Graffin Lecture Series - Winner 1999/2000

The 1999/2000 George D. Graffin Lectureship in Carbon Science and Engineering

The Use of Carbon-Carbon Composites in Aircraft Braking Applications

C-C composites are used in a wide variety of applications including aircraft brakes, automobile brakes, rocket nozzles, as well as structural materials in the aerospace industry.  The largest current market for C-C composites is their application as the heat-sink and friction material for aircraft brakes. Today, carbon brakes are used on most wide-body commercial aircraft and the majority of military aircraft.

In aircraft braking applications carbon-carbon composites fulfill three functions including:

a) Heat sink - The C-C composite friction material acts as the heat sink to convert the kinetic energy of the aircraft into heat.  The friction material must dissipate this heat slowly to prevent melting of nearby metal structures.  Carbon is an attractive material because the heat capacity of carbon is 2.5 times greater than that of steel.

b) Friction - Sufficient friction must also be generated by the brake lining material to bring the aircraft to a smooth, controlled stop under different kinetic energy conditions (taxi, landing and RTO).

c)  Structural member - High mechanical strength is also required at elevated temperatures since the friction material also acts as the structural member and transfers the frictional torque to the wheel during braking applications.  The strength of carbon is comparable to that of steel, while at high temperatures, carbon is nearly twice as strong.

The lecture describes why carbon-carbon composites are used as friction materials.  It discusses the important properties of C-C composites as related to their use as the friction material in aircraft brake applications.  The friction and wear mechanisms of carbons and the influence of carbon structure, physical, thermal, mechanical and chemical properties as well as friction films on the performance of C-C friction materials used in aircraft braking applications are described.