Transducer Misalignment and Contact Pressure Distributions as Error Sources in Friction Measurement on Small-Diameter Pin-on-Disk Experiments

This paper explores the effects of wear track diameter, contact area and pressure distributions (Hertzian and uniform circular) on errors in measuring friction coefficients on rotating pin-on-disk experiments. Integral solutions of the measured friction coefficient are compared to the actual friction coefficient. Errors associated with angular misalignments of the force transducer are also evaluated. It is shown that the errors for small-diameter wear tracks relative to the contact width are lower for sphere-on-flat (Hertzian) contact geometries than circular flat-on-flat contact geometries. Small-diameter experiments result in surprisingly small errors for Hertzian contact pressure distribution. Angular misalignments further collude to increase the error in measured friction coefficient for small track-diameter-to-contact-width ratios, converging to the cosine error for large track-diameter-to-contact-width ratios.