Abstract
The influence of the heat transfer field on anomalous film formation under elastohydrodynamic lubrication (EHL) conditions was studied. Liquid lubricant film shapes between a transparent disc and steel ball friction pair were investigated by white light optical interferometry. The fatty alcohol 1-dodecanol was used as the representative lubricant to develop anomalous film shapes. A sapphire disc and glass disc, which have different thermal conductivities, were used as the transparent bounding surface. Experiments were performed wherein the applied load, sliding conditions and ambient temperature were varied. The temperature of the lubricant film was estimated by a simple model with the measured traction coefficient. The estimated temperature and maximum Hertzian pressure were compared with the phase diagram of 1-dodecanol obtained using a diamond anvil cell to investigate the phase state of the lubricant film. It was found that the anomalous film shape was stably formed in the solid-state regime of the phase diagram whereas the film exhibited unique characteristics such as the collapse behaviour in high sliding conditions and liquid-like behaviour of the traction with a remaining thickened film part in the liquid state regime.
Highlights
Elastohydrodynamic lubrication (EHL) has been one of the most important topics in the tribological field for over a century
The phase state of 1-dodecanol was confirmed from the maximum Hertzian pressure, ambient temperature, and its phase diagram. Both the film thickness and the shape changed with increasing ambient temperature
The thickened part of the film showed a greater tendency to remain at a higher negative S than at positive S at the ambient temperature of 30°C, whereas the trend was reversed at the ambient temperature of 70°C
Summary
Elastohydrodynamic lubrication (EHL) has been one of the most important topics in the tribological field for over a century. The film formed in the lubricated area has a specific shape with a flat part around the contact area and a constricted shape at the exit zone [2]. Traction is generated in the contact area, where a lubricant film of significantly high viscosity is sheared at a high shear rate of the order of 106 s− 1. A lubricant film under significant shearing force does not exhibit the Newtonian rheological behaviour. Instead, it shows shear thinning, viscoelastic, or elastoplastic behaviour [3,4,5,6,7,8]. The formed film has a specific shape; it is flat around the central area and constricted at the exit zone [2]. A fast numerical simulation algorithm has been developed for solving the EHL problems [11]
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