Friction and wear during twin-disc experiments under ambient and cryogenic conditions

Abstract

To cite this version:Luc Chevalier, S. Cloupet, M. Quillien. Friction and wear during twin-disc experiments under ambient and cryogenic conditions. Tribology International, Elsevier, 2006, 39 (11) proposed by Kalker (Fastsim) is used to identify the dynamic friction coefficient between these discs and to study the apparatus parameters influence on dissipated energy. Wear evolution is simulated using classical Archard's law and compared to measured profiles.Influence of ambient conditions is highlighted by comparing friction and wear coefficients.Keywords: Twin-disc experiment, dynamic friction coefficient measurement, wear simulation, Fastsim IntroductionBearing track lubrication limits the dynamic friction coefficient value when the bearing balls are loaded. Consequently, the wear which results from this friction is also limited. In the case of turbopump bearings used in the space shuttle launch engine, the important loading makes this point very sensitive. Moreover, these bearings work in particularly harsh thermal environments since they are bathed in liquid oxygen (90 K) or liquid hydrogen (20 K). At such temperatures one is interested to know the effects of friction and wear. Because it is very difficult to manage lubrication at this temperature, our goal is to study the influence of the temperature on dynamic friction coefficient and wear factor in the absence of lubrication. 3Twin disc apparatus is used to perform dynamic friction coefficient evolution measurements under constant normal load and variable slip (see Quillien & al. [1]). After testing, information on wear may be obtained. In this study we focus on modelling the experiment in order to evaluate dynamic friction coefficient and wear factor for the two situations: ambient temperature and cryogenic conditions (-196°C).First, we briefly recall the mechanical problem to solve and estimate the tangential force during the twin-disc experiment. Then we compare the experimental results to the simulation in order to discuss: (i) the evolution of the apparent friction coefficient versus longitudinal slip; (ii) the influence of temperature on coefficient of friction. Afterwards, we present the wear measurements and recall Archard's law used for simulation. An updated Hertzian approach is used to take into account the wear profile evolution. Finally, we discuss the results of the simulation and make conclusions on the wear factor value in cryogenic or ambient air. Dynamic friction coefficient identification Twin-disc apparatus descriptionA twin-disc experiment is performed on two steel specimens ( Fig.1) under extremely different conditions: ambient air at room temperature and cryogenic conditions (specimens are cooled with liquid nitrogen at -196°C in cryostat box). Different rotating rates are imposed at each disc (controlling the rotate velocity of each brushless motor independently) to insure the same rolling velocity V = R 1 ω 1 = R 2 ω 2 or to impose a relative slip. Two belt-driven mechanical spindles, each of which supports 60 mm diameter specimen ...

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