evaluation of analytical chemistry methods for surface ... · 4 afm & ecs objective - determine...

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

2

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

3

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

4

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

5

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

6

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

7

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




11 Unmodified 18.21 ± 13.28 31.29±3.95 13.09 ± 12.28Modified 9.93 ± 1.20 n/a 2.80 ± 3.57


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

8

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

90

80

70

60

50

40

30

20

10

0

C2

Freq

uenc

y

Mean 16.62StDev 9.327N 256

Histogram of C2Normal

1086420-2-4

60

50

40

30

20

10

0

C1

Freq

uenc

y

Mean 2.996StDev 3.069N 256


9

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

40

30

20

10

0

C2

Fre

qu

en

cy

Mean 37.22StDev 7.930N 242


1413121110987

70

60

50

40

30

20

10

0

C3

Freq

uenc

y

Mean 9.323StDev 1.203N 256


~150nN

120nN

20nN

1501209060300

70

60

50

40

30

20

10

0

C1

Freq

uenc

y

Mean 29.39StDev 20.47N 252


10


10

Sample 5 - BMS 8-79 260 F Fiberglass Fabric – Epoxy, Precision 600001 Polyester –modified probe tips

Region 1 Region 2 Region 3

121086420-2

50

40

30

20

10

0

C6

Freq

uenc

y

Mean 5.475StDev 3.294N 256


4.504.053.603.152.702.251.80

40

30

20

10

0

C4

Freq

uenc

y

Mean 2.997StDev 0.5164N 256


7.56.04.53.01.50.0

35

30

25

20

15

10

5

0

C2

Freq

uenc

y

Mean 3.103StDev 1.753N 256


11


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.

12


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

13

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

14

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

15

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

16

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

17

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

18

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

19


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

20


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)

21


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.

22

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

23

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

24

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.

25

evaluation of analytical chemistry methods for surface ... · 4 afm & ecs objective - determine...

Documents