In this study, we observe that there are two threshold speeds (stability threshold speed and second threshold speed) for the long journal bearing, which is different for the short bearing. When the rotating speed is below the stability threshold speed, the stability boundary nearly coincides with the clearance circle, and the journal center gradually returns to the equilibrium point after being released at an initial point. If the rotating speed is between the stability threshold speed and the second threshold speed, after being released at an initial point, the journal center converges to a contour containing the equilibrium point. In this situation, for a higher rotating speed, the corresponding contour is also larger. When the rotating speed exceeds the second threshold speed, the journal gradually moves towards the bearing surface after being released at an initial point.

The orbital riveting process has been successively adopted in the assembly of wheel hub bearing, due to its special merits of high efficiency, low cost, and so on. The forming process and deformation behavior of the inner ring have significant influence on the axial clamping force and bearing clearance, however, which haven’t been addressed yet. In this study, a numerical simulation platform for the assembly of the hub bearing is established by the joint use of the static implicit and dynamic explicit algorithms. Based on the platform, the deformation process and deformation behavior of the inner ring are investigated, along with the interference assembly and riveting assembly on the loading process of the inner ring. Finally, relevant experimental verifications are carried out to consolidate the simulation results. The research findings could be used to guide the design and optimization of the axial clamping force and bearing clearance.

A new derivation considering the non-linear terms has been proposed to calculate stiffness and damping coefficients for short hydrodynamic journal bearings lubricated with pseudo-plastic fluids. The proposed method has relaxed the constraint of small perturbation method applicable to only small values of non-Newtonian factor α. An analytical solution is also given. The non-linear Reynolds equation is solved with a more reasonable boundary condition ∂p*/∂z* = 0 at the location of z*=0 while the analytical pressure distribution is obtained by seven-point Gauss-Legendre integral formula. When the non-dimensional non-Newtonian factor α is small, the stiffness and damping coefficients of computed by the proposed method can agree well with those from small perturbation method, which could verify the proposed derivation. As for large non-dimensional non-Newtonian factor α, the stiffness coefficients $K_{XX}^*$ , $K_{XY}^*$ and $K_{YX}^*$ as well as the damping coefficients $C_{XX}^*$ , $C_{XY}^*$ and $C_{YX}^*$ decrease with the increasing of non-dimensional non-Newtonian factor α. The significance of the derivation is that it can relax the constraint of small α and simplify the computation process.

During the actual machining process of journal surface, such as milling and fine turning, the surface roughness has strong non-Gaussianity. Thus, the effect of non-Gaussian longitudinal roughness on threshold speed of short journal bearings is investigated in this study. Introducing the parameters of kurtosis and skewness, the model of non-Gaussian surface roughness is established by modifying the Gaussian distribution. It is found that the non-Gaussianity of surface roughness cannot be neglected especially for the journal rotating with a larger eccentricity ratio, the error of Gaussian distribution surface reaches 19.33% when the eccentricity ratio equal 0.7. The increasing of kurtosis would reduce the threshold speed, while the increasing of skewness would enhance the threshold speed. For a larger eccentricity ratio, the effect of kurtosis and skewness on threshold speed is more distinctly.

A high-performance and finite-length bearing system requires that the shaft can be stabilized even under a strong perturbation. The linear stability theory neglects the effects of nonlinear forces and the initial point of the shaft. Therefore, the stability of the bearing system is largely determined by the rotating speed of the shaft. In the present numerical investigation, the nonlinear forces and initial point of the shaft are accounted for to obtain the nonlinear stability boundary. The objective of this study is extended to orifice-compensated and hole-entry hybrid journal bearings with finite length. The critical rotating speed and the shaft center trajectory are acquired by solving Reynolds equation using the finite element method. By identifying the states of the orbits (stable or unstable), the nonlinear stability boundaries can be obtained. Results show that for the hybrid bearing system under the nonlinear conditions, the critical speed is a determinant factor while the initial location is another key factor. The shaft can be unstable if the initial point is outside of the stability boundary, although the speed is lower than the critical speed. There exists an obvious transitional region between the stable and unstable condition when the speed approaches the critical speed.

The temperature rises of the oil film in hydrostatic bearings at high speed lead to a reduction in load capacity, accuracy, and stability. In this paper, a superhydrophobic/oleophobic surface with a micro-bulge structure is proposed. The surface is prepared by laser cross-scanning and chemical modification. The contact angle (CA) of the surface is 138 deg and the boundary condition of the surface is modified from non-slip to slip condition. The relationship between the slip length and the height of the micro-bulge structure is established by rheological experiments. By the simple partial simulations, the validity of the temperature rise reduction on the superhydrophobic/oleophobic surface is verified. Then a bearing test rig was set up to measure the temperature and load capacity of bearings at multiple points, and the performance of smooth primary surface/structured oleophobic surface thrust bearings was compared. Results show that the structured bearing has a lower oil film temperature and higher load capacity than the smooth bearing. The prepared oleophobic surface can effectively suppress the temperature rise at high-speed conditions and significantly increase the bearing load capacity.