ASTM E494-95(2001)
(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:E494–95 (Reapproved 2001)
Standard Practice for
Measuring Ultrasonic Velocity in Materials
This standard is issued under the fixed designation E494; 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 (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.
combination of the above factors can be expected to be much more
1. Scope
accurate (probably within a 1% tolerance).
1.1 This practice covers a test procedure for measuring
1.5 This standard does not purport to address all of the
ultrasonic velocities in materials with conventional ultrasonic
safety concerns, if any, associated with its use. It is the
pulse echo flaw detection equipment in which results are
responsibility of the user of this standard to establish appro-
displayed in an A-scan display. This practice describes a
priate safety and health practices and determine the applica-
method whereby unknown ultrasonic velocities in a material
bility of regulatory limitations prior to use.
sample are determined by comparative measurements using a
reference material whose ultrasonic velocities are accurately
2. Referenced Documents
known.
2.1 ASTM Standards:
1.2 Thisprocedureisintendedforsolidmaterials5mm(0.2
C597 Test Method for Pulse Velocity Through Concrete
in.) thick or greater. The surfaces normal to the direction of
E317 Practice for Evaluating Performance Characteristics
energy propagation shall be parallel to at least 63°. Surface
of Ultrasonic Pulse-Echo Examination Instruments and
finishforvelocitymeasurementsshallbe3.2µm(125µin.)rms
Systems Without the Use of Electronic Measurement
or smoother.
Instruments
NOTE 1—Sound wave velocities are cited in this practice using the
E797 Practice for Measuring Thickness by Manual Ultra-
fundamental units of meters per second, with inches per second supplied
sonic Pulse-Echo Contact Method
for reference in many cases. For some calculations, it is convenient to
E1316 Terminology for Nondestructive Examinations
think of velocities in units of millimeters per microsecond. While these
units work nicely in the calculations, the more natural units were chosen
3. Terminology
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
3.1 Definitions—For definitions of terms used in this prac-
left, that is, 3500 m/s becomes 3.5 mm/µsec.
tice, see Terminology E1316.
1.3 Ultrasonic velocity measurements are useful for deter-
4. Summary of Practice
miningseveralimportantmaterialproperties.Young’smodulus
4.1 Several possible modes of vibration can propagate in
of elasticity, Poisson’s ratio, acoustic impedance, and several
solids. This procedure is concerned with two velocities of
other useful properties and coefficients can be calculated for
propagation,namelythoseassociatedwithlongitudinal(v)and
solid materials with the ultrasonic velocities if the density is
l
transverse (v) waves. The longitudinal velocity is independent
known (see Appendix X1).
t
of sample geometry when the dimensions at right angles to the
1.4 More accurate results can be obtained with more spe-
beamareverylargecomparedwithbeamareaandwavelength.
cialized ultrasonic equipment, auxiliary equipment, and spe-
Thetransversevelocityislittleaffectedbyphysicaldimensions
cialized techniques. Some of the supplemental techniques are
ofthesample.TheproceduredescribedinSection6is,asnoted
described in Appendix X2. (Material contained in Appendix
in the scope, for use with conventional pulse echo flaw
X2 is for informational purposes only.)
detection equipment only.
NOTE 2—Factors including techniques, equipment, types of material,
and operator variables will result in variations in absolute velocity
5. Apparatus
readings, sometimes by as much as 5%. Relative results with a single
5.1 The ultrasonic testing system to be used in this practice
shall include the following:
5.1.1 Test Instrument—Any ultrasonic instrument compris-
This practice is under the jurisdiction of ASTM Committee E07 on Nonde- ing a time base, transmitter (pulser), receiver (echo amplifier),
structive Testing and is the direct responsibility of Subcommittee E07.06 on
Ultrasonic Method.
Current edition approved January 15, 1995. Published March 1995. Originally Annual Book of ASTM Standards, Vol 04.02.
published as E494–73. Last previous edition E494–92a. Annual Book of ASTM Standards, Vol 03.03.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E494–95 (2001)
andanA-scanindicatorcircuittogenerate,receive,anddisplay the leading edge of the last back echo that is clearly defined on
electrical signals related to ultrasonic waves. Equipment shall theknownandunknownsample.Forbetteraccuracy,adjustthe
allow reading the positions of A , A , A, A (defined in 6.1.4
amplitudeofthelastbackechobymeansofthegaincontrolto
k s t l
and 6.2.4), along theA-scan base line within 60.5 mm (0.020 approximately the same height as the first back echo, after the
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
fixed. This allows more accurate time or distance measure-
echoes, and preferably five, shall be used.
ments.Thepositionoftheleadingedgeofthelastbackechois
5.1.2 Search Unit—The search unit containing a search unit
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
methodshallbeused.Contactstraightbeamlongitudinalmode
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
tothelastechomeasuredonbothsamples.Thisnumberwillbe
measurements.
one less than the number of echoes used. Note that the sample
5.1.3 Couplant—For longitudinal velocity measurements,
thickness,numberofroundtrips,anddistancefromfronttolast
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,ahighviscositymaterialsuchasresinorsolidbond
lows:
shall be used. In some materials isopolybutene, honey, or other
v 5 ~A n t v !/~A n t ! (1)
high-viscosity materials have been used effectively. Most 1 k l l k l k k
liquids will not support transverse waves. In porous materials
where:
special nonliquid couplants are required. The couplant must
A = distance from first to Nth back echo on the known
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,
5.1.4.1 Velocity Standard—Anymaterialofknownvelocity,
n = number of round trips, unknown material,
l
that can be penetrated by the acoustical wave, and that has an
t = thickness of unknown material, m (in.),
l
appropriate surface roughness, shape, thickness, and parallel-
v = velocity in known material, m/s (in./s),
k
ism. The velocity of the standard should be determined by
A = distance from the first to the Nth back echo on the
l
some other technique of higher accuracy, or by comparison
unknown material, m (in.), measured along the
with water velocity that is known (see Appendix X2.5 and
baseline of the A-scan display,
AppendixX4).Thereferenceblockshouldhaveanattenuation n = number of round trips, known material, and
k
similar to that of the test material. t = thickness, known material, m (in.).
k
5.1.4.2 For horizontal linearity check, see Practice E317.
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 )
6.1 Longitudinal Wave Velocity—Determine bulk, longitu-
s
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).
of ultrasound in a velocity standard (v ).
t
k
6.1.1 Select samples of each with flat parallel surfaces and
6.2.1 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.
6.1.2 Align the search unit over each sample and obtain a
6.2.2 Alignthesearchunit(seeFig.1)overeachsampleand
nominal signal pattern (see Fig. 1) of as many back echoes as
obtainanoptimumsignalpatternofasmanybackechoesasare
are clearly defined. The time base (sweep control) must be set
clearly defined. The time base (sweep control) must be the
the same for both measurements.
same for both measurements.
6.1.3 Using a scale or caliper measure the distance at the
6.2.3 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
theknownandunknownsample.Forbetteraccuracy,adjustthe
amplitudeofthelastbackechobymeansofthegaincontrolto
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
whichhavebeenattenuated.Thendeterminethepositionofthe
leading edge of the last back echo. Count the number of round
trips from first echo used to the last echo measured on both
FIG. 1 Initial Pulse and 7 Back Echoes samples. This number will be one less than the number of
E494–95 (2001)
echoes used. Note that the sample thickness, number of round 7.1.1.7 t =_________m (in.)
k
trips, and distance from first to last back echo measured need 7.1.1.8 v (using Eq 1)=___m/s (in./s)
l
not be the same. 7.1.2 Transverse Wave:
6.2.4 Calculate the value of the unknown velocity as fol- 7.1.2.1 A =_________m (in.)
t
lows: 7.1.2.2 n =_________
s
7.1.2.3 t =_________m (in.)
s
v 5 ~A n t v !/~A n t ! (2)
s t s s t s t t
7.1.2.4 v =_________m/s (in./s)
t
where:
7.1.2.5 A =_________m (in.)
s
A = distance from first to Nth back echo on the known
7.1.2.6 n =_________
t
t
material, m (in.), measured along the baseline of the
7.1.2.7 t =_________m (in.)
t
A-scan display,
7.1.2.8 v (using Eq 2)=___m/s (in./s)
s
n = number of round trips, unknown material,
s 7.1.3 Horizontal linearity
t = thickness of unknown material, m (in.),
s
7.1.4 Test frequency
v = velocity of transverse wave in known material, m/s
t
7.1.5 Couplant
(in./s),
7.1.6 Search unit:
A = distance from the first to the Nth back echo on the
s
7.1.6.1 Frequency
unknown material, m (in.), measured along the base-
7.1.6.2 Size
line of the A-scan display,
7.1.6.3 Shape
n = number of round trips, known material, and
t
7.1.6.4 Type
t = thickness, known material, m (in.). (See Note 3).
t
7.1.6.5 Serial number
7.1.7 Sample geometry
7. Report
7.1.8 Instrument:
7.1 The following are data which should be included in a
7.1.8.1 Name
report on velocity measurements:
7.1.8.2 Model number
7.1.1 Longitudinal Wave:
7.1.8.3 Serial number
7.1.1.1 A =_________m (in.)
k
7.1.8.4 Pertinent control settings
7.1.1.2 n =_________
l
8. Keywords
7.1.1.3 t =_________m (in.)
l
7.1.1.4 v =_________m/s (in./s) 8.1 measure of ultrasonic velocity; nondestructive testing;
k
7.1.1.5 A =_________m (in.) ultrasonic properties of materials; ultrasonic thickness gages;
l
7.1.1.6 n =_________ ultrasonic velocity
k
APPENDIXES
(Nonmandatory Information)
X1. FORMULAS
X1.1 Using the technique of this practice will give results
where:
3 3
in some instances which are only approximate calculations.
r = density, kg/m (or lb/in. ),
The determination of longitudinal and transverse velocity of v = longitudinal velocity, m/s (or in./s),
l
sound in a material makes it possible to approximately calcu- v = transverse velocity, m/s (or in./s), and
s
2 2
E = Young’s modulus of elasticity, N/m (or lb/in. ) (see
late the elastic constants, Poisson’s ratio, elastic moduli,
Notes X1.2 and X1.3).
acoustic impedance, reflection coefficient, and transmission
coefficient.InthisAppendix,theformulasforcalculatingsome X1.1.3 Acoustic Impedance (see Note X1.3):
of these factors are as follows (see Note X1.1):
z5rv
l
X1.1.1 Poisson’s Ratio:
where:
2 2
2 2
s5 @1 22~v /v ! #/2@1 2 ~v /v ! #
s l s l z = acoustic impedance (kg/m · s (or lb/in. · s)).
X1.1.4 Shear Modulus (see Note X1.3):
where:
s = Poisson’s ratio,
G5rv
s
v = ultrasonic transverse velocity, m/s (or in./s), and
s
X1.1.5 Bulk Modulus (see Note X1.3):
v = ultrasonic longitudinal velocity, m/s (or in./s).
l
2 2
X1.1.2 Young’s Modulus of Elasticity: K5r @v 2 ~4/3!v #
l s
2 2 2 2 2
E 5 ~rv ~3v 24v !#/~v 2 v ! X1.1.6 Reflection Coeffıcient for Energy (R):
s l s l s
E494–95 (2001)
2 2
determined by static tensile measurements. In the case of metals,
R 5 ~Z 2 Z ! /~Z 1 Z !
2 1 2 1
ceramics, and glasses, the differences are of the order of 1%, and may be
corrected by known theoretical formulas. For plastics the differences may
where:
be larger, but can be corrected by correlation.
Z = acoustic impedance in Medium 1, and
2 −4 2
NOTE X1.2—Conversion factor: 1 N/m =1.4504 310 lb/in. .
Z = acoustic impedance in Medium 2.
NOTE X1.3—When using pounds per cubic inch for density and inches
X1.1.7 Transmission Coeffıcient for Energy (T):
per second for velocity, results must be divided by g (acceleration due to
gravity)toobtainresultsinpoundspersquareinchfor E, G,or Kandalso
T 5 4Z Z !/ Z 1 Z !
~ ~
2 1 2 1
to obtain results for Z in pounds per square inch per second.Acceleration
NOTE X1.1—The dynamic elastic constants may differ from those due to gravity (g)=386.4 in./s · s.
X2. IMPORTANT TECHNIQUES FOR MEASURING ULTRASONIC VELOCITY IN MATERIALS
Velocity ~m/s ~orin./s!!5@2thickness ~morin.!#/@Time ~s!#
X2.1 Introduction
X2.1.1 Several techniques are available for precise mea-
X2.4 Electronic Time Marker
surement of ultrasonic velocity
...
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