Using a novel anti-vibration tribometer with a yaw angle misalignment, Kado et al. (Trans. Jpn. Soc. Mech. Eng. C79: 2635-2643, 2013 have recently shown experimentally that frictional vibration in tribotesting causes considerable error, e.g., a 35% underestimation of the kinetic friction coefficient for the sliding contact between a steel ball and a steel plate lubricated with glycerol. In this paper, it is shown that their experimental results can be numerically simulated based on a purely mechanical model, which confirms that their experiments were carried out properly and also that in conventional tribotesting, the "measured kinetic friction coefficient" (obtained from the time-averaged spring force) is not the "inherent kinetic friction coefficient" (determined by the inherent nature of materials in contact as a function of the relative velocity) but the "effective kinetic friction coefficient" (determined by the mean energy consumption rate as a function of the driving velocity). The effective kinetic friction coefficient depends on the mechanical properties of the tribometer used in the test, and it corresponds to the inherent kinetic friction coefficient when the measurement is carried out with no frictional vibration.
To measure true values of kinetic friction coefficient in a force balance between the frictional force and spring force, an anti-vibration tribometer (AVT) has been developed. The AVT utilizes a novel principle that an angular misalignment between the two velocities (i.e., the driving velocity of one of contact surfaces and the moving velocity of the other surface) produces a positive damping effect to stabilize the equilibrium point and suppress frictional vibration autonomously. For example, when a sliding contact between a steel ball and a steel plate is lubricated by glycerin, the AVT provides a force balance situation at a misalignment angle φ = 30° (i.e., an anti-vibration setting), although strong frictional vibration occurs at φ = 0° (i.e., a conventional setting). By comparing the kinetic friction coefficients obtained at φ = 0° and 30°, it has been found that frictional vibration can lead to a serious error of measuring kinetic friction coefficient (e.g., a 35% underestimation at a low driving speed).
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