A Coupled Cavitation Model in an Oscillatory Oil Squeeze Film

In this paper,the oscillatory oil squeeze film is taken as a research object,and a coupled cavitation model based on the theory of bubble dynamics and hydrodynamic lubrication is used and a specific method of numerical calculation is given.Then the parallel-plate squeeze film test apparatus is used to validate the coupled cavitation model.The pictures of the cavitation were captured by a high-speed camera and then processed to obtain the variation of the cavitation area in experiments.Compared with the experimental results,the model can successfully predict the process of generation and development of cavitation.At the same time,the pressure variation calculated by the model is in good agreement with the experimental data and the value of negative pressure is close to the experiment.On this basis,three new parameters that are related to bubble dynamics are studied by comparing the pressure and cavitation area variation in an oscillating squeeze oil film.The results show that surface dilatational viscosity,initial radii of cavitation nuclei and number of bubbles per unit area have a significant influence on the generation time of the cavitation,the maximum tensile stress that the oil film can withstand,and the speed of the cavitation collapse respectively.

Elastohydrodynamic lubrication properties and friction behaviors of several ester base stocks

This paper reports a series of studies on the lubricant properties,elastohydrodynamic film thickness,and coefficients of friction of several commercially available ester base stocks,i.e.,diisooctyl phthalate(DIOP),diisodecyl phthalate(DIDP),diisotridecyl phthalate(DITDP),diisooctyl sebacate(DOS),diisotridecyl sebacate(DTDS),trihydroxymethylpropyl trioleate(TMPTO),and pentaerythritol tetraoleate(PETO).The results include densities and viscosities from 303 to 398 K,and elastohydrodynamic lubricant film thicknesses and friction in the boundary,mixed and full-film lubrication regimes measured at several temperatures,loads,and speeds.These ester base stocks have different lubrication abilities owing to their chain lengths,geometric configurations,and molecular rigidity.This study provides quantitative insight into the use of ester-based lubricants for low friction through the entire lubrication regime(boundary to full film)by utilization of suitable type and size of the ester base stocks.

Experimental investigation of EHD grease lubrication in finite line contacts

The objective of this study was to investigate the grease-lubricated film-forming mechanisms in the finite line contact and to improve the grease-lubricated finite line contact’s film-forming capacity.An elastohydrodynamic lubrication(EHL) test rig with two interferometry microscopes,which could simultaneously monitor two different contact locations in the finite line contact,was constructed in order to study the influences of the grease thickener formulation on the film thickness and lubrication condition.By using the relative light intensity method,the thickness maps of the grease-lubricated film were calculated from the interferometer images captured by the two microscopes.The test results revealed that the grease thickener’s formulation had remarkable effects on film formation and the perturbation of film thickness.For the lithium-based grease,the film’s thickness near the two ends of the roller was prone to severe perturbation caused by the conglomeration of clumps that were hard to shear.For the aluminum-complex-based grease,the fibers tended to accumulate in the middle of the roller rather than at the two ends.The urea-based grease could be easily sheared into smaller particles.In addition to the straight-line profile rollers,the logarithmic profile rollers were tested and found to effectively enhance the axial grease flow,increase the axial shear stress,and thus shear more fibers into particles within the contact area.