Understanding the Mechanism of Load-Carrying Capacity between Parallel Rough Surfaces through a Deterministic Mixed Lubrication Model

Experimental results have confirmed that parallel rough surfaces can be separated by a full fluid film. However, such a lift-off effect is not expected by the traditional Reynolds theory. This paper proposes a deterministic mixed lubrication model to understand the mechanism of the lift-off effect. The proposed model considered the interaction between asperities and the micro-elastohydrodynamic lubrication (micro-EHL) at asperities within parallel rough surfaces for the first time. The proposed model is verified by predicting the measured Stribeck curve taken from literature and experiments conducted in this work. The simulation results highlight that the micro-EHL effect at the asperity scale is critical in building load-carrying capacity between parallel rough surfaces. Finally, the drawbacks of the proposed model are addressed and the directions of future research are pointed out.

Numerical and experimental investigations on the wear behavior of water-lubricated bearings with different materials

Purpose The purpose of this paper is to verify the effectiveness of the proposed transient mixed lubrication and wear coupling model [mixed lubrication and wear (MLW) coupling model] under water lubricated conditions by comparing with the experimental results. Design/methodology/approach Water lubricated bearings are the key parts of the transmission system of an underwater vehicle and some surface ships. In this study, the friction and wear behaviors of rubber, nylon and polyether ether ketone (PEEK) samples with stainless steel underwater lubrication were compared by using ring-block contact structure on multifunctional friction and wear test bench-5000 friction and wear tester. Findings The results show that the transient wear depth and wear amount of PEEK, nylon and rubber samples under water lubrication are in good agreement with the calculated results of the theoretical model, which verifies the rationality and scientific nature of the MLW coupling model. Thus, the numerical model is applicable for the wear prediction of the journal bearing under water-lubricated conditions. Furthermore, numerical and experimental results reveal that the anti-wear performance among three water-lubricated materials can be ranked by: PEEK > nylon > rubber. Originality/value It is expected that this study can provide more information for experimental and numerical research of water-lubricated bearings under water-lubricated conditions.

A study on diesel engine crankshaft bearing failure analysis with consideration of bearing lubrication

Purpose The edge of diesel engine crankshaft main bearing is more likely to fail in its real working condition. This paper aims to study the bearing failure mechanism by finding the relationship between bearing lubrication characteristics and its working condition. Design/methodology/approach This work builds the mixed lubrication model of crankshaft bearing to analyze the cause of bearing abnormal wear, and the finite difference method was used to solving the average Reynolds equation. During the analysis, journal misaligned angle, external load and roughness are considered. Findings The result shows that the wear of the diesel engine crankshaft bearing happens in engine startup phase and the bottom of the bearing are more prone to be excessively worn. Under the influence of journal misalignment, bearing asperity contact load and speed range of mixed lubrication will increase markedly. The edge of the bearing will be excessively worn. The effect of misalignment on bearing lubrication performance varies under different shaft rotation speed. Originality/value The former research studies on crankshaft bearing either just focused on its lubrication characteristics or interested in its failure types (wear, adhere, cavitation). This paper studies the relationship between bearing failure mechanism and lubrication performance.

Numerical and experimental study on the effect of surface texture with roughness orientation considered under a mixed lubrication state

Purpose The purpose of this paper is to investigate the effects of surface texture with roughness orientation considered on tribological properties under a mixed lubrication state numerically and experimentally. Design/methodology/approach Based on the average Reynolds equation and asperity contact model, the impacts of surface texture parameters and roughness orientation on lubrication properties have been calculated using finite difference method. Tin–bronze samples with various prescribed surface texture geometric parameters and roughness orientation were fabricated by laser surface texturing technique, and the tribology performance of the textured surface was studied experimentally. Findings The effects of surface geometric parameters and roughness orientation parameters have been discerned. The experimental observations are in good agreement with the numerical prediction, which suggests that the numerical scheme adopted in this work is suitable in capturing the surface texture and roughness effect under mixed lubrication state. Originality/value By meticulously controlling the surface roughness and surface texture geometric characteristics based on the laser surface texturing process, samples with prescribed surface texture parameters and roughness orientation consistent with that in theoretical studies were fabricated and the theoretical model and results were verified experimentally.

Tribological characteristics and load-sharing of point-contact interface in three-body mixed lubrication

The third particle occurred at the interface of contacting surfaces is common situations in relative motion part. This study involved developing an analysis framework to investigate the contact characteristics in the full range of 3-body mixed lubrication. Conventional 2-body mixed lubrication is a special case of 3-body mixed lubrication analysis with particle size of zero. This study revealed that the values of real contact area, film thickness, contact mode, and the solid contact load in 3-body contact were larger than those in ideal 2-body contact in mixed lubrication, and they increased with an increasing particle size or density under the study conditions. The initial stages and transition processes of four types of 3-body contact modes under mixed lubrication were significantly different for different particle sizes and densities. The size of the third particle increased the values of both minimum and maximum values, λmin and λmax, of film parameter in the mixed lubrication regime. The particle density did not have a significant effect on the λmax value in mixed lubrication. Higher particle density led to a larger λmin value in mixed lubrication. The conventional film parameter, λ, was not a sufficient indicator of the different lubrication regimes in 3-body contact.

Duncan Dowson and elastohydrodynamic lubrication at Leeds University

This paper retraces the fascinating developments made by Professor Dowson at Leeds University in the field of elastohydrodynamic lubrication, starting from the early years of elastohydrodynamic lubrication solutions to his most recent contribution to biotribology and mixed lubrication.