Addressing Practical Challenges of Low Friction Coefficient Measurements

A friction coefficient is defined as the ratio of the friction force to the applied normal force. Despite the disarming simplicity of its calculation, there are practical challenges that make low values of friction coefficient difficult to accurately quantify. The connections of imperfect parts in friction measurement devices (called tribometers) produce small misalignments between the transducer and counterface axes. According to Schmitz et al. (J Tribol Trans ASME 127:673–678, 2005), ‘‘...the measurement of friction coefficient is extremely sensitive to misalignments’’ and ‘‘for materials with friction coefficients below 0.05 the alignment becomes hopelessly difficult if the goal is to have uncertainties below 1%.’’ This method article reviews the challenges of low friction measurements and presents a robust reversal technique that eliminates misalignment bias. Experiments with controlled misalignment angles demonstrate the bias sensitivity and validate its elimination using a low uncertainty tribometer in conjunction with the described reversal technique.