This paper presents the results of an investigation into the resistance to free rolling, under light loads, of a ball bearing ball on a flat track of unhardened En 31 steel using a pendulum arrangement in partial vacuum (5 – 50 Pa). The effect of air resistance (from experiments conducted in air) is demonstrated and results of tests at different frequencies and loads are presented. These include estimates of the effective hysteresis loss factor and of the coefficient of rolling resistance. A detailed examination of the amplitude decay curves shows that the damping, under the experimental conditions described, (i) can be represented neither by the Coulomb nor the viscous models; (ii) is practically independent of frequency (within the limited range possible with the apparatus); (iii) is appreciably dependent on contact load and oscillation amplitude, especially at the higher end of the load range investigated where a gradual transition to plastic behaviour is evident.

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