AATCC poster - Toivola
-
Upload
ryan-toivola -
Category
Documents
-
view
24 -
download
1
Transcript of AATCC poster - Toivola
32
1.0 INTRODUCTION
2.0 OBJECTIVE
Fluorescent Surface Coatings for Aerospace Composite Damage Detection Ryan Toivola, University of Washington MSE
1
4.0 RESULTS AND DISCUSSION
3.0 MATERIALS AND METHODS
5.0 CONCLUSIONS & FUTURE WORK
6.0 REFERENCES
ACKNOWLEDGMENTS
Develop a system of aggregate sensitive fluorescent dye molecules compatible with currently used coating systems (primer and topcoat) (Jen Research Group, UW MSE)Utilize custom dyes designed to crosslink into coating network systemsWhen coatings become stressed, dyes aggregate or deaggregate, causing emission change
Damage in aerospace composites can be extremely difficult to detect using surface inspection techniques – Especially Barely Visible Impact Damage (BVID)1
Damage from BVID can cause subsurface damage that affects composite part performance while being undetectable at the part surface2
Current inspection techniques that can detect BVID (ultrasonic C-scan) are costly and require significant aircraft downtime
A technique with the ability to quickly and inexpensively identify impact events and stressed areas in composite parts is very desirable
Fluorescent molecules with deformation-sensitive fluorescent emission behavior have been identified in solid polymersMethodology: Aggregation induced quenching,
emission, or color change
Aggregation sensitivity of dyes (Jen Research Group, UW MSE)Established by changing monomer to dimer
absorbance ratio with changing concentrationTesting done in liquid solution Mechanism varies, but any detectable
change is acceptable
Fluorescent coatings for use in damage detection were developed using customized dyes and existing aerospace coating systems.
Cure Behavior and Thermal properties of coatings were not affected by dye incorporation
One dye species showed observable color and intensity changes when strained; changes were consistent with design
After coating relaxation, strained coatings did not maintain the changesreversible transition
1. Cantwell, W.J., Curtis, P.T., Morton, J., Comp. Sci. & Tech. 25 (1986), 133-48.
2. Poon, C. et.al., Theor. & Appl. Fract. Mech. 13 (1990) 81-97.
3. Yang et.al., J. Appl. Polym. Sci. 82 (2001) 2041-8.
4. DesoPrime 7501 Product Data Sheet, PPG Aerospace, Pittsburgh, PA. www.ppg.com
Project Principal Investigators: Dr. Brian Flinn, Dr. Alex Jen (UW MSE)Project Collaborators: Dr. Sei-Hum Jang, Dr. Zhengwei Shi (UW MSE), Dr. Gary Georgerson (The Boeing Company)Research was funded by The Boeing Company Project Code B8LDLMaterials were donated by PPG Aerospace, Woodinville, WA
Materials: Aerospace Coating systems (PPG Aerospace)Epoxy-Based Primer (Epoxy)
A 2-part liquid cures to a stiff, opaque primer
Polyurethane Topcoat (PU)A 3 part liquid cures to a flexible, clear
topcoat
BVID – subsurface damage not apparent at surface of impacted
composite part
Left: Aggregated (orange) and separated (green) states of dye molecule emission
Right: dyes in solid PMMA, before and after tensile deformation3
Determine if coatings are changed materially by incorporation of the dyesCure Behavior, Thermal-Mechanical Properties
Characterize Fluorescent Response of dyes in coating systems with and without stress Fluorescent Absorbance in liquid pre-polymer coating componentsFluorescent Absorbance in solid polymer coatingFluorescent response of coatings under tensile stress
Materials: Customized Fluorescent Dyes (Jen Research Group, UW MSE)Based on known and newly developed
aggregation-sensitive dye systems Functionalized end groups to allow dyes to
participate in cure of both epoxy and PU systems
Aggregation State
Separated State
Aggregation State
Aggregation State
Separated State
Methods: Coating synthesis Dyes customized for solubility in liquid componentsMixed and spread cast onto various substrates for testing
Methods: Cure and Thermal AnalysisCure behavior analyzed with Differential Scanning Calorimetry (DSC)Glass transition temperature measured via Dynamic Mechanical Analysis (DMA)
Methods: Fluorescence Response testingAbsorbance of dyes in solid PU coating (epoxy too opaque)Observed emission of dyes on PET substrates as tensile stress applied
Coating schematic4
Various custom dyes
Fluorescent coatings with incorporated custom dye moleculesEstablished by measuring absorbance of dye
in solid PU filmsSimilar absorbance behavior to dye in liquid
solvent
-40 -30 -20 -10 0 10 20-2
-1.5
-1
-0.5
0
PU w/P. 6, 3.3x10^-4 mol/L
Epoxy w/p. 7, 1.3x10^-3 mol/L
Temp. (deg.C)
Pro
be
Po
sit
ion
(m
m)
375 425 475 525 575 6250
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
no dye
3.31x10^-4 mol/L
6.62x10^-5 mol/L
3.31x10^-5 mol/L
1.65x10^-5 mol/L
Wavelength (nm)
No
rma
lize
d a
bs
orb
an
ce
Cure Behavior of coatings with incorporated dye moleculesEstablished by measuring residual
exothermic or endothermic events in cured coatings
No measureable activity in coatings with dye molecules after curing, indicating complete cure reached and all solvents fully evaporated
50 70 90 110 130 150 170 190-0.3
-0.2
-0.1
-2.77555756156289E-16
0.0999999999999997
0.2
0.3
0.4
0.5
Temp. (deg.C)
DS
C, (
mW
/mg)
50 70 90 110 130 150 170 190-0.5
-0.4
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0.4
0.5
Temp. (deg.C)
DS
C (
mw
/mg
)
Glass Transition Temperature of coatings with incorporated dye moleculesEstablished by measuring residual
exothermic or endothermic events in cured coatings
No statisticallly significant effect is caused by dye incorporation
2 dye species in liquid solvent, showing relative monomer and dimer absorbance activity
Dye in solid PU film, showing absorbance activity consistent with dye in liquid solvent
Dyes (colored) in cured epoxy (left) and PU (right). Black curves show uncured exo- and endothermic
activity, not evident in cured filjms
Ep
ox
y
Ep
ox
y ...
Ep
ox
y w
...
Ep
ox
y w
...
Ep
ox
y w
...
Ep
ox
y ...
PU
PU
w/P
. 6
PU
w/P
. 7
PU
w P
. 8
PU
w P
. 9
PU
w P
...
-10
0
10
20
30
40
50
60
45.239.4
48.6 49.8
40.9
49.6
4.6 5.2 5.81.8 3.7 1.7
Gla
ss T
rans
ition
(deg
.C)
Left: representative plot of DMA data for epoxy and PU film. Right: Tg data showing no significant
change due to dye incorporation
Fluorescent Response of Dyes in coating systemsEstablished by measuring emission
spectra caused by excitation at peak absorbance wavelength
Dyes are fluorescent active in coatingsDifferent dye species emit different
spectra
400 450 500 550 600 650 700 750 8001
10
100
1000
10000
Wavelength (nm)
Lo
g I
nte
nsi
ty
Incident photons
Emitted photons
Peak emission λ
Left: representative fluorescent emission due to incident UV light of 2 dye species. Right:
representative emission spectra of dyes in solid films due to mono-wavelength excitation
Fluorescent coatings mechanical testing
Dye-incorporated coatings spread cast onto flexible PET substrates
Dye-substrate bilayer strained in tensile test frame
Testing stopped at various strain levelsDye in solid coating at various strain levels during
tensile testin g. Images taken while sample illuminated with UV light.
Fluorescent behavior of coatings while being strained Evident color change as strain increases for one dye species Possible intensity change as strain increases
1( 0 strain) 2 (25% strain) 3 (50% strain)
Fluorescent behavior of coatings after strainCoatings were elastically deformed and allowed to relax before
quantitative fluorescent emission testingConcentration dependence of peak wavelength and quantum
yield change is consistent with design strategy of dye moleculeNo observed strain dependence of fluorescent behavior
indicates the observed changes are reversible with strain
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.40.600000000000001
0.650000000000001
0.700000000000001
0.750000000000001
0.800000000000001
7.38x10^-4 mol/L 1.48x10^-4 mol/L
7.38x10^-5 mol/L
Tensile Strain (mm/mm)
PL
Qu
antu
m Y
ield
Decreasing concentration
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4550
560
570
580
590
600
7.38x10^-4 mol/L 1.48x10^-4 mol/L
7.38x10^-5 mol/L
Tensile Strain (mm/mm)
Pea
k λ
(nm
)
Decreasing concentration
Left: Fluorescent Quantum yield measurements show increasing intensity with decreasing concentration. Right: Peak emission wavelength shows
shift from red to red-orange emission with decreasing concentration. Both plots show no strain dependence.
Future work will test the coatings’ in-situ strain dependent fluorescent properties in tension and compression
4.0 RESULTS AND DISCUSSION
1