ASTM C1332-18(2023)

Standard Practice for Measurement of Ultrasonic Attenuation Coefficients of Advanced Ceramics by Pulse-Echo Contact Technique

SIGNIFICANCE AND USE
5.1 This practice is useful for characterizing material microstructure or measuring variations in microstructure that occur because of material processing conditions and thermal, mechanical, or chemical exposure (3). When applied to monolithic or composite ceramics, the procedure should reveal microstructural gradients due to density, porosity, and grain variations. This practice may also be applied to polycrystalline metals to assess variations in grain size, porosity, and multiphase constituents.  
5.2 This practice is useful for measuring and comparing microstructural variations among different samples of the same material or for sensing and measuring subtle microstructural variations within a given sample.  
5.3 This practice is useful for mapping variations in the attenuation coefficient and the attenuation spectrum as they pertain to variations in the microstructure and associated properties of monolithic ceramics, ceramic composites and metals.  
5.4 This practice is useful for establishing a reference database for comparing materials and for calibrating ultrasonic attenuation measurement equipment.  
5.5 This practice is not recommended for highly attenuating monolithics or composites that are thick, highly porous, or that have rough or highly textured surfaces. For these materials Practice E664/E664M may be appropriate. Guide E1495/E1495M is recommended for assessing attenuation differences among composite plates and laminates that may exhibit, for example, pervasive matrix porosity or matrix crazing in addition to having complex fiber architectures or thermomechanical degradation (3). The proposed ASTM Standard Practice for Measuring Ultrasonic Velocity in Advanced Ceramics (C1331) is recommended for characterizing monolithic ceramics with significant porosity or porosity variations (4).
SCOPE
1.1 This practice describes a procedure for measurement of ultrasonic attenuation coefficients for advanced structural ceramic materials. The procedure is based on a broadband buffered piezoelectric probe used in the pulse-echo contact mode and emitting either longitudinal or shear waves. The primary objective of this practice is materials characterization.  
1.2 The procedure requires coupling an ultrasonic probe to the surface of a plate-like sample and the recovery of successive front surface and back surface echoes (refer to Fig. 3). Power spectra of the echoes are used to calculate the attenuation spectrum (attenuation coefficient as a function of ultrasonic frequency) for the sample material. The transducer bandwidth and spectral response are selected to cover a range of frequencies and corresponding wavelengths that interact with microstructural features of interest in solid test samples.  
1.3 The purpose of this practice is to establish fundamental procedures for measurement of ultrasonic attenuation coefficients. These measurements should distinguish and quantify microstructural differences among solid samples and therefore help establish a reference database for comparing materials and calibrating ultrasonic attenuation measurement equipment.  
1.4 This practice applies to monolithic ceramics and also polycrystalline metals. This practice may be applied to whisker reinforced ceramics, particulate toughened ceramics, and ceramic composites provided that similar constraints on sample size, shape, and finish are met as described herein for monolithic ceramics.  
1.5 This practice sets forth the constraints on sample size, shape, and finish that will assure valid attenuation coefficient measurements. This practice also describes the instrumentat- ion, methods, and data processing procedures for accomplishing the measurements.  
1.6 This practice is not recommended for highly attenuating materials such as very thick, very porous, rough-surfaced monolithics or composites. This practice is not recommended for highly nonuniform, heterogeneous, cracked, defective, or otherwise flaw...

General Information

• Status: Published
• Publication Date: 30-Nov-2023
• ICS: 81.060.30 - Advanced ceramics
• Technical Committee: E07 - Nondestructive Testing
• Drafting Committee: E07.06 - Ultrasonic Method

Relations

• Replaces: ASTM C1332-18 - Standard Practice for Measurement of Ultrasonic Attenuation Coefficients of Advanced Ceramics by Pulse-Echo Contact Technique
• Effective Date: 01-Dec-2023
• Refers: ASTM E1316-24 - Standard Terminology for <?Pub Dtl?>Nondestructive Examinations
• Effective Date: 01-Feb-2024
• Refers: ASTM E1316-23b - Standard Terminology for Nondestructive Examinations
• Effective Date: 01-Sep-2023

Overview

ASTM C1332-18(2023), titled Standard Practice for Measurement of Ultrasonic Attenuation Coefficients of Advanced Ceramics by Pulse-Echo Contact Technique, establishes procedures for measuring ultrasonic attenuation coefficients in advanced structural ceramics and polycrystalline metals. Using a broadband buffered piezoelectric probe in a pulse-echo contact configuration, this standard enables accurate, non-destructive evaluation of microstructural properties by quantifying how ultrasonic waves are attenuated as they pass through a material.

The main objective of this ASTM standard is reliable material characterization, supporting quality control, material comparison, and advanced process monitoring in ceramics and metals manufacturing.

Key Topics

• Ultrasonic Attenuation Measurement: Focuses on the protocol for coupling a piezoelectric ultrasonic probe to flat, plate-like samples and capturing successive echo signals to determine attenuation coefficients.
• Microstructure Analysis: Enables detailed assessment of material properties such as density, porosity, grain size, and the presence of phases or microstructural gradients in monolithic and composite ceramics, as well as polycrystalline metals.
• Pulse-Echo Technique: Utilizes digital acquisition and computer analysis of ultrasonic waveforms returned from both the front and back surfaces of the sample to map the attenuation spectrum.
• Sample Requirements: Specifies critical constraints on sample size, shape, parallelism, and finish to ensure valid ultrasonic measurements. Samples must have flat, parallel surfaces and must be free from major defects.
• Reference and Calibration: Establishes procedures for building databases of attenuation coefficients for various materials, which are essential for equipment calibration and performance benchmarking.
• Personnel and Equipment Qualification: Recommends that ultrasonic testing personnel and agencies follow recognized qualification standards and practices.

Applications

• Quality Assurance in Ceramics and Metals: Widely used for non-destructive evaluation (NDE) of advanced structural ceramics and polycrystalline metals, enabling detection and quantification of subtle changes in microstructure caused by processing or service exposure.
• Comparative Material Analysis: Facilitates comparison between samples, helping manufacturers and researchers select materials with optimal microstructural characteristics for high-performance applications.
• Process Monitoring and Optimization: Supports monitoring of thermal, mechanical, or chemical treatments by mapping changes in attenuation coefficients, thereby informing manufacturing adjustments or predictive maintenance.
• Reference Database Development: Underpins the creation of material reference datasets, enhancing reproducibility and consistency across different laboratories and quality control environments.
• Calibration of Ultrasonic Testing Equipment: Provides standardized methodology to calibrate ultrasonic instruments, ensuring accuracy and reliability in attenuation measurements.

Note: ASTM C1332-18(2023) is not recommended for highly attenuating or rough-surfaced materials, such as thick, highly porous ceramics or composites, or materials with significant heterogeneity or cracking. For such cases, related practices like ASTM E664/E664M or ASTM E1495/E1495M may offer more appropriate methodologies.

Related Standards

Adherence to ASTM C1332-18(2023) is supported by several complementary standards and guidelines for ultrasonic non-destructive testing:

• ASTM C1331: Practice for Measuring Ultrasonic Velocity in Advanced Ceramics with Broadband Pulse-Echo Cross-Correlation Method.
• ASTM E543: Specification for Agencies Performing Nondestructive Testing.
• ASTM E664/E664M: Practice for Measurement of Apparent Attenuation of Longitudinal Ultrasonic Waves by Immersion Method.
• ASTM E1316: Terminology for Nondestructive Examinations.
• ASTM E1495/E1495M: Guide for Acousto-Ultrasonic Assessment of Composites, Laminates, and Bonded Joints.
• ASNT SNT-TC-1A / ANSI/ASNT CP-189: Practices and standards for nondestructive testing personnel qualification.
• ISO 9712: Non-destructive Testing - Qualification and Certification of NDT Personnel.
• NAS 410: Certification and Qualification of Nondestructive Testing Personnel for the aerospace industry.

Practical Value

By standardizing ultrasonic attenuation measurement for ceramics and metals, ASTM C1332-18(2023) enhances material quality assurance, supports robust NDE methodologies, and facilitates international comparability. The referenced process ensures repeatable, accurate results that help manufacturers and researchers optimize processes and achieve reliable material performance. This standard is a cornerstone for anyone involved in ultrasonic nondestructive testing, particularly for advanced ceramic and metallic materials.

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: C1332 − 18 (Reapproved 2023)
Standard Practice for
Measurement of Ultrasonic Attenuation Coefficients of
Advanced Ceramics by Pulse-Echo Contact Technique
This standard is issued under the fixed designation C1332; 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 monolithics or composites. This practice is not recommended
for highly nonuniform, heterogeneous, cracked, defective, or
1.1 This practice describes a procedure for measurement of
otherwise flaw-ridden samples that are unrepresentative of the
ultrasonic attenuation coefficients for advanced structural ce-
nature or inherent characteristics of the material under exami-
ramic materials. The procedure is based on a broadband
nation.
buffered piezoelectric probe used in the pulse-echo contact
1.7 This standard does not purport to address all of the
mode and emitting either longitudinal or shear waves. The
safety concerns, if any, associated with its use. It is the
primary objective of this practice is materials characterization.
responsibility of the user of this standard to establish appro-
1.2 The procedure requires coupling an ultrasonic probe to
priate safety, health, and environmental practices and deter-
the surface of a plate-like sample and the recovery of succes-
mine the applicability of regulatory limitations prior to use.
sive front surface and back surface echoes (refer to Fig. 3).
1.8 This international standard was developed in accor-
Power spectra of the echoes are used to calculate the attenua-
dance with internationally recognized principles on standard-
tion spectrum (attenuation coefficient as a function of ultra-
ization established in the Decision on Principles for the
sonic frequency) for the sample material. The transducer
Development of International Standards, Guides and Recom-
bandwidth and spectral response are selected to cover a range
mendations issued by the World Trade Organization Technical
of frequencies and corresponding wavelengths that interact
Barriers to Trade (TBT) Committee.
with microstructural features of interest in solid test samples.
1.3 The purpose of this practice is to establish fundamental
2. Referenced Documents
procedures for measurement of ultrasonic attenuation coeffi-
2.1 ASTM Standards:
cients. These measurements should distinguish and quantify
C1331 Practice for Measuring Ultrasonic Velocity in Ad-
microstructural differences among solid samples and therefore
vanced Ceramics with Broadband Pulse-Echo Cross-
help establish a reference database for comparing materials and
Correlation Method
calibrating ultrasonic attenuation measurement equipment.
E543 Specification for Agencies Performing Nondestructive
1.4 This practice applies to monolithic ceramics and also
Testing
polycrystalline metals. This practice may be applied to whisker
E664/E664M Practice for the Measurement of the Apparent
reinforced ceramics, particulate toughened ceramics, and ce-
Attenuation of Longitudinal Ultrasonic Waves by Immer-
ramic composites provided that similar constraints on sample
sion Method
size, shape, and finish are met as described herein for mono-
E1316 Terminology for Nondestructive Examinations
lithic ceramics.
E1495/E1495M Guide for Acousto-Ultrasonic Assessment
of Composites, Laminates, and Bonded Joints
1.5 This practice sets forth the constraints on sample size,
shape, and finish that will assure valid attenuation coefficient
2.2 ASNT Documents:
measurements. This practice also describes the instrumentat-
Recommended Practice SNT-TC-1A for Nondestructive
ion, methods, and data processing procedures for accomplish-
Testing Personnel Qualification and Certification
ing the measurements.
ANSI/ASNT CP-189 Standard for Qualification and Certifi-
cation of Nondestructive Testing Personnel
1.6 This practice is not recommended for highly attenuating
materials such as very thick, very porous, rough-surfaced
1 2
This practice is under the jurisdiction of ASTM Committee E07 on Nonde- For referenced ASTM standards, visit the ASTM website, www.astm.org, or
structive Testing and is the direct responsibility of Subcommittee E07.06 on contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Ultrasonic Method. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved Dec. 1, 2023. Published December 2023. Originally the ASTM website.
approved in 1996. Last previous edition approved in 2018 as C1332 – 18. DOI: Available from American Society for Nondestructive Testing (ASNT), P.O. Box
10.1520/C1332-18R23. 28518, 1711 Arlingate Ln., Columbus, OH 43228-0518, http://www.asnt.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C1332 − 18 (2023)
3.1.6 broadband transducer—an ultrasonic transducer ca-
pable of sending and receiving undistorted signals over a broad
bandwidth, consisting of thin damped piezoelectric crystal in a
buffered probe (search unit).
3.1.7 buffered probe—an ultrasonic search unit as defined in
Terminology E1316 but containing a delay line or buffer rod to
which the piezoelement, that is, transducer consisting of a
piezoelectric crystal, is affixed. The buffer rod separates the
piezoelement from the test sample (see Fig. 1).
3.1.8 buffer rod—an integral part of a buffered probe or
FIG. 1 Cross Section of Buffered Broadband Ultrasonic Probe
search unit, usually a quartz or fused silica cylinder that
provides a time delay between the excitation pulse from the
piezoelement and echoes returning from a sample coupled to
the free end of the buffer rod.
2.3 ISO Standard:
3.1.9 free surface—the back surface of a solid test sample
ISO 9712 Non-destructive Testing – Qualification and Cer-
interfaced with a very low density medium, usually air or other
tification of NDT Personnel
gas, to assure that the back surface reflection coefficient equals
2.4 Aerospace Industries Association Document:
1 to a high degree of precision.
NAS 410 Certification and Qualification of Nondestructive
3.1.10 frequency (f)—number of oscillations per second of
Testing Personnel
ultrasonic waves, measured in megahertz, MHz, herein.
2.5 Additional references are cited in the text and at end of
3.1.11 front surface—the surface of a test sample to which
this practice.
the buffer rod is coupled at normal incidence (designated as test
surface in Terminology E1316).
3. Terminology
3.1.12 inherent attenuation—ultrasound energy loss in a
3.1 Definitions of Terms Specific to This Standard:
solid as a result of scattering, diffusion, and absorption. This
3.1.1 acoustic impedance (Z)—a property (1) defined by a
standard assumes that the dominant inherent losses are due to
material’s density, p, and the velocity of sound within it, v,
Rayleigh and stochastic scattering (2) by the material
where Z = ρv.
microstructure, for example, by grains, grain boundaries, and
3.1.2 attenuation coeffıcient (α)—decrease in ultrasound
micropores. Measured ultrasound energy loss which, if not
intensity with distance expressed in nepers (Np) per unit
corrected, may include losses due to diffraction, individual
length, herein, α = [ln(I /I)]/d, where α is attenuation
macroflaws, surface roughness, couplant variations, and trans-
coefficient, d is path length or distance, I is original intensity,
ducer defects.
and I is attenuated intensity (2).
3.1.13 reflection coeffıcient (R)—measure of relative inten-
3.1.3 attenuation spectrum—the attenuation coefficient, α,
sity of sound waves reflected back into a material at an
expressed as a function of ultrasonic frequency, f, or plotted as
interface, defined in terms of the acoustic impedance of the
α versus f, over a range of ultrasonic frequencies within the
material in which the sound wave originates (Z ) and the
bandwidth of the transducer and associated pulser-receiver
acoustic impedance of the material interfaced with it (Z ),
i
instrumentation.
where R = [(Z − Z )/(Z + Z )] .
i 0 i 0
3.1.4 back surface—the surface of a test sample which is
3.1.14 test sample—a solid coupon or material part that
opposite to the front surface and from which back surface
meets the constraints needed to make the attenuation coeffi-
echoes are returned at normal incidence directly to the trans-
cient measurements described herein, that is, a test sample or
ducer.
part having flat, parallel, smooth, preferably ground/polished
3.1.5 bandwidth—the frequency range of an ultrasonic
opposing (front and back) surfaces and having no discrete
probe, defined by convention as the difference between the
flaws or anomalies that are unrepresentative of the inherent
lower and upper frequencies at which the signal amplitude is
properties of the material.
6 dB down from the frequency at which maximum signal
3.1.15 transmission coeffıcient (T)—measure of relative in-
amplitude occurs. The frequency at which the maximum
tensity of sound waves transmitted through an interface,
occurs is termed the center frequency of the probe or trans-
defined in terms of the acoustic impedance of the material in
ducer.
which the sound wave originates (Z ) and the acoustic imped-
ance of the material interfaced with it (Z ), where T =
i
(4Z Z )/(Z + Z ) so that R + T = 1.
i 0 i 0
Available from International Organization for Standardization (ISO), ISO
3.1.16 wavelength (λ)—distance that sound (of a particular
Central Secretariat, BIBC II, Chemin de Blandonnet 8, CP 401, 1214 Vernier,
Geneva, Switzerland, http://www.iso.org.
frequency) travels during one period (during one oscillation), λ
Available from Aerospace Industries Association of America, Inc., 1250 Eye St.
= v/f, where v is the velocity of sound in the material and
NW, Washington, DC, 20005.
where velocity is measured in cm/μs, and wavelength in cm,
The boldface numbers in parentheses refer to a list of references at the end of
this standard. herein.
C1332 − 18 (2023)
FIG. 2 Block Diagram of Computer System for Ultrasonic Signal Acquisition and Processing for Pulse-Echo Attenuation Measurement
occur because of material processing conditions and thermal,
mechanical, or chemical exposure (3). When applied to mono-
lithic or composite ceramics, the procedure should reveal
microstructural gradients due to density, porosity, and grain
variations. This practice may also be applied to polycrystalline
metals to assess variations in grain size, porosity, and multi-
phase constituents.
5.2 This practice is useful for measuring and comparing
microstructural variations among different samples of the same
material or for sensing and measuring subtle microstructural
variations within a given sample.
5.3 This practice is useful for mapping variations in the
attenuation coefficient and the attenuation spectrum as they
pertain to variations in the microstructure and associated
properties of monolithic ceramics, ceramic composites and
metals.
FIG. 3 Schematic of Signal Acquisition and Data-Processing
Stages for Determining Frequency Dependence of Attenuation
5.4 This practice is useful for establishing a reference
Coefficient by Using Broadband Ultrasonic Pulse-Echo Method
database for comparing materials and for calibrating ultrasonic
attenuation measurement equipment.
3.2 Other terms used in this practice are defined in Termi-
5.5 This practice is not recommended for highly attenuating
nology E1316.
monolithics or composites that are thick, highly porous, or that
have rough or highly textured surfaces. For these materials
4. Summary of Practice
Practice E664/E664M may be appropriate. Guide E1495/
4.1 This practice describes a procedure for determining a
E1495M is recommended for assessing attenuation differences
material’s inherent attenuation coefficient and attenuation spec-
among composite plates and laminates that may exhibit, for
trum by means of a buffered broadband probe operating in the
example, pervasive matrix porosity or matrix crazing in addi-
pulse-echo contact mode on a solid sample that has smooth,
tion to having complex fiber architectures or thermomechanical
flat, parallel surfaces.
degradation (3). The proposed ASTM Standard Practice for
Measuring Ultrasonic Velocity in Advanced Ceramics (C1331)
4.2 The procedure described in this practice involves digital
is recommended for characterizing monolithic ceramics with
acquisition and computer processing of ultrasonic echo wave-
significant porosity or porosity variations (4).
forms returned by the test sample. Test sample constraints,
probing methods, data validity criteria, and measurement
6. Personnel Qualifications
corrections are prescribed herein.
6.1 If specified in the contractual agreement, personnel
5. Significance and Use
performing examinations to this practice shall be qualified in
5.1 This practice is useful for characterizing material mi- accordance with a nationally or internationally recognized
crostructure or measuring variations in microstructure that NDT personnel qualification practice or standard such as
C1332 − 18 (2023)
ANSI/ASNT CP-189, SNT-TC-1A, NAS 410, ISO 9712, or a 8.1.3.4 Dry coupling, for example, with an elastomer or thin
similar document and certified by the employer or certifying deformable polymer film, may be used provided that echo
agency, as applicable. The practice or standard used and its distortions or phase inversions are avoided by acoustic imped-
applicable revision shall be identified in the contractual agree- ance matching (5) and by substantially reducing the couplant
ment between the using parties. layer thickness.
8.1.4 Pulser-Receiver, having a bandwidth exceeding that of
6.2 Knowledge of the principles of ultrasonic testing is
the probe by a factor of 1.5 to 2 and including the probe/
required. Personnel applying this practice shall be experienced
transducer bandwidth to avoid significant distortions of the
practitioners of ultrasonic examinations and associated meth-
received signals. The pulser-receiver should have controls for
ods for signal acquisition, processing, and interpretation.
pulse voltage level, pulse duration, pulse repetition rate, pulse
6.3 Personnel shall have proficiency in computer program-
damping, gain (signal amplification steps), and received signal
ming and signal processing using digital methods for time and
and synchronization outputs to an oscilloscope.
frequency domain signal analysis. Familiarity with the Fourier
8.1.4.1 The pulse voltage should be ≈200 V to ≈250 V.
transform and associated spectrum analysis methods for ultra-
8.1.4.2 The pulse duration should be between 10 ns to 20 ns
sonic signals is required.
to produce the necessary broadband excitation pulses having
7. Qualification of Nondestructive Agencies
center frequencies of 50 MHz or greater.
8.1.4.3 The pulse repetition rate should be set slow enough
7.1 If specified in the contractual agreement, NDT agencies
to avoid overlapped echoes but fast enough to allow the
shall be qualified and evaluated as described in Specification
averaging of 16 to 32 transient signals for digitizing each echo
E543. The applicable edition of Specification E543 shall be
waveform.
specified in the contractual agreement.
8.1.5 Coaxial Cable, connecting the probe and pulser-
8. Apparatus
receiver. The cable should be electrically impedance matched
to both the probe and pulser-receiver to avoid electronic
8.1 The instrumentation and apparatus for pulse-echo con-
reverberations and consequent signal distortions. Short cables,
tact ultrasonic attenuation coefficient measurement should
1 m or less, should be used.
include the following (see Fig. 2). Appropriate equipment can
be assembled from any of several suppliers.
8.1.6 Oscilloscope Voltage Amplifier, preferably a program-
8.1.1 Buffered Probe, meeting the following requirements:
mable vertical amplifier module using a general purpose
8.1.1.1 The probe should have a center frequency that
interface bus (such as the IEEE 488 GPIB) and having
corresponds to an ultrasonic wavelength that is less than one
selectable gains, for example, 20 dB, 40 dB, and 60 dB.
fifth of the thickness, d, of the test sample.
8.1.7 Oscilloscope Time Base, preferably a programmable
8.1.1.2 The probe bandwidth should match the bandwidth of
time base module using a general purpose interface bus (GPIB)
received echoes. This may require transducer bandwidths of
with a resolution of at least 5 ns and selectable ranges including
from 50 MHz to 200 MHz.
a fundamental time base of 200 ns.
8.1.1.3 The probe should be well constructed, carefully
8.1.8 Digital Time Synthesizer, bus programmable module,
selected, and shown to be free of internal defects and structural
to introduce a known time delay between the start of three
anomalies that distort received echoes.
separate time gates in the oscilloscope time base. Each time
8.1.1.4 The frequency spectra of the first two echoes re-
gate must generate a “window” to exclusively contain one of
turned by the free end of the buffer should be essentially
the echoes of interest, that is, front surface and two successive
gaussian (bell shaped).
back surface echoes. The gate, that is, window start times,
8.1.2 Buffer Rod, with length that results in a time delay ≥3
should be program controlled and program readable.
times the interval between two successive echoes from the
8.1.9 Waveform Digitizing Oscilloscope, bus programmable
back surface of the test sample. This imposes a limit on the test
to window and digitize individual time domain ultrasonic echo
sample thickness if the buffer rod length is fixed or predeter-
waveforms into a 512-element array (or 1024-element array)
mined by design.
with a data sampling interval of 1.95 ns (or 0.97 ns).
8.1.3 Couplant, meeting the following requirements:
8.1.10 Video Monitors, one analog, one digital (optional) for
8.1.3.1 The couplant should be a fluid such as glycerine or
real-time visual inspection of echo waveforms and for making
an ultrasonic gel that will not corrode, damage, or be absorbed
interactive manual adjustments to the data acquisition controls.
by the test sample or part being examined.
These control adjustments may include probe realignment/
8.1.3.2 The couplant film or couplant layer thickness should
repositioning, couplant thickness optimization, and other ad-
be much less than the ultrasound wavelength in the couplant at
justments to obtain echo waveforms that meet acceptance
the probe’s center frequency.
criteria given herein.
8.1.3.3 Ideally, to avoid echo distortions, the acoustic im-
8.1.11 XYZ-Axis Micropositioner, motorized and bus pro-
pedance of the couplant should be between that of the buffer
grammable for holding the test sample support and positioning
rod material and test sample (5). With fluid couplants, just
sample and coupling it to the probe buffer rod with a preset
reducing the couplant layer thickness is usually more practical
loading force.
than impedance matching by changing the fluid. For example,
if glycerine is used between a fused quartz buffer and a steel 8.1.12 Load Cell and Controller, bus programmable for
sample, the couplant layer thickness should be less than 1 μm. measuring and controlling the force with which the buffer rod
C1332 − 18 (2023)
is coupled to the test sample so that the couplant thickness can 9. Procedure
be minimized and coupling force between sample and probe
9.1 Preparatory Steps to Assure Optimum Coupling and
can be optimized.
Signal Acquisition:
8.1.13 Probe Fixture, to firmly attach the probe to the load
9.1.1 Clean the face of the buffer rod with ethanol or similar
cell. mild cleaning fluid to remove any dust, dirt, or residual
couplant.
8.1.14 Sample Support, to firmly hold test sample as it is
9.1.2 Place a small drop of fluid couplant on the buffer rod
brought in contact with and coupled to probe buffer rod at
and then place the sample against the buffer. Whether the
normal incidence.
couplant consists of a fluid, elastomer, or plastic film, make
8.1.15 Computer and Instrument Interface, to provide pro-
sure that it completely wets or adheres to the buffer and sample
grammable bus control, data acquisition, data storage, data
surfaces.
processing, graphics display, and output to a printer.
9.1.3 Support the test sample with a hard, dry backing
8.1.16 Control Software, to start and control the interface
material, preferably with a rough-machined or sawtooth sur-
bus; optimize signal digitization and digitizer intensity; set the
face profile. Avoid coupling the sample to the backing material.
voltage scaling on the digitizer; control and set the time
The back surface directly opposite the probe should be free,
synthesizer; control and set the micropositioner and coupling
that is, essentially air-backed.
pressure; monitor the load cell; etc.
9.1.4 Apply pressure until two back surface echoes appear
8.1.17 Signal Processing Software, including FFT (fast
on the video monitor. The optimum force for a 1.2 cm (0.5 in.)
Fourier transform) to acquire, process, and store waveform diameter buffer rod coupled to a test sample with glycerine
data; calculate and display attenuation coefficients and attenu-
couplant will be 44 N to 88 N (10 lb to 20 lb) or a pressure of
ation spectra; etc. 220 KPa to 440 KPa (30 psi to 60 psi).
9.1.5 Minimize losses and signal reverberations within the
8.2 Some of the previously mentioned apparatus may be
couplant layer by reducing the couplant thickness to |LL2 μm.
omitted in favor of manual alignment and coupling of test
9.2 The pulse-echo configuration and echo system for at-
samples to the probe. For example, a manual precision labo-
tenuation measurements is illustrated in Fig. 3.
ratory jack may be used instead of the motorized XYZ-axis
9.2.1 Adjust the pulser-receiver (for example, pulser energy/
micropositioner. The load cell may also be omitted in this case.
damping and receiver gain/bandpass) to optimize the echo
The programmable digital time synthesizer may be omitted by
waveforms displayed by the video monitors.
manually setting the time interval among windows containing
9.2.2 Before digitizing echo waveforms, study the front and
front and back surface echoes.
back surface echoes returned by the test sample. The magni-
8.3 For monolithic ceramics and polycrystalline metals, the
tude (amplitude) spectra of their Fourier transforms should be
frequency range of the pulser-receiver, probe-transducer
essentially gaussian.
should be between 10 MHz and 200 MHz. The specific 9.2.3 Collect the following echoes:
frequency range needed depends on the nature of the material
9.2.3.1 Echo F from the free end of the buffer rod before it
and specimen thickness. For most metallic samples with is coupled to the test sample.
thicknesses between 3 mm and 5 mm, a frequency range from 9.2.3.2 Front surface echo F from the end of the buffer rod
after it is coupled to the test sample.
10 MHz to 100 MHz will suffice while for most ceramic
samples with simila
...