Effect of Braking Speed on Friction Properties of C/C Composite Braking Pad

The friction and wear behavior of C/C composites with carbon cloth laminated structure was investigated on an MM 1000 test rig at different braking speeds. The worn surfaces of the samples were examined with a scanning electron microscope. It has been found that the friction coefficient increases with increasing braking speeds and reaches to maximum in the speed range of 20~25 m/s. When braking speeds increase to 28~30 m/s, the friction coefficient still remains high value, indicating that it might be a candidate as the braking pad of excellent high energy friction performance. The wear rate is much small at low braking speed and rapidly increases with the braking speed rises above 15 m/s. At a relatively low braking speed, the worn surface of the composite was covered with a thin debris layer. When the braking speed rose over 15 m/s, a thicker layer composed of the wear debris was formed on the worn surface. Such a wear debris layer is liable to remove under normal and shearing stress, thus a relatively higher wear rate is observed at higher braking speed. In the meantime, severe oxidation also contributes to increase the wear rate of the composites at higher braking speed, accompanied by the oxidation and spalling of carbon matrix and carbon fibers.