Effect of vibrations on void Effect of vibrations on void content in composite content in composite materialsmaterials

Jelena Muric-NesicJelena Muric-NesicSupervisors: P.Compston, N.Noble, Z.Stachurski

DERF June 2008.DERF June 2008.

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Presentation OverviewPresentation Overview

Project to date aim method results discussion

Current workFuture Conclusions

Vibration Project, Jelena MN

Vibrations…Vibrations…

3/16

Project’s Aim Project’s Aim

What? Good quality laminates Better mechanical

properties Minimize defects Bubbles, fibre wetting Void content < 2%

How?

Vibrations: Suitable frequency Mode of vibration Position Transmission

means

Vibration Project, Jelena MN

4/16

Project’s Method IProject’s Method I Shaker 1-9000 Hz, signal

generator, power amplifier and mould

Hand lay-up of glass fibres (12 plies) and vinyl-ester resin

Laminates (10x10x3mm) UV curing Optical microscope Top cover&Vacuum-later

Vibration Project, Jelena MN

5/16

Project’s Method IIProject’s Method II

Changing Parameters Frequency and

power of vibrations Time length Temperature Top cover plate Vacuum bagging

Hypothesis Void mobility Stokes law

Viscosity (Arrhenius)

Energy-Amplitude: E≈A2

Pressure: PV=RT

Vibration Project, Jelena MN

gr

VB2

9

2.

)exp(0 RT

Q

What’s happening?!What’s happening?! Pressure and temperature variations

internal pressure - external pressure = 2/r

Buoyancy Coalescence/dispersion of voids

6/16Vibration Project, Jelena MN

rPPghP vibrag

2

r

P2

r

P2

Expansion

Shrinkage

- surface tension of a liquid

r - radius of a bubble

7/16

Project’s Results IProject’s Results I

Optical micrograph (64x)Optical micrograph (64x)Void sizes:Void sizes:

<50 μm not observed

A. 50 – 100 μm

B. 100 – 200 μm

C. 200 – 500 μm

D. > 500 μm

__ 100μm

Vibration Project, Jelena MN

Distribution of bubble size cross section

8/16

Project’s Results IIProject’s Results II

10 min

NO COVER TOP COVER

with vibrations without

0

1

2

3

4

5

6

7

8

10 30 50 NO

frequency, Hz

nu

mb

er

of

bu

bb

les

A

B

C

D

with vibrations without

0

1

2

3

4

5

6

7

8

10 30 50 NO

frequency, Hz

nu

mb

er

of

bu

bb

les

A

B

C

D

with vibrations without

0

1

2

3

4

5

6

7

8

10 30 50 NO

frequency, Hz

nu

mb

er

of

bu

bb

les

A

B

C

D

with vibrations without

0

1

2

3

4

5

6

7

8

10 30 50 NO

frequency, Hz

nu

mb

er

of

bu

bb

les

A

B

C

D

30 min

Vibration Project, Jelena MN

with vibrations without

0

1

2

3

4

5

6

7

8

10 30 50 NO

frequency, Hz

nu

mb

er

of

bu

bb

les

A

B

C

D

A. 50 – 100 μm B. 100 – 200 μmC. 200 – 500 μm D. > 500 μm

9/16

Project’s Results IIIProject’s Results IIITop cover, 30 min of vibrations

no vacuum vacuum

with vibrations without

0

1

2

3

4

5

6

7

8

10 30 50 NO

frequency, Hz

nu

mb

er o

f b

ub

ble

s

A

B

C

D

with vibrations without

0

1

2

3

4

5

6

7

8

10 30 50 NO

frequency, Hz

nu

mb

er o

f b

ub

les

A

B

C

D

Vibration Project, Jelena MN

with vibrations without

0

1

2

3

4

5

6

7

8

10 30 50 NO

frequency, Hz

nu

mb

er o

f b

ub

ble

s

A

B

C

D

A. 50 – 100 μm B. 100 – 200 μmC. 200 – 500 μm D. > 500 μm

10/16

Project’s Discussion IProject’s Discussion IVoid percentage observed on 8 images of each laminate’s cross-section

void content for 30 min of vibrationsno cover top cover +vacuum

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

10 30 50 NO 10 30 50 NO 10v 30v 50v NOv

frequency, Hz

%

  No cover

[%]

Top cover

[%]+ vacuum

[%]

10 1.005 0.477 0.104

30 2.124 0.040 0.018

50 5.656 1.076 0.543

NO 8.374 4.502 1.363

Frequency Hz

Vibration Project, Jelena MN

Vacuum Beer

0

1

2

3

4

5

6

7

8

9

10v 30v 50v NOv 10b 30b 50b NObfrequency, Hz

%

11/16

Project’s Discussion IIProject’s Discussion II

Good results from: Low freq (10-50Hz) Higher temperatures Top cover Vacuum

Void % decreased Properties still to

investigate Is it good enough? Can it be better?

Vibration Project, Jelena MN

Hot water tanks, 50l

PumpWater pot

Flexible hosesShakers

Lower chamber

Upper chamber

Silicone membrane

 

Schematic of the system

Current WorkCurrent WorkSmall machine?!?Small machine?!?

With vibrations

Curing at elevated temperatures (80C)

Heat transfer rate liquid/gas = 25

Vacuum

Epoxy resin system

Vibration Project, Jelena MN 13/16

14/16

FutureFuture

Low frequencies High temperatures Vacuum Different fibre/resin 1 to 5 shakers

Optical microscopy and CT scan

Mechanical testing …

Vibration Project, Jelena MN

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ConclusionsConclusions

Vibrations reduce void content (bubbles)

Reduced void % leads to improved laminate quality

…

Vibration Project, Jelena MN

Effect of vibrations on void content Effect of vibrations on void content in composite materialsin composite materials

DERF June 2008.DERF June 2008.

Jelena Muric-NesicJelena Muric-Nesic

Supervisors: P.Compston, N.Noble, Z.Stachurski

Thank you!Thank you!