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In assessment of lubricant properties and in various contact applications, it is of importance to know the frictional qualities. Under quasi-static conditions, normal and transverse forces are measured using force transducers, but the task is more difficult when loads are high and transient as they often are in elastohydrodynamic conjunctions. The experimental method presented in this paper is based on analysis of propagating waves in a beam, due to an impact on its end surface, using FFT analysis. Since the impact is oblique, both non-dispersive compression waves and dispersive flexural waves are generated. The normal force originating from the axial wave is measured using strain gauges, while the transverse force is derived from the FFT's of two lateral acceleration histories using Timoshenko dynamic beam theory. The relation between normal and tangential force histories displays the frictional properties at the impact as a function of time; i.e., variations in frictional properties during loading and unloading (typically 200– 400 μs in ball bearings and gears) can be observed. A variety of lubricants has been studied up to a Hertzian pressure of 2.5 GPa, and the method and results are presented.
transient, impact, fourier, FFT, friction, density, dilatation, pressure, tribology, EHD, EHL, lubricant, oil, ball, bar, wave, beam
Luleå University of Technology, Luleå,