Improved characterization of tribometric test results

As with measurements in general, there is inherent variability in tribometric test results. This variability stems from point-to-point variation in the test surface, from changes in the test foot over time and tests, and from the inherent variability of the measuring process. The friction between the tested foot and tested surface is typically characterized by the sample mean of a number of test replications. The acceptability of the foot/surface combination is typically given with reference to a specified threshold value. This paper discusses the limitations of using such a single-point characterization in determining the acceptability of a given foot/surface combination. Two useful techniques for accommodating the variability in a given tribometer/test-foot/test-surface combination are (1) histogram-based, single and multi-point characterization and (2) ranking methods. This paper will discuss the weaknesses of single-point characterization of tribometric results, how to set multi-point acceptance thresholds, and how to use rank-based characterization for slip-resistance.