1、Designation: C769 09C769 15 An American National StandardStandard Test Method forSonic Velocity in Manufactured Carbon and GraphiteMaterials for Use in Obtaining an Approximate Value ofYoungs Modulus1This standard is issued under the fixed designation C769; the number immediately following the desig
2、nation indicates the 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.1. Scope Scope*1.1 This test method covers
3、a procedure for measuring the sonic velocity in manufactured carbon and graphite which can beused to obtain an approximate value of Youngs modulus.1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.1.3 This standard does not
4、purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:2C
5、559 Test Method for Bulk Density by Physical Measurements of Manufactured Carbon and Graphite ArticlesC747 Test Method for Moduli of Elasticity and Fundamental Frequencies of Carbon and Graphite Materials by Sonic ResonanceIEEE/ASTM SI 10 Standard for Use of the International System of Units (SI) (t
6、he Modern Metric System)3. Terminology3.1 Definitions:3.1.1 elastic modulus, nthe ratio of stress to strain, in the stress range where Hookes law is valid.3.1.2 Youngs modulus or modulus of elasticity (E), nthe elastic modulus in tension or compression.3.2 Definitions of Terms Specific to This Stand
7、ard:3.2.1 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.3.2.2 longitudinal sonic pulsea sonic pulse in which the displacements are in the direc
8、tion of propagation of the pulse.3.2.3 pulse travel time, (Tt)the total time, measured in seconds, required for the sonic pulse to traverse the specimen beingtested, and for the associated electronic signals to traverse the transducer coupling medium and electronic circuits of thepulse-propagation s
9、ystem.3.2.4 zero time, (T0)the travel time (correction factor), measured in seconds, associated with the transducer coupling mediumand electronic circuits in the pulse-propagation system.4. Summary of Test Method4.1 The velocity of longitudinal sound waves passing through the test specimen is determ
10、ined by measuring the distance throughthe specimen and dividing by the time lapse, between the transmitted pulse and the received pulse.3,4 Provided the wavelength of1 This test method is under the jurisdiction ofASTM Committee D02 on Petroleum Products, Liquid Fuels, and Lubricantsand is the direct
11、 responsibility of SubcommitteeD02.F0 on Manufactured Carbon and Graphite Products.Current edition approved June 1, 2009Dec. 1, 2015. Published July 2009January 2016. Originally approved in 1980. Last previous edition approved in 20052009 asC76998(2005).C769 09. DOI: 10.1520/C0769-09.10.1520/C0769-1
12、5.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.3 Schreiber, Anderson, and Soga, Elastic Constants and Thei
13、r Measurement, McGraw-Hill Book Co., 1221 Avenue of the Americas, New York, NY 10020, 1973.4 American Institute of Physics Handbook , 3rd ed., McGraw-Hill Book Co., 1221 Avenue of the Americas, New York, NY 10020, 1972, pp. 398ff.This document is not an ASTM standard and is intended only to provide
14、the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the stan
15、dard as published by ASTM is to be considered the official document.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1the transmitted pulse is a sufficiently small fractio
16、n of the sample laterlateral dimensions, a value of Youngs modulus for isotropicgraphite can then be obtained using Eq 1 and Eq 2:E 5CvV2 (1)where:E = Youngs modulus of elasticity, Pa, = density, kg/m3,V = longitudinal signal velocity, m/s, andCv = Poissons factor.The Poissons factor, C, is related
17、to Poissons ratio, , by the equation:C511!122!12 (2)If Poissons ratio is unknown, it can be assumed as an approximation in the method. For nuclear graphites, a typical Poissonsratio of 0.2 corresponds to a Poissons factor of 0.9.If the wavelength is not a small fraction of the sample lateral dimensi
18、ons, and instead is much larger than the specimen lateraldimensions, then the Youngs modulus, E is given by Eq 1 with C set to one rather than being determined by Eq 2.5. Significance and Use5.1 Sonic velocity measurements are useful for comparing materials.materials with similar elastic properties,
19、 dimensions, andmicrostructure.5.2 AEq 1 value for Youngs modulus provides an accurate value of Youngs modulus only for isotropic, non-attenuative, andnon-dispersive materials of infinite dimensions. For non-isotropic graphite, Eq 1 can be obtained for manymodified to take intoaccount the Poissons r
20、atios in all directions.As graphite is a strongly attenuative material, the value of Youngs modulus obtainedwith Eq 1 applications, which will be in good agreement with the value obtained by otherdependent on specimen length. If thespecimen lateral dimensions are not large compared to the wavelength
21、 of the propagated pulse, then the value of Youngs modulusobtained with Eq 1 methods, such as in Test Methodwill be dependent on the specimen C747. lateral dimensions. The accuracyof the Youngs modulus calculated from Eq 1 will also depend upon the uncertainty in Poissons ratio and its impact on the
22、evaluation of the Poissons factor in Eq 2. However, a value for Youngs modulus can be obtained for many applications, whichis often in good agreement with the value obtained by other more accurate methods, such as in Test Method C747. The technicalissues and typical values of corresponding uncertain
23、ties are discussed in detail in STP 1578.55.3 If the grain size of the carbon or graphite is greater than or about equal to the wavelength of the sonic pulse, the methodmay not be providing a value of Youngs modulus representative of the bulk material. Therefore, it would be desirablerecom-mended to
24、 test a lower frequency (longer wavelength) to demonstrate that velocity is independent of frequency.the range ofobtained velocity values are within an acceptable level of accuracy. Significant signal attenuation should be expected when thegrain size of the material is greater than or about equal to
25、 the wavelength of the transmitted sonic pulse.pulse or the material ismore porous than would be expected for an as-manufactured graphite.NOTE 1Due to frequency dependent attenuation in graphite, the wavelength of the sonic pulse through the test specimen is not necessarily the sameas the wavelength
26、 of the transmitting transducer.5.4 If the sample is only a few grains thick, the acceptability of the methods application should be demonstrated by initiallyperforming measurements on a series of tests covering a range of sample lengths between the proposed test length and a test lengthincorporatin
27、g sufficient grains to adequately represent the bulk material.6. Apparatus6.1 Driving Circuit, consisting of an ultrasonic pulse generator.6.1.1 The user should select a pulse frequency to suit the material microstructure and specimen elastic properties anddimensions being tested. High frequencies a
28、re attenuated by carbon and graphite materials and, while typical practicablefrequencies lie in the range 0.50.5 MHz to 2.6 MHz, the user may show that frequencies outside this range are acceptable.6.2 Transducer, input, with suitable coupling medium (see 8.5).6.3 Transducer, output, with suitable c
29、oupling medium (see 8.5).6.3.1 The signal output will depend upon the characteristics of the chosen transducers and pulser-receiver and the test material.It is recommended that the user analyses the input and output frequency spectra to determine optimum conditions. Band pass filtersand narrow band
30、transducers may be used to simplify the signal output which could improve the measurement of the time of flight.5 ASTM Selected Technical Papers, STP 1578, Graphite Testing for Nuclear Applications: The Significance of Test Specimen Volume and Geometry and the StatisticalSignificance of Test Specime
31、n Population, 2014, edited by Tzelepi and Carroll.C769 1526.4 Computer, with analogue to digital converter, or oscilloscope, and external trigger from driving circuit.6.5 See Fig. 1 for a typical schematic setup.NOTE 2Some manufacturers combine items 6.1 and 6.4 into a single package with direct tim
32、e readout. Such apparatus can operate satisfactorily,provided the frequency of the propagated pulse is already known, in order to check that wavelength requirements for the method are satisfied.7. Test Specimen7.1 Selection and Preparation of SpecimensTake special care to assure obtaining representa
33、tive specimens that are straight,uniform in cross section, and free of extraneous liquids. The specimen end faces shall be perpendicular to the specimen cylindricalsurface to within 0.125 mm 0.125 mm total indicator reading.7.2 Measurement of Weight and DimensionsDetermine the weight and the average
34、 specimen dimensions to within 60.2 %.7.3 Limitations on DimensionsThese cannot be precisely specified as they will depend upon the properties of the materialbeing tested. tested and the experimental setup (for example, transducer frequency). In order to satisfy the theory that supports Eq1, as a gu
35、ide, the specimen should have a diameter that is at least a factor two, and ideally a factor five, greater than the wavelengthof sound in the material under test. In practice, the length of the specimen will be determined taking account of the comments in5.3 and 5.4.7.4 Limitations on Ultrasonic Pul
36、se FrequencyGenerally speaking, a better accuracy of time of flight will be obtained athigher frequencies. However, attenuation increases at higher frequencies leading to weak and distorted signals.8. Procedure8.1 For any given apparatus and choice of coupling medium, it is necessary to follow proce
37、dures to quantify the zero time, T0,and end correction time, Te, correction factors. T0 will be dependent upon the type of transducers and their performance over timeand should be regularly checked (see 8.8). It must be quantified if the test set up setup is changed. Te should be small and reflectst
38、he interaction between the coupling medium and the test material. Te should be determined once for a specific measurement setupand test material.8.1.1 Determine whether an end correction time, Te, is evident in the time of flight by performing time of flight measurementson various length samples tak
39、en from a single bar.As modulus is likely to vary from sample to sample the recommended approachis to continually bisect a long rod, measuring each bi-section, until the required lower limit is reached. The end correction time,Te, is obtained from a regression fit to a graph of time of flight versus
40、 sample length.8.2 Measure and weigh the test specimen as in 7.2.8.3 Calculate the density of the test specimen in accordance with Test Method C559.8.4 Connect the apparatus as shown in Fig. 1, and refer to equipment manufacturers instructions for setup precautions. Allowadequate time for equipment
41、warm-up and stabilization.8.5 Place the transducers against the test specimen end faces.8.5.1 A coupling medium may be necessary to improve transmission of the sonic pulse. In this case, apply a light coating ofthe coupling medium to the faces of the test specimens that will contact the transducers.
42、 Alternatively, “soft rubber” tippedrubber-tipped transducers can be effective if a fully noninvasive measurement is needed.FIG. 1 Basic Experimental Arrangement for the Ultrasonic Pulsed-Wave Transit Time TechniqueC769 153NOTE 3The following coupling media may be used: hydroxyethyl cellulose, petro
43、leum jelly, high vacuum greases and water-based ultrasoniccouplants. However these may be difficult to remove subsequently. Distilled water can provide a very satisfactory coupling medium without significantend effects, and surface water may be removed subsequently by drying. Manufacturers offer sof
44、t rubber-tipped transducers suitable for noninvasivemeasurements. With these transducers either good load control or accurate determination of the soft rubber length is essential during measurement if goodreproducibility is to be achieved.8.6 Bring transducer faces into intimate contact but do not e
45、xceed manufacturers recommended contact pressures.8.7 Follow the vendors instructions to adjust the instrumentation to match the transducer frequency to give good visualamplitude resolution.8.8 Determine T0, the travel time (zero correction) measured in seconds, associated with the electronic circui
46、ts in thepulse-propagation instrument and coupling (Fig. 2(a). Ensure that the repeatability of the measurement is of sufficient precisionto meet the required accuracy in Youngs modulus.8.9 Adjust the gain of electronic components to give good visual amplitude resolution.8.10 Determine Tt, the total
47、 traverse time from the traces (Fig. 2(b). Ensure that the repeatability of the measurement is ofsufficient precision to meet the required accuracy in Youngs modulus.8.11 It is good practice to monitor the performance and reproducibility of the sonic velocity equipment by periodically testinga refer
48、ence sample of similar material and geometry to that typically used by the operator. This will monitor drift arising fromdeterioration in transducer performance. The accuracy of absolute velocity measurements can be checked by using certifiedstandards calibrated using a method such as the resonant b
49、ar technique (Test Method C747). Standards need to be representativeof the material being tested and have a similar geometry.FIG. 2 Schematic Illustrating (a) Zero Time (T0) Measurement for Face to Face Contact Between Transducers and (b) Pulse Travel Time(Tt) Measurement for the Sample Positioned Between the Transducers, based upon a Simplified Received Wave Signal and the Ideal-ized Case where the Onset of the First Peak has been DetectedC769 1549. Calculation9.1 Velocity of Signal:V 5 LTt 2T02Te(3)where:V = velocity o
