1、Designation: C 1331 01 (Reapproved 2007)Standard Test Method forMeasuring Ultrasonic Velocity in Advanced Ceramics withBroadband Pulse-Echo Cross-Correlation Method1This standard is issued under the fixed designation C 1331; the number immediately following the designation indicates the year oforigi
2、nal adoption or, in the case 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 describes a procedure for measurementof ultras
3、onic velocity in structural engineering solids such asmonolithic ceramics, toughened ceramics, and ceramic matrixcomposites.1.2 This test method is based on the broadband pulse-echocontact ultrasonic method. The procedure involves a computer-implemented, frequency-domain method for precise measure-m
4、ent of time delays between pairs of echoes returned by theback surface of a test sample or part.1.3 This test method describes a procedure for using adigital cross-correlation algorithm for velocity measurement.The cross-correlation function yields a time delay between anytwo echo waveforms (1).22.
5、Referenced Documents2.1 ASTM Standards:3B311 Test Method for Density Determination for PowderMetallurgy (P/M) Materials Containing Less Than TwoPercent PorosityC 373 Test Method for Water Absorption, Bulk Density,Apparent Porosity, and Apparent Specific Gravity of FiredWhiteware ProductsE 494 Practi
6、ce for Measuring Ultrasonic Velocity in Mate-rialsE 1316 Terminology for Nondestructive Examinations2.2 ASNT Document:Recommended Practice SNT-TC-1A for NondestructiveTesting Personnel Qualification and Certification42.3 Military Standard:MIL-STD-410 Nondestructive Testing Personnel Qualifica-tion a
7、nd Certification52.4 Additional references are cited in the text and at end ofthis document.3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 back surfacethe surface of a test sample which isopposite to the front surface and from which back surfaceechoes are returned at normal i
8、ncidence directly to the trans-ducer.3.1.2 bandwidththe frequency range of an ultrasonicprobe, defined by convention as the difference between thelower and upper frequencies at which the signal amplitude is 6dB down from the frequency at which maximum signalamplitude occurs.3.1.3 broadband transduce
9、ran ultrasonic transducer ca-pable of sending and receiving undistorted signals over a broadbandwidth, consisting of a thin damped piezocrystal in abuffered probe (search unit).3.1.4 buffered probean ultrasonic search unit as defined inTerminology E 1316 but containing a delay line, or buffer rod,to
10、 which the piezocrystal is affixed within the search unithousing and which separates the piezocrystal from the testsample (Fig. 1).3.1.5 buffer rodan integral part of a buffered probe,usually a quartz or fused silica cylinder that provides a timedelay between the excitation pulse from the piezocryst
11、al andechoes returning from a sample coupled to the free end of thebuffer rod.3.1.6 cross-correlation functionthe cross-correlationfunction, implemented by a digital algorithm, yields a timedelay between any two (ultrasonic) echo waveforms. This timeis used to determine velocity (1).3.1.7 dispersion
12、variation of ultrasonic velocity as a func-tion of wavelength, that is, frequency dependence of velocity.3.1.8 front surfacethe surface of a test sample to whichthe buffer rod is coupled at normal incidence (designated as testsurface in Terminology E 1316.1This test method is under the jurisdiction
13、of ASTM Committee C28 onAdvanced Ceramics and is the direct responsibility of Subcommittee C28.03 onPhysical Properties and Performance.Current edition approved Aug. 1, 2007. Published August 2007. Originallyapproved in 1996. Last previous edition approved in 2001 as C 133101.2The boldface numbers i
14、n parentheses refer to the list of references at the end ofthis test method.3For 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 onth
15、e ASTM website.4Available fromAmerican Society for NondestructiveTesting (ASNT), P.O. Box28518, 1711 Arlingate Ln., Columbus, OH 43228-0518, http:/www.asnt.org.5Available from Standardization Documents Order Desk, DODSSP, Bldg. 4,Section D, 700 Robbins Ave., Philadelphia, PA 19111-5098, http:/www.do
16、dssp.daps.mil.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.1.9 group velocityvelocity of a broadband ultrasonicpulse consisting of many different component wavelengths.3.1.10 test samplea solid coupon or material part thatmeets
17、the constraints needed to make the ultrasonic velocitymeasurements described herein, that is, a test sample or parthaving flat, parallel, smooth, preferably ground or polishedopposing (front and back) surfaces, and having no discreteflaws or anomalies unrepresentative of the inherent propertiesof th
18、e material.3.1.11 wavelength (l)distance that sound (of a particularfrequency) travels during one period (during one oscillation), l= v/f, where v is the velocity of sound in the material andwhere velocity is measured in cm/s, frequency in MHz, andwavelength in cm, herein.3.2 Other terms or nomencla
19、ture used in this test method aredefined in Terminology E 1316.4. Significance and Use4.1 The velocity measurements described in this test methodmay be used to characterize material variations that affectmechanical or physical properties. This procedure is useful formeasuring variations in microstru
20、ctural features such as grainstructure, pore fractions, and density variations in monolithicceramics.4.2 Velocity measurements described herein can assesssubtle variations in porosity within a given material or com-ponent, as, for example, in ceramic superconductors andstructural ceramic specimens (
21、2,3).4.3 In addition to ceramics and ceramic composites, thevelocity measurements described herein may be applied topolycrystalline and single crystal metals, metal matrix com-posites, and polymer matrix composites.4.4 An alternative technique for velocity measurement isgiven in Practice E 494.5. Pe
22、rsonnel Qualifications5.1 It is recommended that nondestructive evaluation/examination personnel applying this test method be qualified inaccordance with a nationally-recognized personnel qualifica-tion practice or standard such asASNT SNT-TC-1A, MILSTD410, or a similar document. The qualification p
23、ractice orstandard used and its applicable revision(s) should be specifiedin a contractual agreement.5.2 Knowledge of the principles of ultrasonic testing isrequired. Personnel applying this test method should be expe-rienced practitioners of ultrasonic examinations and associatedmethods for signal
24、acquisition, processing, and interpretation.5.3 Personnel should have proficiency in computer signalprocessing and the use of digital methods for time andfrequency domain signal analysis. Familiarity with Fourier andassociated transforms for ultrasonic spectrum analysis is re-quired.6. Apparatus and
25、 Test Sample6.1 Instrumentation (Fig. 1 and Fig. 2) for broadbandcross-correlation pulse-echo ultrasonic velocity measurementshould include the following:6.1.1 Buffered Probe:NOTE 1B1and B2are first and second back surface echoes, respec-tively, and T is time interval between the echoes.FIG. 1 Cross
26、 Section of Buffered Ultrasonic Probe (a) andPrinciple Echoes (b) for Velocity MeasurementFIG. 2 Instrumentation Diagram for Acquiring and Separately Windowing Two Successive Back Surface Echoes, B1and B2, for Cross-Correlation Velocity MeasurementC 1331 01 (2007)26.1.1.1 The buffer rod, which is an
27、 integral part of the probe(search unit), should be a right cylinder with smooth flat endsnormal to the axis of the probe.6.1.1.2 The center frequency of the buffered probe shouldproduce a wavelength within the sample that is less than onefifth of the thickness of the sample.6.1.1.3 The buffer rod l
28、ength, that is, time delay should bethree times the interval between two successive back surfaceechoes.6.1.1.4 The wave mode may be either longitudinal or shear.6.1.2 Pulser-Receiver, with a bandwidth that is at leasttwice that of the buffered probe. The bandwidth should includefrequencies in the ra
29、nge from 100 kHz to over 100 MHz.6.1.2.1 The pulser-receiver should have provisions for con-trolling the pulse repetition rate, pulse energy level, pulsedamping, and received signal gain.6.1.2.2 The pulser-receiver should provide a synchroniza-tion pulse and signal output connector.6.1.3 Waveform Di
30、gitizing Oscilloscope (A/D Board), busprogrammable, to window and digitize the echo waveforms.6.1.3.1 A minimum 512-element waveform array with amaximum data sampling interval of 1.95 ns is recommended.For better waveform resolution, a 1024-element array with adata sampling interval of 0.97 ns may b
31、e needed.6.1.3.2 Vertical Amplifier, bus programmable module.6.1.3.3 Time Base, bus programmable module with a reso-lution of at least 5 ns per division and several time base rangesincluding a fundamental time base of at least 200 ns.6.1.4 Digital Time Delay Module, bus programmable, tointroduce a k
32、nown time delay between the start of two separatetime gates, that is, windows each of which containing one oftwo successive back surface echoes.6.1.4.1 Separate windows are preferred for waveform digi-tization. Each waveform should occupy from 60 to 80 % of thewindow.6.1.4.2 The time synthesizer sho
33、uld have an accuracy of 61ns with a precision of 60.1 ns.6.1.5 Video Monitors, (optional) one analog, one digital forreal-time visual inspection of echo waveforms and for makinginteractive manual adjustments to the data acquisition controls.6.1.6 Computer, with adequate speed and storage capacityto
34、provide needed software control, data storage, and graphicscapability.The software should include a fast Fourier transform(FFT) algorithm package containing the cross-correlation al-gorithm.6.1.7 Couplant Layer, to establish good signal transferbetween the buffer rod and test sample. The layer shoul
35、d be asthin as possible to minimize couplant resonances and distortionof the echo waveforms.6.1.7.1 The couplant should not be absorbed by or beotherwise deleterious to the test sample.6.1.7.2 Dry coupling with a thin polymer may be usedwhere liquid contamination by or absorption of liquids by thete
36、st sample or part must be avoided.6.2 The test sample or part should have flat parallel oppos-ing surfaces in the region where the velocity measurements aremade. This will assure good coupling between the transducerand sample and also produce valid echoes for velocity mea-surements.6.2.1 Lack of pre
37、cision in the measurement of the testsample thickness can undermine the nanosecond precision withwhich pulse-echo travel times can be measured. Therefore, thesample thickness should be measurable to an accuracy of60.1 % or better.6.2.2 For most engineering solids, the sample thicknessshould be at le
38、ast 2.5 mm. There is a practical upper bound onsample thickness, for example, if the sample is too thick, theremay be considerable signal attenuation, beam spreading, anddispersion that render the signal useless.7. Procedure7.1 Use instrument control software routines to start andcontrol the interfa
39、ce bus; perform procedures such as optimiz-ing intensity, voltage, and time on the waveform digitizingoscilloscope; control the digital time delay module; and ac-quire, store, and process data.7.1.1 A cross-correlation algorithm should be part of theFFT software.7.1.2 The arguments needed to impleme
40、nt the cross-correlation algorithm are the time domain waveform arrays,that is, digitized echoes B1and B2(Fig. 1).7.2 Prepare samples with front and back surfaces that aresufficiently smooth, flat, and parallel to allow measurement ofthe test sample thickness to an accuracy of 0.1 % or better.7.3 Co
41、uple the sample to the transducer to obtain two strongback surface echoes.7.3.1 Apply pressure to minimize the couplant layer thick-ness. A backing fixture may be necessary to apply pressure.7.3.2 Care shall be taken to avoid coupling the sample to thebacking fixture and thereby losing echo signal s
42、trength byleakage.7.3.3 A dry, hard rubber or composite material with arough-machined or sawtooth surface is recommended for thebacking fixture.7.4 Determine the precise positions, in the time domain, ofthe start of the windows containing echo waveforms B1and B2and program the digital time delay mod
43、ule to sequentially setthese delays.7.4.1 The oscilloscope time base should be adjusted so thateach waveform occupies 60 to 80 % of its window.Window fillmay be as low as 20 % and still produce acceptable results.7.4.2 During data acquisition, the time synthesizer shouldsequence through the predeter
44、mined time positions.7.5 The waveform digitizing oscilloscope (A/D device)should be programmed to automatically maximize the echowaveform amplitude and intensity settings.7.6 Digitize back surface echoes B1and B2into separate512-element waveform arrays. Signal averaging may be nec-essary to accurate
45、ly capture subtle features of the waveforms.Signals with high SNR (signal-to-noise ratio) can be accuratelydigitized by only a few signal averagings while signals withlow SNR may require as much as 32 signal averagings.C 1331 01 (2007)37.7 Ultrasonic velocity is determined by measuring the timedelay
46、 between two successive echoes returned by the backsurface of the test sample. These are shown as the twoseparately-windowed echoes B1and B2(Fig. 3).7.7.1 Echoes B1and B2are separately windowed to getmaximum time and voltage resolution. This is done by preset-ting the digital time delay module to pr
47、oduce two windows thatcapture echoes B1and B2with window start times D1and D2,respectively.7.7.1.1 The centroid of echo B1occurs at time D1+T1.7.7.1.2 The centroid of echo B2occurs at time D2+T2.7.7.2 If the sample thickness and other constraints are met,it should be possible to digitally overlap ec
48、hoes B1and B2asin Fig. 4. Dispersion has occurred if echo B2is spread outrelative to B1and does not have the same zero crossings as B1.If too pronounced, dispersion and beam spreading may beavoided by reducing the sample thickness.7.7.3 The travel time interval T between B1and B2is givenby T = C + W
49、 , where W = D2 D1and C is the echodisplacement time obtained by means of the cross-correlationalgorithm.7.7.4 The cross-correlation algorithm is applied to the echowaveforms B1and B2to provide the value for the echodisplacement time C.7.8 After acquiring waveform records for echoes B1and B2,use the cross-correlation algorithm to obtain the echo displace-ment time,C , relative to the zero reference.7.9 Use the cross-correlation algorithm which transforms B1and B2into the frequency domain, multiplies the complexconjugate of B2(f)byB1(f), and transforms the result back
