FRICTION OSCILLATIONS WITH A PIN-ON-DISC TRIBOMETER

Oscillations on friction force tracings recorded during pin-on-disc experiments were found to be a result of non-uniform surface features and lubrication conditions along the circular wear track. The oscillations were not due to stick slip. Spacings between peaks and valleys on the tracings were observed to correspond directly to the rotations of the disc specimen. The characteristics of the friction force oscillations were more clearly revealed when the chart speed was increased or when the disc rotation was slowed. The amplitude of the oscillations changed with continued sliding. Results indicated that the coefficient of sliding friction for the materials tested under boundary or unlubricated conditions should more property be reported as a range of values rather than one single nominal value. Reporting a range of values provides additional information on the stability of sliding conditions and the uniformity of lubrication for the tribosystem.