1. A Study of Carbon-Carbon Composites for use in Airplane Disc Brakes
Greg Oberson
Advisors: Dr. Bowman and Dr. Trice

2. How a disc brake works

3. Desired properties for an airplane brake
High thermal conductivity
Consistent coefficient of friction
High strength at high temperatures
Oxidation and wear resistance

4. Project objectives
To characterize the microstructure of the composites and relate it to oxidation behavior and mechanical properties
To develop a framework for further testing of the composites

5. Two common microstructures
Laminated carbon fiber matte
Chopped carbon fibers in a graphitic matrix
Honeywell Carbenix 2000 Series
Fabricated via CVD
Honeywell Carbenix 4000 and 4100 Series
Fabricated via impregnation in thermosetting resin

6. Brake surface
Laminated Matte
Chopped Fiber

7. Cross section
Chopped Fiber
Laminated Matte

8. How are the microstructures similar?
Density (1.7 g/cm3) and porosity (10%)
Thermal conductivity (70 W/m/K)
Heat capacity (1.5 J/g/K)
Oxidation and wear resistance
Strength and stiffness
How are the microstructures different?

9. TGA comparison

10. Graphite crystal structure
Edges are susceptible to oxidation
Basal planes are resistant to oxidation

11. Hexagonal unit cell
(100) is perpendicular to basal edges and will be detected when the edges are exposed to the surface of the material.

12. XRD comparison Planes perpendicular to basal planes are detected
Planes perpendicular to basal planes are not detected

13. Mechanical properties of carbon-carbon composites…
Are largely controlled by the properties, volume fraction, and geometry of the fibers.
Are affected by interactions that occur during processing.

14. Four-point bend testing (ASTM standard C1161-94)
Imposes tensile and compressive loading simultaneously
Measures the relative structural soundness of the test material

15. Comparison of flexure strength versus microstructure and fiber orientation

16. Four point bending comparison
Fibers are randomly aligned
Fibers are parallel to tensile axis

17. Conclusions
The chopped fiber microstructure shows better oxidation resistance and flexure strength than the laminated matte microstructure.
The fiber orientation largely controls the thermal and mechanical properties of the composite.