ASTM C730-98

Standard Test Method for Knoop Indentation Hardness of Glass

SCOPE
1.1 This test method covers the determination of the Knoop indentation hardness of glass 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 and health practices and determine the applicability of regulatory limitations prior to use.

General Information

• Status: Historical
• Publication Date: 09-Oct-1998
• Technical Committee: C14 - Glass and Glass Products
• Drafting Committee: C14.04 - Physical and Mechanical Properties

Relations

• Replaced By: ASTM C730-98(2003) - Standard Test Method for Knoop Indentation Hardness of Glass
• Effective Date: 10-Oct-1998
• Referred By: ASTM F1538-03(2017) - Standard Specification for Glass and Glass Ceramic Biomaterials for Implantation
• Effective Date: 10-Oct-1998
• Referred By: ASTM D116-86(2020) - Standard Test Methods for Vitrified Ceramic Materials for Electrical Applications
• Effective Date: 10-Oct-1998
• Referred By: ASTM C1326-13(2023) - Standard Test Method for Knoop Indentation Hardness of Advanced Ceramics
• Effective Date: 10-Oct-1998
• Referred By: ASTM F561-19 - Standard Practice for Retrieval and Analysis of Medical Devices, and Associated Tissues and Fluids
• Effective Date: 10-Oct-1998

Standards Content (Sample)

NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
Designation: C 730 – 98
Standard Test Method for
Knoop Indentation Hardness of Glass
This standard is issued under the fixed designation C 730; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope 3.1.1.4 The indenter should remain in contact with the
specimen between 20 and 30 s. Most of the calibrated
1.1 This test method covers the determination of the Knoop
machines that are used for making Knoop hardness tests are
indentation hardness of glass and the verification of Knoop
dash-pot controlled and this dwell time is consistent with the
indentation hardness testing machines using standard glasses.
adjustment of the dash-pot to meet the loading rate standard.
1.2 This standard does not purport to address all of the
3.1.1.5 Table 1 gives the Knoop hardness of several glasses
safety concerns, if any, associated with its use. It is the
as a function of load when the loading rate and dwell time are
responsibility of the user of this standard to establish appro-
held at the values recommended above.
priate safety and health practices and determine the applica-
3.1.2 Knoop indentation hardness test—an indentation
bility of regulatory limitations prior to use.
hardness test using a calibrated machine to force a pointed,
2. Referenced Documents
rhombic-base, pyramidal diamond indenter having specified
face angles, under a predetermined load, into the surface of the
2.1 ASTM Standards:
material under test and to measure the long diagonal of the
E 4 Practices for Force Verification of Testing Machines
resulting impression after removal of the load.
E 384 Test Method for Microhardness of Materials
NOTE 1—A general description of the Knoop indentation hardness test
3. Terminology
is given in Test Method E 384. The present method differs from this
3.1 Descriptions of Terms Specific to This Standard: description only in areas required by the special nature of glasses.
3.1.1 Knoop hardness number (KHN)—a number obtained
4. Significance and Use
by dividing the applied load in kilograms-force by the pro-
4.1 The Knoop indentation hardness is one of many prop-
jected area of the indentation in square millimetres, computed
erties that is used to characterize glasses. Attempts have been
from the measured long diagonal of the indentation and the
made to relate Knoop indentation hardness to tensile strength,
included edge angles of the diamond. It is assumed that the
grinding speeds, and other hardness scales, but no generally
indentation is an imprint of the undeformed indenter.
accepted methods are available. Such conversions are limited
3.1.1.1 The Knoop hardness number (KHN) is computed as
in scope and should be used with caution, except for special
follows:
cases where a reliable basis for the conversion has been
KHN 5 ~P/A !5~P/d C ! (1)
p p
obtained by comparison tests.
5. Apparatus
P 5 load, kgf,
5.1 Testing Machines:
A 5 projected area of the indentation, mm ,
p
d 5 length of the long diagonal of the indentation, mm, 5.1.1 There are two general types of machines available for
C 5 ⁄2 (cot A/2 3 tan B/2), making this test. One type is a self-contained unit built for this
p
A 5 included longitudinal edge angle (see Fig. 1), and
purpose, and the other type is an accessory available to existing
B 5 included transverse edge angle (see Fig. 1).
microscopes. Usually, this second type is fitted on an inverted-
3.1.1.2 Knoop indentation hardness tests in glass are made
stage microscope. Good descriptions of the various machines
,
3 4
at a test load of 100 gf (0.1 kgf).
are available.
3.1.1.3 The rate of indenter motion prior to contact with the
5.1.2 Design of the machine should be such that the loading
specimen shall be 0.20 6 0.05 mm/min. This low rate of load
rate, dwell time, and applied load can be standardized within
application tends to alleviate the effect of the magnitude of the
the limits set forth in 3.1.1.2-3.1.1.4. It is an advantage to
load on Knoop hardness number.
eliminate the human element whenever possible by appropriate
This test method is under the jurisdiction of ASTM Committee C-14 on Glass
and Glass Products and is the direct responsibility of Subcommittee C14.04 on Specifications for Knoop indenters can be found in the book Small, L.,
Physical and Mechanical Properties. Hardness Theory and Practice (Part I: Practice), Service Diamond Tool Co., Ann
Current edition approved Oct. 10, 1998. Published January 1999. Originally Arbor, MI, 1960, pp. 241–243.
e1 4
published as C 730 – 72 T. Last previous edition C 730 – 85 (1995) . Mott, B. W., Micro-Indentation Hardness Testing, Butterworth’s Scientific
Annual Book of ASTM Standards, Vol 03.01. Publications, London, 1956.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
C 730
FIG. 1 Knoop Indenter Showing Maximum Usable Dimension
A,B
TABLE 1 Knoop Hardness of NIST Standard and Other Glasses
GE
Laboratory NIST 710 NIST 711 NIST 715 Fused NIST 710 NIST 711 NIST 715 GE Fused Quartz
Quartz
25-gf Load 50-gf Load
A 486 411 589 614 497 394 575 559
C 594 450 537 415
D 479 426 505 541 478 380 538 501
E 521 415 608 620 497 392 574 586
F 498 414 568 643 484 403 567 577
G
Avg 516 423 567.5 609.5 499 397 563.5 556
Departure, max, 15 6 11 11 8 5 5 10
%
Range, max, % 22 9 18 17 12 9 7 15
100-gf Load 200-gf Load
A 475 387 558 554 468 380 550 523
C 478 387 554 593 468 371 544 530
D 452 368 521 473 433 360 529 474
E 490 396 544 530 488 372 546 510
F 467 381 538 524 457 367 524 502
G 481 388 550 558
Avg 474 384.5 544 539 463 370 539 508
Departure, max, 544 12 6337
%
Range, max, % 8 7 7 22 12 5 5 11
A
NIST 710—NIST standard soda-lime-silica glass (no longer available; NIST 710a may be substituted), NIST 711—NIST standard lead-silica glass. NIST 715—NIST
standard alkali-free aluminosilicate glass.
B
These data were obtained from ASTM round-robin testing.
machine design. The machine should be designed so that indenters. See Test Method E 384.
vibrations induced at the beginning of a test will be damped out 5.2.2 Fig. 1 shows the indenter and its maximum usable
by the time the indenter touches the sample. dimensions. The diagonals have an approximate ratio of 7:1,
5.1.3 The calibration of the balance beam should be checked and the depth of the indentation is about ⁄30 the length of the
monthly or as needed. Indentations in standard glasses are also long diagonal. A perfect Knoop indenter has the following
used to check calibration when needed. angles:
5.2 Indenter: 5.2.2.1 Included longitudinal angle 172° 308 009.
5.2.1 The indenter shall meet the specifications for Knoop 5.2.2.2 Included transverse angle 130° 008 009.
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
C 730
5.2.3 The constant C for a perfect indenter is 0.07028 and
p
the specifications require a variation of not more than 1 percent
from this value.
5.3 Measuring Microscope—The measurement system shall
be so constructed that the length of the diagonals can be
determined with errors not exceeding 60.0005 mm. The
apparent length of the diagonal should be corrected for the
limit of resolution of the objective being used in the micro-
scope (see Appendix X1).
6. Test Specimen
6.1 The Knoop indentation hardness test is adaptable to a
wide variety of glass specimens, ranging from tubing to
television faceplates to polished plate glass. In general, the
accuracy of the test will depend on the smoothness of the
surface and, whenever possible, ground and polished speci-
mens should be used. The back of the specimen shall be fixed
so that the specimen cannot rock or shift during the test.
6.1.1 Thickness—As long as the specimen is over ten times
as thick as the indentation depth, this will not affect the test. In
general, if specimens are at least 0.10 mm thick, the hardness
will not be affected by variations in the thickness.
6.1.2 Surface Finish—As pointed out above, the accuracy
of the test depends on the surface finish. However, if one is
investigating a s
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