tailieunhanh - Bearing Design in Machinery Episode 3 Part 9

Tham khảo tài liệu 'bearing design in machinery episode 3 part 9', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | steady conditions the journal center O1 does not move relative to the bearing sleeve and the friction force remains constant. In practice these steady conditions will come about after a transient interval for damping of any initial motion of the journal center. When there is a motion of the journal center O1 however the oil film thickness and the friction force are not constant which explains the dynamic effects of unsteady friction. Before proceeding with the development of the dynamic model the model for steady friction in the mixed lubrication region is presented. Dubois and Ocvirk 1953 derived the equations for full hydrodynamic lubrication of a short bearing. The following is an extension of this analysis to the mixed lubrication region. In the mixed region there is direct contact between the surface asperities combined with hydrodynamic load capacity. The theory is for a short journal bearing because it is widely used in machinery and because the steady performance of a short bearing in the full hydrodynamic region is already well understood and can be described by closed-form equations. The mixed lubrication region is where the hydrodynamic minimum film thickness hn is below a certain small transition magnitude htr. Under load the asperities are subject to elastic as well as plastic deformation due to the high-pressure contact at the tip of the asperities. Although the load is distributed unevenly between the asperities the average elastic part of the deformation is described by the elastic recoverable displacement s of the surfaces toward each other in the direction normal to the contact area. The reaction force between the asperities of the two surfaces is an increasing function of the elastic recoverable part of the deformation s. The normal reaction force of the asperities as a function of s is similar to that of a spring however this springlike behavior is not linear. In a journal bearing in the mixed lubrication region the average normal elastic .