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Theses

Influence des films d’eau très minces sur le frottement pneu/chaussée

Abstract : This thesis aims at understanding better how skid resistance is altered by a very thin water film (thickness less than 1 mm) on the road surface. This wetting can cause viscoplaning which is the source of accidents during drizzles or after rainfalls. The final goal of the thesis is to suggest criteria to define conditions for the onset of viscoplaning. Laboratory tests are performed on different types of samples : asphalt concrete but also mosaics composed of sandblasted coarse aggregates which allow studying the influence of microtexture, an essential parameter for the evacuation of thin water films. Tests on actual roads (test tracks) are also performed to validate the representativeness of laboratory tests. Specific tests protocols are developed to monitor the evolution of the friction coefficient from a dry state to a complete wetting of the surface. The curve representing the variation of the friction coefficient with water depth is similar to the Stribeck curve which highlights three lubrication regimes : boundary, mixed and hydrodynamic. The influence of some parameters (speed, microtexture, macrotexture) on this variation is studied. A?critical? water depth, transition between the boundary lubrication regime (value of the friction coefficient close to the value on dry surface) and the mixed lubrication regime (collapse of the friction coefficient), is defined. Relationship between critical water depth, microtexture and speed is analyzed. The relative influence of contact parameters is quantified. A physical model is developed. The theorical friction coefficient results from three contributions (deformation of rubber, adhesion and hydrodynamic effects). Contact parameters such as vertical load and speed are also considered. The model is applied to texture profiles measured by a high resolution laser sensor. A method of profile analysis is developed to detect profile asperities on which deformation and adhesion calculations are made. Comparison between model and measurement is satisfactory, justifying the hypotheses of the model. The model has especially highlighted the importance of the water film at the top of the road asperities. A model from the literature was used, as a first attempt, to estimate the thickness of this water film. Applications of the results of the thesis are mentioned : they contribute to a better understanding of the presence of thin water films on skid resistance but also to the determination of the onset of viscoplaning .
keyword : FROTTEMENT
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Yannick Beautru. Influence des films d’eau très minces sur le frottement pneu/chaussée. Mécanique [physics.med-ph]. Ecole Centrale de Nantes (ECN), 2012. Français. ⟨tel-00851330⟩

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