Étude par la méthode d’homogénéisation des effets combinés de la rugosité de surface et de la rhéologie du lubrifiant sur le comportement d’un contact hydrodynamique

Dans cet article, les effets combinés de la rugosité de surface et de la rhéologie du lubrifiant additivé sur les performances hydrodynamiques d’un patin plan incliné sont étudiés au moyen de la méthode d’homogénéisation. La surface du patin contiguë au film est supposée fixe et rugueuse tandis que la surface inférieure mobile est parfaitement lisse. Le modèle de fluide polaire ou à couple de contrainte de V.K. Stokes est adopté pour décrire le comportement rhéologique du lubrifiant s’écoulant entre les deux surfaces. Les études de simulation sont effectuées en considérant trois formes de rugosités (transversales, longitudinales et anisotropes) et différentes valeurs du paramètre de couple de contrainte. La comparaison des solutions obtenues par les méthodes déterministe et d’homogénéisation a permis de conclure que la méthode d’homogénéisation est efficace pour les trois formes de rugosité envisagées. Les résultats de l’étude paramétrique effectuée montrent que les rugosités de surface et les couples de contraintes dus à la présence des additifs polymériques dans le lubrifiant ont des effets non négligeables sur les performances hydrodynamiques du contact, à savoir : le champ de pression, la capacité de charge, le nombre de frottement et la puissance dissipée

Free vibration analysis of multi-span orthotropic bridge deck with rubber bearings

In this paper, a semi-analytical approach is proposed for free vibration analysis of a multi-span, orthotropic bridge deck with rubber bearings. This allows more realistic modeling of vibration transmission from a bridge’s deck to its supports. The approach is based on modal superposition incorporating intermodal coupling. The bridge deck was modeled as a continuous, multi-span, orthotropic rectangular plate with equivalent rigidities. The rubber bearings were inserted between the girders and rigid supports to absorb traffic induced vibrations. The rubber bearing was modeled by linear elastic, vertical supports as very flexible in rotation and highly rigid in the vertical direction. The method’s efficacy was validated against two numerical examples. The absolute error was less than 10%

Analysis of couple-stresses and piezo-viscous effects in a layered connecting-rod bearing

International audienceIn this work, the combined effects of couple-stresses and piezo-viscosity on the dynamic behavior of a compression ignition engine big-end connecting-rod bearing with elastic layer are investigated using the V. K. Stokes micro-continuum theory. It is assumed that the journal (crankpin) is rigid and the big-end bearing consists of a thin compressible elastic liner fixed in an infinitely stiff housing. The governing Reynolds' equation and the viscous dissipation term appearing on the RHS of energy equation are modified using the V. K. Stokes micro-continuum theory. The non-Newtonian effect is introduced by a new material constant η, which is responsible for couple-stress property, and the piezo-viscosity effect by the pressure–viscosity coefficient α appearing in the well-known Barus' law. In the proposed model, the nonlinear transient modified Reynolds equation is discretized by the finite difference method, and the resulting system of algebraic equations is solved by means of the subrelaxed successive substitutions method to obtain the fluid-film pressure field as well as the film thickness distribution. The crankpin center trajectories for a given load diagram are determined iteratively by solving the nonlinear equilibrium equations of the journal bearing system with the improved and damped Newton–Raphson method for each time step or crankshaft rotation angle. According to the obtained results, the effects of couple-stresses and piezo-viscosity on the nonlinear dynamic behavior of dynamically loaded bearings with either stiff or compliant liners are significant and cannot be overlooked

Steady-state behavior of finite compliant journal bearing using a piezoviscous polar fluid as lubricant

The proposed work is concerned with the theoretical and numerical investigation of the lubricant rheology effects on the steady-state behavior of a plain finite compliant journal bearing operating under isothermal conditions. In the present investigation, the couple-stresses due to the presence of improving viscosity index (VI) additives, the viscosity-pressure (piezoviscosity effect) as well as the density-pressure (compressibility effect) variations are considered. The hydrodynamic lubrication theory is based on the V.K. Stokes micro-continuum mechanics which takes into account the size of macro-molecular chains added to the basic oil. The Barus and Dowson-Higginson laws were used to express the viscosity-pressure and density-pressure variations. Using the classical assumptions of lubrication, a modified Reynolds’ equation is derived and solved numerically by the finite difference method. The displacement field at the fluid film bearing liner interface due to pressure forces is determined using the elastic thin liner model. The proposed work is concerned with the theoretical and numerical investigation of the lubricant rheology effects on the steady-state behavior of a plain finite compliant (elastic liner) journal bearing operating under isothermal conditions and laminar flow. The obtained results show that the couple-stresses have significant effects on the hydrodynamic performance characteristics such as the pressure field, the carrying capacity, the attitude angle and friction number especially when the viscosity-pressure variation is considered. Moreover, it is also shown that the compressibility of lubricant doesn’t affect the hydrodynamic characteristics