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Transitory static and kinetic boundary friction mechanisms Marion, Terence Lionel

Abstract

The purpose of the investigation was to study, by analysis of friction-induced vibration, the underlying physical mechanisms of metallic boundary friction. Dynamic system response and interfacial friction force data, from a pin-on-disc machine operating over a broad range of surface speeds, was electronically monitored and photographically recorded. Excellent agreement in the response curve profiles of recorded rate-sensitive static friction data and a predictive curve developed by assumption of a plastic deformation model of contact area growth suggests strongly that plastic deformation is indeed the controlling physical mechanism of metallic static friction. The existence of an upper asymptote of static friction in the presence of a lubricant, and the existence in the "slip" friction curve of a transient which appears governed by the relative dynamic displacement of the surfaces, has been proven. Vibratory slip and quasi-harmonic oscillation both exhibited simultaneous solid-contact and viscous fluid film characteristics. The "humped" form of friction force vs velocity curve necessary for quasi-harmonic oscillation was concluded to differ from that of non-oscillatory slip only because of thermal variation in the fluid viscosity, similar to that encountered in elastohydrodynamic studies. In every instance rate effects were found to determine or profoundly influence the physical mechanisms of metallic boundary friction.

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