1、Designation: C651 15 An 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 th
2、e 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 U.S
3、. Department of Defense.1. Scope*1.1 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
4、are included 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
5、 prior to use.2. Referenced Documents2.1 ASTM Standards:2C78 Test Method for Flexural Strength of Concrete (UsingSimple Beam with Third-Point Loading)C1161 Test Method for Flexural Strength of AdvancedCeramics at Ambient TemperatureE4 Practices for Force Verification of Testing MachinesE177 Practice
6、 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 Definitions:3.1.1 flexural strength, nproperty of a solid material thatindicates its ability to withstand a flexural or transv
7、erse load,obtained through a measurement of the ultimate load-carryingcapacity of a specified beam in bending.4. Significance and Use4.1 This test method may be used for material development,quality control, characterization, and design data generationpurposes.4.2 This test method determines the max
8、imum loading on agraphite specimen with simple beam geometry in 4-pointbending, and it provides a means for the calculation of flexuralstrength at ambient temperature and environmental conditions.5. Apparatus5.1 The testing machine shall conform to the requirementsof Practices E4.5.2 The four-point
9、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 eccentricity through the use ofspherical bearing blocks (see Test Method C
10、78) or articulatingroller bearing assemblies (see Test Method C1161).5.3.1 The bearing block or roller bearing diameter shall bebetween110 and120 of the specimen support span. A hardenedsteel bearing block or its equivalent is necessary to preventdistortion of the loading member. Support surfaces mu
11、st befree 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 can be avoided by theuse of spherical bearing blocks or articulating roller bea
12、rings.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 PreparationThe test specimen shall be prepared toyield a parallelepiped of re
13、ctangular cross section. The facesshall be parallel and flat within 0.025 mm mm of length. Inaddition, the samples having a maximum particle size less than0.150 mm in diameter must be finished so that the surface1This test method is under the jurisdiction of ASTM Committee D02 onPetroleum Products,
14、Liquid Fuels, and Lubricants and is the direct responsibility ofSubcommittee D02.F0 on Manufactured Carbon and Graphite Products.Current edition approved Oct. 1, 2015. Published November 2015. Originallyapproved in 1970. Last previous edition approved in 2013 as C651 13.DOI:10.1520/C0651-15.2For ref
15、erenced 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.*A Summary of Changes section appears at the end of this standardCopy
16、right ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1roughness 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 finishing
17、 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 the
18、 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 measu
19、red to thenearest 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 C to 150 C for a period of 2 h. The sample must thenbe stored in a dry environment or a
20、desiccator and held thereprior to 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 app
21、lying 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
22、within 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.
23、Use 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 in 5 s ormore.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 l
24、oad at 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 fle
25、xural strength as follows:S 5 PL/ bd2where:S = flexural strength, MPa,P = maximum applied load indicated by the testing machine,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
26、bearing 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.NOTE 3Angular fractures that effecti
27、vely traverse the load rollercontact point but are determined to have initiated at or inside of the loadroller span can be reasonably attributed to failure at the maximum flexurestress, and should be recorded as having fractured inside of the span lengthbetween the load roller blocks.9.3 If fracture
28、 occurs in less than 5 s, 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 supp
29、ort roller, mm.NOTE 4It should 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/comp
30、ression inequality in modulus (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
31、 identification,10.1.2 Average 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
32、 calculated to the nearest 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 carry
33、ing out the statistical analysis 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 the3Supporting data have been filed at ASTM International Headquarters and maybe obtained
34、 by requesting Research Report RR:C05-1011.C651 152FIG. 1 Beam with Four-Point LoadingC651 153average strength values measured by each laboratory can beconsidered statistically equal to 95 percent confidence level.11.1.2 Repeatability (Single Instrument)The precisionwithin laboratory of two single v
35、alues of measured strengthusing 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 robinof 257 psi (1.8 MPa). This value converts into a strengthpercentage of
36、65.5.11.1.3 Repeatability (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 val
37、ue for the material used in this roundrobin of 46 psi (0.3 MPa). This converts into a strength per-centage of 61.11.2 BiasNo true statement on bias can be made becauseno reference carbon or graphite material exists.12. Keywords12.1 carbon; flexural strength; graphiteSUMMARY OF CHANGESSubcommittee D0
38、2.F0 has identified the location of selected changes to this standard since the last issue(C651 13) that may impact the use of this standard. (Approved Oct. 1, 2015.)(1) Updated Section 3, Terminology, and the term in subsection3.1.1.ASTM International takes no position respecting the validity of an
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