ASTM D7625-22
(Test Method)Standard Test Method for Laboratory Determination of Abrasiveness of Rock Using the CERCHAR Abrasiveness Index Method
Standard Test Method for Laboratory Determination of Abrasiveness of Rock Using the CERCHAR Abrasiveness Index Method
SIGNIFICANCE AND USE
5.1 The CERCHAR test and associated CAI were developed at a time of more demand for application of mechanical excavation machines at the Laboratoire du Center d' Études et Recherches des Charbonnages de France (CERCHAR) (5). CAI is used to assess the abrasiveness of rock for mechanical excavation. Rock abrasiveness governs the performance of disc cutters, the rate of its replacement and therefore subsequent tunnel costs. Advances in methods of underground excavation, in particular the use of the tunnel boring machine (TBM), necessitates knowledge of rock abrasiveness. Abrasiveness expresses a behavioral characteristic of rock rather than a fundamental physical or mechanical property.
5.2 CAI tests were originally carried out on natural broken surfaces. In heterogeneous rock types such as conglomerates, coarse grained granite or schistose rock, suitable fresh test surfaces are not achieved by mechanical breakage using a hammer. In these cases CAI values for “smooth” surfaces cut with a diamond saw are acceptable for use but shall be normalized by Eq 2 or Eq 3 before they can be reported (4).
5.3 The test velocity for the Original CERCHAR apparatus is approximately 10 mm/s and 1 mm/s for the West CERCHAR apparatus. The CAI values obtained for both testing velocities (4) are estimated to be equal.
Note 1: The quality of the result produced by these practices is dependent upon the competence of the personnel performing it and the suitability of the equipment and facilities used. Agencies that meet the criteria of Practice D3740 are generally considered capable of competent and objective testing and sampling. Users of these practices are cautioned that compliance with Practice D3740 does not in itself assure reliable results. Reliable results depend on many factors; Practice D3740 provides a means of evaluating some of those factors.
SCOPE
1.1 This test method covers the determination of the abrasiveness of rock by the CERCHAR Abrasiveness Index (CAI) method. The test method consists of measuring the wear on the tip of steel stylus with a cone shape and known Rockwell Hardness, caused by scratching against a freshly broken or saw cut rock surface for a prescribed 10 mm distance using one of the two test apparatus.
1.2 This test method is intended for freshly broken rock surfaces; however, saw cut surfaces are covered for when a satisfactory rock surface cannot be obtained.
1.3 The Rockwell Hardness (HR) of the stylus can have a profound effect on the results. The focus of this test method is an HRC value of 55 for every test (1, 2).2 However, there are situations where styli with different Rockwell Hardness can be used. Therefore, this test method includes discussions on stylus with different Rockwell Hardness.
1.3.1 The Rockwell hardness (HR) value is based on the indentation hardness of a material. The Rockwell test, E18, measures the depth of penetration of an indenter under a large load (major load) compared to the penetration made by a preload (minor load). (3) There are different scales, denoted by a single letter (A to F), that use different loads or indenters. The result is a dimensionless number noted as HRA, HRB, HRC, etc., where the last letter is the respective Rockwell scale which in this test method is the scale C, which is for harden‐steel.
1.4 Basically, the CERCHAR test is a measurement of the relative different hardness of stylus tip and rock specimen surface. The stylus tip is made of steel having a known Rockwell Hardness. Experiments have shown that CAI varies inversely with stylus hardness. Test results with the same steel type stylus but with different hardness need to be normalized to standard stylus hardness (2).
1.5 The scratch distance shall be limited to 10 mm. In general, 85 % of the stylus wear occurs during the first 2 mm of scratch’s length. The remaining 15 % of the stylus wear occurs during the last 8 mm of the scratch’s length. Therefore,...
General Information
- Status
- Published
- Publication Date
- 30-Sep-2022
- Technical Committee
- D18 - Soil and Rock
- Drafting Committee
- D18.12 - Rock Mechanics
Relations
- Effective Date
- 01-Nov-2023
- Effective Date
- 01-Oct-2019
- Effective Date
- 01-Mar-2019
- Effective Date
- 01-Jul-2018
- Effective Date
- 01-Jul-2017
- Effective Date
- 01-Aug-2014
- Effective Date
- 01-Dec-2012
- Effective Date
- 01-May-2012
- Effective Date
- 01-Mar-2012
- Effective Date
- 01-Nov-2011
- Effective Date
- 01-Sep-2011
- Effective Date
- 01-Sep-2011
- Effective Date
- 01-Jul-2010
- Effective Date
- 01-Mar-2010
- Effective Date
- 01-Jan-2009
Overview
ASTM D7625-22: Standard Test Method for Laboratory Determination of Abrasiveness of Rock Using the CERCHAR Abrasiveness Index Method provides a standardized laboratory procedure for assessing the abrasiveness of rock samples. The core focus is on determining the CERCHAR Abrasiveness Index (CAI), a key metric for predicting the wear behavior of rock on excavation equipment. Developed in response to the growing use of mechanical excavation methods, including tunnel boring machines (TBMs), this test method helps optimize machine component selection, plan maintenance, and control tunneling costs. Knowledge of rock abrasiveness is critical in gauging the performance and lifespan of disc cutters, as well as the economic feasibility of underground projects.
Key Topics
- CERCHAR Abrasiveness Index (CAI): The test measures the wear on a standard steel stylus with known Rockwell Hardness as it scratches a 10 mm distance across the surface of a rock specimen.
- Sample Preparation: Testing is preferably conducted on freshly broken rock surfaces; however, saw-cut surfaces may be used when natural fracture surfaces cannot be obtained. Results from saw-cut surfaces must be normalized.
- Stylus Hardness: The Rockwell Hardness of the stylus (commonly HRC 55) significantly influences the CAI. The test method provides considerations for using styluses of different hardness and procedures for normalizing results.
- Test Procedure: Involves securing the specimen, performing a controlled scratch, and measuring the resulting stylus tip wear under a microscope. Five individual tests per specimen are recommended for accuracy.
- Reporting and Classification: Test results are classified into categories ranging from very low to extreme abrasiveness, providing actionable guidance for equipment selection and project planning.
Applications
- Tunnel and Mining Engineering: The CERCHAR test is widely used in tunnel boring machine (TBM) projects, mining operations, and other applications where rock excavation is critical. The CAI is instrumental in selecting cutter materials, estimating tool wear rates, and scheduling maintenance.
- Rock Mechanics and Geotechnical Studies: Laboratories and engineering firms utilize this method to characterize the abrasive nature of various rock types, including conglomerates, granites, and schistose rocks, which are complex to assess with traditional methods.
- Project Feasibility and Cost Control: Accurate abrasiveness testing with ASTM D7625-22 helps forecast machine downtime, cutting tool replacement rates, and overall project costs, reducing unforeseen expenses and delays.
- Site Investigation and Design Optimization: Integrating CAI results into geotechnical baseline reports enables engineers to design more efficient and cost-effective excavation strategies tailored to site-specific rock properties.
Related Standards
- ASTM D653 - Terminology Relating to Soil, Rock, and Contained Fluids: Provides the necessary vocabulary for interpreting geotechnical and rock mechanics test methods.
- ASTM D2216 - Test Methods for Laboratory Determination of Water (Moisture) Content of Soil and Rock by Mass: Relevant for preparing specimens in conditions representative of field moisture.
- ASTM D3740 - Practice for Minimum Requirements for Agencies Engaged in Testing and/or Inspection of Soil and Rock: Ensures quality and competence in laboratory testing.
- ASTM E18 - Test Methods for Rockwell Hardness of Metallic Materials: Specifies procedures for determining the Rockwell Hardness of steel styluses used in the CERCHAR test.
- ASTM D6026 - Practice for Using Significant Digits and Data Records in Geotechnical Data: Offers practices for proper data recording and reporting.
Keywords: ASTM D7625, CERCHAR Abrasiveness Index method, rock abrasiveness test, CAI, TBM cutter wear, mechanical excavation, Rockwell Hardness, tunnel boring, geotechnical laboratory test, equipment wear prediction.
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Frequently Asked Questions
ASTM D7625-22 is a standard published by ASTM International. Its full title is "Standard Test Method for Laboratory Determination of Abrasiveness of Rock Using the CERCHAR Abrasiveness Index Method". This standard covers: SIGNIFICANCE AND USE 5.1 The CERCHAR test and associated CAI were developed at a time of more demand for application of mechanical excavation machines at the Laboratoire du Center d' Études et Recherches des Charbonnages de France (CERCHAR) (5). CAI is used to assess the abrasiveness of rock for mechanical excavation. Rock abrasiveness governs the performance of disc cutters, the rate of its replacement and therefore subsequent tunnel costs. Advances in methods of underground excavation, in particular the use of the tunnel boring machine (TBM), necessitates knowledge of rock abrasiveness. Abrasiveness expresses a behavioral characteristic of rock rather than a fundamental physical or mechanical property. 5.2 CAI tests were originally carried out on natural broken surfaces. In heterogeneous rock types such as conglomerates, coarse grained granite or schistose rock, suitable fresh test surfaces are not achieved by mechanical breakage using a hammer. In these cases CAI values for “smooth” surfaces cut with a diamond saw are acceptable for use but shall be normalized by Eq 2 or Eq 3 before they can be reported (4). 5.3 The test velocity for the Original CERCHAR apparatus is approximately 10 mm/s and 1 mm/s for the West CERCHAR apparatus. The CAI values obtained for both testing velocities (4) are estimated to be equal. Note 1: The quality of the result produced by these practices is dependent upon the competence of the personnel performing it and the suitability of the equipment and facilities used. Agencies that meet the criteria of Practice D3740 are generally considered capable of competent and objective testing and sampling. Users of these practices are cautioned that compliance with Practice D3740 does not in itself assure reliable results. Reliable results depend on many factors; Practice D3740 provides a means of evaluating some of those factors. SCOPE 1.1 This test method covers the determination of the abrasiveness of rock by the CERCHAR Abrasiveness Index (CAI) method. The test method consists of measuring the wear on the tip of steel stylus with a cone shape and known Rockwell Hardness, caused by scratching against a freshly broken or saw cut rock surface for a prescribed 10 mm distance using one of the two test apparatus. 1.2 This test method is intended for freshly broken rock surfaces; however, saw cut surfaces are covered for when a satisfactory rock surface cannot be obtained. 1.3 The Rockwell Hardness (HR) of the stylus can have a profound effect on the results. The focus of this test method is an HRC value of 55 for every test (1, 2).2 However, there are situations where styli with different Rockwell Hardness can be used. Therefore, this test method includes discussions on stylus with different Rockwell Hardness. 1.3.1 The Rockwell hardness (HR) value is based on the indentation hardness of a material. The Rockwell test, E18, measures the depth of penetration of an indenter under a large load (major load) compared to the penetration made by a preload (minor load). (3) There are different scales, denoted by a single letter (A to F), that use different loads or indenters. The result is a dimensionless number noted as HRA, HRB, HRC, etc., where the last letter is the respective Rockwell scale which in this test method is the scale C, which is for harden‐steel. 1.4 Basically, the CERCHAR test is a measurement of the relative different hardness of stylus tip and rock specimen surface. The stylus tip is made of steel having a known Rockwell Hardness. Experiments have shown that CAI varies inversely with stylus hardness. Test results with the same steel type stylus but with different hardness need to be normalized to standard stylus hardness (2). 1.5 The scratch distance shall be limited to 10 mm. In general, 85 % of the stylus wear occurs during the first 2 mm of scratch’s length. The remaining 15 % of the stylus wear occurs during the last 8 mm of the scratch’s length. Therefore,...
SIGNIFICANCE AND USE 5.1 The CERCHAR test and associated CAI were developed at a time of more demand for application of mechanical excavation machines at the Laboratoire du Center d' Études et Recherches des Charbonnages de France (CERCHAR) (5). CAI is used to assess the abrasiveness of rock for mechanical excavation. Rock abrasiveness governs the performance of disc cutters, the rate of its replacement and therefore subsequent tunnel costs. Advances in methods of underground excavation, in particular the use of the tunnel boring machine (TBM), necessitates knowledge of rock abrasiveness. Abrasiveness expresses a behavioral characteristic of rock rather than a fundamental physical or mechanical property. 5.2 CAI tests were originally carried out on natural broken surfaces. In heterogeneous rock types such as conglomerates, coarse grained granite or schistose rock, suitable fresh test surfaces are not achieved by mechanical breakage using a hammer. In these cases CAI values for “smooth” surfaces cut with a diamond saw are acceptable for use but shall be normalized by Eq 2 or Eq 3 before they can be reported (4). 5.3 The test velocity for the Original CERCHAR apparatus is approximately 10 mm/s and 1 mm/s for the West CERCHAR apparatus. The CAI values obtained for both testing velocities (4) are estimated to be equal. Note 1: The quality of the result produced by these practices is dependent upon the competence of the personnel performing it and the suitability of the equipment and facilities used. Agencies that meet the criteria of Practice D3740 are generally considered capable of competent and objective testing and sampling. Users of these practices are cautioned that compliance with Practice D3740 does not in itself assure reliable results. Reliable results depend on many factors; Practice D3740 provides a means of evaluating some of those factors. SCOPE 1.1 This test method covers the determination of the abrasiveness of rock by the CERCHAR Abrasiveness Index (CAI) method. The test method consists of measuring the wear on the tip of steel stylus with a cone shape and known Rockwell Hardness, caused by scratching against a freshly broken or saw cut rock surface for a prescribed 10 mm distance using one of the two test apparatus. 1.2 This test method is intended for freshly broken rock surfaces; however, saw cut surfaces are covered for when a satisfactory rock surface cannot be obtained. 1.3 The Rockwell Hardness (HR) of the stylus can have a profound effect on the results. The focus of this test method is an HRC value of 55 for every test (1, 2).2 However, there are situations where styli with different Rockwell Hardness can be used. Therefore, this test method includes discussions on stylus with different Rockwell Hardness. 1.3.1 The Rockwell hardness (HR) value is based on the indentation hardness of a material. The Rockwell test, E18, measures the depth of penetration of an indenter under a large load (major load) compared to the penetration made by a preload (minor load). (3) There are different scales, denoted by a single letter (A to F), that use different loads or indenters. The result is a dimensionless number noted as HRA, HRB, HRC, etc., where the last letter is the respective Rockwell scale which in this test method is the scale C, which is for harden‐steel. 1.4 Basically, the CERCHAR test is a measurement of the relative different hardness of stylus tip and rock specimen surface. The stylus tip is made of steel having a known Rockwell Hardness. Experiments have shown that CAI varies inversely with stylus hardness. Test results with the same steel type stylus but with different hardness need to be normalized to standard stylus hardness (2). 1.5 The scratch distance shall be limited to 10 mm. In general, 85 % of the stylus wear occurs during the first 2 mm of scratch’s length. The remaining 15 % of the stylus wear occurs during the last 8 mm of the scratch’s length. Therefore,...
ASTM D7625-22 is classified under the following ICS (International Classification for Standards) categories: 91.100.15 - Mineral materials and products. The ICS classification helps identify the subject area and facilitates finding related standards.
ASTM D7625-22 has the following relationships with other standards: It is inter standard links to ASTM D3740-23, ASTM D3740-19, ASTM D2216-19, ASTM E18-18, ASTM E18-17, ASTM D653-14, ASTM E18-12, ASTM D3740-12a, ASTM D3740-12, ASTM E18-11, ASTM D3740-11, ASTM D653-11, ASTM D2216-10, ASTM D3740-10, ASTM D653-09. Understanding these relationships helps ensure you are using the most current and applicable version of the standard.
ASTM D7625-22 is available in PDF format for immediate download after purchase. The document can be added to your cart and obtained through the secure checkout process. Digital delivery ensures instant access to the complete standard document.
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: D7625 − 22
Standard Test Method for
Laboratory Determination of Abrasiveness of Rock Using
the CERCHAR Abrasiveness Index Method
This standard is issued under the fixed designation D7625; 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* typestylusbutwithdifferenthardnessneedtobenormalizedto
standard stylus hardness (2).
1.1 This test method covers the determination of the abra-
siveness of rock by the CERCHARAbrasiveness Index (CAI) 1.5 The scratch distance shall be limited to 10 mm. In
method.Thetestmethodconsistsofmeasuringthewearonthe
general, 85% of the stylus wear occurs during the first 2 mm
tip of steel stylus with a cone shape and known Rockwell of scratch’s length. The remaining 15% of the stylus wear
Hardness,causedbyscratchingagainstafreshlybrokenorsaw
occurs during the last 8 mm of the scratch’s length. Therefore,
cut rock surface for a prescribed 10 mm distance using one of minor variation in the scratch’s length from test to test doesn’t
the two test apparatus. significantly affect the total stylus wear and the resulting CAI
when variation in scratch length is kept between 60.5mm in
1.2 This test method is intended for freshly broken rock
length (3).
surfaces; however, saw cut surfaces are covered for when a
satisfactory rock surface cannot be obtained. 1.6 All observed and calculated values shall conform to the
guidelines for significant digits and rounding established in
1.3 The Rockwell Hardness (HR) of the stylus can have a
Practice D6026.
profound effect on the results. The focus of this test method is
1.6.1 Theproceduresusedtospecifyhowdataarecollected/
an HRC value of 55 for every test (1, 2). However, there are
recorded or calculated, in this standard are regarded as the
situations where styli with different Rockwell Hardness can be
industry standard. In addition, they are representative of the
used.Therefore,thistestmethodincludesdiscussionsonstylus
significant digits that generally should be retained. The proce-
with different Rockwell Hardness.
dures used do not consider material variation, purpose for
1.3.1 The Rockwell hardness (HR) value is based on the
obtaining the data, special purpose studies, or any consider-
indentation hardness of a material. The Rockwell test, E18,
ations for the user’s objectives; and it is common practice to
measures the depth of penetration of an indenter under a large
increase or reduce significant digits of reported data to be
load (major load) compared to the penetration made by a
commensuratewiththeseconsiderations.Itisbeyondthescope
preload(minorload). (3)Therearedifferentscales,denotedby
of this standard to consider significant digits used in analysis
asingleletter(AtoF),thatusedifferentloadsorindenters.The
methods for engineering design.
result is a dimensionless number noted as HRA, HRB, HRC,
etc.,wherethelastletteristherespectiveRockwellscalewhich
1.7 Units—The values stated in SI units are to be regarded
in this test method is the scale C, which is for harden{steel.
asstandard.Nootherunitsofmeasurementareincludedinthis
standard.
1.4 Basically, the CERCHAR test is a measurement of the
relative different hardness of stylus tip and rock specimen 1.8 This standard does not purport to address all of the
surface. The stylus tip is made of steel having a known safety concerns, if any, associated with its use. It is the
Rockwell Hardness. Experiments have shown that CAI varies responsibility of the user of this standard to establish appro-
inversely with stylus hardness. Test results with the same steel priate safety, health, and environmental practices and deter-
mine the applicability of regulatory limitations prior to use.
1 1.9 This international standard was developed in accor-
ThistestmethodisunderthejurisdictionofASTMCommitteeD18onSoiland
dance with internationally recognized principles on standard-
Rock and is the direct responsibility of Subcommittee D18.12 on Rock Mechanics.
Current edition approved Oct. 1, 2022. Published October 2022. Originally
ization established in the Decision on Principles for the
approved in 2010. Last previous edition approved in 2010 as D7625–10, which
Development of International Standards, Guides and Recom-
waswithdrawnJune2019andreinstatedinOctober2022.DOI:10.1520/D7625-22.
mendations issued by the World Trade Organization Technical
The bold numbers in parenthesis refer to a list of references at the end of this
standard. Barriers to Trade (TBT) Committee.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7625 − 22
2. Referenced Documents necessitates knowledge of rock abrasiveness. Abrasiveness
3 expresses a behavioral characteristic of rock rather than a
2.1 ASTM Standards:
fundamental physical or mechanical property.
D653Terminology Relating to Soil, Rock, and Contained
Fluids 5.2 CAI tests were originally carried out on natural broken
D2216Test Methods for Laboratory Determination ofWater surfaces. In heterogeneous rock types such as conglomerates,
(Moisture) Content of Soil and Rock by Mass coarse grained granite or schistose rock, suitable fresh test
D3740Practice for Minimum Requirements for Agencies surfaces are not achieved by mechanical breakage using a
Engaged in Testing and/or Inspection of Soil and Rock as hammer. In these cases CAI values for “smooth” surfaces cut
Used in Engineering Design and Construction with a diamond saw are acceptable for use but shall be
D5079Practices for Preserving andTransporting Rock Core normalized by Eq 2 or Eq 3 before they can be reported (4).
Samples (Withdrawn 2017)
5.3 The test velocity for the Original CERCHAR apparatus
D6026Practice for Using Significant Digits and Data Re-
isapproximately10mm/sand1mm/sfortheWestCERCHAR
cords in Geotechnical Data
apparatus. The CAI values obtained for both testing velocities
E18Test Methods for Rockwell Hardness of Metallic Ma-
(4) are estimated to be equal.
terials
NOTE 1—The quality of the result produced by these practices is
dependent upon the competence of the personnel performing it and the
3. Terminology
suitability of the equipment and facilities used. Agencies that meet the
3.1 Definitions:
criteria of Practice D3740 are generally considered capable of competent
3.1.1 For definitions of common technical terms used in
and objective testing and sampling. Users of these practices are cautioned
that compliance with Practice D3740 does not in itself assure reliable
this test method, refer to Terminology D653.
results. Reliable results depend on many factors; Practice D3740 provides
3.2 Definitions of Terms Specific to This Standard:
a means of evaluating some of those factors.
3.2.1 abrasiveness, n—in rock, the wear or loss of material,
6. Apparatus
which the rock produces on contact with another material such
as TBM cutter or drill bit.
6.1 Apparatus—Two types of CERCHAR apparatus (4) are
in use today (See Fig. 1). Both devices employ a vice to clamp
4. Summary of Test Method
the specimen and a constant force of 70 N acting axially on a
4.1 Asteelstylushavinga90degreeconicaltipwithitsaxis stylus tip when place against the test surface. The original
perpendicular, and in contact with a rock surface, under a total apparatus employs a manually operated hand lever to displace
constantforceof70N,isscratchedinadirectionparalleltothe the stylus tip on the stationary rock surface held fixed in place
rock surface over a distance of 10 mm. by a vice. The West apparatus displaces the vice holding the
rock by use of a hand crank and driving screw under a
4.2 After the test, width of the wear flatness is measured on
stationary stylus.
stylus tip surface in units of 0.1 mm and number of units
reported as the CERCHAR Abrasiveness Index, 0.1mm (= 6.2 Stylus—AsmentionedintheScope,CERCHARtestisa
1CAI). measurement of the relative different hardness between the
stylus tip and rock specimen surface. The stylus tip shall be
4.3 Five individual CAI tests shall be conducted for each
made of steel having a known Rockwell Hardness. The
rock specimen to achieve a defined average value (4). If there
diameter of stylus should be minimum 6mm and its length
is not an apparent preference, for example, different colors,
shall be minimum 15mm between the tip and surface of rock.
beddings, foliations, schistosity, large inclusions, weakness
6.2.1 Experiments have shown that CAI varies inversely
planes; on specimen, then a set of three parallel tests in one
with steel hardness.Test results with the same steel type stylus
direction,andtwomoreperpendiculartofirstsetshallbedone.
but with different hardness shall be normalized to standard
stylus hardness (2). The use of stylus hardened to 55 HRC
5. Significance and Use
(3,1), and conforming to Test Methods E18 is advised.
5.1 The CERCHAR test and associated CAI were devel-
6.3 Mass—The static mass for either test apparatus shall be
oped at a time of more demand for application of mechanical
appropriately sized and configured so that the total force of 70
excavation machines at the Laboratoire du Center d’ Études et
Recherches des Charbonnages de France (CERCHAR) (5). N, including other components that would contribute addi-
tional force to the stylus tip during testing. This force shall act
CAI is used to assess the abrasiveness of rock for mechanical
excavation.Rockabrasivenessgovernstheperformanceofdisc axially on the stylus tip in contact with the specimen surface
during the test.
cutters, the rate of its replacement and therefore subsequent
tunnel costs.Advances in methods of underground excavation,
6.4 Vice—TheviceinFig.1(a)shallbeofsufficientrigidity,
in particular the use of the tunnel boring machine (TBM),
suchthattheclampedspecimenisimmobilizedduringthetest.
The vice in Fig. 1(b) holds the specimen and moves under the
stylusbyusingthehandcrankthatadvancesthedrivingscrew.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Small wooden wedges may be used to make sure tightness of
Standards volume information, refer to the standard’s Document Summary page on
fit. Also, the vice shall have precise control of movement in
the ASTM website.
two horizontal planes, with accurate positioning and change of
The last approved version of this historical standard is referenced on
www.astm.org. position of the specimen with a secure hold.
D7625 − 22
FIG. 1 Illustrations of Two Types of CERCHAR Testing Apparatuses
6.5 Resting Support—a mechanism or configuration to hold
the mass and stylus in a stationary position above the test
surface location while setting up and removing the test
specimen. The original CERCHAR apparatus uses a resting
support to place the lever arm on and the West CERCHAR
apparatus has a set of lock screws to grip onto the static mass.
6.6 Hand Lever—The hand lever arm shall be articulated
andhavesufficientstiffnesstodisplacethestylusovertherock
surface allowing unrestrained vertical displacement of the
stylus under the total force of 70 N (Fig. 1(a)).
6.7 Hand Crank—The hand crank screw-feed attached to
the vice and powered manually with a crank displaces the vice
holdingaspecimenunderthestationarystylus.Thescrew-feed
thread shall be machined such that displacement of the rock
surface occurs at a constant displacement per revolution under
the stationary stylus while allowing unrestrained vertical dis-
placementofthestylusunderthetotalforceof70N(Fig.1(b)).
6.8 Microscope—A toolmaker’s microscope equipped with
digital micrometer heads, XY stage and LCD (Liquid Crystal
FIG. 2 Toolmaker’s Microscope
Display)readoutarerecommended.Themicroscopeshallhave
a minimum magnification of 30×. The XY stage micrometer
headsshallhaveaminimumrangeof50mmgraduatedto0.01 6.10 Rock Saw—A cutting device equipped with a seg-
mm and readable to 0.001 mm (5). Fig. 2 shows one example mented circular diamond saw blade, with a moveable platform
of this microscope with a stylus tip positioned under it, during for holding and feeding the sample, perpendicular to the rock
flatness measurements.As an alternative, a digital microscope core or block, into the cutting surface of the blade. The
having the same capabilities as the toolmaker’s microscope moveable platform may be a manual or automatic feed. The
(Fig. 3) could be used for stylus flatness measurements. apparatus is also equipped to apply appropriate cooling and
cutting agents (if needed) at the cutting surface to cool the
6.9 Grinder—An apparatus that uses an abrasive stone
blade and wash away cuttings.
wheel that is rotated and when place in contact with softer
6.11 Miscellaneous—Machinist’s blue dye, wood shims,
material removes material from that surface without appre-
ciable wear to the stone wheel, or other suitable metal work timer, digital or film camera.
apparatus, capable of shaping metal pen stock or sharpening
7. Sampling and Test Specimens
theendofthestylusaccordingtodesiredgeometry.Coolingof
the surface being ground by some type of fluid is advised in 7.1 The samples shall be selected by visual observation to
order not to heat up the metal excessively and change the include a range of specimens based on rock type, mineral
original Rockwell hardness of the metal being used for the constituents, grain sizes and shape, partings, and defects such
stylus. as pores and fissures.
D7625 − 22
such as water-/air-cooled diamond saw blade to expose fresh
specimen surfaces provided the resulting surfaces are reason-
ably planar.
7.6 The specimen’s test surface shall have sufficient length
that edge chipping within the 10 mm test path does not occur
as the stylus approaches the specimen outer dimension.
7.7 Specimens with either natural or saw cut test surfaces
shall be trimmed to fit in the CERCHAR test machine by
cutting the rock sample with a cooling agent such as water-/
air-cooled diamond saw blade.
7.8 Before and after photographs shall be taken of tested
surfaces.
8. Preparation of Apparatus
8.1 The stylus shall be in good condition and verified under
a microscope before use. The tip shall exhibit
...
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