Identification of the coefficient of sliding friction from an apparent non-Coulomb behavior between wood and steel

This study investigates the sliding friction fluctuations through hysteresis cycles, observed between a steel sphere and wood specimens of beech and spruce, by using a tribometer and a profilometer. At first, the tracked wear profiles revealed a correlation between the normal force variation and the surface waviness. However, the normal force variation alone was not able to explain the observed friction force fluctuation. Hence, to explain most of the observed non-Coulomb friction hysteresis behavior, the wear-scar interaction is taken into account through an optimization framework used for data post-processing and leading to an optimal friction coefficient. A comparative study showed similar values between the identified optimal friction coefficient, the mean and energy-based friction coefficients.