Evaluation of Analytical Chemistry Methods for Surface ... · 4 AFM & ECS Objective - Determine and...
Transcript of Evaluation of Analytical Chemistry Methods for Surface ... · 4 AFM & ECS Objective - Determine and...
Evaluation of Analytical Chemistry Methods for Surface Contamination and the Effect of Contamination on Composite Bond Integrity and Durability
2011 Technical ReviewDwayne McDanielFlorida International University
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Evaluation of Analytical Chemistry Methods for Surface Contamination and the Effect of Contamination on Composite Bond Integrity and Durability • Motivation and Key Issues
– Adhesive bonding is now used in manufacture and repair and its importance is beginning to increase.
– Adherend surface preparation is a critical issue to the structural integrity and durability of bonded structures.
• Objective– Benchmark knowledge of surface preparation quality assurance
methods. – Identify and evaluate definitive analytical chemistry methods to
provide sufficient in-field quality assurance.• Approach
– Literature review – Selection of analytical chemistry methods– Electrochemical sensor (ECS) and Atomic Force Microscopy
(AFM) evaluation
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Evaluation of Analytical Chemistry Methods for Surface Contamination and the Effect of Contamination on Composite Bond Integrity and Durability
• Principal Investigators & Researchers– Dwayne McDaniel, Xiangyang Zhou, Tomas Pribanic
• Students– Rakesh Guduru, Zedong Wang
• FAA Technical Monitor– David Westlund
• Industry Participation– Boeing, Exponent
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AFM & ECSObjective - Determine and evaluate the capabilities of AFM and ECS to provide informationon composite surfaces that have been prepared for adhesive bonding.
Samples have been supplied by Boeing that were manufactured using a combination of materials. Results of the failure modes were provided (green - cohesive, red - adhesive).
Approach Utilize AFM/CFM and a solid-state ECS to evaluate various composite surfaces prepared with polyester and nylon peel plies.
AFM – topography, friction images and adhesion force curves. Using a force volume approach, adhesion force contours and corresponding histograms can be obtained.
Solid-state electrochemical sensor (ECS) – obtain surface electrochemical activity measurements via electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV)
Establish correlations between failure modes with AFM and ECS tests.
Precision 60001 Polyester
Precision 52006 nylon
Henkel EA9895 - impregnated polyester
Porcher Polyester
BMS 8-256 355F cure Carbon Fabric - Epoxy 1 2 3 4BMS 8-79 260F Cure Fiberglass Fabric Epoxy 5 6 7 8BMS 8-276 355F cure Carbon Tape - Epoxy 9 10 11 12
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AFM/CFM Analysis
Analysis conducted with silicon nitride tips (unmodified) and with epoxy modified tips
Analysis conducted in environmental chamber to reduce capillary effects
Three scans were taken at random locations for each sample Scan area was increased to 30 microns x 30 microns for carbon
fabrics and 5 microns x 5 microns for fiberglass fabrics. (Previousscans were at peaks - only 1 micron)
AFM – general approach and methodology Obtain adhesion force contours and histograms Determine background adhesion force values Establish trends and correlations with mechanical data Evaluate phobicity trends – Epoxide tip (hydrophobic),
unmodified tip (hydrophilic), nylon peel plyand polyester peel ply
Generally, functional group interactions followphilic-philic > phobic-phobic > philic-phobic
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ECS Analysis
Sensor design was evaluated with a new configuration Reduction in internal resistance - improves CV response Working electrode is coated with the mediators/Nafion Reusable counter and reference electrodes
ECS – general approach and methodology Obtain maximum current peak from CV plots – corresponds to maximum electrochemical activity and potential contamination Obtain impedances from EIS analysis Establish trends and correlations with mechanical data and AFM data
Schematic of the solid-state ECS Operation principle of the solid-state ECS
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CFM Adhesion Force MeasurementsRaw CFM Adhesion Force Average (nN)
Sample no Type of Tip Region 1 Region 2 Region 3
1 Unmodified 50.18 ± 37.47 62.73 ± 50.64 33.22 ± 13.51Modified 7.25 ± 1.90 n/a 7.90 ± 5.86
2 Unmodified 21.55 ± 7.44 42.07 ± 16.42 13.41 ± 4.63Modified 29.96 ± 58.98 5.48 ± 1.43 3.66 ± 2.63
3 Unmodified 29.39 ± 20.47 37.20 ± 7.93 9.32 ± 1.20Modified 37.03 ± 48.98 0.30 ± 1.21 27.09 ± 0.764
4Unmodified 18.96 ± 44.57 3.62 ± 3.30 83.34 ± 12.58
Modified 16.62 ± 9.32 3.00 ± 3.07 10.08 ± 16.62
5 Unmodified 2.65 ± 0.53 2.25 ± 1.25 3.51 ± 2.11Modified 5.48 ± 3.29 2.99±0.52 3.10 ± 1.75
6 Unmodified 14.04 ± 5.80 11.50±4.87 15.65 ± 6.80Modified 12.03±0.87 12.88±1.99 12.53 ± 1.31
7 Unmodified 128.9 ± 105.6 11.07±7.27 9.13 ± 3.02Modified 24.07 ± 2.75 21.02±0.58 10.58 ± 12.82
8 Unmodified 17.87 ± 9.23 20.89±7.80 20.03 ± 2.71Modified 2.23 ± 1.01 1.47±1.21 3.31 ± 1.60
9 Unmodified 50.51 ± 5.97 6.15±2.34 4.33 ± 1.25Modified 5.50 ± 6.79 6.74±4.89 9.06 ± 9.82
10 Unmodified 20.11 ± 1.51 21.06±1.10 71.98 ± 4.86Modified 28.42 ± 16.82 13.65±5.59 10.70 ± 14.71
11 Unmodified 18.21 ± 13.28 31.29±3.95 13.09 ± 12.28Modified 9.93 ± 1.20 n/a 2.80 ± 3.57
12 Unmodified 18.56 ± 12.93 4.49±2.14 13.53 ± 10.07Modified 19.58 ± 17.95 15.66±7.83 26.84 ± 31.79
Does not follow phobic/philic trends
Variation in the data – difficult to assess background values
Values for modified and unmodified are close and difficult to differentiate
Values generally followed the phobic/philic trends.
Evaluate with histograms
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CFM Adhesion Force Measurements
Sample 4 - BMS 8-256 355 F Carbon Fabric – Epoxy, Porcher Polyester – modified probe tips
Region 1 Region 2 Region 3
363024181260
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C2
Freq
uenc
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Mean 16.62StDev 9.327N 256
Histogram of C2Normal
1086420-2-4
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C1
Freq
uenc
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Mean 2.996StDev 3.069N 256
Histogram of C1Normal
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CFM Adhesion Force MeasurementsSample 3 - BMS 8-256 355 F Carbon Fabric – Epoxy, Henkel EA9895 Polyester – unmodified
probe tipsRegion 1
Region 2 Region 3
60.052.545.037.530.022.5
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C2
Fre
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Mean 37.22StDev 7.930N 242
Histogram of C2Normal
1413121110987
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C3
Freq
uenc
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Mean 9.323StDev 1.203N 256
Histogram of C3Normal
~150nN
120nN
20nN
1501209060300
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C1
Freq
uenc
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Mean 29.39StDev 20.47N 252
Histogram of C1Normal
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CFM Adhesion Force Measurements
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Sample 5 - BMS 8-79 260 F Fiberglass Fabric – Epoxy, Precision 600001 Polyester –modified probe tips
Region 1 Region 2 Region 3
121086420-2
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C6
Freq
uenc
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Mean 5.475StDev 3.294N 256
Histogram of C6Normal
4.504.053.603.152.702.251.80
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C4
Freq
uenc
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Mean 2.997StDev 0.5164N 256
Histogram of C4Normal
7.56.04.53.01.50.0
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C2
Freq
uenc
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Mean 3.103StDev 1.753N 256
Histogram of C2Normal
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CFM Adhesion Force Measurements
Average Background Adhesion Force DataUnmodified Modified
1 14.0 7.0
2 26.7 6.0
3 23.0 12.7
4 5.5 5.3
5 2.7 4.7
6 14.0 12.3
7 13.3 19.7
8 18.3 2.0
9 5.0 5.0
10 20.5 9.7
11 5.5 5.0
12 4.5 10.0
Note – 5 of the 12 samples had 1 of the 3 scans for the unmodified tips significantly different from the other values obtained. These values were considered anomalies and were not used in the averages.CFM adhesion force values can potentially be affected by substrate topography and tip radii. All measurements were taken with the same tips.
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CFM Adhesion Force Measurements
Sorted Average Background Adhesion Force Data
Sorted - Unmodified Sorted - Modified
2 26.7 7 19.7
3 23.0 3 12.7
10 20.5 6 12.3
8 18.3 12 10.0
1 14.0 10 9.7
6 14.0 1 7.0
7 13.3 2 6.0
4 5.5 4 5.3
11 5.5 9 5.0
9 5.0 11 5.0
12 4.5 5 4.7
5 2.7 8 2.0
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ECS CV Measurements
CV Data – Peak CurrentsUnits are in mA
Scan #1 Scan #2 Scan #31 1.255 1.655 0.4212 1.880 1.255 0.2853 1.755 1.230 0.9974 1.355 1.030 0.3095 1.955 1.805 1.310 6 1.330 1.430 0.7437 1.430 1.750 0.3058 1.355 n/a 0.7569 1.155 1.405 0.345
10 1.480 0.954 0.29911 1.405 1.580 0.31712 1.505 1.380 0.347
Scan #3 conducted with different electrode material
CV Graph – Sample 5BMS 8-79 260 F Fiberglass Fabric – Epoxy, Precision 60001 Polyester
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ECS CV Measurements
CV Data (Sorted) – Peak CurrentsUnits are in mA
Scan #3 conducted with different electrode material
Sample Scan #1 Sample Scan #2 Sample Scan #35 1.955 5 1.805 5 1.3102 1.880 7 1.750 3 0.9973 1.755 1 1.655 8 0.756
12 1.505 11 1.580 6 0.74310 1.480 6 1.430 1 0.4217 1.430 9 1.405 12 0.348
11 1.405 12 1.380 9 0.3454 1.355 2 1.255 11 0.3178 1.355 3 1.230 4 0.3096 1.330 4 1.030 7 0.3051 1.255 10 0.954 10 0.2999 1.155 8 2 0.285
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ECS CV Measurements
EIS Data – ImpedanceUnits are in ohms
Sample 5 has the lowest impedance – highest potential contamination
Sample Scan #1 Sample Scan #1
1 940 3 14392 1201 2 12013 1439 1 9404 721 6 8805 314 8 8726 880 4 7217 416 10 6298 872 9 5109 510 12 481
10 629 7 41611 357 11 357
12 481 5 314
Sorted dataRaw data
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ECS CV Measurements
Previous Work
Demonstrated the capabilities of the ECS on sample surfaces with gross contamination
Bombardier samples with EIS measurements
Demonstrated the capabilities of the ECS on sample surfaces prepared with various peel plies
Nylon and polyester peel ply samples manufactured at FIU
Tests conducted with CV measurements correlated with lap-shear strength tests
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ECS Measurements – Bombardier Samples
Sample[O]
wt%[Al]wt%
[K]wt%
[Si]wt%
[Na] wt%
[S]wt%
[Fe]wt%
[Zn]wt%
PolarizationImpedance
(ohm)
Pristine 13.63 3.89 0 0 0 0 0 0 2.0 x106
Cleanser HFP 15.89 6.47 0 0 0 0 0 1.53 1.8 x 105
UV dye 13.70 0.60 0.28 0 1.33 0 0 0 6.0 x105
UltrasonicCoupling gel
36.45 5.67 8.03 0 0 0 0 0 6.0 x105
Silicone rubber glove residue
9.05 8.28 0 0 0 22.89 0 0 1.8 x106
Solution from a marker
18.43 2.56 0 0 0 0 0 0 8.0 x105
Tape Residue 11.28 3.04 0 0 0 0 0 0 1.7 x106
Soda 26.57 0.57 0 0 0 0 12.16 0 6.5 x105
Coffee 15.73 0.93 2.07 0 0 0 0 0 6.0 x105
Protective Cream 6.39 0.13 0.82 0 1.31 0 0 0 1.2 x103
Dust 18.54 5.80 3.47 2.07 1.64 2.47 8.90 0 2.0 x 104
Fingerprint Residue
13.1 3.25 0 0 0 5.56 0 0 2.5 x104
Cleanser MEK 31.50 3.80 0 0 0 0 0 0 4.9 x 104
Breather Cloth 18.41 0.42 0 0 0 0 0 0 2.7 x 104
Breather Cloth
Fingerprint Residue
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Effect of Contamination on Composite Bond Integrity and Durability
• Motivation and Key Issues – Demonstrate whether existing state-of-the-industry surface analysis
methods can be effectively integrated into a quality management system to significantly enhance the reliability of bonded composite structures
– Develop standardized methods that can be used to assess the durability of composite bonded joints when less-than-desirable bonding conditions have occurred
• Objective– Benchmark knowledge of long-term durability test methods– Characterize the durability performance of composite bonds when
undesirable bonding conditions have been imposed
• Approach– Literature review of available durability test methods– Design protocol for evaluating initial strength and durability of adhesive
bonds– Evaluate the effects of contamination on bond durability
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Effect of Contamination on Composite Bond Integrity and Durability
Assessment Procedure
Prepare Pristine Specimens
Baseline Bonding Characterization - Pristine
SpecimensInitial Strength
Long-Term Durability
Surface Characterization
Characterization -Contaminated Specimens
Initial StrengthLong-Term Durability
Surface Characterization
Prepare Contaminated Specimens
Assessment of Contamination Effects on Long-Term Durability
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Effect of Contamination on Composite Bond Integrity and Durability
Literature Review Methods for conditioning specimens Various testing methods: Shear tests, DCB tests and Wedge tests Notes
“Durability is a general term that is related to the residual strength of the joint when subjected to water or temperature. The loading can be static or dynamic (fatigue or impact). This subject is probably the major challenge that the adhesion community faces today.“ (Silva, ‘09)
“A recent survey of organizations that use adhesive bonding indicated that 77 percent of designers use lap-shear test results to establish design allowables.” (Davis & Tomblin, ‘07)
“The most important thing to note about durability testing of adhesively bonded joints is that the MODE of failure is more important than the failing load.” (Hart-Smith, ’99)
Forward wedge test should be dismissed as a scientific test and is strongly recommended to not be used. (Adams, et al., ‘09)
DCB test generally uses specimens which have been exposed but not loaded while the BWT uses a specimen which is loaded while it is exposed to the aggressive environment, the load decreasing as the crack extends. (Adams, et al., ‘09)
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Effect of Contamination on Composite Bond Integrity and Durability
Mechanical Loading in Harsh Environment
Lloyd Smith – utilized customized load frames to apply static and cyclic loads on various types of adhesively bonded composite specimens. The frames could be placed in hot/wet baths for simultaneous loading. Used thick wide lap-shear coupons with constant loads in a
hot/wet environment – effects of moisture and peel ply. Used DCB coupons with constant and cyclic loading in a hot/wet
environment – effects of surface treatment.
Briskham and Smith – used a string of lap shear joints in a hot/wet bath under cyclic loading.
Ashcroft, et al. – used double lap joints with composite and metal adherends to study environmental effects on fatigue behavior.
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Potential Mechanical Conditioning Approaches
Modified Three Point Bending TestAdvantages- Apply uniform shear stress at bondline- Simple to set up – potential to include in an environmental chamber
- Can use DCB or wedge specimens
Disadvantages- Specimen geometry made need to be alteredto limit fatigue in adherend
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Potential Mechanical Conditioning Approaches
Extended Lap-Shear Specimen
Advantages- Larger bond area for fatigue- More realistic representation of adhesivelybonded structures
- DCB or wedge specimens
Disadvantages- Non-uniform shear distribution- Difficult to manufacture test rig for environmental exposure
Pseudo-Distributed Peel Type Loading
Advantages- approximation of distributed load in Mode 1- Fatigue in Mode 1 and test in Mode 1- Can use DCB or wedge specimens
Disadvantages- Not completely continuous loading - Difficult to implement the loading
- effects on DCB tests
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Looking Forward
• Future work– Close out study on AFM and ECS – prepare report– Validate the use of chosen conditioning method– Implement conditioning approaches on composite
adherends– Evaluate surfaces prior to bonding with selected
analytical methods– Conduct baseline analysis for initial strength and
durability of adhesive bonds– Repeat with undesirable bonding conditions
End of Presentation.
Thank you.
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