ASTM E494-95
(Practice)Standard Practice for Measuring Ultrasonic Velocity in Materials
Standard Practice for Measuring Ultrasonic Velocity in Materials
SCOPE
1.1 This practice covers a test procedure for measuring ultrasonic velocities in materials with conventional ultrasonic pulse echo flaw detection equipment in which results are displayed in an A-scan display. This practice describes a method whereby unknown ultrasonic velocities in a material sample are determined by comparative measurements using a reference material whose ultrasonic velocities are accurately known.
1.2 This procedure is intended for solid materials 5 mm (0.2 in.) thick or greater. The surfaces normal to the direction of energy propagation shall be parallel to at least ±3°. Surface finish for velocity measurements shall be 3.2 μm (125 μin.) rms or smoother.
Note 1—Sound wave velocities are cited in this practice using the fundamental units of meters per second, with inches per second supplied for reference in many cases. For some calculations, it is convenient to think of velocities in units of millimeters per microsecond. While these units work nicely in the calculations, the more natural units were chosen for use in the tables in this practice. The values can be simply converted from m/sec to mm/μsec by moving the decimal point three places to the left, that is, 3500 m/s becomes 3.5 mm/μsec.
1.3 Ultrasonic velocity measurements are useful for determining several important material properties. Young's modulus of elasticity, Poisson's ratio, acoustic impedance, and several other useful properties and coefficients can be calculated for solid materials with the ultrasonic velocities if the density is known (see Appendix X1).
1.4 More accurate results can be obtained with more specialized ultrasonic equipment, auxiliary equipment, and specialized techniques. Some of the supplemental techniques are described in Appendix X2. (Material contained in Appendix X2 is for informational purposes only.)
Note 2—Factors including techniques, equipment, types of material, and operator variables will result in variations in absolute velocity readings, sometimes by as much as 5%. Relative results with a single combination of the above factors can be expected to be much more accurate (probably within a 1% tolerance).
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: E 494 – 95 An American National Standard
Standard Practice for
Measuring Ultrasonic Velocity in Materials
This standard is issued under the fixed designation E 494; 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 (e) indicates an editorial change since the last revision or reapproval.
This specification has been approved for use by agencies of the Department of Defense.
1. Scope 1.5 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
1.1 This practice covers a test procedure for measuring
responsibility of the user of this standard to establish appro-
ultrasonic velocities in materials with conventional ultrasonic
priate safety and health practices and determine the applica-
pulse echo flaw detection equipment in which results are
bility of regulatory limitations prior to use.
displayed in an A-scan display. This practice describes a
method whereby unknown ultrasonic velocities in a material
2. Referenced Documents
sample are determined by comparative measurements using a
2.1 ASTM Standards:
reference material whose ultrasonic velocities are accurately
C 597 Test Method for Pulse Velocity Through Concrete
known.
E 317 Practice for Evaluating Performance Characteristics
1.2 This procedure is intended for solid materials 5 mm (0.2
of Ultrasonic Pulse-Echo Testing Systems Without the Use
in.) thick or greater. The surfaces normal to the direction of
of Electronic Measurement Instruments
energy propagation shall be parallel to at least 6 3°. Surface
E 797 Practice for Measuring Thickness by Manual Ultra-
finish for velocity measurements shall be 3.2 μm (125 μin.) rms
sonic Pulse-Echo Contact Method
or smoother.
E 1316 Terminology for Nondestructive Examinations
NOTE 1—Sound wave velocities are cited in this practice using the
fundamental units of meters per second, with inches per second supplied
3. Terminology
for reference in many cases. For some calculations, it is convenient to
3.1 Definitions—For definitions of terms used in this prac-
think of velocities in units of millimeters per microsecond. While these
tice, see Terminology E 1316.
units work nicely in the calculations, the more natural units were chosen
for use in the tables in this practice. The values can be simply converted
4. Summary of Practice
from m/sec to mm/μsec by moving the decimal point three places to the
left, that is, 3500 m/s becomes 3.5 mm/μsec.
4.1 Several possible modes of vibration can propagate in
solids. This procedure is concerned with two velocities of
1.3 Ultrasonic velocity measurements are useful for deter-
propagation, namely those associated with longitudinal (v ) and
mining several important material properties. Young’s modulus l
transverse (v ) waves. The longitudinal velocity is independent
t
of elasticity, Poisson’s ratio, acoustic impedance, and several
of sample geometry when the dimensions at right angles to the
other useful properties and coefficients can be calculated for
beam are very large compared with beam area and wave length.
solid materials with the ultrasonic velocities if the density is
The transverse velocity is little affected by physical dimensions
known (see Appendix X1).
of the sample. The procedure described in Section 6 is, as noted
1.4 More accurate results can be obtained with more spe-
in the scope, for use with conventional pulse echo flaw
cialized ultrasonic equipment, auxiliary equipment, and spe-
detection equipment only.
cialized techniques. Some of the supplemental techniques are
described in Appendix X2. (Material contained in Appendix
5. Apparatus
X2 is for informational purposes only.)
5.1 The ultrasonic testing system to be used in this practice
NOTE 2—Factors including techniques, equipment, types of material,
shall include the following:
and operator variables will result in variations in absolute velocity
5.1.1 Test Instrument—Any ultrasonic instrument compris-
readings, sometimes by as much as 5%. Relative results with a single
ing a time base, transmitter (pulser), receiver (echo amplifier),
combination of the above factors can be expected to be much more
and an A-scan indicator circuit to generate, receive, and display
accurate (probably within a 1% tolerance).
electrical signals related to ultrasonic waves. Equipment shall
allow reading the positions of A , A , A , A (defined in 6.1.4
k s t l
and 6.2.4), along the A-scan base line within 60.5 mm (0.020
This practice is under the jurisdiction of ASTM Committee E-7 on Nonde-
structive Testing and is the direct responsibility of Subcommittee E07.06 on
Ultrasonic Testing Procedure.
Current edition approved Jan. 15, 1995. Published March 1995. Originally Annual Book of ASTM Standards, Vol 04.02.
published as E 494 – 73. Last previous edition E 494 – 92a. Annual Book of ASTM Standards, Vol 03.03.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
E 494
in.). For maximum accuracy, the highest possible frequency position of the leading edge of the first back echo has been
that will present at least two easily distinguishable back echos, fixed. This allows more accurate time or distance measure-
and preferably five, shall be used. ments. The position of the leading edge of the last back echo is
5.1.2 Search Unit—The search unit containing a transducer then determined. The signal has traversed a distance twice the
that generates and receives ultrasonic waves of an appropriate thickness of the specimen between each back echo. The signal
size, type and frequency, designed for tests by the contact traversing the specimen and returning is called a round trip. In
method shall be used. Contact straight beam longitudinal mode Fig. 1 the signal has made six round trips between Echo 1 and
shall be used for longitudinal velocity measurements, and Echo 7. Count the number of round trips from first echo used
contact straight beam shear mode for transverse velocity to the last echo measured on both samples. This number will be
measurements. one less than the number of echoes used. Note that the sample
5.1.3 Couplant—For longitudinal velocity measurements, thickness, number of round trips, and distance from front to last
the couplant should be the material used in practice, for back echo measured need not be the same.
example, clean light-grade oil. For transverse velocity mea-
6.1.4 Calculate the value of the unknown velocity as fol-
surements, a high viscosity material such as resin or solid bond
lows:
shall be used. In some materials isopolybutene, honey, or other
v 5 A n t v / A n t (1)
~ ! ~ !
1 k l l k l k k
high-viscosity materials have been used effectively. Most
liquids will not support transverse waves. In porous materials
where:
A = distance from first to Nth back echo on the known
special nonliquid couplants are required. The couplant must
k
not be deleterious to the material. material, m (in.), measured along the baseline of the
5.1.4 Standard Reference Blocks: A-scan display,
n = number of round trips, unknown material,
5.1.4.1 Velocity Standard—Any material of known velocity,
l
t = thickness of unknown material, m (in.),
that can be penetrated by the acoustical wave, and that has an
l
v = velocity in known material, m/s (in./s),
appropriate surface roughness, shape, thickness, and parallel- k
A = distance from the first to the Nth back echo on the
l
ism. The velocity of the standard should be determined by
unknown material, m (in.), measured along the
some other technique of higher accuracy, or by comparison
baseline of the A-scan display,
with water velocity that is known (see Appendix X2.5 and
n = number of round trips, known material, and
k
Appendix X4). The reference block should have an attenuation
t = thickness, known material, m (in.).
k
similar to that of the test material.
5.1.4.2 For horizontal linearity check, see Practice E 317.
NOTE 3—The units used in measurement are not significant as long as
the system is consistent.
6. Procedure
6.2 Transverse Velocity—Determine transverse velocity (v )
s
6.1 Longitudinal Wave Velocity—Determine bulk, longitu-
by comparing the transit time of a transverse wave in an
dinal wave velocity (v ) by comparing the transit time of a
l
unknown material to the transit time of a transverse wave in a
longitudinal wave in the unknown material to the transit time
material of known velocity (v ).
t
of ultrasound in a velocity standard (v ).
k
6.2.1 Select samples of each with flat parallel surfaces and
6.1.1 Select samples of each with flat parallel surfaces and
measure the thickness of each to an accuracy of 60.02 mm
measure the thickness of each to an accuracy of 60.02 mm
(0.001 in.) or 0.1 %, whichever is greater.
(0.001 in.) or 0.1%, whichever is greater.
6.2.2 Align the transducer (see Fig. 1) over each sample and
6.1.2 Align the transducer over each sample and obtain a
obtain an optimum signal pattern of as many back echoes as are
nominal signal pattern (see Fig. 1) of as many back echoes as
clearly defined. The time base (sweep control) must be the
are clearly defined. The time base (sweep control) must be set
same for both measurements.
the same for both measurements.
6.2.3 Using a scale or caliper measure the distance at the
6.1.3 Using a scale or caliper measure the distance at the
base line between the leading edge of the first back echo and
base line between the leading edge of the first back echo and
the leading edge of the last back echo that is clearly defined on
the leading edge of the last back echo that is clearly defined on
the known and unknown sample. For better accuracy, adjust the
the known and unknown sample. For better accuracy, adjust the
amplitude of the last back echo by means of the gain control to
amplitude of the last back echo by means of the gain control to
approximately the same height as the first back echo, after the
approximately the same height as the first back echo, after the
position of the leading edge of the first back echo has been
fixed. This adds high frequency components of the signal
which have been attenuated. Then determine the position of the
leading edge of the last back echo. Count the number of round
trips from first echo used to the last echo measured on both
samples. This number will be one less than the number of
echoes used. Note that the sample thickness, number of round
trips, and distance from first to last back echo measured need
not be the same.
6.2.4 Calculate the value of the unknown velocity as fol-
FIG. 1 Initial Pulse and 7 Back Echoes lows:
E 494
v 5 ~A n t v !/~A n t ! (2) 7.1.2.1 A = _________m (in.)
s t s s t s t t
t
7.1.2.2 n = _________
s
where:
7.1.2.3 t = _________m (in.)
s
A = distance from first to Nth back echo on the known
t
7.1.2.4 v = _________m/s (in./s)
t
material, m (in.), measured along the baseline of the
7.1.2.5 A = _________m (in.)
s
A-scan display,
7.1.2.6 n = _________
t
n = number of round trips, unknown material,
s
7.1.2.7 t = _________m (in.)
t
t = thickness of unknown material, m (in.),
s
7.1.2.8 v (using Eq 2) = ___m/s (in./s)
s
v = velocity of transverse wave in known material, m/s
t
7.1.3 Horizontal linearity
(in./s),
7.1.4 Test frequency
A = distance from the first to the Nth back echo on the
s
7.1.5 Couplant
unknown material, m (in.), measured along the base-
7.1.6 Search unit:
line of the A-scan display,
7.1.6.1 Frequency
n = number of round trips, known material, and
t
t = thickness, known material, m (in.). (See Note 3). 7.1.6.2 Size
t
7.1.6.3 Shape
7. Report
7.1.6.4 Type
7.1.6.5 Serial number
7.1 The following are data which should be included in a
7.1.7 Sample geometry
report on velocity measurements:
7.1.8 Instrument:
7.1.1 Longitudinal Wave:
7.1.8.1 Name
7.1.1.1 A = _________m (in.)
k
7.1.8.2 Model number
7.1.1.2 n = _________
l
7.1.8.3 Serial number
7.1.1.3 t = _________m (in.)
l
7.1.8.4 Pertinent control settings
7.1.1.4 v = _________m/s (in./s)
k
7.1.1.5 A = _________m (in.)
l
8. Keywords
7.1.1.6 n = _________
k
7.1.1.7 t = _________m (in.) 8.1 measure of ultrasonic velocity; nondestructive testing;
k
7.1.1.8 v (using Eq 1) = ___m/s (in./s) ultrasonic properties of materials; ultrasonic thickness gages;
l
7.1.2 Transverse Wave: ultrasonic velocity
APPENDIXES
(Nonmandatory Information)
X1. FORMULAS
X1.1 Using the technique of this practice will give results
v = transverse velocity, m/s (or in./s), and
s
2 2
in some instances which are only approximate calculations.
E = Young’s modulus of elasticity, N/m (or lb/in. ) (see
The determination of longitudinal and transverse velocity of
Notes X1.2 and X1.3).
sound in a material makes it possible to approximately calcu-
X1.1.3 Acoustic Impedance (see Note X1.3):
late the elastic constants, Poisson’s ratio, elastic moduli,
z5r v
l
acoustic impedance, reflection coefficient, and transmission
coefficient. In this Appendix, the formulas for calculating some where:
2 2
of these factors are as follows (see Note X1.1): z = acoustic impedance (kg/m · s (or lb/in. · s)).
X1.1.4 Shear Modulus (see Note X1.3):
X1.1.1 Poisson’s Ratio:
G5r v
2 2
s
s5 @1 2 2~v /v ! #/2@1 2 ~v /v ! #
s l s l
X1.1.5 Bulk Modulus (see Note X1.3):
where:
2 2
K5r v 2 4/3!v
@ ~ #
l s
s = Poisson’s ratio,
v = ultrasonic transverse velocity, m/s (or in./s), and
X1.1.6 Reflection Coeffıcient for Energy (R):
s
v = ultrasonic logitudinal velocity, m/s (or in./s).
l
2 2
R 5 ~Z 2 Z ! /~Z 1 Z !
2 1 2 1
X1.1.2 Young’s Modulus of Elasticity:
2 2 2 2 2 where:
E 5 ~r v ~3v 2 4v !#/~v 2 v !
s l s l s
Z = acoustic impedance in Medium 1, and
Z = acoustic impedance in Medium 2.
where: 2
3 3
r = density, kg/m (or lb/in. ), X1.1.7 Transmission Coeffıcient for Energy (T):
v = longitudinal velocity, m/s (or in./s),
l 2
T 5 ~4Z Z !/~Z 1 Z !
2 1 2 1
E 494
NOTE X1.1—The dynamic elastic constants may differ from those NOTE X1.3—When using pounds per cubic inch for density and inches
determined by static tensile measurements. In the case of metals,
per second for velocity, results must be divided by g (acceleration due to
ceramics, and glasses, the differences are of the order of 1 %, and may be
gravity) to obtain results in pounds per square inch for E, G,or K and also
corrected by known theoretical formulas. For plastics the differences may
to obtain results for Z in pounds per square inch per second. Acceleration
be larger, but can be corrected by correlation.
due to gravity (g) = 386.4 in./s · s.
2 −4 2
NOTE X1.2—Conversion factor: 1 N/m = 1.4504 3 10 lb/in. .
X2. IMPORTANT TECHNIQUES FOR MEASURI
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