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

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A Study of Carbon-Carbon Composites for use in
Airplane Disc Brakes
Greg Oberson Advisors Dr. Bowman and Dr. Trice
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How a disc brake works
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Desired properties for an airplane brake

• High thermal conductivity
• Consistent coefficient of friction
• High strength at high temperatures
• Oxidation and wear resistance

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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

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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
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Brake surface
Laminated Matte
Chopped Fiber
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Cross section
Chopped Fiber
Laminated Matte
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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?
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TGA comparison
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Graphite crystal structure
Edges are susceptible to oxidation
Basal planes are resistant to oxidation
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Hexagonal unit cell
(100) is perpendicular to basal edges and will be
detected when the edges are exposed to the
surface of the material.
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XRD comparison
Planes perpendicular to basal planes are detected
Planes perpendicular to basal planes are not
detected
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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.

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Four-point bend testing (ASTM standard C1161-94)

• Imposes tensile and compressive loading
  simultaneously
• Measures the relative structural soundness of the
  test material

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Comparison of flexure strength versus
microstructure and fiber orientation
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Four point bending comparison
Fibers are randomly aligned
Fibers are parallel to tensile axis
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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.