A Study of Carbon-Carbon Composites for use in Airplane Disc Brakes

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.