The mechanism of the cavitation in a lubricant of a textured sliding bearing is studied based on multiphase flow theories and tribological equations. First, a physical model for a bearing with a series of semi-spherical dimples is modeled through commercial software ANSYS. Then, influences of dimple position and sizes on the vapor volume fraction, and cavitated area of the bearing are studied with computational fluid dynamic method. Numerical results show that the obvious fluctuation of the vapor volume rate and changes in the starting and end angles of the cavitation region due to varied dimple position can occur, when the dimples are located in the cavitated region. Moreover, with increasing cavitation starting angle, the changing trend of the cavitated area is the same as that of the load-carrying capacity, but opposite to the variation trends of the friction force and further friction coefficient.
Combined influences of inter-asperity cavitation and elastic deformation of rough surfaces on flow factors were investigated based on an extended Reynolds equation for flow factor analyses. The numerical results reveal that when effect of cross-flow of lubricant is not obvious, the pressure flow factor increases, whereas the shear flow factor decreases, for a small ratio of film thickness to roughness, due to influences of inter-asperity cavitation and the elastic deformation of rough surfaces. When the ratio of film thickness to roughness becomes big, however, the influences become weak and can even be negligible. Moreover, the above influences are sensitive to the orientations of rough surfaces. Therefore, combined effects of inter-asperity cavitation and elastic deformation of rough surfaces should be considered in flow factor analyses.
Influences of hard particles lying in the lubrication region between piston ring face and cylinder wall, including the effects of a non-contact particle and contact particle, on tribological performances of the piston ring were numerically analysed. A modified Reynolds equation incorporating a non-contact particle effect was presented. The total friction force, deformation, and contact stress of the ring, with a non-contact particle and contact particle consideration, were solved separately by using finite-element program code of the authors and software ANSYS 5.7. The numerical results show that obvious changes in the total friction force and deformation of the ring can occur, if the diameter and height across the film thickness of a non-contact particle and axial velocity difference between the non-contact particle and ring are considered. The maximum contact stress of the ring is obviously affected by the contact particle's interfering time and velocity, and hardness value of the plastically deformed particle.
The influence of cylinder liner vibration on the lateral motion and tribological behaviors for the piston in an internal combustion engine is investigated using an extended secondary motion equation for the piston. By solving this equation and other associated equations with the Broyden algorithm and finite difference method, the vibration effect on the piston behavior is revealed. Numerical results show that the cylinder liner vibration can result in fluctuations in the dynamic and tribological performances of the piston, especially at the expansion stroke of an internal combustion engine. The fluctuations decay with increasing mass, stiffness and damping of the cylinder. There exists a critical rotational speed of internal combustion engine changing the above fluctuations. In addition, the averaged friction power assumption for the piston skirt increases due to the vibration.
A three-dimensional elastic contact problem has been investigated in this article with the emphasis on analysis of the partial slip phenomenon which occurs at certain areas in nominal contact zone when the local shear tractions exceed the limit specified by the friction. The investigation has been made for the contacts between similar or dissimilar materials and under general conditions in which the applied loads consist of a normal load, a tangential force, and a torque normal to the contact plane. The partial slip contact problem is solved through a numerical procedure based on a semi-analytical method. The conjugate gradient method and the fast Fourier transform technique are employed to speed up the computation. The contact pressures, surface shear tractions, stick ratios, tangential body displacements, and rotational angles are analysed under different loads and for similar or dissimilar contact materials. The coupling effects among the normal load, the tangential force, and the twisting moment are studied. Results show that for the contact of dissimilar materials and under a pure torque, the surface shear tractions q x and q y will produce normal deformations until the gross slip occurs. The combined actions of tangential force and twisting moment are prone to cause gross slip in comparison with those under tangential force or twisting moment alone. Moreover, the increasing twisting moment will cause the shrinking of the stick zone, but it evolves in different ways for the contacts of similar or dissimilar materials.
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