Greg Oberson

Johns Hopkins University

Materials Science and Engineering

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

Carbon-carbon composites have been used for airplane disc brakes since the 1960s. This material consists of high strength, high modulus carbon fibers embedded in a graphitic carbon matrix. Carbon-carbon composites exhibit a number of properties that make them ideal for brakes and give them an advantage over traditional metal brakes. The composite material shows high thermal conductivity and high heat capacity, allowing them to operate at temperatures up to 1800oC. Further, the lubricating properties of graphite provide a consistent frictional surface and excellent wear resistance, resulting in a long service life. Finally, the low density of the carbon-carbon composites yields a significant weight savings compared to metal brakes.

Objectives

  • To characterize the microstructure of carbon-carbon composites and relate it to observed thermal and mechanical properties
  • To study the oxidation behavior of carbon-carbon composites at temperatures up to 1000oC
  • To determine the strength of the composites under a variety of loading conditions.

Experimental Approach

  • Optical microscopy and x-ray diffraction to examine the microstructure of the composites
  • Thermogravimetric analysis of composite specimens to measure the oxidation rate
  • Four-point bend test to determine the flexure strength of the composite

Research Findings

  • Orientation of graphite planes within the composite is highly dependent upon its fabrication and processing.
  • Oxidation occurs preferentially on graphite plane edges and in the composite matrix.
  • High modulus fibers give the composite a high flexure strength.

Carbon-carbon specimens flexure tested to measure their structural integrity
A TGA scan shows that the brake material oxidizes rapidly at temperatures above 800oC.
Final Research Presentation

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