can sometimes be related to other material properties like tensile strength or grinding resistance, the standard emphasizes caution in such conversions. Direct comparison to other hardness scales is discouraged unless experimentally validated.

Related Standards

For comprehensive ceramic testing strategies, the following related ASTM standards are frequently referenced alongside ASTM C849-88(2020):

• ASTM E384 - Test Method for Microindentation Hardness of Materials: Provides a general description of Knoop and Vickers microindentation hardness tests, applicable to a broad range of materials including ceramics.
• ASTM E4 - Practices for Force Verification of Testing Machines: Covers calibration and verification of force application in testing equipment.
• Relevant NIST Standard Glasses - Used as reference materials for machine verification as outlined in the standard.

Summary

ASTM C849-88(2020) is a crucial standard for determining the Knoop indentation hardness of ceramic whitewares. By following its guidelines, laboratories and manufacturers can ensure accurate, repeatable hardness measurements, enhance product quality, and maintain compliance with industry best practices. This standard is recognized internationally and adheres to the principles of standardization established by the World Trade Organization’s Technical Barriers to Trade (TBT) Committee, supporting global trade and regulatory alignment in the ceramic sector.

Keywords: ASTM C849, Knoop indentation hardness, ceramic whitewares, hardness testing, ceramic testing standards, quality control, material characterization.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: C849 − 88 (Reapproved 2020)
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.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope pyramidal diamond indenter having specified face angles,
under a predetermined load, into the surface of the material
1.1 This test method covers the determination of the Knoop
under test and to measure the long diagonal of the resulting
indentation hardness of ceramic whitewares and the verifica-
impression after removal of the load.
tion of Knoop indentation hardness testing machines using
standard glasses.
NOTE 1—Ageneral description of the Knoop indentation hardness test
is given in Test Method E384. The present method differs from this
1.2 This standard does not purport to address all of the
description only in areas required by the special nature of ceramic
safety concerns, if any, associated with its use. It is the
whitewares.
responsibility of the user of this standard to establish appro-
priate safety, health, and environmental practices and deter- 5. Significance and Use
mine the applicability of regulatory limitations prior to use.
5.1 The Knoop indentation hardness is one of many prop-
1.3 This international standard was developed in accor-
ertiesthatisusedtocharacterizeceramicwhitewares.Attempts
dance with internationally recognized principles on standard-
havebeenmadetorelateKnoopindentationhardnesstotensile
ization established in the Decision on Principles for the
strength, grinding speeds, and other hardness scales, but no
Development of International Standards, Guides and Recom-
generally accepted methods are available. Such conversions
mendations issued by the World Trade Organization Technical
arelimitedinscopeandshouldbeusedwithcaution,exceptfor
Barriers to Trade (TBT) Committee.
specialcaseswhereareliablebasisfortheconversionhasbeen
obtained by comparison tests.
2. Referenced Documents
2.1 ASTM Standards:
6. Apparatus
E4Practices for Force Verification of Testing Machines
6.1 Testing Machines:
E384Test Method for Microindentation Hardness of Mate-
6.1.1 There are two general types of machines available for
rials
making this test. One type is a self-contained unit built for this
3. Terminology
purpose,andtheothertypeisanaccessoryavailabletoexisting
microscopes. Usually, this second type is fitted on an inverted-
3.1 Definitions:
stage microscope. Good descriptions of the various machines
3.1.1 Knoop hardness number (KHN)—a number obtained
3,4
are available.
by dividing the applied load in kilograms-force by the pro-
6.1.2 Designofthemachineshouldbesuchthattheloading
jected area of the indentation in square millimetres, computed
rate, dwell time, and applied load can be standardized within
from the measured long diagonal of the indentation and the
the limits set forth in 3.1.1. It is an advantage to eliminate the
included edge angles of the diamond; it is assumed that the
human element whenever possible by appropriate machine
indentation is an imprint of the undeformed indenter.
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
time the indenter touches the sample.
4.1 This test method describes an indentation hardness test
6.1.3 Thecalibrationofthebalancebeamshouldbechecked
using a calibrated machine to force a pointed, rhombic-base,
monthlyorasneeded.Indentationsinstandardglassesarealso
used to check calibration when needed.
ThistestmethodisunderthejurisdictionofASTMCommitteeC21onCeramic
Whitewares and Related Productsand is the direct responsibility of Subcommittee
6.2 Indenter:
C21.03 on Methods for Whitewares and Environmental Concerns.
Current edition approved Nov. 1, 2020. Published December 2020. Originally
approved in 1976. Last previous edition approved in 2016 as C849–88(2016).
DOI: 10.1520/C0849-88R20. SpecificationsforKnoopindenterscanbefoundinSmall,L., Hardness Theory
For referenced ASTM standards, visit the ASTM website, www.astm.org, or and Practice, Part 1, Service Diamond Tool Co., Ann Arbor, MI, 1960,
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM pp.241–243.
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 (2020)
6.2.1 The indenter shall meet the specifications for Knoop 7.1.2 Surface Finish—Aspointedoutabove,theaccuracyof
indenters. See Test Method E384. the test depends on the surface finish. However, if one is
6.2.2 Fig. 1 shows the indenter and its maximum usable
investigating a surface coating or treatment, he cannot grind
dimensions. The diagonals have an approximate ratio of 7:1, and polish the sample. Experience has shown that six inden-
and the depth of the indentation is about ⁄30 the length of the
tations on a ground and polished surface of glass will repro-
long diagonal. A perfect Knoop indenter has the following
duce within 61%. Six indentations on an “as-received”
angles:
surfacemaybeasbadas 610%.Groundandpolishedsurfaces
6.2.2.1 Included longitudinal angle 172° 30 min 00 s.
should be used. If this is not possible, the number of indenta-
6.2.2.2 Included transverse angle 130° 00 min 00 s.
tions should be increased.
6.2.3 Theconstant C foraperfectindenteris0.07028,and
p
7.1.3 Radius of Curvature—The KHN obtained will be
thespecificationsrequireavariationofnotmorethan1%from
affected even when the curvature is only in the direction of the
this value.
shortdiagonal.CareshouldbeusedwhenrelatingKHNvalues
6.3 Measuring Microscope—The measurement system shall obtained on curved surfaces to those obtained on polished flat
be so constructed that the length of the diagonals can be surfaces.
determined with errors not exceeding 60.0005 mm. The
apparent length of the diagonal is corrected in the calculations
8. Preparation of Apparatus
for the limit of resolution of the objective being used in the
8.1 Verification of Load—Most of the machines available
microscope.
for Knoop hardness testing use a loaded beam. This beam
should be tested for zero load. An indentation should not be
7. Test Specimens
visible with zero load, but the indenter should contact the
7.1 The Knoop indentation hardness test is adaptable to a
sample.Avisibleindentationshouldbeobtainedwithaloadof
wide variety of ceramic whiteware specimens. In general, the
0.1 gf. Other methods of verifying the load application are
accuracy of the test will depend on the smoothness of the
given in Practice E4.
surface and, whenever possible, ground and polished speci-
8.2 Verification by Standard Glasses—Table 1 gives the
mens should be used. The back of the specimen shall be fixed
so that the specimen cannot rock or shift during the test. Knoop hardness of several National Institute of Standards and
Technology (NIST) standard glasses. Knoop hardness mea-
7.1.1 Thickness—As long as the specimen is over ten times
as thick as the indentation depth, this will not affect the test. In surement on a piece of one of these glasses that has been
general, if specimens are at least 0.10 mm thick, the hardness ground and polished within the last 24 h should agree with the
will not be affected by variations in the thickness. value in the table 65%. Tests should be made using 100 gf.
FIG. 1 Knoop Indenter Showing Maximum Usable Dimension
C849 − 88 (2020)
A,B
TABLE 1 Knoop Hardness of NIST Standard Glasses
GE Fused GE Fused
NIST 710 NIST 711 NIST 71
...