ASTM C1331-01(2012)
(Test Method)Standard Test Method for Measuring Ultrasonic Velocity in Advanced Ceramics with Broadband Pulse-Echo Cross-Correlation Method
Standard Test Method for Measuring Ultrasonic Velocity in Advanced Ceramics with Broadband Pulse-Echo Cross-Correlation Method
SIGNIFICANCE AND USE
4.1 The velocity measurements described in this test method may be used to characterize material variations that affect mechanical or physical properties. This procedure is useful for measuring variations in microstructural features such as grain structure, pore fractions, and density variations in monolithic ceramics.
4.2 Velocity measurements described herein can assess subtle variations in porosity within a given material or component, as, for example, in ceramic superconductors and structural ceramic specimens (2,3).
4.3 In addition to ceramics and ceramic composites, the velocity measurements described herein may be applied to polycrystalline and single crystal metals, metal matrix composites, and polymer matrix composites.
4.4 An alternative technique for velocity measurement is given in Practice E494.
SCOPE
1.1 This test method describes a procedure for measurement of ultrasonic velocity in structural engineering solids such as monolithic ceramics, toughened ceramics, and ceramic matrix composites.
1.2 This test method is based on the broadband pulse-echo contact ultrasonic method. The procedure involves a computer-implemented, frequency-domain method for precise measurement of time delays between pairs of echoes returned by the back surface of a test sample or part.
1.3 This test method describes a procedure for using a digital cross-correlation algorithm for velocity measurement. The cross-correlation function yields a time delay between any two echo waveforms (1).2
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Standards Content (Sample)
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Contact ASTM International (www.astm.org) for the latest information
Designation: C1331 − 01 (Reapproved 2012)
Standard Test Method for
Measuring Ultrasonic Velocity in Advanced Ceramics with
Broadband Pulse-Echo Cross-Correlation Method
This standard is issued under the fixed designation C1331; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope E494Practice for Measuring Ultrasonic Velocity in Materi-
als
1.1 Thistestmethoddescribesaprocedureformeasurement
E1316Terminology for Nondestructive Examinations
of ultrasonic velocity in structural engineering solids such as
2.2 ASNT Document:
monolithic ceramics, toughened ceramics, and ceramic matrix
Recommended Practice SNT-TC-1A for Nondestructive
composites.
Testing Personnel Qualification and Certification
1.2 This test method is based on the broadband pulse-echo
2.3 Military Standard:
contactultrasonicmethod.Theprocedureinvolvesacomputer-
MIL-STD-410Nondestructive Testing Personnel Qualifica-
implemented, frequency-domain method for precise measure-
tion and Certification
ment of time delays between pairs of echoes returned by the
2.4 Additional references are cited in the text and at end of
back surface of a test sample or part.
this document.
1.3 This test method describes a procedure for using a
digital cross-correlation algorithm for velocity measurement.
Thecross-correlationfunctionyieldsatimedelaybetweenany
3. Terminology
two echo waveforms (1).
3.1 Definitions of Terms Specific to This Standard:
1.4 This international standard was developed in accor-
3.1.1 back surface—the surface of a test sample which is
dance with internationally recognized principles on standard-
opposite to the front surface and from which back surface
ization established in the Decision on Principles for the
echoes are returned at normal incidence directly to the trans-
Development of International Standards, Guides and Recom-
ducer.
mendations issued by the World Trade Organization Technical
3.1.2 bandwidth—the frequency range of an ultrasonic
Barriers to Trade (TBT) Committee.
probe, defined by convention as the difference between the
lowerandupperfrequenciesatwhichthesignalamplitudeis6
2. Referenced Documents
3 dB down from the frequency at which maximum signal
2.1 ASTM Standards:
amplitude occurs.
B311Test Method for Density of Powder Metallurgy (PM)
3.1.3 broadband transducer—an ultrasonic transducer ca-
Materials Containing Less Than Two Percent Porosity
pableofsendingandreceivingundistortedsignalsoverabroad
C373Test Methods for Determination of Water Absorption
bandwidth, consisting of a thin damped piezocrystal in a
andAssociated Properties byVacuum Method for Pressed
buffered probe (search unit).
Ceramic Tiles and Glass Tiles and Boil Method for
Extruded Ceramic Tiles and Non-tile Fired Ceramic
3.1.4 buffered probe—anultrasonicsearchunitasdefinedin
Whiteware Products
Terminology E1316 but containing a delay line, or buffer rod,
to which the piezocrystal is affixed within the search unit
housing and which separates the piezocrystal from the test
This test method is under the jurisdiction of ASTM Committee E07 on
sample (Fig. 1).
Nondestructive Testing and is the direct responsibility of Subcommittee E07.06 on
Ultrasonic Method. 3.1.5 buffer rod—an integral part of a buffered probe,
Current edition approved Aug. 1, 2012. Published November 2012. Originally
usually a quartz or fused silica cylinder that provides a time
approved in 1996. Last previous edition approved in 2007 as C1331– 01 (2007).
DOI: 10.1520/C1331-01R12.
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
this test method. AvailablefromAmericanSocietyforNondestructiveTesting(ASNT),P.O.Box
For referenced ASTM standards, visit the ASTM website, www.astm.org, or 28518, 1711 Arlingate Ln., Columbus, OH 43228-0518, http://www.asnt.org.
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Available from Standardization Documents Order Desk, DODSSP, Bldg. 4,
Standardsvolume information,referto thestandard’sDocumentSummary page on Section D, 700 Robbins Ave., Philadelphia, PA 19111-5098, http://
the ASTM website. www.dodssp.daps.mil.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C1331 − 01 (2012)
component, as, for example, in ceramic superconductors and
structural ceramic specimens (2,3).
4.3 In addition to ceramics and ceramic composites, the
velocity measurements described herein may be applied to
polycrystalline and single crystal metals, metal matrix
composites, and polymer matrix composites.
4.4 An alternative technique for velocity measurement is
given in Practice E494.
5. Personnel Qualifications
5.1 It is recommended that nondestructive evaluation/
examinationpersonnelapplyingthistestmethodbequalifiedin
accordance with a nationally-recognized personnel qualifica-
NOTE 1—B and B are first and second back surface echoes,
1 2
tionpracticeorstandardsuchasASNTSNT-TC-1A,MILSTD
respectively, and T is time interval between the echoes.
410, or a similar document. The qualification practice or
FIG. 1 Cross Section of Buffered Ultrasonic Probe (a) and Prin-
standardusedanditsapplicablerevision(s)shouldbespecified
ciple Echoes (b) for Velocity Measurement
in a contractual agreement.
5.2 Knowledge of the principles of ultrasonic testing is
delay between the excitation pulse from the piezocrystal and
required. Personnel applying this test method should be expe-
echoes returning from a sample coupled to the free end of the
riencedpractitionersofultrasonicexaminationsandassociated
buffer rod.
methods for signal acquisition, processing, and interpretation.
3.1.6 cross-correlation function—the cross-correlation
5.3 Personnel should have proficiency in computer signal
function, implemented by a digital algorithm, yields a time
processing and the use of digital methods for time and
delaybetweenanytwo(ultrasonic)echowaveforms.Thistime
frequencydomainsignalanalysis.FamiliaritywithFourierand
is used to determine velocity (1).
associated transforms for ultrasonic spectrum analysis is re-
3.1.7 dispersion—variation of ultrasonic velocity as a func-
quired.
tion of wavelength, that is, frequency dependence of velocity.
3.1.8 front surface—the surface of a test sample to which
6. Apparatus and Test Sample
thebufferrodiscoupledatnormalincidence(designatedastest
6.1 Instrumentation (Fig. 1 and Fig. 2) for broadband
surface in Terminology E1316.
cross-correlation pulse-echo ultrasonic velocity measurement
3.1.9 group velocity—velocity of a broadband ultrasonic
should include the following:
pulse consisting of many different component wavelengths.
6.1.1 Buffered Probe:
3.1.10 test sample—a solid coupon or material part that
6.1.1.1 Thebufferrod,whichisanintegralpartoftheprobe
meets the constraints needed to make the ultrasonic velocity (search unit), should be a right cylinder with smooth flat ends
measurements described herein, that is, a test sample or part
normal to the axis of the probe.
having flat, parallel, smooth, preferably ground or polished 6.1.1.2 The center frequency of the buffered probe should
opposing (front and back) surfaces, and having no discrete
produce a wavelength within the sample that is less than one
flaws or anomalies unrepresentative of the inherent properties
fifth of the thickness of the sample.
of the material.
6.1.1.3 The buffer rod length, that is, time delay should be
three times the interval between two successive back surface
3.1.11 wavelength (λ)—distance that sound (of a particular
echoes.
frequency)travelsduringoneperiod(duringoneoscillation), λ
6.1.1.4 The wave mode may be either longitudinal or shear.
= v/f, where v is the velocity of sound in the material and
6.1.2 Pulser-Receiver,withabandwidththatisatleasttwice
where velocity is measured in cm/µs, frequency in MHz, and
that of the buffered probe. The bandwidth should include
wavelength in cm, herein.
frequencies in the range from 100 kHz to over 100 MHz.
3.2 Othertermsornomenclatureusedinthistestmethodare
6.1.2.1 The pulser-receiver should have provisions for con-
defined in Terminology E1316.
trolling the pulse repetition rate, pulse energy level, pulse
damping, and received signal gain.
4. Significance and Use
6.1.2.2 The pulser-receiver should provide a synchroniza-
4.1 Thevelocitymeasurementsdescribedinthistestmethod
tion pulse and signal output connector.
may be used to characterize material variations that affect
6.1.3 Waveform Digitizing Oscilloscope (A/D Board), bus
mechanical or physical properties.This procedure is useful for
programmable, to window and digitize the echo waveforms.
measuring variations in microstructural features such as grain
6.1.3.1 A minimum 512-element waveform array with a
structure, pore fractions, and density variations in monolithic
maximum data sampling interval of 1.95 ns is recommended.
ceramics.
For better waveform resolution, a 1024-element array with a
4.2 Velocity measurements described herein can assess data sampling interval of 0.97 ns may be needed.
subtle variations in porosity within a given material or 6.1.3.2 Vertical Amplifier, bus programmable module.
C1331 − 01 (2012)
FIG. 2 Instrumentation Diagram for Acquiring and Separately Windowing Two Successive Back Surface Echoes,B andB , for Cross-
1 2
Correlation Velocity Measurement
6.1.3.3 Time Base, bus programmable module with a reso- 6.2.2 For most engineering solids, the sample thickness
lutionofatleast5nsperdivisionandseveraltimebaseranges should be at least 2.5 mm.There is a practical upper bound on
including a fundamental time base of at least 200 ns. sample thickness, for example, if the sample is too thick, there
6.1.4 Digital Time Delay Module, bus programmable, to may be considerable signal attenuation, beam spreading, and
introduceaknowntimedelaybetweenthestartoftwoseparate dispersion that render the signal useless.
time gates, that is, windows each of which containing one of
two successive back surface echoes. 7. Procedure
6.1.4.1 Separate windows are preferred for waveform digi-
7.1 Use instrument control software routines to start and
tization.Eachwaveformshouldoccupyfrom60to80%ofthe
control the interface bus; perform procedures such as optimiz-
window.
ing intensity, voltage, and time on the waveform digitizing
6.1.4.2 Thetimesynthesizershouldhaveanaccuracyof 61
oscilloscope; control the digital time delay module; and
ns with a precision of 60.1 ns.
acquire, store, and process data.
6.1.5 Video Monitors, (optional) one analog, one digital for
7.1.1 A cross-correlation algorithm should be part of the
real-time visual inspection of echo waveforms and for making
FFT software.
interactivemanualadjustmentstothedataacquisitioncontrols.
7.1.2 The arguments needed to implement the cross-
6.1.6 Computer,withadequatespeedandstoragecapacityto
correlation algorithm are the time domain waveform arrays,
provide needed software control, data storage, and graphics
that is, digitized echoes B and B (Fig. 1).
1 2
capability.ThesoftwareshouldincludeafastFouriertransform
(FFT) algorithm package containing the cross-correlation al-
7.2 Prepare samples with front and back surfaces that are
gorithm.
sufficiently smooth, flat, and parallel to allow measurement of
6.1.7 Couplant Layer, to establish good signal transfer
the test sample thickness to an accuracy of 0.1% or better.
between the buffer rod and test sample.The layer should be as
7.3 Couplethesampletothetransducertoobtaintwostrong
thinaspossibletominimizecouplantresonancesanddistortion
back surface echoes.
of the echo waveforms.
7.3.1 Apply pressure to minimize the couplant layer thick-
6.1.7.1 The couplant should not be absorbed by or be
ness. A backing fixture may be necessary to apply pressure.
otherwise deleterious to the test sample.
7.3.2 Careshallbetakentoavoidcouplingthesampletothe
6.1.7.2 Dry coupling with a thin polymer may be used
backing fixture and thereby losing echo signal strength by
where liquid contamination by or absorption of liquids by the
leakage.
test sample or part must be avoided.
7.3.3 A dry, hard rubber or composite material with a
6.2 The test sample or part should have flat parallel oppos-
rough-machined or sawtooth surface is recommended for the
ingsurfacesintheregionwherethevelocitymeasurementsare
backing fixture.
made. This will assure good coupling between the transducer
7.4 Determine the precise positions, in the time domain, of
and sample and also produce valid echoes for velocity mea-
thestartofthewindowscontainingechowaveformsB andB
surements.
1 2
and program the digital time delay module to sequentially set
6.2.1 Lack of precision in the measurement of the test
these delays.
samplethicknesscanunderminethenanosecondprecisionwith
which pulse-echo travel times can be measured.Therefore, the 7.4.1 The oscilloscope time base should be adjusted so that
sample thickness should be measurable to an accuracy of eachwaveformoccupies60to80%ofitswindow.Windowfill
60.1% or better. may be as low as 20% and still produce acceptable results.
C1331 − 01 (2012)
NOTE 1—Time delay, W, between the two window start times is predetermined. Time interval, T, between echoes B and B is calculated from T =
1 2
W+(T − T ).
2 1
FIG. 3 Separately Windowed and Digitized Back Surface EchoesB andB
1 2
7.7.1.2 The centroid of echo B occurs at time D +T .
2 2 2
7.7.2 If the sample thickness and other constraints are met,
itshouldbepossibletodigitallyoverlapechoes B and B asin
1 2
Fig.4.DispersionhasoccurredifechoB isspreadoutrelative
to B and does not have the same zero crossings as B .Iftoo
1 1
pronounced,dispersionandbeamspreadingmaybeavoidedby
reducing the sample thickness.
7.7.3 The travel time interval T between B and B is given
1 2
by T = C + W , where W = D − D and C is the echo
2 1
displacement time obtained by means of the cross-correlation
algorithm.
7.7.4 The cross-correlation algorithm is applied to the echo
waveforms B and B to provide the value for the echo
1 2
displacement timeC.
7.8 Afteracquiringwaveformrecordsforechoes B and B ,
FIG. 4 Results of Digital Overlap of EchoesB (Solid Line) and 1 2
B (Dotted Line) When Dispersion is Not Present usethecross-correlationalgorithmtoobtaintheechodisplace-
ment time,C, relative to the zero reference.
7.9 Usethecross-correlationalgorithmwhichtransforms B
7.4.2 During data acquisition, the time synthesizer should
and B into the frequency domain, multiplies the complex
sequence through the predetermined time position
...
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