Effects of fibre orientation on the tribology of a model carbon–carbon composite

Wear rates and friction coefficients were measured for a PAN fibre–CVI matrix carbon–carbon composite with different fibre orientations at the wear faces. A constant torque dynamometer operating at rotational speeds in the range 1800–8000 rpm (3.5–15.7 m s−1 average linear sliding velocity) was used in a ring on ring configuration sliding wear test. Fibre orientations parallel to the wear face favour the formation of friction films by easy shear deformation of the graphitic CVI sheaths around the fibres. Fibre ends emerging at the wear face inhibit formation of a friction film at low rotational speeds. The resulting high wear rates suggest that particulate debris forms by microfracture of fibre ends emerging at the wear face. At faster rotational speeds, the wear face temperatures and shear forces are sufficiently high to allow friction films to develop. Different wear rates for stators and rotors were found when different fibre orientations were exposed at the two wear faces. The largest differences in wear were seen where fibre ends emerged at the rotor wear face when sliding against a parallel fibre orientated stator. This was also attributed to transverse microfracture of the fibre ends.