ASTM C1331-18(2023)
(Practice)Standard Practice for Measuring Ultrasonic Velocity in Advanced Ceramics with Broadband Pulse-Echo Cross-Correlation Method
Standard Practice 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 practice 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 practice covers a procedure for measurement of ultrasonic velocity in structural engineering solids such as monolithic ceramics, toughened ceramics, and ceramic matrix composites.
1.2 This practice 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 practice 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
1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
General Information
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Standards Content (Sample)
This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: C1331 − 18 (Reapproved 2023)
Standard Practice 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. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope E494 Practice for Measuring Ultrasonic Velocity in Materi-
als by Comparative Pulse-Echo Method
1.1 This practice covers a procedure for measurement of
E543 Specification for Agencies Performing Nondestructive
ultrasonic velocity in structural engineering solids such as
Testing
monolithic ceramics, toughened ceramics, and ceramic matrix
E1316 Terminology for Nondestructive Examinations
composites.
2.2 ASNT Documents:
1.2 This practice is based on the broadband pulse-echo
Recommended Practice SNT-TC-1A for Nondestructive
contact ultrasonic method. The procedure involves a computer-
Testing Personnel Qualification and Certification
implemented, frequency-domain method for precise measure-
ANSI/ASNT CP-189 Standard for Qualification and Certifi-
ment of time delays between pairs of echoes returned by the
cation of Nondestructive Testing Personnel
back surface of a test sample or part.
2.3 ISO Document:
1.3 This practice describes a procedure for using a digital
ISO 9712 Non-destrtuctive Testing – Qualification and Cer-
cross-correlation algorithm for velocity measurement. The 5
tification of NDT Personnel
cross-correlation function yields a time delay between any two
2.4 Aerospace Industries Association Document:
echo waveforms (1).
NAS 410 Certification and Qualification of Nondestructive
1.4 This international standard was developed in accor-
Testing Personnel
dance with internationally recognized principles on standard-
2.5 Additional references are cited in the text and at end of
ization established in the Decision on Principles for the
this document.
Development of International Standards, Guides and Recom-
mendations issued by the World Trade Organization Technical
3. Terminology
Barriers to Trade (TBT) Committee.
3.1 Definitions of Terms Specific to This Standard:
3.1.1 back surface—the surface of a test sample which is
2. Referenced Documents
opposite to the front surface and from which back surface
2.1 ASTM Standards:
echoes are returned at normal incidence directly to the trans-
B311 Test Method for Density of Powder Metallurgy (PM)
ducer.
Materials Containing Less Than Two Percent Porosity
3.1.2 bandwidth—the frequency range of an ultrasonic
C373 Test Methods for Determination of Water Absorption
probe, defined by convention as the difference between the
and Associated Properties by Vacuum Method for Pressed
lower and upper frequencies at which the signal amplitude is 6
Ceramic Tiles and Glass Tiles and Boil Method for
dB down from the frequency at which maximum signal
Extruded Ceramic Tiles and Non-tile Fired Ceramic
amplitude occurs.
Whiteware Products
3.1.3 broadband transducer—an ultrasonic transducer ca-
pable of sending and receiving undistorted signals over a broad
This practice is under the jurisdiction of ASTM Committee E07 on Nonde- bandwidth, consisting of a thin damped piezocrystal in a
structive Testing and is the direct responsibility of Subcommittee E07.06 on
buffered probe (search unit).
Ultrasonic Method.
Current edition approved Dec. 1, 2023. Published December 2023. Originally
approved in 1996. Last previous edition approved in 2018 as C1331 – 18. DOI:
10.1520/C1331-18R23. Available from American Society for Nondestructive Testing (ASNT), P.O. Box
The boldface numbers in parentheses refer to the list of references at the end of 28518, 1711 Arlingate Ln., Columbus, OH 43228-0518, http://www.asnt.org.
this practice. Available from International Organization for Standardization (ISO), ISO
For referenced ASTM standards, visit the ASTM website, www.astm.org, or Central Secretariat, BIBC II, Chemin de Blandonnet 8, CP 401, 1214 Vernier,
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Geneva, Switzerland, http://www.iso.org.
Standards volume information, refer to the standard’s Document Summary page on Available from Aerospace Industries Association of America, Inc., 1250 Eye St.
the ASTM website. NW, Washington, DC, 2005.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C1331 − 18 (2023)
3.1.4 buffered probe—an ultrasonic search unit as defined in mechanical or physical properties. This procedure is useful for
Terminology E1316 but containing a delay line, or buffer rod, measuring variations in microstructural features such as grain
to which the piezocrystal is affixed within the search unit structure, pore fractions, and density variations in monolithic
housing and which separates the piezocrystal from the test ceramics.
sample (Fig. 1).
4.2 Velocity measurements described herein can assess
3.1.5 buffer rod—an integral part of a buffered probe,
subtle variations in porosity within a given material or
usually a quartz or fused silica cylinder that provides a time
component, as, for example, in ceramic superconductors and
delay between the excitation pulse from the piezocrystal and
structural ceramic specimens (2, 3).
echoes returning from a sample coupled to the free end of the
4.3 In addition to ceramics and ceramic composites, the
buffer rod.
velocity measurements described herein may be applied to
3.1.6 cross-correlation function—the cross-correlation
polycrystalline and single crystal metals, metal matrix
function, implemented by a digital algorithm, yields a time
composites, and polymer matrix composites.
delay between any two (ultrasonic) echo waveforms. This time
4.4 An alternative technique for velocity measurement is
is used to determine velocity (1).
given in Practice E494.
3.1.7 dispersion—variation of ultrasonic velocity as a func-
tion of wavelength, that is, frequency dependence of velocity.
5. Personnel Qualifications
3.1.8 front surface—the surface of a test sample to which
5.1 If specified in the contractual agreement, personnel
the buffer rod is coupled at normal incidence (designated as test
performing examinations to this practice shall be qualified in
surface in Terminology E1316.
accordance with a nationally or internationally recognized
3.1.9 group velocity—velocity of a broadband ultrasonic
NDT personnel qualification practice or standard such as
pulse consisting of many different component wavelengths.
ANSI/ASNT-CP-189, SNT-TC-1A, NAS 410, ISO 9712, or a
similar document and certified by the employer or certifying
3.1.10 test sample—a solid coupon or material part that
agency, as applicable. The practice or standard used and its
meets the constraints needed to make the ultrasonic velocity
applicable revision shall be identified in the contractual agree-
measurements described herein, that is, a test sample or part
ment between the using parties.
having flat, parallel, smooth, preferably ground or polished
opposing (front and back) surfaces, and having no discrete
5.2 Knowledge of the principles of ultrasonic testing is
flaws or anomalies unrepresentative of the inherent properties
required. Personnel applying this practice should be experi-
of the material.
enced practitioners of ultrasonic examinations and associated
methods for signal acquisition, processing, and interpretation.
3.1.11 wavelength (λ)—distance that sound (of a particular
frequency) travels during one period (during one oscillation), λ
5.3 Personnel should have proficiency in computer signal
= v/f, where v is the velocity of sound in the material and
processing and the use of digital methods for time and
where velocity is measured in cm/μs, frequency in MHz, and
frequency domain signal analysis. Familiarity with Fourier and
wavelength in cm, herein.
associated transforms for ultrasonic spectrum analysis is re-
quired.
3.2 Other terms or nomenclature used in this practice are
defined in Terminology E1316.
6. Qualification of Nondestructive Agencies
4. Significance and Use
6.1 If specified in the contractual agreement, NDT agencies
4.1 The velocity measurements described in this practice
shall be qualified and evaluated as described in Specification
may be used to characterize material variations that affect
E543. The applicable edition of Specification E543 shall be
specified in the contractual agreement.
7. Apparatus and Test Sample
7.1 Instrumentation (Fig. 1 and Fig. 2) for broadband
cross-correlation pulse-echo ultrasonic velocity measurement
should include the following:
7.1.1 Buffered Probe:
7.1.1.1 The buffer rod, which is an integral part of the probe
(search unit), should be a right cylinder with smooth flat ends
normal to the axis of the probe.
7.1.1.2 The center frequency of the buffered probe should
produce a wavelength within the sample that is less than one
fifth of the thickness of the sample.
7.1.1.3 The buffer rod length, that is, time delay should be
NOTE 1—B and B are first and second back surface echoes,
1 2
three times the interval between two successive back surface
respectively, and T is time interval between the echoes.
echoes.
FIG. 1 Cross Section of Buffered Ultrasonic Probe (a) and Prin-
ciple Echoes (b) for Velocity Measurement 7.1.1.4 The wave mode may be either longitudinal or shear.
C1331 − 18 (2023)
FIG. 2 Instrumentation Diagram for Acquiring and Separately Windowing Two Successive Back Surface Echoes, B and B , for Cross-
1 2
Correlation Velocity Measurement
7.1.2 Pulser-Receiver, with a bandwidth that is at least twice 7.1.7.1 The couplant should not be absorbed by or be
that of the buffered probe. The bandwidth should include otherwise deleterious to the test sample.
frequencies in the range from 100 kHz to over 100 MHz.
7.1.7.2 Dry coupling with a thin polymer may be used
7.1.2.1 The pulser-receiver should have provisions for con-
where liquid contamination by or absorption of liquids by the
trolling the pulse repetition rate, pulse energy level, pulse
test sample or part must be avoided.
damping, and received signal gain.
7.2 The test sample or part should have flat parallel oppos-
7.1.2.2 The pulser-receiver should provide a synchroniza-
ing surfaces in the region where the velocity measurements are
tion pulse and signal output connector.
made. This will assure good coupling between the transducer
7.1.3 Waveform Digitizing Oscilloscope (A/D Board), bus
and sample and also produce valid echoes for velocity mea-
programmable, to window and digitize the echo waveforms.
surements.
7.1.3.1 A minimum 512-element waveform array with a
7.2.1 Lack of precision in the measurement of the test
maximum data sampling interval of 1.95 ns is recommended.
sample thickness can undermine the nanosecond precision with
For better waveform resolution, a 1024-element array with a
which pulse-echo travel times can be measured. Therefore, the
data sampling interval of 0.97 ns may be needed.
sample thickness should be measurable to an accuracy of
7.1.3.2 Vertical Amplifier, bus programmable module.
60.1 % or better.
7.1.3.3 Time Base, bus programmable module with a reso-
7.2.2 For most engineering solids, the sample thickness
lution of at least 5 ns per division and several time base ranges
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
7.1.4 Digital Time Delay Module, bus programmable, to
may be considerable signal attenuation, beam spreading, and
introduce a known time delay between the start of two separate
dispersion that render the signal useless.
time gates, that is, windows each of which containing one of
two successive back surface echoes.
8. Procedure
7.1.4.1 Separate windows are preferred for waveform digi-
tization. Each waveform should occupy from 60 % to 80 % of 8.1 Use instrument control software routines to start and
the window.
control the interface bus; perform procedures such as optimiz-
7.1.4.2 The time synthesizer should have an accuracy of 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
7.1.5 Video Monitors, (optional) one analog, one digital for acquire, store, and process data.
real-time visual inspection of echo waveforms and for making
8.1.1 A cross-correlation algorithm should be part of the
interactive manual adjustments to the data acquisition controls.
FFT software.
7.1.6 Computer, with adequate speed and storage capacity to
8.1.2 The arguments needed to implement the cross-
provide needed software control, data storage, and graphics
correlation algorithm are the time domain waveform arrays,
capability. The software should include a fast Fourier transform
that is, digitized echoes B and B (Fig. 1).
1 2
(FFT) algorithm package containing the cross-correlation al-
8.2 Prepare samples with front and back surfaces that are
gorithm.
sufficiently smooth, flat, and parallel to allow measurement of
7.1.7 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
thin as possible to minimize couplant resonances and distortion 8.3 Couple the sample to the transducer to obtain two strong
of the echo waveforms. back surface echoes.
C1331 − 18 (2023)
8.3.1 Apply pressure to minimize the couplant layer thick-
ness. A backing fixture may be necessary to apply pressure.
8.3.2 Care shall be taken to avoid coupling the sample to the
backing fixture and thereby losing echo signal strength by
leakage.
8.3.3 A dry, hard rubber or composite material with a
rough-machined or sawtooth surface is recommended for the
backing fixture.
8.4 Determine the precise positions, in the time domain, of
the start of the windows containing echo waveforms B and B
1 2
and program the digital time delay module to sequentially set
these delays.
8.4.1 The oscilloscope time base should be adjusted so that
each waveform occupies 60 % to 80 % of its window. Window
fill may be as low as 20 % and still produce acceptable results.
FIG. 4 Results of Digital Overlap of Echoes B (Solid Line) and
8.4.2 During data acquisition, the time synthesizer should
B (Dotted Line) W
...
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