eddy current inspection of composites - jentek sensors … asnt spring... · eddy current...
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Slide 1 Copyright © 2013 JENTEK Sensors All Rights Reserved.
MWM sensors and MWM-Arrays are covered by several issued and pending patents, including, but not limited to: 8,237,433, 8,222,897,8,050,883, 7,994,781, 7,876,094, 7,812,601, 7,696,748, 7,589,526, 7,533,575, 7,528,598, 7,526,964, 7,518,360, 7,467,057, 7,451,657, 7,451,639,7,411,390, 7,385,392, 7,348,771, 7,289,913, 7,280,940, 7,230,421, 7,188,532, 7,183,764, 7,161,351, 7,161,350, 7,106,055, 7,095,224, 7,049,811,6,995,557, 6,992,482, 6,952,095, 6,798,198, 6,784,662, 6,781,387, 6,727,691, 6,657,429, 6,486,673, 6,433,542, 6,420,867, 6,380,747, 6,377,039,6,351,120, 6,198,279, 6,188,218, 6,144,206, 5,966,011, 5,793,206, 5,629,621, 5,990,677 and RE39,206 (other US/foreign patents issued and pending).
ASNT Spring Research Symposium 2013Memphis, TN
March 18-21, 2013
© JENTEK Sensors 2013
Eddy CurrentInspection of CompositesZachary Thomas, Neil Goldfine, Christopher Martin,
Robert Lyons, and Andrew Washabaugh
JENTEK Sensors, Inc., 110-1 Clematis Avenue, Waltham, MA 02453-7013 Phone: 781-642-9666; Email: jentek@jenteksensors.com
Copyright © 2013 JENTEK Sensors All Rights Reserved.
Slide 2 Copyright © 2013 JENTEK Sensors All Rights Reserved.
Presentation Outline
• Background– Development program goals– MWM-Array® technology– Depth of penetration of sensing fields
• Basic model predictions and validation measurements– Eddy-current extension of micromechanical model– Orientation effects– Field spatial variations
• Example imaging applications– Volumetric imaging of damage– Composite Overwrapped Pressure Vessel imaging
• Summary
Slide 3 Copyright © 2013 JENTEK Sensors All Rights Reserved.
Development Program Approach
• Goals– To develop model-based methods for (primarily) carbon fiber composite NDT– To demonstrate high resolution damage and condition imaging for composites– To develop volumetric stress sensing magnetic stress gages for composites
• Approach– Focus on eddy current methods and sensor designs that are readily modeled.– MWM-Arrays uses a linear drive eddy current sensor array construct
• Can induce eddy currents in the linear fibers of carbon fiber composites• Use winding geometry changes to alter penetration depth and assess
material condition (e.g., damage and stress)• Funding
– NASA for micromechanical model development and application to composite overwrapped pressure vessels (COPVs)
– Army for rotorblade NDT– Navy for NDT of aircraft composites
Slide 4 Copyright © 2013 JENTEK Sensors All Rights Reserved.
MWM®-Array Technology• Eddy current array geometry designed to match (isotropic) models for responses• The voltage induced on sense element(s) is measured.• Measurement grid methods provide conversion of measured responses into physical
properties (e.g., conductivity, lift-off, permeability)
MeasurementGrid Methods
Magnetic field interactingwith test material
Slide 5 Copyright © 2013 JENTEK Sensors All Rights Reserved.
Example MWM®-Arrays• MWM-Array dimensions can be adjusted for the application
=> Drive-sense gap (spatial wavelength) affects penetration depth
FA1547 elements
medium wavelength
FA497 elements
several wavelengths
FA2837 elements
small wavelength
FA2437 elements
large wavelength
Slide 6 Copyright © 2013 JENTEK Sensors All Rights Reserved.
MWM-Array Depth of Penetration• Magnetic field decays exponentially with distance away from sensor
– Decay rate determined by skin depth at high frequencies and sensor dimensions at low frequency
increasing size
Skin depthlimited
0.1
2
3
456
1
2
3
456
Pen
etra
tion
Dep
th (
mm
)
103 104 105 106 107 108 109
Frequency (Hz)
456
10
2
3
456
100
2
3
Pen
etration D
epth (m
ils)
FA28
FA24 Electrical Conductivity
(kS/m)
10100 1
MWM-Array
FA154
0
Slide 7 Copyright © 2013 JENTEK Sensors All Rights Reserved.
Micromechanical Model: Eddy-Current Extension• Model considers fiber bundles as a composite cylinder assemblage
– Solve for field around a single fiber and extend to fiber bundle– Effective complex permeability and conductivity depend upon orientation with respect to fiber axis,
fiber density and fiber contact• For carbon fiber composites
– Graphite fibers: ~7 m diameter, nonmagnetic, ~20 kS/m (0.0344%IACS)– Radius << skin depth for typical eddy-current frequencies
• Indicates a strong orientation dependence of the properties– MWM-Arrays with linear drives can provide a measure of these orientation dependent responses
perp
Fiber par
perp
Radius a
perp
par
perp
* *par perp o par f fv 0perp
This first order model neglectsinterconnections (touching)
between fibers
Slide 8 Copyright © 2013 JENTEK Sensors All Rights Reserved.
Composite Measurements: Orientation Effect• Center element for FA28 MWM-Array• Strong response when aligned with fibers in individual plies
UnidirectionalLayup
0.35
0.34
0.33
0.32
0.31
0.30
0.29
Re
al P
art
(H/m
)
720630540450360270180900-80
-60
-40
-20
0
20
40
Imag
inary P
art (x10
-3 H/m
)
FA28, Channel 18, 10 MHzUniaxial specimen
Real part Imaginary part
0.35
0.34
0.33
0.32
0.31
0.30
0.29
Re
al P
art
(H/m
)
720630540450360270180900
Orientation Angle (deg)
-80
-60
-40
-20
0
20
40
Imag
. Part (x10
-3 H/m
)FA28, Channel 18, 10 MHzLMT Bend Panel 1
Real part Imaginary part
Quasi-isotropic Layup(alternating layers at
-45º, 0º, 45º, 90º)
Slide 9 Copyright © 2013 JENTEK Sensors All Rights Reserved.
Simple layered-Media Composite Representation• Layup for quasi-isotropic test panel
– Uniaxial properties for each layer• MWM-Array sensitive to composite layers with fibers
oriented parallel to drive windings• Composite layer considered insulating if fibers NOT
within several degrees• This visualization indicates that each sensor
orientation is only sensitive to a subset of plies at varying depths within the composite.
MWM-Arrayh
0 DEGREES45 DEGREES90 DEGREES-45 DEGREES
eff
eff
eff
eff
eff
eff
eff
eff
MWM-Arrayh
MWM-Arrayh
eff
eff
eff
eff
eff
eff
eff
eff
eff
effeff
eff
effeff
eff
eff
eff
eff
eff
effeff
eff
eff
eff
MWM-Arrayh
MWM-Arrayh
MWM-Arrayh
MWM-Arrayh
MWM-Arrayh
MWM-Arrayh
0º orientation 45º orientation 90º orientation -45º orientation
(note that the angle is relativeto the fibers at the surface)
Slide 10 Copyright © 2013 JENTEK Sensors All Rights Reserved.
Layered-Media Composite Grid Example• Conductivity/lift-off measurement grids
assuming quasi-isotropic layup– Non-zero conductivity only for aligned layers
in each orientation• Primarily observe response shift as
effective lift-off changes with orientation• General agreement with measurement
data in each orientation– Data is below the grids for the deep plies (0º
and 90º), so other factors need to be considered
0 45
90
-45
45º
90º
0º
-45º
Quasi-isotropic Layup(note that the angle here refers
to the panel orientation)
FA49, Far channel
Increasingconductivity
Increasinglift-off
Slide 11 Copyright © 2013 JENTEK Sensors All Rights Reserved.
Example COPV Layup
• Representative layup for Composite Overwrapped Pressure Vessels (COPV)
• MWM-Array sensitive to composite layers with fibers oriented parallel to drive windings
• This indicates that the sensor orientation is important for assessing the fiber properties
non-fiber orientationAl liner
MWM-Array
h
Al liner
MWM-Array
h
eff/2
eff/2
eff/2
±17º or ±18º orientationAl liner
MWM-Array
h
Al liner
MWM-Array
h
eff
eff
±90º orientationAl liner
MWM-Array
h
Al liner
MWM-Array
h
eff/2
±60º orientationAl liner
MWM-Array
h
Al liner
MWM-Array
h
Slide 12 Copyright © 2013 JENTEK Sensors All Rights Reserved.
Simpl Layered-Media Model with Measurements
0.35
0.34
0.33
0.32
0.31
0.30
Rea
l Par
t of T
rans
indu
ctan
ce (H
/m)
600550500450400350300250200150100500
Orientation Angle (deg)
-60
-40
-20
0
20
Imag. P
art of Transinductance (x10-3 H
/m)
FA28, Ch 18, 10 MHz, LMT08Real Imag
MeasModel
0.35
0.34
0.33
0.32
0.31
0.30
0.29
Rea
l Par
t of T
rans
indu
ctan
ce (H
/m)
600550500450400350300250200150100500
Orientation Angle (deg)
-60
-40
-20
0
20
40 Imag. P
art of Transinductance (x10-3 H
/m)
FA28, Ch 18, 10 MHz, COPVReal Imag
MeasModel
0.10
0.05
0.00
-0.05
Rea
l Par
t of T
rans
indu
ctan
ce (H
/m)
600550500450400350300250200150100500
Orientation Angle (deg)
-60
-40
-20
0
20
40
60 Imag. Part of Transinductance (x10
-3 H/m
)
FA24, Ch 18, 10 MHz, COPVReal Imag
MeasModel
FA24
Qua
si-is
otro
pic
CO
PV
FA28
• Gaussian distribution model assumed for fiber conductivity in each layer• FA28 shows reasonable agreement with rotation measurements• FA24 shows broader response and background variation consistent with low-level
background conductivity (i.e., fiber touching should be considered)
0.10
0.05
0.00
-0.05
Rea
l Par
t of T
rans
indu
ctan
ce (H
/m)
600550500450400350300250200150100500
Orientation Angle (deg)
-60
-40
-20
0
20
40
60 Imag. P
art of Transinductance (x10-3 H
/m)
FA24, Ch 18, 10 MHz, LMT08Real Imag
MeasModel
Slide 13 Copyright © 2013 JENTEK Sensors All Rights Reserved.
Model Response: Field Variations for Composite• 3D model for field distribution around drive• Plots show normal field component along nominal
position of sense elements in rectangular loops– Drive winding aligned with uniaxial composite fibers
• Field varies with position along sense element array and degree of anisotropy Composite material
(anisotropic properties)
Air [insulating dielectric](isotropic properties)
z
Plane for MWM-Array
-10
-8
-6
-4
-2
0
2
4
6
Rea
l par
t of B
z (x1
0-9 T
)
-0.4 -0.2 0.0 0.2 0.4
y position (m) [x value at center of sense element array]
-50
-40
-30
-20
-10
0
10 Imaginary part of B
z (x10-9 T)
span of drivespan of sense element array
fields outside drive
field varies across array
FA24, 10 MHzperp/par Real Imag1.00.0050.0010.00010.00001
y
Double-D Drive Winding
Slide 14 Copyright © 2013 JENTEK Sensors All Rights Reserved.
Uniaxial Specimens: FA28 parallel to fibers• Channel-to-channel variation consistent with field variation along drive winding
“High” conductivity composite
“Low” conductivity composite
“High” conductivity composite
“Low” conductivity composite
Slide 15 Copyright © 2013 JENTEK Sensors All Rights Reserved.
Field Mapping Setup• Excite drive of a FA24 and scan with sense elements from
a second array • Sense element responses proportional to normal
component of field– The calibration led to the responses having a negative polarity
compared to the previous results
CH.1
CH.37 (FA24)0.100” SPACING
CH.37 (FA28)0.040” SPACING
5.071”
Calibration(sense elements parallel to drive)
Scanning(sense elements perpendicular to drive)
FA24
Slide 16 Copyright © 2013 JENTEK Sensors All Rights Reserved.
Field Mapping: C-Scans• Greater field variation for carbon fiber composite
– Significant field extending beyond the drive winding in the horizontal direction– Within the drive, the imaginary part goes though a maximum near the center
Aluminum Alloy
Rea
l Par
tIm
agin
ary
part
Uniaxial Composite
Slide 17 Copyright © 2013 JENTEK Sensors All Rights Reserved.
Field Mapping: B-scan, composite• One channel passing along the center of the drive
Rea
l Par
tIm
agin
ary
part
Horizontal Position
field variation acrosssense element location
Fiel
ds e
xten
dou
tsid
e dr
ive
Slide 18 Copyright © 2013 JENTEK Sensors All Rights Reserved.
Field Mapping: B-scan, aluminum alloy• One channel passing along the center of the drive
Rea
l Par
tIm
agin
ary
part
Horizontal Position
fields relatively uniformacross sense element location
Fiel
ds d
o no
t ext
end
outs
ide
driv
e
Slide 19 Copyright © 2013 JENTEK Sensors All Rights Reserved.
Volumetric Property Imaging Approach
• Combination of sensor orientation and geometry can isolate depth and region of damage– sensor orientation determines plies– sensor geometry determines depth of sensitivity– spatial extent of damage determined from scan image
MWM-Arrayh
Damage regionFA26
0ºFA2690º
FA280º
FA2890º
Quasi-isotropic panelwith impact damage
Slide 20 Copyright © 2013 JENTEK Sensors All Rights Reserved.
Volumetric Imaging of Composite Impact Damage
Representative MWM-Array Scan Image Sample provided courtesy of Lockheed Martin
Slide 21 Copyright © 2013 JENTEK Sensors All Rights Reserved.
Representative Quasi-isotropic Panel Scan ImagesSubtractedAfter ImpactBefore Impact Subtracted and Smoothed
5 M
Hz
10 M
Hz
15.8
MH
z
Slide 22 Copyright © 2013 JENTEK Sensors All Rights Reserved.
Summary of Scans• Individual scans combined together to create composite cross-sectional view
Slide 23 Copyright © 2013 JENTEK Sensors All Rights Reserved.
Cross Sectional Images: Panel 1, Low Impact Level
Cross Sectional View along X-axis
Cross Sectional View along Y-axis
MWM-Array FA28 Data for 0.085-in. thick panels
0.000
-0.0850 5Horizontal distance (inches)
Dep
th (i
nche
s)
0.000
-0.0850 7Horizontal distance (inches)
Dep
th (i
nche
s)
Slide 24 Copyright © 2013 JENTEK Sensors All Rights Reserved.
Cross Sectional Images: Panel 2, Medium Impact Level
Cross Sectional View along X-axis
Cross Sectional View along Y-axis
MWM-Array FA28 Data for 0.085-in. thick panels
0.000
-0.0850 5Horizontal distance (inches)
Dep
th (i
nche
s)
0.000
-0.0850 7Horizontal distance (inches)
Dep
th (i
nche
s)
Slide 25 Copyright © 2013 JENTEK Sensors All Rights Reserved.
Cross Sectional Images: Panel 3, High Impact Level
Cross Sectional View along X-axis
Cross Sectional View along Y-axis
MWM-Array FA28 Data for 0.085-in. thick panels
0.000
-0.0850 5Horizontal distance (inches)
Dep
th (i
nche
s)
0.000
-0.0850 7Horizontal distance (inches)
Dep
th (i
nche
s)
Slide 26 Copyright © 2013 JENTEK Sensors All Rights Reserved.
Composite Overwrapped Pressure Vessels (COPVs)• Helical wraps at several different orientations with a metallic liner• Eddy current scans can image both liner and composite properties
Slide 27 Copyright © 2013 JENTEK Sensors All Rights Reserved.
COPV: Low Frequency Inspection• 50 kHz• 90° drive orientation with 0.066-in. thick overwrap • At this frequency the sensor responds primarily to the liner• Effective lift-off images show dents in liner• Higher impact energy results in larger dents in the aluminum liner
Preliminary FilteringBefore Impact Damage After Impact Damage Baseline Subtracted
axial
angu
lar 30 ft-lbs
~46 mils
15 ft-lbs~22 mils 10 ft-lbs
~6 mils
20 ft-lbs~26 mils
Slide 28 Copyright © 2013 JENTEK Sensors All Rights Reserved.
COPV: High Frequency Inspection• 5 MHz
– At this frequency more of the signal related to the composite overwrap properties• 90° drive orientation with 0.066-in. thick overwrap• The conductivity images show significant spatial variations in the overwrap properties• Changes in the effective conductivity images highlight the damage
axial
Preliminary FilteringBefore Impact Damage After Impact Damage Baseline Subtracted
30 ft-lbs
angu
lar
20 ft-lbs
15 ft-lbs 10 ft-lbs
Slide 29 Copyright © 2013 JENTEK Sensors All Rights Reserved.
Summary
An eddy current extension to a micromechanical model has been developed for conducting fiber composites
Layered-media models have been developed to account for anisotropic properties
Measurements have verified the orientation dependence of the sensor response and field spatial variations in the vicinity of the sensor
Ongoing work is aimed at refining the models and correlating electrical properties to the properties of interest, such as:
- Fiber density variations within a ply- Stress dependent changes in the electrical properties- Volumetric assessment of stress and damage conditions
Slide 30 Copyright © 2013 JENTEK Sensors All Rights Reserved.
Questions?
Phone: 781-642-9666Email: jentek@jenteksensors.com
www.jenteksensors.com
The views and opinions expressed in this presentation are those of the authors and do not necessarily represent official policy or position of JENTEK Sensors, Inc.,
or any Department of the U.S. Government.
Copyright © 2013 JENTEK Sensors All Rights Reserved.
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