1、Designation: C651 11An American National StandardStandard Test Method forFlexural Strength of Manufactured Carbon and GraphiteArticles Using Four-Point Loading at Room Temperature1This standard is issued under the fixed designation C651; the number immediately following the designation indicates the
2、 year oforiginal adoption or, in the case of revision, the year 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.This standard has been approved for use by agencies of the Depa
3、rtment of Defense.1. Scope1.1 This test method covers determination of the flexuralstrength of manufactured carbon and graphite articles using asimple beam in four-point loading at room temperature.1.2 The values stated in SI units are to be regarded asstandard. No other units of measurement are inc
4、luded in thisstandard.1.3 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 and health practices and determine the applica-bility of regulatory limitations prior
5、to use.2. Referenced Documents2.1 ASTM Standards:2C78 Test Method for Flexural Strength of Concrete (UsingSimple Beam with Third-Point Loading)C709 Terminology Relating to Manufactured Carbon andGraphiteC1161 Test Method for Flexural Strength of AdvancedCeramics at Ambient TemperatureE4 Practices fo
6、r Force Verification of Testing MachinesE177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method3. Terminology3.1 DefinitionsFor definitions of terms relating to manu-factured carbon and
7、graphite, see Terminology C709.3.2 Definitions of Terms Specific to This Standard:3.2.1 flexural strengtha measure of the ultimate load-carrying capacity of a specified beam in bending.4. Significance and Use4.1 This test method may be used for material development,quality control, characterization,
8、 and design data generationpurposes.4.2 This test method determines the maximum loading on agraphite specimen with simple beam geometry in 4pointbending, and it provides a means for the calculation of flexuralstrength at ambient temperature and environmental conditions.5. Apparatus5.1 The testing ma
9、chine shall conform to the requirementsof Practices E4.5.2 The four-point loading fixture shall consist of bearingblocks or cylindrical bearings spaced in a third-point loadingconfiguration (see Test Method C78).5.3 The fixture shall ensure that forces applied to the beamare normal only and without
10、eccentricity through the use ofspherical bearing blocks (see Test Method C78) or articulatingroller bearing assemblies (see Test Method C1161).5.3.1 The bearing block or roller bearing diameter shall bebetween 1/10 and 1/20 of the specimen support span. Ahardened steel bearing block or its equivalen
11、t is necessary toprevent distortion of the loading member. Support surfacesmust be free to pivot or rotate to relieve frictional constraints.5.4 The directions of loads and reactions may be maintainedparallel by judicious use of linkages, rocker bearings, andflexure plates. Eccentricity of loading c
12、an be avoided by theuse of spherical bearing blocks or articulating roller bearings.Provision must be made in fixture design for the relief oftorsional loading to less than 5 % of the nominal specimenstrength. Refer to the attached figure for a suggested four-pointloading fixture.6. Test Specimen6.1
13、 PreparationThe test specimen shall be prepared toyield a parallelepiped of rectangular cross section. The facesshall be parallel and flat within 0.025 mm/mm of length. Inaddition, the samples having a maximum particle size less than1This test method is under the jurisdiction of ASTM Committee D02 o
14、nPetroleum Products and Lubricants and is the direct responsibility of SubcommitteeD02.F0 on Manufactured Carbon and Graphite Products.Current edition approved June 1, 2011. Published July 2011. Originally approvedin 1970. Last previous edition approved in 2010 as C65191(2010)1. DOI:10.1520/C065111.
15、2For 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
16、C700, West Conshohocken, PA 19428-2959, United States.0.150 mm in diameter must be finished so that the surfaceroughness is less than 3 m Ra. Sample edges should be freefrom visible flaws and chips.NOTE 1For ease of machining to conventional standards, 3 m Ra isequivalent to 125 in. AA. For finishin
17、g of specimens with maximumparticle sizes of greater than 0.150 mm, grain structure and porosity canlimit the accurate measurement of roughness. In these cases, the surfaceroughness should be visually equivalent to 3 m Ra as estimated based onthe visible surface of the graphite6.2 SizeThe size of th
18、e test specimen shall be selectedsuch that the minimum dimension of the specimen is greaterthan 5 times the largest particle dimension. The test specimenshall have a length to thickness ratio of at least 8, and a widthto thickness ratio not greater than 2.6.3 MeasurementsAll dimensions shall be meas
19、ured tothe nearest 0.5 %.6.4 OrientationThe specimen shall be marked or other-wise identified to denote its orientation with respect to theparent stock.6.5 DryingEach specimen must be dried in a vented ovenat 120 to 150C for a period of 2 h. The sample must then bestored in a dry environment or a de
20、siccator and held there priorto testing.NOTE 2Water, either in the form of liquid or as humidity in air, canhave an effect on flexural mechanical behavior. Excessive adsorbed watercan result in a reduced failure stress due to a decrease in fracture surfaceenergy.7. Procedure7.1 Center the load apply
21、ing bearing surfaces and the testspecimen on the support bearing surfaces. The load span is atleast two times the sample thickness, and the support spanthree times the load span, but not less than 40 mm. The loadand support bearings shall be carefully positioned such that thespans are accurate to wi
22、thin 0.5%. Overlap each end of thespecimen by at least the specimen thickness. Refer to Fig. 1.7.2 The load applying bearing surfaces shall make contactwith the upper surface of the test specimen. Load and supportbearing blocks must be parallel to each other and perpendicularto the test surfaces. Us
23、e a loading rate of 1.25 mm/min or lesson screw-driven testing machines. On other test devices, loadthe part at a uniform rate such that breakage occurs in5sormore.8. Test Data Record8.1 Measurements to 0.025 mm shall be made to determinethe average width and thickness of the specimen.8.2 The load a
24、t failure must be recorded to an accuracy of62 % of the full-scale value. A full-scale value of 5 kN wouldrequire recording to an accuracy of 6100 N.9. Calculation9.1 If the fracture occurs within the span length between theload bearing surfaces (that is, within the load span), calculatethe flexural
25、 strength as follows:S 5 PL/bd2where:S = flexural strength, MPa,P = maximum applied load indicated by the testing ma-chine, N,L = support span length, mm,b = average width of specimen, mm, andd = average thickness of specimen, mm.9.2 If the fracture occurs outside of the span length betweenload bear
26、ing blocks, the location of the fracture shall berecorded as such, and the results of the test shall be reported.Occasional breaks outside the inner load span in 4-point flexureare not unusual, and can often be attributed to large naturalflaws in the material.9.3 If fracture occurs in less than 5 s,
27、 the results shall bediscarded but reported.9.4 An alternative calculation for flexural strength can beused if the span length between the load bearing surfaces is notaccurately measured to three times the load span:S 5 3 Pa/bd2(1)where:a = distance between the load and support roller, mm.NOTE 3It s
28、hould be recognized that the above equations do notnecessarily give the stress that was acting directly on the origin that causedfailure. The equations do not account for subsurface origins or breaksoutside of the load span, nor do they correct for the potential tension/compression inequality in mod
29、ulus (behavior that is not linear elastic)commonly accepted in graphite. For conventional Weibull analysis, usethe calculated maximum stress in the specimen at failure from theequations as shown.10. Report10.1 The report of each test shall include the following:10.1.1 Sample identification,10.1.2 Av
30、erage width to the nearest 0.025 mm,10.1.3 Average thickness to the nearest 0.025 mm,10.1.4 Support span length, (and load span length if accu-rate third point loading is not measured), mm,10.1.5 Rate of loading, mm/min,10.1.6 Maximum applied load, N,10.1.7 Flexural strength calculated to the neares
31、t 10 kPa,10.1.8 Defects in specimen,10.1.9 Orientation and location of specimen, and10.1.10 Failure location.11. Precision and Bias311.1 PrecisionThe precision statements given in this sec-tion are based on the comparison of the mean strength by theStudent “t” test and carrying out the statistical a
32、nalysis of thedata obtained in a round robin as recommended by PracticeE691.11.1.1 Comparison of the MeansThe comparison of themeans by the Student “t” test leads to the conclusion that theaverage strength values measured by each laboratory can beconsidered statistically equal to 95 percent confiden
33、ce level.3Supporting data have been filed at ASTM International Headquarters and maybe obtained by requesting Research Report RR:C05-1011.C651 112FIG. 1 Beam with Four-Point LoadingC651 11311.1.2 Repeatability (Single Instrument)The precisionwithin laboratory of two single values of measured strengt
34、husing Practice E177 definition with the pooled standard devia-tion calculated using Practice E691 is:Repeatability within laboratory 5 2 Sr!j,which yields a value for the material used in the round robin of257 psi (1.8 MPa). This value converts into a strengthpercentage of 65.5.11.1.3 Repeatability
35、 (Multi-Instrument) The precision be-tween laboratories of two single values of measured strengthusing Practice E177 definition with the component of variancebetween laboratories calculated using Practice E691 is:Repeatability between laboratories 5 2 SL!j,which yields a value for the material used
36、in this round robinof 46 psi (0.3 MPa). This converts into a strength percentage of61.11.2 BiasNo true statement on bias can be made becauseno reference carbon or graphite material exists.12. Keywords12.1 carbon; flexural strength; graphiteASTM International takes no position respecting the validity
37、 of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject
38、to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters
39、. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is
40、 copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org). Permission rights to photocopy the standard may also be secured from the ASTM website (www.astm.org/COPYRIGHT/).C651 114
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