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Frictional transition effects in unlubricated sliding Pomeroy, Richard James


The object of this research was to study the effect of initial surface -finish and finish mark orientation on intermetallic friction under unlubricated sliding contact conditions. The metal used was mild steel and the parameters investigated were sliding speed and load. Qualitative assessments of wear were also made. The basic apparatus consisted of a rotating disc and an elastically supported slider. The disc and slider each had the same-initial surface finish. Six different surface finishes were examined ranging in roughness from a peak to valley distance of 6.9 thousandths of an inch to 35 microinches R.M.S. Speed was varied from 1.25 to 60 inches per second and normal load from 1.025 to 3.075 pounds. No significant correlation was found, between the theory of Ernst and Merchant and the experimental results. Friction was more dependent on surface parameters affecting load concentration than, on the particular details of each surface asperity. The effects of finish mark orientation were only significant when they produced appreciable load concentration. Friction was found to increase as "wear-in" progressed and remain approximately constant once wear-in was complete. No relation between friction and velocity could be deduced. Wear-in was found to be influenced by initial surface geometry. The sufaces which gave high load concentration at sharp protuberances "wore-in" more quickly than those-with low load concentration. Smooth compatible surfaces which required little surface alteration also wore-in rapidly. Wear debris was found to influence both friction and wear-in. Evidence of mechanical working of debris between the surfaces was obtained. A quasi-harmonic oscillation of the slider supporting system was observed to result from wear-in. The frequency of vibration was a function of disc speed and load. The amplitude of the vibration increased linearly with disc speed up to a maximum value. The magnitude-of this maximum was dependent on normal load.

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