1、Designation: D7625 10Standard Test Method forLaboratory Determination of Abrasiveness of Rock Usingthe CERCHAR Method1This standard is issued under the fixed designation D7625; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the ye
2、ar of last revision. 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 abra-siveness of rock by the CERCHAR Abrasiveness Index (CAI)me
3、thod. The test method consists of measuring the wear on thetip of steel stylus with a cone shape and known RockwellHardness, caused by scratching against a freshly broken or sawcut rock surface for a prescribed 10 mm distance using one ofthe two test apparatus.1.2 This test method is intended for fr
4、eshly broken rocksurfaces; however, saw cut surfaces are covered for when asatisfactory rock surface cannot be obtained.1.3 Stylus Rockwell Hardness (HRC) can have a profoundeffect on the results and the focus of this test method is an HRCvalue of 55 for every test (1,2).2However, there are situatio
5、nswhere stylus with different Rockwell Hardness can be usedTherefore, this test method includes discussions on stylus withdifferent Rockwell Hardness.1.4 All observed and calculated values shall conform to theguidelines for significant digits and rounding established inPractice D6026.1.5 The values
6、stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.6 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
7、 and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:3D653 Terminology Relating to Soil, Rock, and ContainedFluidsD2216 Test Methods for Laboratory Determination of Wa-ter (Moisture) Content of Soil and Rock by MassD3
8、740 Practice for Minimum Requirements for AgenciesEngaged in Testing and/or Inspection of Soil and Rock asUsed in Engineering Design and ConstructionD5079 Practices for Preserving and Transporting RockCore SamplesD6026 Practice for Using Significant Digits in GeotechnicalDataE18 Test Methods for Roc
9、kwell Hardness of Metallic Ma-terials3. Terminology3.1 Definitions:For definitions of terms used in this test method, refer toTerminology D653.3.2 Definitions of Terms Specific to This Standard:3.2.1 abrasiveness, nthe wear or loss of material whichthe rock produces on contact with another material
10、such asTBM cutter or drill bit.3.2.2 Rockwell Hardness Scale (HRC), na hardness scalebased on the indentation hardness of a material, which corre-lates linearly with its tensile strength. The Rockwell testdetermines the hardness by measuring the depth of penetrationof an indenter under a large load
11、compared to the penetrationmade by a preload. The results, as a dimensionless number, arenoted by HR followed by the designation letter fromA-F basedupon used scale. For current standard, letter C is used as thescale letter for hard steel.4. Summary of Test Method4.1 A steel stylus having a 90E coni
12、cal tip with its axisperpendicular, and in contact with a rock surface, under a totalconstant force of 70 N, is scratched in a direction parallel to therock surface over a distance of 10 mm.4.2 Basically, the CERCHAR test is a measurement of therelative different hardness of stylus tip and rock spec
13、imensurface. The stylus tip is made of steel having a knownRockwell Hardness. Experiments have shown that CAI variesinversely with stylus hardness. Test results with the same steeltype stylus but with different hardness need to be normalized tostandard stylus hardness (4).1This test method is under
14、the jurisdiction ofASTM Committee D18 on Soil andRock and is the direct responsibility of Subcommittee D18.12 on Rock Mechanics.Current edition approved May 15, 2010. Published July 2010. DOI: 10.1520/D762510.2The bold numbers in parenthesis refer to a list of references at the end of thisstandard.3
15、For 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 Harbor Drive, PO Box C
16、700, West Conshohocken, PA 19428-2959, United States.4.3 After the test, width of the wear flatness is measured onstylus tip surface in units of 0.1 mm and number of unitsreported as the CERCHAR Abrasiveness Index, 0.1mm (=1CAI).4.4 The scratch distance shall be limited to 10 mm. A CAIof 85 % is ach
17、ieved after the first 2 mm of the scratchs length,and 15 % of the change in CAI is achieved on the last 8 mm ofthe testing length. Deviations in CAI due to variations ofscratch length shall not be significant when the variation intesting length is kept between 60.5 mm in length (1).4.5 Five individu
18、al CAI tests shall be conducted for eachrock specimen to achieve a defined average value (1). If thereis not any obvious preference, for example, different colors,beddings, foliations on specimen, a set of three parallel tests inone direction, and two more perpendicular to first set shall bedone.5.
19、Significance and Use5.1 The CERCHAR test and associated CAI were devel-oped at a time of more demand for application of mechanicalexcavation machines at the Laboratoire du Center d tudes etRecherches des Charbonnages de France (CERCHAR) (3).CAI is used to assess the abrasiveness of rock for mechanic
20、alexcavation. Rock abrasiveness governs the performance of disccutters, the rate of its replacement and therefore subsequenttunnel costs. Advances in methods of underground excavation,in particular the use of the tunnel boring machine (TBM),necessitates knowledge of rock abrasiveness. Abrasivenessex
21、presses a behavioral characteristic of rock rather than afundamental physical or mechanical property.5.2 CAI tests were originally carried out on natural brokensurfaces. In heterogeneous rock types such as conglomerates,coarse grained granite or schistose rock, suitable fresh testsurfaces are not ac
22、hieved by mechanical breakage using ahammer. In these cases CAI values for “smooth” surfaces cutwith a diamond saw are acceptable for use but shall benormalized by Eq 2 before they can be used (1).5.3 The test velocity for the Original Cerchar apparatus isapproximately 10 mm/s and 1 mm/s for the Wes
23、t Cercharapparatus. The CAI values obtained for both testing velocities(1) are estimated to be equal.NOTE 1The quality of the result produced by these practices isdependent upon the competence of the personnel performing it and thesuitability of the equipment and facilities used. Agencies that meet
24、thecriteria of Practice D3740 are generally considered capable of competentand objective testing and sampling. Users of these practices are cautionedthat compliance with Practice D3740 does not in itself assure reliableresults. Reliable results depend on many factors; Practice D3740 providesa means
25、of evaluating some of those factors.6. Apparatus6.1 CERCHAR ApparatusTwo types of Cerchar apparatus(1) are in use today (See Fig. 1). Both devices employ a viceto clamp the specimen and a constant force of 70 N actingaxially on a stylus tip when place against the test surface. Theoriginal apparatus
26、employs a manually operated hand lever todisplace the stylus tip on the stationary rock surface held fixedin place by a vice. The West apparatus displaces the viceholding the rock by use of a hand crank and driving screwunder a stationary stylus.6.2 StylusAs mentioned in the Scope, CERCHAR test isa
27、measurement of the relative different hardness between thestylus tip and rock specimen surface. The stylus tip shall bemade of steel having a known Rockwell Hardness. Experi-ments have shown that CAI varies inversely with steel hard-ness. Test results with the same steel type stylus but withdifferen
28、t hardness should be normalized to standard stylushardness (4). The use of stylus hardened to 55 HRC (1,2), andconforming to Test Methods E18 is advised. The length anddiameter of stylus shall be greater than 15 mm and 10 mmrespectively, and have a sharpened profile at one end to aconical angle of 9
29、0, and 1 mm in length.6.3 MassThe static mass for either test apparatus shall beappropriately sized and configured so that the total force of 70N, including any other components which would contributeany force to the stylus tip during testing. This force shall actaxially on the stylus tip in contact
30、 with the specimen surface allthe time during the test.FIG. 1 Illustrations of Two Types of CERCHAR Testing ApparatusesD7625 1026.4 ViceThe vice in Fig. 1a shall be of sufficient rigidity,such that the clamped specimen is immobilized during the test.The vice in Fig. 1b holds the specimen and moves u
31、nder thestylus by using the hand crank that advances the driving screw.Small wooden wedges may be used to ensure tightness of fit.Also, the vice shall have precise control of movement in twohorizontal planes, with accurate positioning and change ofposition of the specimen with a secure hold.6.5 Rest
32、ing Supporta mechanism or configuration to holdthe mass and stylus in a stationary position above the testsurface location while setting up and removing the testspecimen. The original Cerchar uses a resting support to placethe lever arm on and the West Cerchar apparatus has a set oflock screws to gr
33、ip onto the static mass.6.6 Hand LeverThe articulated hand lever arm shall be ofsufficient stiffness to displace the stylus over the rock surfaceallowing unrestrained vertical displacement of the stylus underthe total force of 70 N (Fig. 1a).6.7 Hand CrankThe hand crank screw-feed attached tothe vic
34、e and powered manually with a crank displaces the viceholding a specimen under the stationary stylus. The screw-feedthread shall be machined such that displacement of the rocksurface occurs at a constant displacement per revolution underthe stationary stylus while allowing unrestrained vertical dis-
35、placement of the stylus under the total force of 70 N (Fig. 1b).6.8 MicroscopeA toolmakers microscope equipped withdigital micrometer heads, XY stage and LCD readout arerecommended. The microscope shall have a minimum magni-fication of 30X. The XY stage micrometer heads shall have aminimum range of
36、50 mm graduated to 0.01 mm and readableto 0.001 mm (3). Fig. 2 shows one example of this microscopewith a stylus tip positioned under it, during flatness measure-ments.6.9 GrinderAn apparatus that uses an abrasive stonewheel that is rotated and when place in contact with softermaterial removes mater
37、ial from that surface without appre-ciable wear to the stone wheel, or other suitable metal workapparatus, capable of shaping metal pen stock or sharpeningthe end of the stylus according to desired geometry. Cooling ofthe surface being ground by some type of fluid may be requiredin order not to heat
38、 up the metal excessively and change theoriginal Rockwell hardness of the metal being used for thestylus.6.10 MiscellaneousMachinists blue dye, wood shims,timer.7. Sampling and Test Specimens7.1 The specimen shall be selected from the core sample orpieces of in situ rock to represent a true average
39、of the type ofrocks to be drilled or bored. This can be achieved on a largescale by viewing rock types encountered at the project and ona smaller scale by visual observations of mineral constituents,grain sizes and shape, partings, and defects such as pores andfissures. Core or irregular shape speci
40、mens with a typicaldiameter or length of approximately 50 mm are recommended.7.2 The moisture conditions of the specimen at the time oftest can have a significant effect upon the indicated strength ofthe rock. The field moisture condition for the specimen shall bepreserved until the time of test in
41、accordance with PracticesD5079. This may be problematic when saw cut or drilled rocksurfaces that need a water coolant are used instead of naturalrock surfaces.7.3 Specimens displaying apparent anisotropic features suchas bedding or schistosity shall be prepared so that the orienta-tion of the CAI t
42、est surface relative to anisotropic features canbe determined precisely.7.4 Specimen test surface shall be either fresh flat naturalsurface or saw cut one. For saw cut surface, specimen surfacesshall be prepared by cutting the rock sample with a watercooled diamond saw blade to expose fresh specimen
43、 surfacesprovided the resulting surfaces are reasonably planar.7.5 The specimen test surface should be of sufficient lengthsuch that edge chipping within the 10 mm test path does notoccur as the stylus approaches the specimen outer dimension.7.6 Specimens with either natural or saw cut test surfaces
44、shall be trimmed to fit in the CERCHAR test machine bycutting the rock sample with a water cooled diamond sawblade.7.7 Before and after photographs shall be taken of testedsurfaces.8. Preparation of Apparatus8.1 The stylus shall be in good condition and verified undera microscope before use.8.2 If s
45、tylus is not in good condition or previously used,then prior to testing, stylus tip shall be sharpened to theprescribed shape and condition described in 6.2. Special careshall be taken when re-sharpening used styli. High tempera-tures induced from sharpening too quickly can influence thestyli hardne
46、ss. Therefore application of a water coolant duringre-sharpening process is recommended.8.3 Regularly re-examining of stylus hardness is advised;Rockwell Hardness of stylus shall be 55.FIG. 2 Toolmakers MicroscopeD7625 1038.4 Rockwell Hardness of stylus shall be verified in accor-dance with Test Met
47、hods E18.8.5 Prior to testing, coating of each stylus tip with machin-ists blue dye makes the wear flat area of the tip more visibleunder the microscope, and also helps to differentiate ready fortest styli from used ones.9. Procedure9.1 Orient and securely clamp the test specimen in the vicesuch tha
48、t the test surface is horizontal and parallel to thedirection of displacement with the stylus. If necessary, usewood or other suitable materials between the vice and speci-men surface to assist clamping and orienting the specimen.9.2 The stylus and associated components are lowered withcare to bear
49、on the specimen test surface so that the stylus tipis not damaged before testing.9.3 The static mass and any associated components arepositioned and checked for functionality ensuring there are nofrictional impediments to the specified 70 N total force.9.4 Two scratching velocities are used depending on whichdevice is available. A scratching distance of 10 mm is used forboth devices.9.4.1 The articulated hand lever is pulled over the testsurface with a stylus scratching speed (1) of approximately 10mm/s (Fig. 1a).9.4.2 The hand crank is turned at a rate consist
