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FAA Hughes Technical CenterInnovative Materials Testing Technologies, Inc.
A Highly Sensitive System For Aircraft Crack Detection
– The Rotational Remote Field Eddy Current Probe And Super Sensitive Eddy Current
System Yushi Sun
Innovative Materials Testing Technologies, Inc.2501 N. Loop Drive, Suite 1601, Ames, IA 50010
Tel. 515 296-5328; Fax. 515 296-9910, Email. suny@imtt-usa.com
Cu NguyenFAA William J. Hughes Technical Center, AAR-480
Airport & Aircraft Safety R&D Division, Atlantic City Intl Airport, NJ 08405Tel. 609 485-6649 Fax: (609) 485-4569 Email. cu.nguyen@faa.gov
[1] The work is currently supported by Federal Aviation Administration William J. Hughes Technical Center (FAA/HTC), its Airworthiness Assurance NDI Validation Center (AANC). It was partly supported by The Center for Advanced Technology Development of Iowa State University.
FAA Hughes Technical CenterInnovative Materials Testing Technologies, Inc.
Challenge in Aircraft Inner Layer Crack Detection
1. Detect inner layer cracks from outside aircraft skin (to avoid expensive and time-consuming work of
removal of aircraft interior inspection).2. Deep penetration.3. Sensitivity to small-sized inner layer crack.4. Reliability of detection.5. High-speed and large-area inspection.6. Discriminate noises from different factors, such as edge
effect, etc.7. Low cost – affordable by commercial airlines.8. Convenience in use.
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FAA Hughes Technical CenterInnovative Materials Testing Technologies, Inc.
FG RFEC1 & SSEC2 System
1. Deep penetration in multi-layered aircraft structures – up to 0.8”.
2. High sensitivity to hidden cracks/corrosion.
3. No limit to customized software for enhanced features
4. Simplicity in use
5. Low cost
6. Portability1 FG RFEC – Remote Field Eddy Current technique for inspection of conductive
objects of Flat Geometries.2 SSEC – Super-Sensitive Eddy Current system.
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FAA Hughes Technical CenterInnovative Materials Testing Technologies, Inc.
Indirect energy coupling path
ΦRF
Drive coilPick-up coil
Φ
Indirect energy coupling path
Direct energy coupling path
Energy from indirect coupling path dominates in remote field region, therefore, pick-up coil signal represents the wall
conditions.
RFEC Technique – A Brief Introduction
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FAA Hughes Technical CenterInnovative Materials Testing Technologies, Inc.
FG RFEC Probe
Drive Coil Pickup CoilDirect Coupling Path
Indirect Coupling Path
Specially designed FG RFEC probe blocks direct couple path and forces energy going along indirect
coupling path
FG RFEC Probe
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FAA Hughes Technical CenterInnovative Materials Testing Technologies, Inc.
RF-4 mm V.3Footprint: 0.85” x 2.15”
Coil Center-to-Center DistanceCCD = 1.15”
RF-2 mm V.3Footprint: 0.3” x 0.62”
Coil Center-to-Center DistanceCCD = 0.3”
FG RFEC Probe (Continued)
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FAA Hughes Technical CenterInnovative Materials Testing Technologies, Inc.
Monitor
FG RFEC Probe
Test Panel
SSEC Board & SoftwareInstalled In a Book-Size
PC
Current System Configuration: a PCB inserted in a book-size PC
SSEC System
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FAA Hughes Technical CenterInnovative Materials Testing Technologies, Inc.
Notebook or PC
SSEC SystemFG RFEC Probe
New System Configuration: System connected to PC via USB
USB
SSEC System (Continued)
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FAA Hughes Technical CenterInnovative Materials Testing Technologies, Inc.
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Faster Hole Crack Detection
Mode 1
Raster Scan Using A Sliding FG RFEC Probe
A Traditional Way of Crack Detection
FAA Hughes Technical CenterInnovative Materials Testing Technologies, Inc.
Bottom View
Top View
Inspected Area
Crown Left
0.4”0.3”
DC-10 Crown Panel & Inspected AreaFive layers with a total thickness varying from 0.4” to 0.3”
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FAA Hughes Technical CenterInnovative Materials Testing Technologies, Inc.
L16L15L14L13
L26L25L24L23
Detected EDM #1 on the 5th layer EDM #1
A raster-scan over the standard top.A 5th layer EDM notch is detected, but challenge to signal Interpretation .
Raster-Scan Using An FG RFEC Probe
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FAA Hughes Technical CenterInnovative Materials Testing Technologies, Inc.
Possible Ways for Future Improvement
1. Improve probe design and performances;
2. Reduce/remove fastener signals/(background noises);
3. Develop signal process methods that enhance crack signal or suppress fastener signals;
4. Develop pattern recognition algorithms;
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FAA Hughes Technical CenterInnovative Materials Testing Technologies, Inc.
Faster Hole Crack Detection
Mode 2
Rotational Scan Using A Rotational FG RFEC Probe
A Way to Minimize Fastener Signal In Crack Detection
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FAA Hughes Technical CenterInnovative Materials Testing Technologies, Inc.
Probe Assembly
Probe head
Rotation Guide & Suction System
First Prototype of Rotational Probe
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FAA Hughes Technical CenterInnovative Materials Testing Technologies, Inc.
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Noise/edge effect
EDM Notch
Noise/edge effect Noise/edge effect
Real Component, X Imaginary Component, Y Impendence Plane
EDM Notch EDM Notch
Initial Test ResultsSignal detected from a fifth layer fastener hole EDM Notch on
DC-10 Crown Standard
FAA Hughes Technical CenterInnovative Materials Testing Technologies, Inc.
Requirement in Accurate Centering Probe Rotation & 1st Centering Device Prototype
Non-powered suction cups
Strain-releaser
Slip-ring
FG RFEC Rotational probe
Rotation guide/Theta-Y table
X-adjustment screw
Y/theta-adjustment screw
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FAA Hughes Technical CenterInnovative Materials Testing Technologies, Inc.
Rotation, ϑ, control motor
Y – control motor
X – control motor
Rotational probe Assembly
Cable & connectors
From Miniature Vacuum
Specimen
1st Prototype of Motorized Centering Device
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FAA Hughes Technical CenterInnovative Materials Testing Technologies, Inc.
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Study on Probe Signal Behavior with Variation of Probe Rotational Center
No. 07 No. 08 No. 09 No. 10 No. 11 No. 12 No. 13 No. 14 No. 15
FastenerCenter
Minimum magnitude
locationSignal Magnitude
Signal magnitude evolution as probe rotation center passing over a cracked fastener from its cracked side
8 mils per step
FAA Hughes Technical CenterInnovative Materials Testing Technologies, Inc.
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Y = F(X)MagnitudeReal, X Imaginary, Y
Y = F(X)Real, X MagnitudeImaginary, Y
No. 10
No. 13
FAA Hughes Technical CenterInnovative Materials Testing Technologies, Inc.
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Min = 0.0334 v
Min = 0.0165 v
Signal magnitude variations when rotation center moves around fastener center
A Crack-free fastener hole A Cracked (left) fastener hole
FAA Hughes Technical CenterInnovative Materials Testing Technologies, Inc.
Challenges –
1. Signal/electric center may not be the geometric center of a fastener head;
2. For a cracked fastener hole the location with minimum signal magnitude is neither a geometrical center, nor an electric center.
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FAA Hughes Technical CenterInnovative Materials Testing Technologies, Inc.
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Developing Auto-Centering System
1. To automatically discriminate a cracked fastener hole from crack-free holes;
2. To find the signal/electric center for each fastener hole and provide a right crack signal at the location.
FAA Hughes Technical CenterInnovative Materials Testing Technologies, Inc.
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Current Progresses Made
1. Capable of automatically discriminating cracked fastener holes from crack-free holes in tested panels; It takes 40 – 60 seconds.
2. Working on the issue of finding the signal/electric centers for cracked fastener holes and provide right crack signals at the location for a tested panels.
FAA Hughes Technical CenterInnovative Materials Testing Technologies, Inc.
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Rotational probe carriage
ϑ rotational drive motor
Y-axis drive motor
X-axis drive motor
Test panel
Protection case
2nd Auto-Center Device Prototype
FAA Hughes Technical CenterInnovative Materials Testing Technologies, Inc.
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Next Step & Future Work
1. Continue to study probe behavior around a fastener hole on different panels and fasteners;
2. Continue to develop auto-centering software and to find more efficient indicator(s) for crack discrimination and quantification;
3. Test real aircraft panels with different situations of fastener installation;
4. Consider possible solutions for moving a probe from one faster to another;
5. 3rd prototype design, fabrication, test and POD study.
FAA Hughes Technical CenterInnovative Materials Testing Technologies, Inc.
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CONCLUSIONS1. An FG RFEC rotational probe, is currently under
development. It shows a great potential of rapid detection of deeply hidden cracks and corrosion with high sensitivity and reliability.
2. An accurate centering of probe rotation center is a key to meet the increasing demands in detecting deep and small cracks hidden in aircraft structures and components;
3. A 3D ϑ-X-Y scan mode shows when an FG RFEC probe is rotating around a fastener hole, the signal/electric center may not be the geometrical center of a fastener head.
FAA Hughes Technical CenterInnovative Materials Testing Technologies, Inc.
CONCLUSIONS(continued)
4. When scanning over a cracked hole, the minimum magnitude location is not the signal/electric center where to collect crack signal.
5. An automatic centering device that is capable of discriminating crack signals, locating signal electric center, and providing representative crack signals in currently under development and is supported by FAA William J. Hughes Technical Center.
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