1、Designation: C 749 92 (Reapproved 2002)An American National StandardStandard Test Method forTensile Stress-Strain of Carbon and Graphite1This standard is issued under the fixed designation C 749; the number immediately following the designation indicates the year oforiginal adoption or, in the case
2、of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the testing of carbon andgraphite in tension to obtain the tensile s
3、tress-strain behavior,to failure, from which the ultimate strength, the strain tofailure, and the elastic moduli may be calculated as may berequired for engineering applications. Table 1 lists suggestedsizes of specimens that can be used in the tests.NOTE 1The results of about 400 tests, on file at
4、ASTM as RR:C05-1000, show the ranges of materials that have been tested, the ranges ofspecimen configurations, and the agreement between the testers.NOTE 2For safety considerations, it is recommended that the chainsbe surrounded by suitable members so that at failure all parts of the loadtrain behav
5、e predictably and do not constitute a hazard for the operator.1.2 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
6、-bility of regulatory limitations prior to use.1.3 The values stated in inch-pound units are to be regardedas the standard. The values given in parentheses are forinformation only.2. Referenced Documents2.1 ASTM Standards:E 4 Practices for Force Verification of Testing Machines2E 6 Terminology Relat
7、ing to Methods of Mechanical Test-ing2E 177 Practice for Use of the Terms Precision and Bias inASTM Test Methods3E 691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method33. Terminology3.1 DefinitionsThe terms as related to tension testing asgiven in Terminolo
8、gy E 6 shall be considered as applying to theterms used in this test method.4. Summary of Test Method4.1 A tensile specimen (Fig. 1) is placed within a load trainassembly made up of precision chains and other machinedparts (Fig. 2). A load is applied to the specimen provided withmeans of measuring s
9、train until it is caused to fracture. Thistest yields the tensile strength, elastic constants, and strain tofailure of carbons and graphites.5. Significance and Use5.1 This test method is intended to be used for both carbonsand graphites whose particle sizes are of the order of 1 mil to14 in. (0.025
10、4 to 6.4 mm) and larger. This wide range ofcarbons and graphites can be tested with uniform gage diam-eters with minimum parasitic stresses to provide quality datafor use in engineering applications rather than simply forquality control. This test method can be easily adapted toelevated temperature
11、testing of carbons and graphites withoutchanging the specimen size or configuration by simply utilizingelevated temperature materials for the load train. This testmethod has been utilized for temperatures as high as 4352F(2400C). The design of the fixtures (Figs. 2-9 and Table 2) anddescription of t
12、he procedures are intended to bring about, onthe average, parasitic stresses of less than 5 %. The specimensfor the different graphites have been designed to ensurefracture within the gage section commensurate with experi-enced variability in machining and testing care at differentfacilities. The co
13、nstant gage diameter permits rigorous analyti-cal treatment.6. Apparatus6.1 Testing MachineThe machine used for tensile testingshall conform to the requirements of Practices E 4. The testingmachine shall have a load measurement capacity such that thebreaking load of the test specimen falls between 1
14、0 and 90 %of the scale capacity. This range must be linear to within 1 %over 1 % increments either by design or by calibration.6.2 Strain Measurements:6.2.1 The axial strain can be measured at room temperatureby the use of strain gages, mechanical extensometers, Tucker-man gages, optical systems, or
15、 other devices applied diametri-cally opposite in the gage length portion of the specimen. Twoopposing gages provide some compensation for bending andsome assurance that it was not severe. Different graphites1This test method is under the jurisdiction of ASTM Committee D02 onPetroleum Products and L
16、ubricants and is the direct responsibility of SubcommitteeD02.F on Manufactured Carbon and Graphite Products .Current edition approved Aug. 15, 1992. Published October 1992. Originallypublished as C 749 73. Last previous edition C 749 87.2Annual Book of ASTM Standards, Vol 03.01.3Annual Book of ASTM
17、 Standards, Vol 14.02.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.require different attachment procedures and extreme care isnecessary. A proven device for mounting the specimen withminimum damage and for enabling the specimen to
18、 receivedifferent extensometers is shown in Fig. 10. When attachingstrain gages, the modification of the surface may result in aglue-graphite composite at the skin and thus the resulting strainvalues may be erroneous and typically low. When using clip-onextensometers, the knife edges can initiate fr
19、acture. Record,but do not include the fractures at the attachments in theaverages. If more than 20 % of the failures occur at theattachment location, change the strain monitoring system orattachment device.6.2.2 The circumferential strain can be measured at roomtemperature by use of strain gages app
20、lied circumferentially.Knowledge of the anisotropy in the billet and orientation of thespecimen is necessary in order to properly place the strain-measuring device. Generally, one can expect three values ofPoissons ratio for a nonisotropic material. Hence, the strainTABLE 1 Sample Sizes Used in Roun
21、d-Robin TestsA(Suggested Specimen SizeA)MaterialBMax GrainSize, in.Sample, in. SpecimenSize, in.RecommendedShank andMaximum Gage,in.AXM-50 0.001 5 by 5 by 5, molded12 by 0.200C 12 by31634 by149326 0.001 20 by 10 by 2, molded12 by1434 by 0.312 by316C12 by31634 by149326A 0.001 20 by 10 by 2, molded12
22、by1412 by31634 by3834 by 0.334 by 0.334 by38ATJ 0.006 13, rounds, molded12 by1412 by1434 by3834 by1434 by3834 by1434 by38HLM 0.033 molded, 10 by 18 by 2512 by1434 by3834 by3834 by3834 by38CS 0.030 10, rounds, extruded 2 by 134 by3834 by3812 by1412 by14AGR 0.250 25, rounds, extruded 2 by 1 2 by 12by1
23、 114 by582by1114 by58CGE 0.265 14, rounds, extruded 2 by 11434 by12 2by1Graphitar . . . carbon-graphite, resin impregnated34 by1434 by14Grade 8612 by14C 12 by 0.212 by14Purebon P-59 . . . carbon-graphite, copper treated34 by1434 by1412 by14C 12 by31612 by14ABased on RR:C5-1000 (see Note 1).BIdentity
24、 of suppliers available from ASTM Headquarters.CGas-bearings.NOTE 1Standard Specimen:r1= r2,A1= A2/1.2,l1= D2/2, andl2= 2 in. (51 mm) or 8 D1, whichever is greater.FIG. 1 Double Reduction Used to Minimize Radii-FracturesC 7492sensing devices must be sized and positioned carefully. Notethe limitation
25、s on strain gages mentioned in 6.2.1.6.2.3 The diametral strains can be measured by most of thedevices with limitations mentioned in 6.2.1 and 6.2.2.6.3 Parasitic Stress MonitorAn optional parasitic stressmonitor can be inserted as an extension of one of the grips. Itshall be a steel rod about 4 in.
26、 long with strain gages mountedat 90 angles to monitor axial bending moments on the rod andthus on the specimen. The rod shall be sized so that the bendingmoment applied to the specimen being used can be detected towithin a 5 % parasitic stress in the outer fiber of the specimen.The parasitic stress
27、 shall be calculated elastically by translatingthe moment and assuming that the specimen is a free-endbeam.6.4 Gripping DevicesGripping devices that conform tothose shown in Fig. 2 shall be used. The centerlines of allconnections must align to within the tolerances shown through-out the test.FIG. 2
28、Tensile Load Train AssemblyC 74936.5 General Test ArrangementThe general arrangementof the specimen, flexible linkages, and crossheads shall be asshown in the schematic of Fig. 3.7. Test Specimens7.1 Test specimens shall be produced to the general con-figurations shown in Fig. 9. The selection of th
29、e proper ratio ofshank to gage diameter is important to prevent excessivehead-pops or fracture of the specimen at the groove in theshanks. The ratios shown in Table 1 have been found satisfac-tory for this use. It is acceptable to double reduce gagediameters as necessary (see Fig. 1) to eliminate he
30、ad pops (orout-of-gage fractures) or reduce them to an acceptable 20 %maximum of the total fractures. However, the reducing radiusmust be maintained near the values shown or excessive radiibreaks will be obtained. Also, the gage diameter should not bereduced to less than three to five times the maxi
31、mum particlessize in the material, or the failure mode may be atypical.7.2 Improperly prepared test specimens often cause unsat-isfactory test results. It is important, therefore, that care beexercised in the preparation of specimens both in minimizingend and side thrusts and in providing a quality
32、surface. Stressesinduced during preparation should not exceed 10 % of ultimatefracture stress. Either tool cutting or grinding is acceptable, butthe latter is preferred. Surface roughness should be no greaterthan the maximum particle or void size, whichever is greater.Usually, they are about equal.7
33、.3 The gage length of the specimen will be measured fromthe axial center of the specimen. Gage marks can be appliedwith ink or layout dope but no scratching, punching, ornotching of the specimen is permissible. The gage length is tobe used in referencing the point of fracture within 0.1 in. (2.5mm).
34、 The total gage length is defined as that section with thesmaller uniform diameter extending from radius tangent toradius tangent plus 10 %. The additional 10 % is intended toaccommodate the normal statistics of fracture for a materiallike graphite. However, at least 50 % of the specimens shouldfrac
35、ture within the uniform diameter or the specimen should beredesigned and the system checked. Acceptable fractured areshown in Fig. 11.7.4 To determine the cross-sectional area, the diameter ofthe specimen at the smaller or constant diameter region shall beused. The dimension shall be recorded to the
36、 nearest 0.001 in.(0.254 mm).8. Procedure8.1 CalibrationCalibrate the micrometres that are to beused for measurement of diameters by measuring the dimen-sions of blocks provided by the NBS that are accurate within60.0001 in. (0.00254 mm). Calibrate all instrumentation andestablish shunt calibration
37、for each recorded and each param-eter. Zero all recorders.FIG. 3 Schematic of Tensile System for Carbon and GraphiteDimensions,in. (mm)Item101 115A 0.250 6 0.001(6.35 6 0.03)0.312 6 0.001(7.92 6 0.03)B 0.500 6 0.001(12.70 6 0.03)0.625 6 0.001(15.88 6 0.03)C 1.000(25.40)1.500(38.10)D316(4.76)38(9.52)
38、NOTE 1Refer to Fig. 2, Items 101 and 115.FIG. 4 Crosshead Attachment YokeC 74948.2 SpecimenAdapt to the specimen the appropriate straininstrumentation by bonding strain gages to its surface, adapt-ing, or any other strain measuring system so that strain can bemeasured during the test. Place the spec
39、imen within the loadtrain. Make sure all instrumentation is properly calibrated andzeroed.8.3 LoadingApply the load at a predetermined constantstress rate by following the appropriate load time curve eithermanually or automatically. Continuously apply the load untilfracture is induced.8.4 RecordingD
40、uring the entire load application duration,record the output of the load cell on the vertical axis of an X-Yrecorder and the strain on the horizontal axis, and obtain apermanent record of the stress-strain curve for the specimenbeing tested during the entire test.8.5 Post TestObserved the specimen f
41、racture surface. Ifthe specimen failed outside the gage length as defined in 6.3(including head pops), the strength value measured must bereported but not included in the average.9. Calculation9.1 Calculate the strength as follows:sult5PmaxA(1)where:sult= tensile strength, psi (Pa),Pmax= maximum loa
42、d, lbf (N), andA = cross-sectional area of the specimen in the constantdiameter region or gage section, in.2(m2).9.1.1 The cross-sectional area is given by the equation:A 5pD24(2)where:D = average diameter of the constant diameter region (gagesection) of the specimen, in. (m).9.2 Calculate modulus o
43、f elasticity of the specimen from thestress-strain curve as follows:E 5 initial slope of stress2strain curve 5DsDe(3)where:E = modulus of elasticity, psi (Pa),Ds = incremental stress corresponding to the incrementalstrain, psi (Pa), andDe = incremental strain corresponding to the incrementalstress,
44、in./in. (m/m).Dimensionsin. (mm)Item103 117E91658(14.29) (15.88)F51612(7.94) (12.7)G 0.250 6 0.001 0.3126 0.001(6.35 6 0.03) (7.92 6 0.03)H 0.500 0.625(12.70) (15.88)J31638(4.76) (9.52)K18316(3.18) (4.76)NOTE 1Refer to Fig. 2, Items 103 and 117.FIG. 5 Chain JournalC 74959.3 Calculate the strain-to-f
45、ailure from the stress-straincurve as the strain where the maximum stress was obtained andthe specimen failed.10. Report10.1 Report the following information:10.1.1 Method of testing, load rate, load calibrations, andother general testing information,10.1.2 Material identification: manufacturer, gra
46、de number,lot number, original billet size, grain size, and other data,where available,10.1.3 Description of the specimen including orientationand position in billet,10.1.4 Description of procedures and other environmentalexposures,10.1.5 All individual and average ultimate tensile strengthvalues,10
47、.1.6 Individual and average strain-to-failure values anddetails on the method of attachment of the strain sensingdevice. If elastic constants are given, the method of determin-ing them should be reported,10.1.7 Data for all samples tested including the monitoredparasitic moment and calculated parasi
48、tic stress,10.1.8 A record of all specimens that broke during machin-ing or subsequent handling after they had been reduced to thenominal diameter used in the grips,10.1.9 Standard deviation, coefficient of variation of allproperties, or both. Usually, at least five to ten values arerequired for the
49、se numbers to have significance, and10.1.10 Axial fracture location (see Fig. 11).11. Precision and Bias11.1 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 analysis of the dataobtained on materials tested in a round-robin as recommendedby Practice E 691.11.1.1 Comparison of the MeansThe comparison of themeans by the student t test leads to the conclusion that the
