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Tuesday, July 9 • 11:30 - 11:50

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Normal contact vibrations of dry rough nominally flat solid surfaces induced by sliding friction is a formidable nonlinear problem. Indeed, it includes both microscopic and macroscopic scales (roughness versus body size), short time scales, non-smooth dynamics (loss of contact) and stochastic excitations induced by roughness. In previous experimental works, we have shown that the friction force and associated normal contact dynamics are mainly governed by successive impacts between the micro asperities. Two different dynamic behaviours have been observed : (i) for low velocities, the slider remains very close to the above solid (grazing regimes) leading to a constant friction force and (ii) for high velocities, it jumps over it with free flights (bouncing regime) leading to an increasing friction force. In this context, the main goal is to propose a heuristic approach of the vertical dynamics of the slider in terms of a randomly excited nonlinear bouncing ball model. Characteristics of the tribological system are considered, i.e. the self-affine topographies, the size of the slider, the normal load and the sliding velocity. An effective random excitation source is identified from the separation at first contact between moving topographies. The level and the spectral contents of the effective excitation depend on the ratio of the slider's lateral size over the correlation length of topographies. In particular, the level appears much smaller than that of the equivalent roughness of the sum surface. Numerical simulations, as well as analytical considerations based on the framework of Extreme Value Theory, allow us to characterize the statistical and spectral properties of this vibrational excitation. Finally, by transforming the excitation in the time domain through the sliding velocity, we demonstrate the relevance of the random bouncing ball model to reproduce experimental observations. More generally, we provide an improved understanding of roughness-induced vibration problems and the associated friction.


Elsa Piollet

Dr, Polytechnique Montréal
avatar for Mohammad Rafiee

Mohammad Rafiee

Postdoctoral Fellow, Polytechnique Montréal
Mohammad Rafiee received his Ph.D. degree in Mechanical Engineering from the University of Ottawa in 2018. Currently, he is a Postdoctoral Fellow at Polytechnique Montreal in Canada. His research interests are primarily focused on the development of advanced composite materials, smart... Read More →

Annie Ross

Professor, Polytechnique Montreal


Tuesday July 9, 2019 11:30 - 11:50 EDT
St-Laurent 8
  T07 Struct. dyn. & nonlin. vib., RS02 Vibr & cntrl of nonlin mech syst