ASTM C1331-01(2007)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation: C1331 − 01(Reapproved 2007)
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 2.3 Military Standard:
MIL-STD-410Nondestructive Testing Personnel Qualifica-
1.1 Thistestmethoddescribesaprocedureformeasurement
tion and Certification
of ultrasonic velocity in structural engineering solids such as
monolithic ceramics, toughened ceramics, and ceramic matrix 2.4 Additional references are cited in the text and at end of
composites. this document.
1.2 This test method is based on the broadband pulse-echo
contactultrasonicmethod.Theprocedureinvolvesacomputer-
3. Terminology
implemented, frequency-domain method for precise measure-
ment of time delays between pairs of echoes returned by the 3.1 Definitions of Terms Specific to This Standard:
back surface of a test sample or part. 3.1.1 back surface—the surface of a test sample which is
opposite to the front surface and from which back surface
1.3 This test method describes a procedure for using a
echoes are returned at normal incidence directly to the trans-
digital cross-correlation algorithm for velocity measurement.
ducer.
Thecross-correlationfunctionyieldsatimedelaybetweenany
3.1.2 bandwidth—the frequency range of an ultrasonic
two echo waveforms (1).
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 Method for Water Absorption, Bulk Density,
bandwidth, consisting of a thin damped piezocrystal in a
ApparentPorosity,andApparentSpecificGravityofFired
buffered probe (search unit).
Whiteware Products
E494Practice for Measuring Ultrasonic Velocity in Materi-
3.1.4 buffered probe—anultrasonicsearchunitasdefinedin
als
Terminology E1316 but containing a delay line, or buffer rod,
E1316Terminology for Nondestructive Examinations
to which the piezocrystal is affixed within the search unit
housing and which separates the piezocrystal from the test
2.2 ASNT Document:
sample (Fig. 1).
Recommended Practice SNT-TC-1A for Nondestructive
Testing Personnel Qualification and Certification
3.1.5 buffer rod—an integral part of a buffered probe,
usually a quartz or fused silica cylinder that provides a time
delay between the excitation pulse from the piezocrystal and
This test method is under the jurisdiction of ASTM Committee C28 on echoes returning from a sample coupled to the free end of the
Advanced Ceramics and is the direct responsibility of Subcommittee C28.03 on
buffer rod.
Physical Properties and Non-Destructive Evaluation.
3.1.6 cross-correlation function—the cross-correlation
Current edition approved Aug. 1, 2007. Published August 2007. Originally
approved in 1996. Last previous edition approved in 2001 as C1331–01. DOI:
function, implemented by a digital algorithm, yields a time
10.1520/C1331-01R07.
delaybetweenanytwo(ultrasonic)echowaveforms.Thistime
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
is used to determine velocity (1).
this test method.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standardsvolume information,referto thestandard’sDocumentSummary page on
the ASTM website. Available from Standardization Documents Order Desk, DODSSP, Bldg. 4,
AvailablefromAmericanSocietyforNondestructiveTesting(ASNT),P.O.Box Section D, 700 Robbins Ave., Philadelphia, PA 19111-5098, http://
28518, 1711 Arlingate Ln., Columbus, OH 43228-0518, http://www.asnt.org. www.dodssp.daps.mil.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C1331 − 01 (2007)
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-
tionpracticeorstandardsuchasASNTSNT-TC-1A,MILSTD
410, or a similar document. The qualification practice or
standardusedanditsapplicablerevision(s)shouldbespecified
in a contractual agreement.
5.2 Knowledge of the principles of ultrasonic testing is
required. Personnel applying this test method should be expe-
NOTE 1—B and B are first and second back surface echoes, respec-
1 2 riencedpractitionersofultrasonicexaminationsandassociated
tively, and T is time interval between the echoes.
methods for signal acquisition, processing, and interpretation.
FIG. 1 Cross Section of Buffered Ultrasonic Probe (a) and Prin-
ciple Echoes (b) for Velocity Measurement 5.3 Personnel should have proficiency in computer signal
processing and the use of digital methods for time and
frequencydomainsignalanalysis.FamiliaritywithFourierand
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.
6. Apparatus and Test Sample
3.1.8 front surface—the surface of a test sample to which
thebufferrodiscoupledatnormalincidence(designatedastest
6.1 Instrumentation (Fig. 1 and Fig. 2) for broadband
surface in Terminology E1316.
cross-correlation pulse-echo ultrasonic velocity measurement
should include the following:
3.1.9 group velocity—velocity of a broadband ultrasonic
6.1.1 Buffered Probe:
pulse consisting of many different component wavelengths.
6.1.1.1 Thebufferrod,whichisanintegralpartoftheprobe
3.1.10 test sample—a solid coupon or material part that
(search unit), should be a right cylinder with smooth flat ends
meets the constraints needed to make the ultrasonic velocity
normal to the axis of the probe.
measurements described herein, that is, a test sample or part
6.1.1.2 The center frequency of the buffered probe should
having flat, parallel, smooth, preferably ground or polished
produce a wavelength within the sample that is less than one
opposing (front and back) surfaces, and having no discrete
fifth of the thickness of the sample.
flaws or anomalies unrepresentative of the inherent properties
6.1.1.3 The buffer rod length, that is, time delay should be
of the material.
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-
tion pulse and signal output connector.
4.1 Thevelocitymeasurementsdescribedinthistestmethod
6.1.3 Waveform Digitizing Oscilloscope (A/D Board), bus
may be used to characterize material variations that affect
programmable, to window and digitize the echo waveforms.
mechanical or physical properties.This procedure is useful for
6.1.3.1 A minimum 512-element waveform array with a
measuring variations in microstructural features such as grain
maximum data sampling interval of 1.95 ns is recommended.
structure, pore fractions, and density variations in monolithic
For better waveform resolution, a 1024-element array with a
ceramics.
data sampling interval of 0.97 ns may be needed.
4.2 Velocity measurements described herein can assess
6.1.3.2 Vertical Amplifier, bus programmable module.
subtle variations in porosity within a given material or com-
6.1.3.3 Time Base, bus programmable module with a reso-
ponent, as, for example, in ceramic superconductors and
lutionofatleast5nsperdivisionandseveraltimebaseranges
structural ceramic specimens (2,3).
including a fundamental time base of at least 200 ns.
4.3 In addition to ceramics and ceramic composites, the 6.1.4 Digital Time Delay Module, bus programmable, to
velocity measurements described herein may be applied to introduceaknowntimedelaybetweenthestartoftwoseparate
polycrystalline and single crystal metals, metal matrix com- time gates, that is, windows each of which containing one of
posites, and polymer matrix composites. two successive back surface echoes.
C1331 − 01 (2007)
FIG. 2 Instrumentation Diagram for Acquiring and Separately Windowing Two Successive Back Surface Echoes,B andB , for Cross-
1 2
Correlation Velocity Measurement
6.1.4.1 Separate windows are preferred for waveform digi- 7. Procedure
tization.Eachwaveformshouldoccupyfrom60to80%ofthe
7.1 Use instrument control software routines to start and
window.
control the interface bus; perform procedures such as optimiz-
6.1.4.2 Thetimesynthesizershouldhaveanaccuracyof 61
ing intensity, voltage, and time on the waveform digitizing
ns with a precision of 60.1 ns.
oscilloscope; control the digital time delay module; and ac-
6.1.5 Video Monitors, (optional) one analog, one digital for
quire, store, and process data.
real-time visual inspection of echo waveforms and for making
7.1.1 A cross-correlation algorithm should be part of the
interactivemanualadjustmentstothedataacquisitioncontrols.
FFT software.
6.1.6 Computer,withadequatespeedandstoragecapacityto
7.1.2 The arguments needed to implement the cross-
provide needed software control, data storage, and graphics
correlation algorithm are the time domain waveform arrays,
capability.ThesoftwareshouldincludeafastFouriertransform
that is, digitized echoes B and B (Fig. 1).
1 2
(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
7.4.1 The oscilloscope time base should be adjusted so that
which pulse-echo travel times can be measured.Therefore, the
eachwaveformoccupies60to80%ofitswindow.Windowfill
sample thickness should be measurable to an accuracy of
may be as low as 20% and still produce acceptable results.
60.1% or better.
7.4.2 During data acquisition, the time synthesizer should
6.2.2 For most engineering solids, the sample thickness
sequence through the predetermined time positions.
should be at least 2.5 mm.There is a practical upper bound on
sample thickness, for example, if the sample is too thick, there 7.5 The waveform digitizing oscilloscope (A/D device)
may be considerable signal attenuation, beam spreading, and should be programmed to automatically maximize the echo
dispersion that render the signal useless. waveform amplitude and intensity settings.
C1331 − 01 (2007)
7.6 Digitize back surface echoes B and B into separate
1 2
512-element waveform arrays. Signal averaging may be nec-
essary to accurately capture subtle features of the waveforms.
SignalswithhighSNR(signal-to-noiseratio)canbeaccurately
digitized by only a few signal averagings while signals with
low SNR may require as much as 32 signal averagings.
7.7 Ultrasonicvelocityisdeterminedbymeasuringthetime
delay between two successive echoes returned by the back
surface of the test sample. These are shown as the two
separately-windowed echoes B and B (Fig. 3).
1 2
7.7.1 Echoes B and B are separately windowed to get
1 2
maximum time and voltage resolution. This is done by preset-
tingthedigitaltimedelaymoduletoproducetwowindowsthat
capture echoes B and B with window start times D and D ,
1 2 1 2
respectively.
FIG. 4 Results of Digital Overlap of EchoesB (Solid Line) and
7.7.1.1 The centroid of echo B occurs at time D + T . B (Dotted Line) When Dispersion is Not Present
1 1 1
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,
7.9.1.1 If T = T , then C = 0 as in Fig. 5a.
1 2
it should be possible to digitally overlap echoes B and B as
1 2
7.9.1.2 If T < T , then C > 0 as in Fig. 5b.
1 2
in Fig. 4. Dispersion has occurred if echo B is spread out
7.9.1.3 If T >T , then C < 0 as in Fig. 5c.
1 2
relative to B and does not have the same zero crossings as B
1 1
7.9.2 Insomecases,becauseofthenatureofthetestsample
. If too pronounced, dispersion and beam spreading may be
material,echo B maybeinve
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