Wear phenomena involve a large number of physical and mechanical parameters which are not always well known or controlled during relative movement between two bodies. Numerous industrial applications necessitate an evaluation of technological component life time and wear modelling often fails to give accurate estimation.We use the classical Archard's wear model where wear is related to dissipated power. It appears that great dispersion can occur in the estimation of dissipated power related to a lack of knowledge of certain parameters.We present here a probabilistic approach of the contact problem resolution. We consider the specific contact problem in the case of steady state rolling. A wear apparatus has been used to test different materials and we use the simplified model Fastsim to evaluate slip and tangential traction in the contact zone. For each parameter of the simulation, we construct a probabilistic density function with the only information available.A Monte-Carlo method is implemented and the resolution of numerous cases allows the dissipated energy to be evaluated as a mean value and a confidence region for 95% viability.

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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 ...

We deal with rolling contact between quasi-identical bodies. As normal and tangential problems are uncoupled in that case, the simplified approach to determine contact area and normal loading distribution for rolling contact problems is presented in Sec. 2. In Sec. 3, the solution of the tangential problem is used to update the rolling profiles and enables to follow the wear evolution versus time. The method used to solve the normal problem is called semi-Hertzian approach with diffusion. It allows fast determination of the contact area for non-Hertzian cases. The method is based on the geometrical indentation of bodies in contact: The contact area is found with correct dimensions but affected by some irregularities coming from the curvature’s discontinuity that may arise during a wear process. Diffusion between independent stripes smoothes the contact area and the pressure distribution. The tangential problem is also solved on each stripe of the contact area using an extension of the simplified approach developed by Kalker and called FASTSIM. At the end, this approach gives the dissipated power distribution in the contact during rolling and this power is related to wear by Archard’s law. This enables the profiles of the bodies to be updated and the evolution of the geometry to be followed.