1. CompTest 2003, 28-30 January 2003, Châlons-en-Champagne © CRC for Advanced Composite Structures Ltd Measurement of Thermal Conductivity for Fibre Reinforced Composites By R. Sweeting* and X.L. Liu CRC-ACS, Australia Phone: +61 3 9646 6544 *rods@duigen.dsto.defence.gov.au

2. 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

3. 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

4. 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

5. 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)

6. 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

7. 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

8. 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

9. 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 Numerical temperatures calculated using 1D finite difference method Fortran program written to perform the analysis

10. 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.

11. 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

12. 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%

13. 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

14. 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

15. 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

16. 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 In-plane Through-Thickness

17. 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

18. CompTest 2003, 28-30 January 2003, Châlons-en-Champagne © CRC for Advanced Composite Structures Ltd Questions ?