A study has been made to investigate boundary sliding and its accommodation mode with respect to the variation of grain size and α/β volume fraction during superplastic deformation of a two-phase Ti-6Al-4V alloy. A load relaxation test has been performed at 600 °C and 800 °C to obtain the flow stress curves and to analyze the deformation characteristics by the theory of inelastic deformation. The results show that grain matrix deformation (GMD) is found to be dominant at 600 °C and is well described by the plastic state equation. Whereas, at 800 °C, phase/grain boundary sliding (P/GBS) becomes dominant and is fitted well with the viscous flow equation. The accommodation mode for fine-grained microstructures (3 µm) well agrees with the isostress model, while that for large-grained structures (11 µm) is a mixed mode of the isostress and isostrain-rate models. The sliding resistance analyzed for the different boundaries is lowest in the α/β boundary, and increases on the order of α/β≪α/α≈β/β, which plays an important role in controlling the superplasticity of the alloys with various α/β phase ratios.

Quantitative analysis on boundary sliding and its accommodation mode during superplastic deformation of two-phase Ti-6Al-4V alloy

The analysis of the mixed lubrication phenomena in journal and axial bearings represents nowadays the next step towards a better understanding of these devices, subjected to more and more severe operating conditions. While the theoretical bases required for an in-depth analysis of the mixed-lubrication regime have long been established, only small-scale numerical modeling was possible due to computing power limitations. This led to the appearance of averaging models, thus making it possible to generalize the trends observed in very small contacts, and to include them in large-scale numerical analyses. Unfortunately, a lack of experimental or numerical validations of these averaging models is observed, so that their reliability remains to be demonstrated. This paper proposes a deterministic numerical solution for the hydrodynamic component of the mixed-lubrication problem. The model is applicable to small partial journal bearings, having a few centimeters in width and diameter. Reynolds' equation is solved on a very thin mesh, and pad deformation due to hydrodynamic pressure is taken into account. Deformation due to contact pressure is neglected, which limits the applicability of the model in those cases where extended contact is present. The results obtained with this deterministic model are compared to the stochastic solution proposed by Patir and Cheng, in both hydrodynamic and elastohydrodynamic regimes. The rough surfaces used in this study are numerically generated (Gaussian) and are either isotropic or oriented, having different correlation lengths. It is shown that the stochastic model of Patir and Cheng correctly anticipates the influence of roughness over the pressure field, for different types of roughness. However, when compared to the smooth surface solution, the correction introduced by this model only partially compensates for the differences observed with a deterministic analysis.

Mixed Elastohydrodynamic Lubrication in a Partial Journal Bearing—Comparison Between Deterministic and Stochastic Models

Stability of a rigid rotor in turbulent hydrodynamic worn journal bearings

Dynamic tilt characteristics of aerostatic rectangular double-pad thrust bearings with compound restrictors

Thermohydrodynamic analysis of journal bearings lubricated with couple stress fluids

A theoretical study of submerged oil journal bearing is made considering surface roughness and thermal effects. The total load-supporting ability under such condition is due to the thermohydrodynamic as well as the asperity contact pressure. The effect of surface roughness and viscosity-temperature dependency on hydrodynamic pressure has been found by solving the average Reynolds equation, energy equation and heat conduction equations simultaneously. The cavitation model of Jacobsson-Floberg has been modified to take the surface roughness effects into consideration. A parametric study of steady-state behavior has been carried out. Finally, the isothermal, thermohydrodynamic, and contact loads for a model bearing have been calculated, assuming the surface height distribution as Gaussian.

Thermohydrodynamic Analysis of Submerged Oil Journal Bearings Considering Surface Roughness Effects

Presentation d'une solution theorique permettant de prevoir les caracteristiques de fonctionnement en regime permanent de paliers poreux aerostatiques d'epaisseur finie en considerant l'ecoulement tridimensionnel dans le milieu poreux. Analyse tenant compte du glissement de vitesse a l'interface palier/film en utilisant le critere de Beavers-Joseph. Presentation des resultats sous forme non dimensionnelle pour la capacite de charge et le debit massique, pour differentes conditions de fonctionnement et differentes dimensions de palier

Effect of Slip Flow on the Steady-State Performance of Aerostatic Porous Journal Bearings

Paliers a gaz poreux hybrides; solutions en regime stationnaire tenant compte de la vitesse de glissement

N. S. Rao

Papers

Thermohydrodynamic Analysis of Submerged Oil Journal Bearings Considering Surface Roughness Effects

Effect of Slip Flow on the Steady-State Performance of Aerostatic Porous Journal Bearings

Hybrid porous gas journal bearings: steady state solution incorporating the effect of velocity slip

Stability characteristics of rough submerged oil elliptical bearings under dynamic load

Steady state performance of finite hydrodynamic porous journal bearings in turbulent regimes