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CompTest 2003, 28-30 January 2003, Châlons-en-Champagne
Measurement of Thermal
Conductivity for
Fibre Reinforced
Composites
By R. Sweeting* and X.L. Liu
CRC-ACS, Australia
Phone: +61 3 9646 6544
*[email protected]
© CRC for Advanced Composite Structures Ltd
CompTest 2003, 28-30 January 2003, Châlons-en-Champagne
Introduction
• Thermal conductivity
required to perform accurate
thermal modelling
• No standard test for
composites
• Reliance on estimation by
micromechanics equations
© CRC for Advanced Composite Structures Ltd
CompTest 2003, 28-30 January 2003, Châlons-en-Champagne
Present Work
Develop a simple and reliable method for
measuring the thermal conductivity in the three
principal directions of a composite laminate
• One-dimensional thermal gradient developed in
the composite
• Environment designed to limit heat losses
• Thermocouples measure temperature gradient
• Data analysis performed using a numerical
inverse approach
© CRC for Advanced Composite Structures Ltd
CompTest 2003, 28-30 January 2003, Châlons-en-Champagne
Test Methodology
• Create a one-dimensional heat flow
• Reduce thermal edge effects to negligible
levels
• Minimise losses perpendicular to temperature
gradient
– Conduction
– Convection
– Radiation
• Simplify solution and reduces the number of
unknowns
© CRC for Advanced Composite Structures Ltd
CompTest 2003, 28-30 January 2003, Châlons-en-Champagne
Test Methodology
• Finite element analysis performed to find
optimal test design (in-plane test)
© CRC for Advanced Composite Structures Ltd
CompTest 2003, 28-30 January 2003, Châlons-en-Champagne
Test Set-up and Procedure
• 2 different test designs
– In-plane conductivity
– Through-thickness conductivity
• Testing performed from
room temperature to 180ºC
• Performed in 20ºC
increments
• High temperature
environment controlled by
oven
• Thermocouple baseline
taken before each test
© CRC for Advanced Composite Structures Ltd
CompTest 2003, 28-30 January 2003, Châlons-en-Champagne
In-Plane Conductivity Test Set-up
• Central measurement laminate containing
embedded thermocouples
• Surrounding environment designed to minimise
losses
Insulation
Heaters
Laminates
Vacuum Bag
© CRC for Advanced Composite Structures Ltd
Thermocouple
Spacers
CompTest 2003, 28-30 January 2003, Châlons-en-Champagne
Through-Thickness Conductivity
Test Set-up
Insulation
Heater
Laminate
• Ideal test similar
to in-plane test
Spacer
Laminate
Heater
Vacuum Bag
• Test design
modified to use
existing hotplate
Thermocouple
Insulation
Aluminium
Spacer
Laminate
Raised and Lowered during test
Heater
Vacuum Bag
© CRC for Advanced Composite Structures Ltd
Thermocouple
CompTest 2003, 28-30 January 2003, Châlons-en-Champagne
Data Analysis
• Thermal conductivity calculated using a
numerical inverse approach
• Error function minimised
d 
 T κ   T 
n
j 1
j
num
2
j
exp
• Numerical temperatures calculated using 1D
finite difference method
• Fortran program written to perform the
analysis
© CRC for Advanced Composite Structures Ltd
CompTest 2003, 28-30 January 2003, Châlons-en-Champagne
Validation of Method
• Validation of the in-plane conductivity test
method was performed using 7075-0
aluminium alloy for which the thermal
conductivity is 173 W/m.K
• Three 200 x 200 x 4.2mm plates were used
for a in-plane validation test
• Thermocouple spacing was relatively large at
50 mm
• One-dimensional, no loss finite element
model constructed for comparison using
known properties.
© CRC for Advanced Composite Structures Ltd
CompTest 2003, 28-30 January 2003, Châlons-en-Champagne
Validation of Method - Results
• Very good agreement between predicted and
experimental profiles
• Calculated conductivity 178 W/m.K, less than
3% higher
50
Position 1
Applied Ramp
Temperature [ºC]
45
Position 2
40
Position 3
35
Position 4
30
Test Data
Calculated
25
0
20
40
60
Time [s]
© CRC for Advanced Composite Structures Ltd
80
100
CompTest 2003, 28-30 January 2003, Châlons-en-Champagne
Composite laminates
• Tests were conducted using Hexcel F593
plain weave carbon-epoxy laminates
• 0° ply orientation
• Volume fraction = 49%
© CRC for Advanced Composite Structures Ltd
CompTest 2003, 28-30 January 2003, Châlons-en-Champagne
In-plane Test
• Three 12 ply
laminates were
manufactured
• Centre laminate had
4 embedded
thermocouples at
5mm increments
© CRC for Advanced Composite Structures Ltd
CompTest 2003, 28-30 January 2003, Châlons-en-Champagne
Through Thickness Test
• 24 ply laminate
• Thermocouples embedded after the 1st, 6th,
12th and 18th plies
© CRC for Advanced Composite Structures Ltd
CompTest 2003, 28-30 January 2003, Châlons-en-Champagne
Conductivity Results
• Conductivity
increases linearly
with temperature
Thermal Conductivity [W/m.K]
3.5
3
2.5
• In-plane
conductivity 4 times
through-thickness
conductivity
In-Plane
2
1.5
1
0.5
Through Thickness
0
0
50
100
Temperature [ºC]
© CRC for Advanced Composite Structures Ltd
150
200
CompTest 2003, 28-30 January 2003, Châlons-en-Champagne
Conductivity Results
• Excellent correlation between measured and
calculated temperature profiles
In-plane
40
Through-Thickness
38
Temperature [ºC]
Position 2
30
Position 3
25
Position 4
20
Test Data
Calculated
36
Temperature [ºC]
Position 1
Applied Ramp
35
Position 1
Applied Ramp
Position 2
34
32
Position 3
Position 4
30
28
26
24
22
Test Data
Calculated
20
15
30
50
70
90
110
130
150
170
190
Time [s]
© CRC for Advanced Composite Structures Ltd
210
30
35
40
45
50
55
60
Time [s]
65
70
75
80
CompTest 2003, 28-30 January 2003, Châlons-en-Champagne
Conclusion
• New and simple method developed to
measure thermal conductivity
• Validation using aluminium alloy shows
excellent correlation
• Conductivity of F593 laminates increases
linearly with temperature
• In-plane conductivity 4 times throughthickness conductivity
© CRC for Advanced Composite Structures Ltd
CompTest 2003, 28-30 January 2003, Châlons-en-Champagne
Questions ?
Thermal Conductivity [W/m.K]
3.5
3
2.5
In-Plane
2
1.5
1
0.5
Through Thickness
0
0
50
100
Temperature [ºC]
© CRC for Advanced Composite Structures Ltd
150
200