1、Designation: C 769 09An American National StandardStandard Test Method forSonic Velocity in Manufactured Carbon and GraphiteMaterials for Use in Obtaining Youngs Modulus1This standard is issued under the fixed designation C 769; the number immediately following the designation indicates the year ofo
2、riginal 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.1. Scope1.1 This test method covers a procedure for measuring thesonic v
3、elocity in manufactured carbon and graphite which canbe used to obtain Youngs modulus.1.2 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.3 This standard does not purport to address all of thesafety concerns, if any, associate
4、d 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 to use.2. Referenced Documents2.1 ASTM Standards:2C 559 Test Method for Bulk Density by Physical Measure-ments o
5、f Manufactured Carbon and Graphite ArticlesC 747 Test Method for Moduli of Elasticity and Fundamen-tal Frequencies of Carbon and Graphite Materials by SonicResonanceIEEE/ASTM SI 10 Standard for Use of the InternationalSystem of Units (SI) (the Modern Metric System)3. Terminology3.1 Definitions of Te
6、rms Specific to This Standard:3.1.1 end correction time (Te)the non-zero time of flight(correction factor), measured in seconds, that may arise byextrapolation of the pulse travel time, corrected for zero time,back to zero sample length.3.1.2 longitudinal sonic pulsea sonic pulse in which thedisplac
7、ements are in the direction of propagation of the pulse.3.1.3 pulse travel time, (Tt)the total time, measured inseconds, required for the sonic pulse to traverse the specimenbeing tested, and for the associated electronic signals totraverse the transducer coupling medium and electronic circuitsof th
8、e pulse-propagation system.3.1.4 zero time, (T0)the travel time (correction factor),measured in seconds, associated with the transducer couplingmedium and electronic circuits in the pulse-propagation sys-tem.4. Summary of Test Method4.1 The velocity of longitudinal sound waves passingthrough the tes
9、t specimen is determined by measuring thedistance through the specimen and dividing by the time lapse,between the transmitted pulse and the received pulse.3,4Pro-vided the wavelength of the transmitted pulse is a sufficientlysmall fraction of the sample later dimensions, a value ofYoungs modulus for
10、 isotropic graphite can then be obtainedusing Eq 1 and Eq 2:E 5 CvrV2(1)where:E = Youngs modulus of elasticity, Pa,r = density, kg/m3,V = longitudinal signal velocity, m/s, andCv= Poissons factor.The Poissons factor, Cn, is related to Poissons ratio, n,bythe equation:Cn51 1n!12n!1n(2)If Poissons rat
11、io is unknown, it can be assumed as anapproximation in the method. For nuclear graphites, a typicalPoissons ratio of 0.2 corresponds to a Poissons factor of 0.9.If the wavelength is not a small fraction of the sample lateraldimensions, and instead is much larger than the specimenlateral dimensions,
12、then the Youngs modulus, E is given by Eq1 with Cnset to one rather than being determined by Eq 2.5. Significance and Use5.1 Sonic velocity measurements are useful for comparingmaterials.1This test method is under the jurisdiction of ASTM Committee D02 onPetroleum Products and Lubricants and is the
13、direct responsibility of SubcommitteeD02.F0 on Manufactured Carbon and Graphite Products.Current edition approved June 1, 2009. Published July 2009. Originally approvedin 1980. Last previous edition approved in 2005 as C 76998(2005).2For referenced ASTM standards, visit the ASTM website, www.astm.or
14、g, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Schreiber, Anderson, and Soga, Elastic Constants and Their Measurement,McGraw-Hill Book Co., 1221Avenue of theAmericas, New Yor
15、k, NY 10020, 1973.4American Institute of Physics Handbook , 3rd ed., McGraw-Hill Book Co.,1221 Avenue of the Americas, New York, NY 10020, 1972, pp. 398ff.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.5.2 A value for Youngs modulus
16、 can be obtained for manyapplications, which will be in good agreement with the valueobtained by other methods, such as in Test Method C 747. Theaccuracy of the Youngs modulus calculated from Eq 1 willdepend upon the uncertainty in Poissons ratio and its impacton the evaluation of the Poissons facto
17、r in Eq 2.5.3 If the grain size of the carbon or graphite is greater thanor about equal to the wavelength of the sonic pulse, the methodmay not be providing a value of Youngs modulus representa-tive of the bulk material. Therefore, it would be desirable totest a lower frequency (longer wavelength) t
18、o demonstrate thatvelocity is independent of frequency. Significant signal attenu-ation should be expected when the grain size of the material isgreater than or about equal to the wavelength of the transmittedsonic pulse.5.4 If the sample is only a few grains thick, the acceptabilityof the methods a
19、pplication should be demonstrated by initiallyperforming measurements on a series of tests covering a rangeof sample lengths between the proposed test length and a testlength incorporating sufficient grains to adequately representthe bulk material.6. Apparatus6.1 Driving Circuit, consisting of an ul
20、trasonic pulse gen-erator.6.1.1 The user should select a pulse frequency to suit thematerial being tested. High frequencies are attenuated bycarbon and graphite materials and, while typical practicablefrequencies lie in the range 0.5 to 2.6 MHz, the user may showthat frequencies outside this range a
21、re acceptable.6.2 Transducer, input, with suitable coupling medium (see8.5).6.3 Transducer, output, with suitable coupling medium (see8.5).6.3.1 The signal output will depend upon the characteristicsof the chosen transducers and the test material. It is recom-mended that the user analyses the input
22、and output frequencyspectra to determine optimum conditions. Band pass filters andnarrow band transducers may be used to simplify the signaloutput which could improve the measurement of the time offlight.6.4 Computer, with analogue to digital converter, or oscil-loscope, and external trigger from dr
23、iving circuit.6.5 See Fig. 1 for a typical schematic setup.NOTE 1Some manufacturers combine items 6.1 and 6.4 into a singlepackage with direct time readout. Such apparatus can operate satisfacto-rily, provided the frequency of the propagated pulse is already known, inorder to check that wavelength r
24、equirements for the method are satisfied.7. Test Specimen7.1 Selection and Preparation of SpecimensTake specialcare to assure obtaining representative specimens that arestraight, uniform in cross section, and free of extraneousliquids. The specimen end faces shall be perpendicular to thespecimen cyl
25、indrical surface to within 0.125 mm total indicatorreading.7.2 Measurement of Weight and DimensionsDeterminethe weight and the average specimen dimensions to within60.2 %.7.3 Limitations on DimensionsThese cannot be preciselyspecified as they will depend upon the properties of thematerial being test
26、ed. In order to satisfy the theory thatsupports Eq 1, as a guide, the specimen should have a diameterthat is at least a factor two, and ideally a factor five, greaterthan the wavelength of sound in the material under test. Inpractice, the length of the specimen will be determined takingaccount of th
27、e comments in 5.3 and 5.4.7.4 Limitations on Ultrasonic Pulse FrequencyGenerallyspeaking, a better accuracy of time of flight will be obtained athigher frequencies. However, attenuation increases at higherfrequencies leading to weak and distorted signals.8. Procedure8.1 For any given apparatus and c
28、hoice of coupling me-dium, it is necessary to follow procedures to quantify the zerotime, T0, and end correction time, Te, correction factors. T0willFIG. 1 Basic Experimental Arrangement for the Ultrasonic Pulsed-Wave Transit Time TechniqueC769092be dependent upon the type of transducers and their p
29、erfor-mance over time and should be regularly checked (see 8.8). Itmust be quantified if the test set up is changed. Teshould besmall and reflects the interaction between the coupling mediumand the test material. Teshould be determined once for aspecific measurement setup and test material.8.1.1 Det
30、ermine whether an end correction time, Te,isevident in the time of flight by performing time of flightmeasurements on various length samples taken from a singlebar. As modulus is likely to vary from sample to sample therecommended approach is to continually bisect a long rod,measuring each bi-sectio
31、n, until the required lower limit isreached. The end correction time, Te, is obtained from aregression fit to a graph of time of flight versus sample length.8.2 Measure and weigh the test specimen as in 7.2.8.3 Calculate the density of the test specimen in accordancewith Test Method C 559.8.4 Connec
32、t the apparatus as shown in Fig. 1, and refer toequipment manufacturers instructions for setup precautions.Allow adequate time for equipment warm-up and stabilization.8.5 Place the transducers against the test specimen endfaces.8.5.1 A coupling medium may be necessary to improvetransmission of the s
33、onic pulse. In this case, apply a lightcoating of the coupling medium to the faces of the testspecimens that will contact the transducers. Alternatively, “softrubber” tipped transducers can be effective if a fully noninva-sive measurement is needed.NOTE 2The following coupling media may be used: hyd
34、roxyethylcellulose, petroleum jelly, high vacuum greases and water-based ultra-sonic couplants. However these may be difficult to remove subsequently.Distilled water can provide a very satisfactory coupling medium withoutsignificant end effects, and surface water may be removed subsequently bydrying
35、. Manufacturers offer soft rubber-tipped transducers suitable fornoninvasive measurements. With these transducers either good loadcontrol or accurate determination of the soft rubber length is essentialduring measurement if good reproducibility is to be achieved.8.6 Bring transducer faces into intim
36、ate contact but do notexceed manufacturers recommended contact pressures.8.7 Follow the vendors instructions to adjust the instrumen-tation to match the transducer frequency to give good visualamplitude resolution.8.8 Determine T0, the travel time (zero correction) measuredin seconds, associated wit
37、h the electronic circuits in thepulse-propagation instrument and coupling (Fig. 2(a). Ensurethat the repeatability of the measurement is of sufficientprecision to meet the required accuracy in Youngs modulus.FIG. 2 Schematic Illustrating (a) Zero Time (T0) Measurement for Face to Face Contact Betwee
38、n Transducers and (b) Pulse Travel Time(Tt) Measurement for the Sample Positioned Between the Transducers, based upon a Simplified Received Wave Signal and theIdealized Case where the Onset of the First Peak has been DetectedC7690938.9 Adjust the gain of electronic components to give goodvisual ampl
39、itude resolution.8.10 Determine Tt, the total traverse time from the traces(Fig. 2(b). Ensure that the repeatability of the measurement isof sufficient precision to meet the required accuracy in Youngsmodulus.8.11 It is good practice to monitor the performance andreproducibility of the sonic velocit
40、y equipment by periodicallytesting a reference sample of similar material and geometry tothat typically used by the operator. This will monitor driftarising from deterioration in transducer performance. Theaccuracy of absolute velocity measurements can be checked byusing certified standards calibrat
41、ed using a method such as theresonant bar technique (Test Method C 747). Standards need tobe representative of the material being tested and have a similargeometry.9. Calculation9.1 Velocity of Signal:V 5LTt2 T02 Te(3)where:V = velocity of signal, m/s,L = specimen length, m,Tt= traverse time, s,T0=
42、travel time, s, andTe= end correction time, s.9.2 Since graphites are not necessarily isotropic, the valueof Youngs modulus cannot be determined solely from avelocity measurement in one direction. However, an approxi-mate Youngs modulus for each direction may be obtainedusing Eq 4 (based upon an ass
43、umed Poissons ratio of 0.2).More accurate estimates of the Youngs moduli require thedetermination of the full compliance matrix from a set ofmeasurements of longitudinal and shear wave velocities alongprincipal axes together with measurements of a sonic velocityat 45 to the principal axes.E 50.9 rV2
44、(4)where:E = Youngs modulus, Pa (approximate),r = density, kg/m3, andV = velocity of sound, m/s.9.3 Conversion FactorsSee IEEE/ASTM SI 10.10. Report10.1 The report shall include the following:10.1.1 Specimen dimensions, weight, and test specimenorientation with respect to forming direction.10.1.2 So
45、nic velocity for each specimen, along with adescription of the method of time of flight determination.10.1.3 Density of each specimen, if calculated.10.1.4 Youngs modulus of each specimen, if calculated.10.1.5 It is recommended that average and standard devia-tion values be included for each group o
46、f specimens.10.1.6 Environmental conditions of test, including tempera-ture, humidity, and special atmosphere (if used).10.1.7 The wavelength or frequency of the transmitted pulseand sonic velocity equipment identification.NOTE 3Due to the strong frequency dependent attenuation of ultra-sound in gra
47、phite, the frequency of the transmitted pulse may becompletely different from the nominal ultrasonic transducer frequency.10.1.8 Method of coupling the transducers to the specimenalong with any end correction times used.10.1.9 As available, complete identification of the materialbeing tested includi
48、ng manufacturer, grade identification, lotnumber and grain orientation, original billet size, and specimensampling plan.10.2 It is advisable to store the full trace of the receivedsignal for each measurement.11. Precision and Bias511.1 A round-robin series of sonic velocity measurementswas performed
49、 on four different materials by two laboratories.In the reported analysis of the data, the parameter Cnis set tounity. Conclusions 11.2 to 11.6 were drawn initially.11.2 Twelve samples of each material were measured. In all,four sets of measurements were made on each group of twelvesamples for a total of sixteen sets of data. The averagecoefficient of variance for the sixteen sets was 3.8 %, which isindicative of the sample-to-sample and measurement-to-measurement variation in each set of twelve.11.3 There was a difference between the
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