New strategy for reducing the EHL friction in steel contacts using additive-formed oleophobic boundary films

In this study we present a mechanism for the elastohydrodynamic (EHD) friction reduction in steel/steel contacts, which occurs due to the formation of oleophobic surface boundary layers from common boundary-lubrication additives. Several simple organic additives (amine, alcohol, amide, and fatty acid) with different molecular structures were employed as the model additives. It was found that the stronger chemisorption at 100 °C, rather than the physisorption at 25 °C, is more effective in friction reduction, which reaches 22%. What is more, EHD friction reduction was obtained in steel/steel contacts without use of the diamond-like carbon (DLC) coatings with their wetting or thermal effect, which was previously suggested as possible EHD friction reduction mechanism; yet about the same friction reduction of about 20% was obtained here—but with much simpler and less expensive technology, namely with the adsorbed oleophobic surface layers. A small variation in the additive’s molecular structure results in significant changes to the friction, indicating good potential in future EHD lubrication technology, where these additives could be designed and well optimised for notable reduction of the friction losses in the EHD regime.

A Strongly Coupled Finite Difference Method–Finite Element Method Model for Two-Dimensional Elastohydrodynamically Lubricated Contact

This paper presents a partitioned strongly coupled fluid–solid interaction (FSI) model to solve the 2D elastohydrodynamic (EHD) lubrication problem. The FSI model passes information between a control volume finite-difference discretized Reynolds equation and abaqus finite element (fe) software to solve for the fluid pressure and elastic deformation within heavily loaded lubricated contacts. Pressure and film thickness results obtained from the FSI model under a variety of load and speed conditions were corroborated with open published results. The results are in excellent agreement. Details of the model developed for this investigation are presented with a focus on the simultaneous solution of the Reynolds equation, load balance, and the coupling of the solid abaqus fe with the finite-difference fluid (Reynolds) model. The coupled FSI model developed for this investigation provides the critical venue needed to investigate many important tribological phenomena such as plasticity, subsurface stress, and damage. The current FSI model was used to explore and demonstrate the efficacy of the model to investigate the effects of microstructure inhomogeneity, material fatigue damage, and surface features on heavily loaded lubricated contacts as can be found in a wide range of industrial, automotive, and aeronautical drive systems.

Digital twin by DEM for ball bearing operating under EHD conditions

In this paper we investigate the elastohydrodynamic (EHD) lubrication in ball bearings by means of a digital twin. Based on an original description involving the discrete element method (DEM), the digital twin integrates all the components of ball bearings and enables realistic behavior under mechanical loading and kinematic conditions. In order to check the standard indicators recommended by most ball bearing manufactures, a stiffness model for elliptical Hertzian contact and an improved EHD formulation for lubricated contact are implemented in the numerical tool. In addition, we have introduced into the discrete modeling an electrical capacitance model correlated to the fluid film thickness and the contact pressure. The numerical predictions of lubricant film capacitance provided by digital twin are in good accordance, both qualitatively and quantitatively, with the experimental data available in the literature. The coupling of the discrete method with the electrical approach enables efficient solutions to be provided in terms of lubrication regime in relation to the lubricant properties to optimize the bearing lifetime.

Numerical Modeling and Analysis of Flexure-Pivot Tilting-Pad Bearing

This paper presents a new approach for modeling flexure-pivot journal bearings (FPJB) employing a three-dimensional (3D) elasto-hydro-dynamic (EHD) lubrication model. The finite element (FE) method is adopted for an analysis of the (1) pad-pivot dynamic behavior and the (2) fluid force. The isoviscosity Reynolds equation is utilized to calculate the fluid force acting on a flexure-pivot pad bearing and spinning journal. Computational efficiency is achieved utilizing modal coordinate transformation for the flexible pad-pivot dynamic analysis. Fluid film thickness plays a critical role in the solution of Reynolds equation and is evaluated on a node-by-node basis accounting for the pad and web deflections. The increased fidelity of the novel modeling approach provides rotating machinery designers with a more effective tool to analyze and predict rotor–bearing dynamic behavior.