Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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SYSTEMS AND METHODS FOR DETERMINING THE VELOCITY
OF ULTRASONIC SURFACE SKIMMING LONGITUDINAL WAVES
ON VARIOUS MATERIALS
FIELD OF THE INVENTION
[0001] The present invention relates generally to non-destructive measuring
techniques, and more specifically, to determining the velocity of ultrasonic
surface
skimming longitudinal waves on various materials and/or to determining the
crystallographic orientations of various materials based upon the velocity of
the
ultrasonic surface skimming longitudinal waves thereon.
BACKGROUND OF THE INVENTION
[0002] Recently, cracks in some gas turbine engine components were attributed
to
the directionally solidified grains therein having a primary crystal grain
orientation
that deviated from the [0011 axis much further than expected. Therefore, there
has
become a need to be able to non-destructively determine the primary crystal
grain
orientation in directionally solidified and single crystal materials to ensure
that the
primary crystal grain orientation falls within certain limits of a
predetermined crystal
axis.
[0003] One conventional non-destructive method of determining the
crystallographic orientations of single crystal materials, commonly known as
the Laue
method, involves directing x-rays onto the material, where they are reflected
therefrom and/or therethrough and captured as an x-ray diffraction pattern,
which can
then be analyzed to determine the crystallographic orientations of the
material. The
Laue method, while capable of determining both the primary and secondary grain
orientations of single crystal materials, is time consuming and cannot be
easily
utilized to determine the crystallographic orientations of various gas turbine
engine
components on-wing or in production environments, etc. Furthermore, the Laue
method cannot be feasibly used on columnar-grained materials (i.e.,
directionally
solidified materials) because it would be too expensive and too cumbersome to
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reorient the material with respect to the stacking axis to determine the
crystallographic
orientations of each individual grain therein.
[0004] Therefore, it would be desirable to have improved systems and methods
for accurately and non-destructively determining the crystallographic
orientations of
directionally solidified and/or single crystal materials. It would be
desirable if the
crystallographic orientations of such materials could be determined based upon
the
measured velocity of ultrasonic surface skimming longitudinal waves thereon.
It
would also be desirable if such systems and methods could be easily used in
various
environments (i.e., on-wing, in production environments, in engine overhaul
shops,
etc.). It would be even further desirable if these velocity determining
systems and
methods could be used for other purposes, such as for sorting various
materials, etc.
SUMMARY OF THE INVENTION
[00051 The above-identified shortcomings of existing systems and methods
for determining the crystallographic orientations of a material are overcome
by
embodiments of the present invention, which relates to systems and methods for
non-
destructively measuring the velocity of ultrasonic surface skimming
longitudinal
waves on a material. The measured velocity can then be used for various
purposes,
such as for determining the crystallographic orientations of the material,
sorting
various materials, etc.
[00061 Embodiments of this invention comprise methods for determining the
velocity of an ultrasonic surface skimming longitudinal wave on a material.
These
methods may comprise: generating an ultrasonic surface skimming longitudinal
wave
at a first location on the material; detecting at least a portion of the
ultrasonic surface
skimming longitudinal wave at a second location on the material; and
determining the
velocity of the ultrasonic surface skimming longitudinal wave between the
first
location and the second location. Once the velocity is determined, the method
may
further comprise: determining at least one crystallographic orientation of the
material
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based upon the velocity; sorting a plurality of materials from one another
based upon
the velocity; etc.
[0007] Embodiments of this invention also comprise methods for determining
one or more crystallographic orientations of a material. These methods may
comprise: generating an ultrasonic wave at a first location on the material;
detecting at
least a portion of the ultrasonic wave at a second location on the material;
determining
at least one crystallographic orientation of the material from the detected
ultrasonic
wave. The determining step may comprise: measuring the time of flight of the
ultrasonic wave; determining the longitudinal velocity of the material based
upon the
distance between the first location and the second location and the time of
flight of the
ultrasonic wave; and determining at least one crystallographic orientation of
the
material utilizing the longitudinal velocity of the material. These ultrasonic
waves
may comprise surface skimming longitudinal waves having a longitudinal
velocity
that is dependent upon the primary crystallographic orientation of the
material, but not
upon the secondary crystallographieorientation of the material.
[0008] Embodiments of this invention comprise systems for measuring the
velocity of an ultrasonic surface skimming longitudinal wave on a material.
These
systems may comprise: an ultrasonic wave emitter; an ultrasonic wave detector;
and
means for determining the velocity of an ultrasonic surface skimming
longitudinal
wave on the material. The systems may further comprise means for determining
at
least one crystallographic orientation of the material utilizing the velocity
of the
ultrasonic surface skimming longitudinal wave. The ultrasonic wave emitter
should
be capable of emitting ultrasonic waves at a predetermined angle with respect
to the
surface of the material. The ultrasonic wave detector should be capable of
detecting
at least a portion of the ultrasonic surface skimming longitudinal wave at a
predetermined location.
[0009] Embodiments of this invention may be utilized on directionally
solidified materials, single crystal materials, and/or polycrystalline
materials. These
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materials may comprises various gas turbine engine components, such as, but
not
limited to, turbine blades, combustor liners, blade outer air seals, etc.
[0010] Embodiments of this invention may be utilized in various
environments, such as, but not limited to, (a) while the component is on-wing;
(b)
while the component is in a production environment; (c) while the component is
in an
engine overhaul facility; (d) while the component is in a material salvage
facility;
and/or (e) while the component is in a re-work facility.
[0011] The systems and methods of this invention may utilize contact
configurations, immersion configurations, and/or bubbler configurations.
[0012] Further details of this invention will be apparent to those skilled in
the
art during the course of the following description.
DESCRIPTION OF THE DRAWINGS
[0013] Embodiments of this invention are described herein with reference to
various figures, wherein like characters of reference designate like parts
throughout
the drawings, in which:
[0014] Figure 1 is a schematic drawing showing an embodiment of this
invention utilizing a contact technique having a pitch-catch ultrasonic wave
configuration;
[0015] Figure 2 is a schematic drawing showing an embodiment of this
invention utilizing an immersion technique having a pitch-catch ultrasonic
wave
configuration; and
[0016] Figure 3 is a schematic drawing showing an embodiment of this
invention utilizing a bubbler technique having a pitch-catch ultrasonic wave
configuration.
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DETAILED DESCRIPTION OF THE INVENTION
[0017] For the purposes of promoting an understanding of the invention,
reference will now be made to some embodiments of this invention as
illustrated in
FIGURES 1-3 and specific language used to describe the same. The terminology
used herein is for the purpose of description, not limitation. Specific
structural and
functional details disclosed herein are not to be interpreted as limiting, but
merely as a
basis for teaching one skilled in the art to variously employ the present
invention.
Any modifications or variations in the depicted structures and methods, and
such
further applications of the principles of the invention as illustrated herein,
as would
normally occur to one skilled in the art, are considered to be within the
spirit and
scope of this invention as described and claimed.
[0018] This invention relates to systems and methods for measuring the
velocity of ultrasonic surface skimming longitudinal waves on various
materials.
Embodiments of these systems and methods may be used for non-destructively
determining at least one crystal grain orientation (i.e., primary and/or
secondary, etc.)
of various materials based upon the measured velocity of the ultrasonic
surface
skimming longitudinal waves thereon. Such embodiments may be utilized on any
single grain of material (i.e., on columnar grains in directionally solidified
materials,
on single grains in single crystal materials, and/or on single grains in
polycrystalline
materials), provided the grain is large enough to allow the emitter and the
detector to
be properly positioned with respect thereto. Embodiments of this invention may
also
be used for other purposes, such as, for example, for sorting various
materials, for any
purposes where only one surface of a material is available for evaluation,
and/or for
any purposes where longitudinal velocity measurements may be useful, etc. The
systems of this invention may be small and compact enough to be used almost
anywhere in various environments, such as in production environments, on-wing,
in
engine overhaul facilities, in material salvage or re-work facilities, etc.
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[0019] Embodiments of this invention utilize a contact technique having a
pitch-catch ultrasonic wave configuration as shown in Figure 1. An emitter 10
positioned within a contact transducer 50 at a predetermined angle 30
generates
ultrasonic shear waves 16 and ultrasonic compressional waves 17 in the
material 40.
When the compressional waves 17 are refracted at angles that include waves
propagating along the surface 42 of the material 40, a surface skimming
longitudinal
wave 18 is created. Generally, this means that the incident wave 14 should be
near
the first critical angle as defined by Snell's law for the wedge material of
the contact
transducers 50, 60 and the material 40 be analyzed. The surface skimming
longitudinal wave 18 is a leaky wave that emits leaking ultrasonic energy 19
from the
surface 42 of the material 40. This leaking ultrasonic energy 19 is
transmitted to the
detector when the detector 20 is in direct contact with the surface 42 of the
material
40. A detector 20 positioned within a contact transducer 60 detects the
leaking
ultrasonic waves 19, and the time-of-flight of the surface skimming
longitudinal
waves 18 between points A and B can be determined therefrom. The surface
skimming longitudinal waves 18 and the associated leaking ultrasonic waves 19
arrive
at the detector 20 first because they travel faster than the shear wave 16 and
any of its
reflected components. The time-of-flight of the surface skimming longitudinal
wave
18 is indicative of the longitudinal velocity of the material 40, which varies
depending
upon the primary crystal grain orientation of the material.
[0020] The emitter 10 may comprise any ultrasonic wave emitter capable of
emitting suitable ultrasonic waves. The detector 20 may comprise any
ultrasonic
wave detector capable of detecting the desired ultrasonic waves. In
embodiments, the
ultrasonic waves may have a frequency of about 5-15 MHz, but many other
suitable
frequencies are also possible, and this invention is not limited to any
particular
frequency range.
[0021] In operation, the emitter 10 may be adjusted to emit ultrasonic waves
at any suitable angle 30, such as, but not limited to, about 22-28 from
normal to the
surface 42 of the material 40, so as to create compressional waves 17 at an
angle near
the longitudinal critical angle of the average velocity of the material 40.
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[0022] The precise locations of points A and B can be easily determined by
utilizing two reference samples having known velocities (V 1 and V2,
respectively) to
calibrate the transducers 50 and 60, which are held at a constant distance
from one
another. First, the time of flight (TOFt and TOF2, respectively) of the
surface
skimming longitudinal waves 18 can be measured on each of the two reference
samples. The two unknowns (surface distance between points A and B, SD, and
time
within the contact transducers 50, 60, TW) can then be determined for the
ultrasonic
wave. The surface distance, SD, can be determined by the following equation.
SD = (TOFI - TOF2) * (V2*Vl)/(V2-Vl)
The time of flight attributable to the time that the ultrasonic wave spends
within the
contact transducers 50 and 60, TW, can be determined by the following
equation.
TW = TOF, - SDNI
Once the values of SD and TW are known, one can then determine the velocity
(V,,,,k)
of an unknown material by measuring the time of flight (TOF,u,0 of the
ultrasonic
surface skimming wave thereon and utilizing that TOF,,,,k in the following
equation.
V,,,,k = SD/(TOFõnk - TW)
Thereafter, since longitudinal wave velocity variations are primary crystal
grain
orientation dependent, the primary crystal grain orientation of the material
40 may be
determined.
[0023] The primary crystal grain orientations of the material 40 may be
determined in various ways. In some embodiments, the primary crystal grain
orientations of the material 40 may be determined by comparing the
measured/calculated longitudinal velocity of the material 40 with samples
having
known crystal grain orientations and known longitudinal velocities. In other
embodiments, the primary crystal grain orientations of the material 40 may be
determined from theoretical calculations based on single crystal elastic
constants.
[0024] The secondary crystal grain orientations of the material 40 may also be
determined. This may be accomplished by orienting the contact transducer pair
50,
60 in a direction parallel to the secondary orientation and performing the
same
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calculations as performed for determining the primary orientation. As with the
primary orientation, velocity is first deduced from the time of flight
measurement, and
then the associated orientation may be determined either from the measured or
calculated values.
[0025] Embodiments of this invention may also utilize an immersion
technique having a pitch-catch ultrasonic wave configuration as shown in
Figure 2.
The immersion technique may be carried out in a fluid bath 200 in any suitable
fluid
medium 100, such as, but not limited to, water, oil, etc. The immersion
technique is
similar to the contact technique described above, except in the immersion
technique,
there are no contact transducers 50, 60, and instead, a constant fluid path is
maintained between the emitter 10 and the detector 20. A constant fluid path
is also
maintained between the emitter 10 and the surface 42 of the material 40, and
between
the detector 20 and the surface 42 of the material 40. In immersion
embodiments, the
leaking ultrasonic energy 19 will be transmitted to the detector 20, and may
also be
emitted into the fluid medium 100. In the immersion technique, as in the
contact
technique, the distance between the emitter 10 and the detector 20 is
constant, and the
emitter 10 and the detector 20 are held in fixed positions, so the distance
between
points A and B is constant. The calculations and measurements in the immersion
technique are otherwise similar to those discussed above for the contact
technique.
[0026] Embodiments of this invention may also utilize a bubbler technique
having a pitch-catch ultrasonic wave configuration as shown in Figure 3. The
bubbler
technique is similar to the contact technique described above, but in the
bubbler
technique, any suitable fluid (i.e., water, oil, etc.) may be used to carry
the ultrasonic
wave from the emitter 10 to the material 40, and from the material 40 to the
detector
20. Tubes or other suitable bubbler transducers 11, 21 may be used to carry
fluid to
maintain a fluid path between the emitter 10 and the material 40, and between
the
detector 20 and the material 40. In bubbler embodiments, the leaking
ultrasonic
energy 19 will be transmitted to the detector 20 through the fluid in the
bubbler
transducer 21. The calculations and measurements in the bubbler technique are
otherwise similar to those discussed above for the contact technique.
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[0027] This invention can be used to determine the crystallographic
orientations of many directionally solidified or single crystal materials,
such as those
used in aero and/or land based gas turbine engine components. Some exemplary
components that this invention may be utilized with include, but are not
limited to,
high pressure turbine blades, low pressure turbine blades, combustor liners,
blade
outer air seals, etc.
[0028] This invention can be used for various purposes. In addition to using
the velocity of the surface skimming longitudinal waves 18 to determine the
crystal
grain orientations of various materials, the velocity of the surface skimming
longitudinal waves 18 may also be used for other purposes, such as, for
example, to
sort various materials from one another, to determine a longitudinal velocity
that
could then be used for a thickness measurement, etc. Various materials may be
sorted
from one another because different materials would have different velocities.
[0029] Various contact, immersion and bubbler techniques were utilized to
verify the feasibility and accuracy of this invention. Ultrasonic surface
skimming
longitudinal waves were observed and measured for various polycrystalline,
directionally solidified and single crystal materials, including various
nickel alloys,
titanium alloys, aluminum alloys and copper alloys.
[0030] In embodiments, the contact technique utilized wedges made of
Perspex'o material having 5-15 MHz transducers embedded therein. The incident
angles 30 tested varied from about 25-30 from normal to the surface 42 of the
material 40. Several samples comprised single crystal materials so the
velocity
dependence upon primary crystal grain orientation could be tested. Bulk
longitudinal
velocities of various materials were also measured at specific orientations so
comparisons thereof could be made with the velocities of the surface skimming
longitudinal waves.
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[0031] In embodiments, the immersion technique utilized 10 MHz transducers
and water. Several measurements were made on various materials having known
velocities. Some embodiments utilized a single transducer in pulse/echo mode,
and
measurements of time-of-flight for a reflected signal from an edge were
obtained.
Other embodiments utilized two immersion transducers in a pitch/catch
configuration
in a fixture having a known separation therebetween, and measurements of time-
of-
flight for an ultrasonic surface skimming longitudinal wave were obtained.
[0032] In embodiments, the bubbler technique utilized a fixture that held
small bubbler transducers 11, 21 at fixed positions, and measurements of time-
of-
flight for an ultrasonic surface skimming longitudinal wave were obtained.
[0033] The velocities of the ultrasonic surface skimming longitudinal waves
of samples having unknown crystal grain orientations were compared to
velocities of
samples having known crystal grain orientations, which had their crystal grain
orientations previously determined via the Laue x-ray technique. Such
velocities
were measured on unknown samples at various positions and orientations on the
surfaces thereof (i.e., throughout 360 ), and crystal grain orientations were
determined
therefrom. The crystal grain orientations obtained by the methods of this
invention
were found to match those obtained by the Laue technique within about +/- 1 .
[0034] While ultrasonic waves (i.e., longitudinal waves and shear waves) have
been used to inspect for subsurface reflectors in polycrystalline materials,
and
ultrasonic waves (i.e., Rayleigh surface waves) have been used to
measure/inspect for
surface anomalies in various polycrystalline materials, ultrasonic waves
(i.e., surface
skimming longitudinal waves) have not been used to determine velocities of
various
materials to determine crystal grain orientations of directionally solidified
or single
crystal materials and/or to sort various materials, etc. When ultrasonic
longitudinal
and shear waves are used to inspect for subsurface reflectors in
polycrystalline
materials, the amplitude and time-of-flight of reflected ultrasonic waves can
be used
to detect and evaluate features within the volume of a material. When
ultrasonic
Rayleigh surface waves are used to measure/inspect for surface anomalies in
various
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polycrystalline materials, the anomalies in the Rayleigh surface waves can be
used to
evaluate surface defects on a material. When ultrasonic surface skimming
longitudinal waves are used, the velocity at which an ultrasonic surface
skimming
longitudinal wave travels along the surface of a material can be used to
determine the
crystal grain orientations of the material, among other things. These are
three very
different techniques, which measure very different items of interest on
different types
of materials.
[0035] As described above, this invention provides systems and methods for
non-destructively determining the velocity of surface skimming longitudinal
waves on
various materials. Advantageously, the systems and methods of this invention
can be
easily and economically used in various environments (i.e., on-wing, in
production
environments, in engine overhaul facilities, in material salvage facilities,
in re-work
facilities, etc.). Furthermore, the systems and methods of this invention can
be used
for various purposes (i.e., to determine crystal grain orientations of various
materials,
to sort various materials, for any purposes where longitudinal velocity
measurements
may be useful, etc.). In addition to being able to use the systems and methods
of this
invention in environments where the Laue technique cannot be used, this
invention
could also be used instead of, and much easier than, the Laue technique in
many
instances. Many other advantages will be apparent to those skilled in the
relevant art.
[0036] Various embodiments of this invention have been described in
fulfillment of the various needs that the invention meets. These embodiments
are
merely illustrative of the principles of various embodiments of the present
invention.
Numerous modifications and adaptations thereof will be apparent to those
skilled in
the art without departing from the spirit and scope of the present invention.
Thus, it is
intended that the present invention cover all suitable modifications and
variations as
come within the scope of the appended claims and their equivalents.
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