Tribological Performances Of Porous Bearings Under Micro-load

In appliances of IT and MEMS equipments, the tribological characteristics especially friction stability under micro-loads become key factors for the performances of porous bearings, but the study of these topics has not been carried out in the past. The friction performance under micro-load is defined as instability due to bearing configurations that include clearance, roughness, lubricants and velocity etc. after the load is small to some extent, and the unsteady state is a typical tribology character of bearings under micro-load. The goals of this dissertation are to investigate tribological performance factors, bionic porous design, measurement of friction coefficients and chaos state of friction of porous bearings under micro-load. The detail contents and results are as follows1) The lubrication mechanism of porous bearing was discussed. And, Darcy model, Slip-flow model, Brinkman model and other models for lubrication were comparatively analyzed. The tribological factors and the experimental methods of porous bearings were reviewed. The lubricant property and surface topography of bearings under micro-load play largely influences on the tribological performances than those under general conditions. And, tribological performances under micro-load show comprehensive characteristics, and suggest the investigation necessity of the interactions between lubricants and friction surfaces, the lubrication capability etc., of which the requirement of lowest friction coefficient is replaced by friction stability.2) The porous capillarity, magnetism distribution and/or its thermal effects are fundamental problems. The capillarity effects of porous bearings were analyzed and summarized, because the capillarity carries a part of hydrodynamic pressure in lubrication film. The electromagnetic effects on bearing functions should not be neglected under some cases. Thus, the distribution characters of magnetic field in journal bearings are obtained by FEM. And, the results show that an edge effect emerges at axial ends of bearings, and an aggregation effect appears at radial eccentricity. Hence, the above influences on bearings are not structural uniform. The eddy thermal effect in the rotating shaft can be neglected at low speeds but brings a temperature rise beyond 20℃ at high speeds, and the rise range of temperature ascends with the increase of speed.3) Micro-pores structures of some natural materials were studied with SEM. The results show that the micro structures can be classified into three types, namely uniform pores, gradient pores and multi-pores in terms of the distribution variation of porous density, size and geometry. An optimal design of porous bearings was proposed based on the gradient configuration. For the structure design requiring coordination of strength, mass and vibration, bionic design has superiority to conventional methods.4) Based on the Brinkman model, Elrod algorithm was used to compute the lubrication performances. The results show that permeability significantly influences friction coefficient for large permeability, and computed load is very trivial; the above influence difference can be neglected as permeability is smaller than a certain value. Under general permeability and mi-...