Screening Tests of Composites for Use in Tidal Energy DevicesAnderson Ogg

Master Thesis

Committee Members:

Mark Tuttle - Chair

Brian Fabian

Brian Polagye

Tidal Energy

In this context, tidal energy refers to the use of hydrokinetic devices, such as turbines, to extract energy from the water flow created by the changing of the tides.

Some Advantages:• Sustainable• Predictable - Base Load Power

Overall Goal

To provide device developers with useful information that

enables them to make more informed design tradeoff

decisions.

Why Composites?

• Large rotational surfaces – Weight will be important

• Lack of information in the public domain

• Potential maintenance advantages• May not need to preserve (paint)• May be less susceptible to biofouling

GFRE

GFRV

Pre-Preg

CFRE

Materials Chosen• Glass Fiber Reinforced Epoxy – GFRE

• Carbon Fiber Reinforced Epoxy – CFRE

• Pre-Impregnated Carbon Fiber – Pre-Preg

• Glass Fiber Reinforced Vinylester – GFRV

A Quick Review• Stress is force divided by area (F/A)

• A shear force acts tangent to a surface

• Shear Stress is the shear force divided by area (V/A)

• Strain is the change in length divided by the original length

• Shear Strain is the change in angle

From Professor Tuttle’s ME 556 Review of Concepts Presentation

From Professor Tuttle’s ME 556 Review of Concepts Presentation

Why Shear Modulus?• Just a screening test

• Changes in strength and stiffness properties were expected to be primarily caused by changes in the matrix

• The shear modulus is a matrix dominated property

• After determining the longitudinal and transverse strain, you can calculate the shear strain and shear modulus

• ASTM standard D3518 “Standard Test Method for In-Plane Shear Response of Polymer Matrix Composite Materials by Tensile Test of a ±45° Laminate.”

0 0.005 0.01 0.015 0.02 0.025 0.030.00

5.00

10.00

15.00

20.00

25.00

30.00

35.00

40.00

45.00

50.00

Specimen G3 Shear Stress v. Shear Strain

Stress v. Strain Curve

Shear Strain (radians)

Sh

ea

r S

res

s (

MP

A)

Experiment Plan• As-produced

• In situ exposure

• Accelerated exposure

• Weight monitoring

• Changes in shear modulus

• Optical microscopy

In Situ Experimental Setup• One panel of each system kept at the UW in a as-

produced condition

• Two panels of each system placed on NNMREC’s Sea Spider

• One panel of each system removed after 9 months

• One panel of each system is still on the Sea Spider and should be removed after 18 months (November 2011)

SS Location at Admiralty Inlet

Accelerated Experimental Setup• Chose to only use the GFRV system

• 3 panels, each subjected to one month exposure in heated artificial seawater at 30, 40 and 50˚C

• Similar techniques used throughout the literature.

• Continuous weight monitoring

Specimen Construction

Testing Procedures

Data Collection Example

SpecimenShear Modulus

Slope (GPa)

D1 2.51

D2 2.45

D3 2.51

D4 2.40  

B1 0.84

B2 0.81

B3 0.77

B4 0.92

Results• Shear Modulus

• Weight Gain

• Microscopy

• Biofouling

Shear Modulus Results

Panel

Shear Modulus Change (GPa)

Standard Deviation

(GPa)

Coefficient of Variation Percent Loss

GFRE 1.63 0.08 5% 66%

CFRE 0.88 0.10 12% 26%

Pre-Preg 0.28 0.09 32% 7%

GFRV 0.29 0.07 24% 13%

GFRV @ 30 0.84 0.15 17% 38%

GFRV @ 40 0.73 0.08 11% 33%

GFRV @ 50 0.74 0.09 12% 33%

GFRE (D and B) CFRE (G and E) Pre Preg (T and U) GFRV (Y,M,Q,R and X)0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

Shear Modulus of All Panels

As Produced

Exposed 9 Months

30˚C

40˚C

50˚C

Material System

Me

an

Sh

ea

r M

od

ulu

s (

GP

a)

SystemPanel

Pre PregGRFEGFRVCFREUTDBYMGE

4

3

2

1

0

Shear

Modulu

s (G

Pa)

95% CI for the MeanInterval Plot of Shear Modulus for In Situ Panels

0.40.30.20.10.0

X_

Ho

Differences

Boxplot of Differences for Panels T and U(with Ho and 95% t-confidence interval for the mean)

SystemPanel

GFRVYXRQM

2.5

2.0

1.5

1.0

0.5

0.0

Shear

Modulu

s (G

Pa)

95% CI for the MeanInterval Plot of Shear Modulus for GFRV

0.20.10.0-0.1-0.2-0.3-0.4

X_

Ho

Differences

Boxplot of Differences for Panels Q and R(with Ho and 95% t-confidence interval for the mean)

Weight Gain of In Situ Panels

Panel SystemInitial weight

(grams)

Weight with biofouling

±.05 (grams)

Weight after biofouling removed (grams)**

Weight after drying

(grams)

Difference between

initial and final (grams)

Percent change

B GFRE 154.08 194.15 164.91 164.34 10.26 6.24%

E CFRE 128.11 154.7 133.64 132.23 4.12 3.12%

U Pre-Preg 157.64 160.45 158.44 158.39 0.75 0.47%

M GFRV 150.96 219.98 159.95 157.11 6.15 3.91%

1/7/

2011

1/12

/201

1

1/17

/201

1

1/22

/201

1

1/27

/201

1

2/1/

2011

2/6/

2011

74.4

74.6

74.8

75

75.2

75.4

75.6

75.8

76

76.2

76.4

740.0

745.0

750.0

755.0

760.0

765.0

770.0

775.0

780.0

GFRV @ 30˚C (Panel Q) Weight Change

Scale Weight

Barometric Pressure

Date

Sc

ale

We

igh

t (g

ram

s)

Pre

ss

ure

(m

m o

f m

erc

ury

)

Weight Gain of Accelerated PanelsPanel

Exposure Temperature (˚C)

Initial Weight (grams)

Final Weight (grams)

Weight Difference (grams)

Percent Change

Q 30 191.90 192.77 0.87 0.45%

R 40 193.29 194.23 0.94 0.48%

X 50 188.67 190.01 1.34 0.71%

PanelExposure

Temperature (˚C)

Initial Weight Shown on

Balance (grams)

Final Weight Shown on

Balance (grams)

Weight Difference (grams)

Percent Change

Q 30 75.04 76.13 1.09 1.43%

R 40 136.74 137.92** 1.18 0.86%

X 50 69.52 73.38 3.86 5.26%

Microscopy

GFRE Panels D and B

CFRE Panels G and E

Biofouling

Barnacle Removal

Flake Off at About 2% Shear Strain

Conclusions• The GFRV system was the least expensive and had the

second best performance

• From the literature, it was expected that the GFRV would absorb less moisture but that the epoxy based systems would perform better; these were not the results obtained in the experiment

• Depending on weight tradeoffs, the GFRV system may be perfectly acceptable for use in tidal energy devices.

• Biofouling had little effect

• Accelerated testing results need to be used with caution

Differences in B and D

Voids

Future Work• Further examination into the mechanism that caused such

a change in the GFRE system

• Remove the 18 month panels in November and test them

• When does the loss of shear modulus level out?

Acknowledgements• Mariette• Bill and Tuesday Kuykendall• My Committee and Professors• Fellow Graduate Students• U.S. Coast Guard

Questions?

Extra Material