U.S. patent application number 13/032348 was filed with the patent office on 2011-06-30 for method for structural health monitoring using a smart sensor system.
This patent application is currently assigned to DREXEL UNIVERSITY. Invention is credited to MICHEL W. BARSOUM, SANDIP BASU, PETER FINKEL, AIGUO ZHOU.
Application Number | 20110154903 13/032348 |
Document ID | / |
Family ID | 40382959 |
Filed Date | 2011-06-30 |
United States Patent
Application |
20110154903 |
Kind Code |
A1 |
FINKEL; PETER ; et
al. |
June 30, 2011 |
METHOD FOR STRUCTURAL HEALTH MONITORING USING A SMART SENSOR
SYSTEM
Abstract
The structural health monitoring method of the present invention
utilizes ultrasound to determine information about deformation,
stress and/or damage in structural elements. The method propagates
ultrasound through at least a portion of a material having
fully-reversible nonlinear elasticity, receives the ultrasound
which has been propagated through at least a portion of the
material and determining information about the structural element
from attenuation and/or time of flight of said received
ultrasound.
Inventors: |
FINKEL; PETER; (DOWNINGTOWN,
PA) ; BARSOUM; MICHEL W.; (MOORESTOWN, NJ) ;
BASU; SANDIP; (SECANE, PA) ; ZHOU; AIGUO;
(PHILADELPHIA, PA) |
Assignee: |
DREXEL UNIVERSITY
PHILADELPHIA
PA
|
Family ID: |
40382959 |
Appl. No.: |
13/032348 |
Filed: |
February 22, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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12130234 |
May 30, 2008 |
7917311 |
|
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13032348 |
|
|
|
|
60941865 |
Jun 4, 2007 |
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Current U.S.
Class: |
73/598 |
Current CPC
Class: |
G01M 5/0033 20130101;
G01M 5/0066 20130101; G01M 5/0041 20130101; G01B 17/04 20130101;
G01N 29/4427 20130101; G01N 29/07 20130101; G01D 5/48 20130101;
G01N 29/11 20130101; G01N 2291/0258 20130101 |
Class at
Publication: |
73/598 |
International
Class: |
G01N 29/07 20060101
G01N029/07 |
Goverment Interests
STATEMENT OF GOVERNMENT INTEREST
[0002] This invention was reduced to practice with Government
support under Grant No. DAAD19-03-1-0213 awarded by Army Research
Office; the Government is therefore entitled to certain rights to
this invention.
Claims
1. A method for monitoring a structure comprising: propagating
ultrasound through at least a portion of the structure which
exhibits fully-reversible nonlinear elasticity; receiving the
ultrasound after it has propagated through said portion of the
structure which exhibits fully-reversible nonlinear elasticity, and
determining information relating to said portion of the structure
which exhibits fully-reversible nonlinear elasticity from at least
one of attenuation and time of flight of said received
ultrasound.
2. The method of claim 1, wherein said method is capable of being
carried out within a temperature range of about 123.15 K to about
973.15 K.
3. The method of claim 1, wherein said portion of said structure
which exhibits fully-reversible non-linear elasticity comprises a
material selected from the group consisting of materials having MAX
phases.
4. The method of claim 3, wherein the portion of the structure
having fully-reversible non-linear elasticity comprises a material
selected from the group consisting of Ti.sub.3SiC.sub.2,
Ti.sub.2AlC, graphite, hexagonal-boron nitride, mica, and hexagonal
metals.
5. The method of claim 4, wherein the hexagonal metal is selected
from the group consisting of Co, Mg, and Ti.
6. The method of claim 1, further comprising a step of identifying
a site of deformation, stress or damage in the structure prior to
said step of propagating ultrasound through at least a portion of
the structure.
7. The method of claim 1, wherein said method provides a maximum
stress said structure experienced before a potential occurrence of
structural failure
8. The method of claim 1 wherein said method provides a deformation
history of said structure.
9. The method of claim 1, wherein said method provides an image of
deformation, stress or damage to said structure.
10. The method of claim 1, wherein said information about said
structure is determined from attenuation of said ultrasound by said
portion of the structure.
11. The method of claim 1, wherein said information about said
structure is determined from time of flight of said ultrasound
through said portion of the structure.
12. The method of claim 1, wherein said portion of the structure
which exhibits fully-reversible nonlinear elasticity comprises a
material having a c/a ratio of at least 1.2.
13. The method of claim 1, wherein said portion of the structure
which exhibits fully-reversible nonlinear elasticity comprises a
material having a c/a ratio of at least 1.5.
14. The method of claim 1, wherein said ultrasound is propagated
through an entire part of said structure.
15. The method of claim 1, wherein said ultrasound is propagated
through said entire structure.
16. The method of claim 1, wherein said portion of the structure
which exhibits fully-reversible nonlinear elasticity comprises a
material selected from the group consisting of materials of the
formula: M.sub.n+1AX.sub.n, where M is an early transition metal, A
is an A-group element, X is carbon and/or nitrogen, and n=1-3.
17. The method of claim 16, wherein said portion of the structure
which exhibits fully-reversible nonlinear elasticity comprises a
material selected from the group consisting of ternary carbides and
ternary nitrides.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. patent application
Ser. No. 12/130,234, filed on May 30, 2008, which in turn is a
non-provisional of U.S. provisional application No. 60/941,864,
filed on Jun. 4, 2007, the disclosures of which are hereby
incorporated by reference in their entirety.
BACKGROUND OF THE INVENTION
[0003] 1. Field of the Invention
[0004] The present invention relates to a method for structural
health monitoring (SHM) using a sensor system and ultrasound. The
sensor system may be used to monitor the structural health of
structures including civil engineering structures, such as bridges,
buildings and underwater structures, critical structural elements
in the automobile, aerospace and petrochemical industry as well as
storage structures and reactors.
[0005] 2. Description of the Related Technology
[0006] SHM is used to maintain and preserve the structural
integrity of structures, which degrade over time from exposure to
excipient factors, such as earthquakes, storms, pollution,
vibration, traffic, and other environmental factors. In the last
few decades there has been tremendous interest in developing
methods and sensors, such as strain gages, displacement sensors,
accelerometers, magneto-strictive sensors, fiber optic sensors and
piezoelectric sensors, for detecting structural degradation or
damage.
[0007] Current SHM techniques utilize either global sensing methods
or local sensing methods. Global dynamic methods excite a structure
using low frequency acoustic waves and detect the resulting
corresponding natural frequencies of the structure. The natural
frequency data may then be manipulated with various algorithms to
locate and quantify damage in simple structures. Global dynamic
methods, however, rely on a relatively small number of low order
modes that are insufficiently sensitive to detect localized
incipient damage, which may be critical to structural integrity.
Additionally, the application and detection of low frequency
excitation, typically below 100 Hz, is easily contaminated by
surrounding vibrations and noise. Global static methods, such as
static displacement response and static strain measurement, are
also impractical since they are too expensive to enable a cost and
time efficient structural evaluation.
[0008] Local sensing methods, such as ultrasonic wave propagation
techniques, acoustic emissions, magnetic field analysis, electrical
methods, dye penetrant testing, impact echo testing and X-ray
radiography, are also problematic. A common limitation of local
sensing methods is that a probe needs to be moved around the
structure to first identify a potential site of structural damage
if the location of structural weakness is not already known.
Attempts to overcome this difficulty, with varying success,
included measuring the response from an array of piezoelectric
patches on the surface, magneto-elastic sensors and fiber Bragg
grating methods.
[0009] Of the various local sensing methods, ultrasonic wave
propagation is one of the most promising, enabling detection of
damage and structural flaws with a high degree of sensitivity.
Examples of ultrasonic wave propagation are disclosed in U.S. Pat.
No. 6,996,480 and Lars Lading, et al., "Fundamentals for Remote
Structural Health Monitoring of Wind Turbine Blades", Riso National
Laboratory, 2002. The main drawback of the ultrasonic method is
that it requires several transducers to be installed at various
locations to monitor a particular structure due to the attenuation
and absorption of sound waves in these structures. Often,
ultrasonic transducer installation is time-consuming and expensive
making such methods impractical.
[0010] Ultrasonic methods also typically require complex data
processing. In addition to being expensive, ultrasonic methods also
render the structure unavailable for use throughout the duration of
the test. Due to the nature of sound waves, excitation means for
the ultrasonic transducers has to be coupled directly onto the
structure being monitored. In addition, such systems typically only
work over relatively narrow temperature ranges and under limited
environmental conditions.
[0011] In spite of recent innovations, as far as the inventors are
aware, no sensor, to date, enables highly sensitive detection of
various types of deformation under a wide range of variable
atmospheric, corrosive and temperature conditions. Current sensors
additionally require complex data processing and large amounts of
information to analyze structural deformation. Therefore, there is
a need to develop a sensor system capable of extracting important
parameters from minimal amounts of data using simple data
processing techniques and which is further capable of highly
sensitive detection irrespective of environmental conditions.
SUMMARY OF THE INVENTION
[0012] In one aspect, the present invention relates to a method for
structural health monitoring using ultrasonic wave propagation
through a system including one or more smart sensor elements
comprising at least one material which exhibits fully-reversible
nonlinear elasticity (FRNE).
[0013] Another aspect of the invention is directed to a method
comprising operatively associating at least one smart sensor
element with a structure, propagating ultrasound through the smart
sensor element, receiving the ultrasound propagated through the
smart sensor element, and determining information relating to the
structure from the attenuation and/or the speed of the received
ultrasound. The smart sensor element comprises at least one
material which exhibits fully-reversible nonlinear elasticity
(FRNE).
[0014] Another aspect of the invention is directed to a sensor
system comprising at least one smart sensor, an ultrasound emitter
and a receiver for receiving ultrasound propagated through the
sensor.
[0015] Another aspect of the invention is applicable if the
structural component itself, is made of a material that exhibits
fully-reversible nonlinear elasticity (FRNE), in which case it can
be monitored directly using ultrasound.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1(a) is a schematic showing the formation of incipient
kink bands.
[0017] FIG. 1(b) is a schematic showing mobile dislocation
walls.
[0018] FIG. 1(c) is a schematic showing permanent kink bands.
[0019] FIG. 2 is a schematic diagram of a complex loading unloading
stress-strain response of a kinking nonlinear elastic solid. The
arrows in the figure represent the loading direction.
[0020] FIG. 3 is a graph of
c 44 c 33 ##EQU00001##
vs. c/a.
[0021] FIG. 4 is a schematic of an ultrasonic sensor system in
accordance with the present invention.
[0022] FIG. 5 is a graph of fully reversible hysteretic
stress-strain behavior of Ti.sub.3SiC.sub.2.
[0023] FIG. 6 is a graph of ultrasound attenuation versus stress
for coarse-grain Ti.sub.3SiC.sub.2 under load.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0024] In one aspect, the invention is directed to a method for
structural health monitoring (SHM) of materials using ultrasound
and a smart sensor system. The method involves operatively
associating at least one smart sensor element 1 including at least
one material which has a fully-reversible nonlinear elasticity
(FRNE).sup.3, with a surface of a structure or structural element 2
and using an ultrasonic transducer to propagate ultrasound through
the smart sensor element 1. As the structure 2 degrades over time,
structural stresses will be physically transferred to the sensor 1.
By monitoring and recording changes in the ultrasound attenuation
and/or time of flight of ultrasound propagated through sensor 1 by
means of ultrasonic transducer 3, it is possible to determine one
or more of the presence of, location of and severity of damage to
the structure, as well as generate an image of the structural
damage by using a properly spaced array of sensors 1.
[0025] Sensor 1 should be associated with the structural element 2
in a manner whereby deformation of structural element 2 causes a
corresponding deformation of sensor 1. Thus, it is often desirable
to have a surface of sensor 1 maintained in direct contact with a
surface of structural element 2 for this purpose. Any suitable
means for maintaining sensor 1 in association with structural
element 2 may be employed. In one embodiment, sensor 1 may be
bonded to structural element 2. This bond is sufficiently secure so
as to essentially prevent relative movement between a sensor 1 and
structural element 2 to thereby provide excellent transmission of
stress from structural element 2 to sensor 1. In another
embodiment, sensor 1 may be clamped to structural element 2.
[0026] One aspect of the SHM method and the sensor system of the
present invention involves selecting an appropriate material for
use in sensor 1. The material should have FRNE characteristics to
enable sensor 1 to record and reconstruct the applied stress and
deformation of a structure over time. This deformation phenomenon
may be partially attributed to the reversible formation and the
disassociation of incipient kink bands (IKB). Such materials are
sometimes referred to as kinking nonlinear-elastic materials or KNE
materials.
[0027] FIG. 1(a) shows that as a KNE material is stressed, IKBs
having approximately parallel walls of opposite sign dislocations
that are not dissociated, i.e. still attracted to each other at
their ends, are formed prior to the generation of regular kink
bands (KB). The IKBs dissociate when the load is very high and
produce mobile dislocation walls (MDW), shown in FIG. 1(b), which
lead to permanent deformation. Once the MDW coalesce, kink
boundaries are formed and subsequently produce the kind band
structure depicted in FIG. 1(c). --It is important to note that
this invention is not restricted to the micromechanisms shown in
FIG. 1. Any solid in which fully reversible dislocation motion
occurs--such as dislocation pileups in plastically anisotropic
solids--can be used for this invention. The key aspect is fully
reversible dislocation motion.
[0028] The characterizing feature of KNE material deformation
suitable for the sensor elements of the present invention is the
formation of fully reversible, rate-independent, closed hysteresis
loops in stress-strain curves, delineates deformation process
described in FIG. 1(a)-1(c). These loops are strongly influenced by
grain size, with the energy dissipated per unit volume per cycle,
W.sub.d, being significantly larger in the coarse-grained material.
As the stresses become larger, the hysteresis loops become larger
until the structure fails. FIG. 2 demonstrates a complex loading
and unloading stress-strain response of KNE solids, which are
stress memory materials capable of remembering the highest and/or
lowest points of these hysteresis loops or cycles.
[0029] KNE solids are further characterized by plastic anisotropy,
which typically occurs in materials having high c/a ratio, and/or a
complicated multi-atom unit cells. Plastic anisotropy only allows
for deformation by slip on one easy slip system, which for
hexagonal solids is basal slip. Dislocation motion on other slip
systems is very difficult. The plastic anisotropy due to high c/a
ratio only allows for dislocations on one easy slip system. Any
other kinds of dislocations are of extremely low probability and
thus are insignificant.
[0030] FIG. 3 identifies materials capable of kinking non-linear
deformation by graphing c.sub.44/c.sub.33 versus c/a. KNE solids
having a large c/a ratio lie to the right of the vertical line.
Materials having a c/a ratio of above about 1.2 may be suitable for
use in the present invention if they exhibit fully-reversible
nonlinear elasticity. More preferably, materials having a c/a ratio
above about 1.5 are employed. Solids that allow for more than one
slip system are typically unsuitable for fabricating the sensor 1
of the present invention. KNE solids that exhibit FRNE should thus
have a c/a ratio of at least 1.2, more preferably, the c/a ratio
should be at least 1.5. There is no upper limit on the c/a ratio
since the higher the c/a ratio, the better the material will
perform as a sensing element.
[0031] In one embodiment, sensor 1 is constructed from at least one
KNE solid that is stable over a temperature range of about 4 K to
about 1000 K, more preferably over a temperature range of about 77
K to about 1000 K and most preferably over a temperature range of
about 123.15 K to about 973.15 K. In another embodiment, the KNE
solid is chemically stable, inert and resistant to aggressive
environmental and atmospheric conditions. More preferably, the KNE
solid is generally corrosion resistant, and most preferably, the
KNE solid is specifically resistant to acidic, basic, salt
containing and other corrosive atmospheres such as S-containing
ones.
[0032] Any material exhibiting FRNE behavior and have a c/a ratio
above about 1.2, preferably, above about 1.5 can be used as a
sensor material depending on the maximum possible stress,
temperature and ambient conditions that the material can withstand
without undergoing significant alterations. Sensor 1 may be
configured in various shapes to increase the working range of
stress and/or strain according to the requirements of the
structural element 2.
[0033] In an exemplary SHM method of the present invention, at
least one sensor 1 containing a material exhibiting FRNE behavior
is clamped to a portion of a structural element 2. Optionally, the
method includes a preliminary step of identifying a defect, damage
or stress within structural element 2 or identifying a particular
portion of structural element 2 for which monitoring is desirable,
using any standard technique. Sensor 1 can be employed in
conjunction with a suitable system, to detect and image stress and
damage within structural element 2. Alternatively, sensor 1 may be
used in a sensor system to detect inherent defects in structural
element 2.
[0034] In one embodiment, a conventional ultrasound sensor can be
used to measure the inherent/existing defects in structural element
2 prior to installation of the sensing system of the present
invention. After installation of the sensing system of the present
invention, the sensing system will measure how the existing
inherent defects grow or change by detecting the changing
stress-state in the structural element 2.
[0035] As shown in FIG. 4, sensor 1 may be associated with a
structural element 2 by bonding or using a clamp or other suitable
means such that structural deformation and stress can be
effectively transmitted from structural element 2 to sensor 1. The
securing means should also enable secure long-term retention of
sensor 1 on structural element 2. In a preferred embodiment,
hardened steel clamps can be employed for associating sensor 1 with
structural element 2 for application in bridges or civil
structures; and the clamp can be a hard ceramic if the application
temperature is high and/or the atmosphere is corrosive.
[0036] Sensor 1 may be calibrated by propagating an ultrasonic
pulse through sensor 1 to obtain an initial calibration of the
state of sensor 1 for use as a baseline to monitor the state of
structural element 2. As structural element 2 deforms, is stressed
or degrades over time, the deformation and/or stress will be
physically transferred from structural element 2 to sensor 1.
Ultrasonic pulses may be periodically propagated through sensor 1
to obtain measurements and monitor the condition of structural
element 2 relative to the baseline condition measured during
calibration of sensor 1.
[0037] It is the intention that the ultrasonic pulses should pass
solely through sensor 1 and not penetrate structural element 2 so
as to obtain measurements of the attenuation and time of flight of
the ultrasonic pulses, as influenced by sensor 1 only. A transducer
3 optically coupled to sensor 1 emits ultrasonic pulses and may be
used to receive the ultrasonic pulses after they have passed
through at least a portion of sensor 1. The collected data may be
recorded by a data storage unit associated with a data processing
unit 4. Data processing unit 4 can generate an accurate image of
deformation, stress and/or damage to structural element 2 in real
time. Data processing unit 4 may also determine the location of
deformation, stress or damage based on time of flight data as well
as determine the severity of structural damage using ultrasonic
attenuation by sensor 1. In a preferred embodiment, data may be
transmitted wirelessly to data processing unit 4. Over time it is
possible to generate a history of the changes in structural element
2.
[0038] The SHM method and sensor system of the present application
are capable of providing significant information regarding
structural damage, stress and deformation to structural elements
using a minimal amount of data by interpolating the deformation
history between two consequent measurements. Furthermore, the
sensor system is capable of measuring a wide range of stresses
and/or deformation while requiring a relatively minor amount of
data processing.
[0039] The SHM method and sensor system of the present invention
function by capturing ultrasound attenuation, which is used to
determine the nonlinear elasticity or reversible dislocation motion
within sensor 1. When sensor 1 experiences stress or deformation
transferred from structural element 2, IKBs and/or reversible
dislocations are nucleated and interact with the ultrasound pulses,
causing attenuation and influencing time of flight of the pulses.
Upon unloading, the reversible dislocations or IKBs annihilate and
the attenuation and time of flight influence is no longer observed.
This reversible behavior of stress, ultrasound attenuation and
influence on time of flight may be used to determine the induced
stress for every point of the hysteretic loop, shown in FIG. 2.
Furthermore, the ultrasound attenuation may also be used to
determine the maximum stress structural element 2 experienced
before failure and to deduce the stress/strain deformation history
of structural element 2.
[0040] The sensor system of one embodiment of the present invention
may be useful for structural health monitoring of numerous
structures, particularly civil engineering structures such as
bridges, buildings and underwater structures; structural elements
of automobiles, trains, aircraft, aerospace devices, watercraft,
submersibles and other man made devices and machines; and reactors,
storage structures, etc., that degrade with time due to exposure to
excipient factors, such as earthquakes, storms, pollution,
vibration, traffic, and other environmental factors. The SHM
methods and sensor systems of the present invention enable an
accurate determination of the integrity of these structures,
relative to baseline integrity, at any point in time, and may
enable engineers to determine when and where structural repair is
necessary. The method of the present invention is equally
applicable to historical as well as modern structures and may be
used to maintain and preserve structural elements, monitor
structural damage over time and warn of impending structural
failure. It is envisioned that the SHM method of the present
invention may be particularly beneficial to the aerospace,
automobile and petrochemical industries.
An example of KNE solids are materials having M.sub.n+1AX.sub.n- or
MAX-phases, where M is an early transition metal, A is an A-group
element, X is carbon and/or nitrogen, and n=1-3. The MAX phases,
numbering over 50, are ternary carbides and nitrides. The crystal
structure of MAX phases comprise hexagonal nets of "A" atoms
separated by three nearly close-packed "M" layers that accommodate
"X" atoms in the octahedral sites between them. Typically, suitable
materials are solid, crystalline materials with a crystal lattice
structure. Materials having high temperature capabilities such
Ti.sub.2AlC, are particularly useful since such materials will be
better able to withstand significant atmospheric temperature
variations in use.
[0041] In another embodiment, the actual structural component is
fabricated with a material exhibiting fully-reversible nonlinear
elasticity. In which case, the entire part can be used to monitor
its health and all that required is to propagate ultrasound through
the entire or parts of the structure and measuring its
attenuation.
[0042] Of the MAX phase compounds, Ti.sub.3SiC.sub.2 and
Ti.sub.2AlC are some of the most promising, lightweight candidate
materials for use in sensing elements suitable for high temperature
structural monitoring and other applications. Despite having a
density of about 4.5 gm/cm.sup.3, Ti.sub.3SiC.sub.2 and Ti.sub.2AlC
have a stiffness about three times as high as titanium, but are as
readily machinable as titanium. With a Vickers hardness of
approximately 3 GPa, they are relatively soft, unusually resistant
to thermal shock and highly damage tolerant. Unlike most brittle
solids, edge cracks do not emanate from the corners of hardness
indentations. Rather, intensive kinking, buckling and bending of
individual grains take place in the vicinity of the indentations,
resulting in pseudo-plastic behavior over a wide range of
temperature.
[0043] Polycrystalline Ti.sub.3SiC.sub.2 are further capable of
being cyclically loaded in compression at room temperature to
stresses up to 1 GPa, and fully recover on the removal of the load,
while dissipating about 25% (0.7 MJm.sup.-3) of the mechanical
energy, as shown in FIG. 5. These loss factors are higher than most
woods, and comparable to polypropylene and nylon. FIG. 5 depicts
the typical behavioral plot of a structure composed of
coarse-grained Ti.sub.3SiC.sub.2. The stress-strain curve
delineates a fully reversible, rate-independent, closed hysteresis
loop characteristic of KNE solids. Furthermore, Ti.sub.2AlC,
graphite, hexagonal-boron nitride, most of the hexagonal metals and
mica have similar deformation behavior, which can be attributed to
the reversible formation of dislocations and can be used to
fabricate sensing elements in accordance with the present invention
if the particular material is suitable for the stress, temperature
and atmospheric conditions to which it will be subjected in
use.
[0044] The behavior of the KNE materials allows use of a
calibration curve similar to that shown in FIG. 6, to correlate
ultrasound attenuation by the KNE materials with the stress exerted
on sensor 1. In addition, since KNE materials exhibit reversible
deformation but provide a different response as a result of such
reversible deformation, additional information such as the prior
maximum deformation and deformation history can be obtained from
the ultrasound attenuation data obtained from the KNE materials.
This can be seen in, for example, FIG. 6, where, upon reduction of
the applied stress on the KNE material, the attenuation followed a
different curve (downward arrow) than was followed during
application of the applied stress (upward arrow) to the KNE
material.
[0045] This behavior of the KNE material also permits imaging of
the deformation, stress or damage to a structural element since the
information required for such imaging can be obtained by comparison
to a calibration curve and/or via application of simple algorithms
to correlate ultrasound attenuation and/or time of flight with
specific structural stress and/or damage in the structural
element.
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