comptest 2003, 28-30 january 2003, châlons-en-champagne © crc for advanced composite structures...
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CompTest 2003, 28-30 January 2003, Châlons-en-Champagne
© CRC for Advanced Composite Structures Ltd
Measurement of Thermal Conductivity forFibre Reinforced
Composites
By R. Sweeting* and X.L. LiuCRC-ACS, Australia
Phone: +61 3 9646 6544*rods@duigen.dsto.defence.gov.au
CompTest 2003, 28-30 January 2003, Châlons-en-Champagne
© CRC for Advanced Composite Structures Ltd
Introduction
• Thermal conductivity required to perform accurate thermal modelling
• No standard test for composites
• Reliance on estimation by micromechanics equations
CompTest 2003, 28-30 January 2003, Châlons-en-Champagne
© CRC for Advanced Composite Structures Ltd
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
CompTest 2003, 28-30 January 2003, Châlons-en-Champagne
© CRC for Advanced Composite Structures Ltd
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
CompTest 2003, 28-30 January 2003, Châlons-en-Champagne
© CRC for Advanced Composite Structures Ltd
Test Methodology
• Finite element analysis performed to find optimal test design (in-plane test)
CompTest 2003, 28-30 January 2003, Châlons-en-Champagne
© CRC for Advanced Composite Structures Ltd
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
CompTest 2003, 28-30 January 2003, Châlons-en-Champagne
© CRC for Advanced Composite Structures Ltd
In-Plane Conductivity Test Set-up
• Central measurement laminate containing embedded thermocouples
• Surrounding environment designed to minimise losses
CompTest 2003, 28-30 January 2003, Châlons-en-Champagne
© CRC for Advanced Composite Structures Ltd
Through-Thickness Conductivity Test Set-up
• Ideal test similar to in-plane test
• Test design modified to use existing hotplate
CompTest 2003, 28-30 January 2003, Châlons-en-Champagne
© CRC for Advanced Composite Structures Ltd
Data Analysis
• Thermal conductivity calculated using a numerical inverse approach
• Error function minimised
n
1j
2jexp
jnum TκTd
• Numerical temperatures calculated using 1D finite difference method
• Fortran program written to perform the analysis
CompTest 2003, 28-30 January 2003, Châlons-en-Champagne
© CRC for Advanced Composite Structures Ltd
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.
CompTest 2003, 28-30 January 2003, Châlons-en-Champagne
© CRC for Advanced Composite Structures Ltd
Validation of Method - Results
• Very good agreement between predicted and experimental profiles
• Calculated conductivity 178 W/m.K, less than 3% higher
25
30
35
40
45
50
0 20 40 60 80 100
Time [s]
Tem
pe
ratu
re [
ºC]
Test Data Calculated
Position 1Applied Ramp
Position 2
Position 4
Position 3
CompTest 2003, 28-30 January 2003, Châlons-en-Champagne
© CRC for Advanced Composite Structures Ltd
Composite laminates
• Tests were conducted using Hexcel F593 plain weave carbon-epoxy laminates
• 0° ply orientation• Volume fraction = 49%
CompTest 2003, 28-30 January 2003, Châlons-en-Champagne
© CRC for Advanced Composite Structures Ltd
In-plane Test
• Three 12 ply laminates were manufactured
• Centre laminate had 4 embedded thermocouples at 5mm increments
CompTest 2003, 28-30 January 2003, Châlons-en-Champagne
© CRC for Advanced Composite Structures Ltd
Through Thickness Test
• 24 ply laminate• Thermocouples embedded after the 1st, 6th,
12th and 18th plies
CompTest 2003, 28-30 January 2003, Châlons-en-Champagne
© CRC for Advanced Composite Structures Ltd
Conductivity Results
• Conductivity increases linearly with temperature
• In-plane conductivity 4 times through-thickness conductivity
0
0.5
1
1.5
2
2.5
3
3.5
0 50 100 150 200
Temperature [ºC]
Th
erm
al C
on
du
cti
vit
y [
W/m
.K]
In-Plane
Through Thickness
CompTest 2003, 28-30 January 2003, Châlons-en-Champagne
© CRC for Advanced Composite Structures Ltd
Conductivity Results
• Excellent correlation between measured and calculated temperature profiles
15
20
25
30
35
40
30 50 70 90 110 130 150 170 190 210
Time [s]
Tem
per
atu
re [
ºC]
Test Data Calculated
Position 1Applied Ramp
Position 2
Position 4
Position 3
20
22
24
26
28
30
32
34
36
38
30 35 40 45 50 55 60 65 70 75 80
Time [s]
Tem
pe
ratu
re [
ºC]
Test Data Calculated
Position 1Applied RampPosition 2
Position 4
Position 3
In-plane Through-Thickness
CompTest 2003, 28-30 January 2003, Châlons-en-Champagne
© CRC for Advanced Composite Structures Ltd
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 through-thickness conductivity
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