comptest 2003, 28-30 january 2003, châlons-en-champagne © crc for advanced composite structures...

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*[email protected]



Introduction

• Thermal conductivity required to perform accurate thermal modelling

• No standard test for composites

• Reliance on estimation by micromechanics equations



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



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



Test Methodology

• Finite element analysis performed to find optimal test design (in-plane test)



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



In-Plane Conductivity Test Set-up

• Central measurement laminate containing embedded thermocouples

• Surrounding environment designed to minimise losses



Through-Thickness Conductivity Test Set-up

• Ideal test similar to in-plane test

• Test design modified to use existing hotplate



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



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.



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



Composite laminates

• Tests were conducted using Hexcel F593 plain weave carbon-epoxy laminates

• 0° ply orientation• Volume fraction = 49%



In-plane Test

• Three 12 ply laminates were manufactured

• Centre laminate had 4 embedded thermocouples at 5mm increments



Through Thickness Test

• 24 ply laminate• Thermocouples embedded after the 1st, 6th,

12th and 18th plies



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



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]


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]


Position 1Applied RampPosition 2

Position 4

Position 3

In-plane Through-Thickness



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



Questions ?

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...

Documents

advanced composite structures

champagne crc

plane test slide

plane test test design

plane conductivity test

standard test

composite environment

analysis slide