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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.
2/16
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
15/16
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!