A Contact-Wear Model for the EHL Analysis of Engine Journal Bearings

Engine journal bearings are now routinely analysed using elasto-hydrodynamic lubrication (EHL) methods [1,2]. This analysis technique takes into account interaction of the hydrodynamic film with the elastic distortion produced in both the bearing and the journal. It has proved a robust analytic tool for designers in predicting the value and location of such parameters as minimum oil film thickness and maximum film pressure. However, for some very heavily loaded cases, the normal EHL analysis technique may fail to produce realistic solutions. Due to ‘cusping’ of the bearing surface under extreme pressures the edges of bearing may be predicted to penetrate the journal surface leading to a ‘negative’ film thickness. In reality, the surfaces will interact and a ‘running-in’ process will result in subtle changes to the bearing surface profile such that a hydrodynamic film can be maintained across the whole bearing surface. This study introduces a contact-wear model which attempts to model this situation.

Observations of Tool Life and Wear Mechanisms in High Speed Machining of Ti-6Al-4V With PCD Tools Using High Pressure Coolant Supply

Usage of titanium alloys has increased since the past 50 years despite difficulties encountered during machining. In this study PCD tools were evaluated when machining Ti-6Al-4V alloy at high speed conditions under high pressure coolant supplies. Increase in coolant pressure tend to improve tool life and minimise adhesion of the work material on the cutting tool during machining. Adhesion can be accelerated by the susceptibility of titanium alloy to galling during machining.

Performance Evaluation of Magnetohydrodynamic Bearing

The present paper introduces a concept of hydrodynamic-permanent-magnetic hybrid bearing. The hybrid bearing uses repulsive force between permanent magnets and fluid force developed due to relative speed in a single assembly arrangement. Repulsive type passive magnetic levitation has advantage of minimum starting torque. Hydrodynamic lubrication mechanism has advantage of low friction at medium and high speed. This hybridization will be an attractive choice in commercial applications for its low cost, structural-simplicity and no metal-to-metal contact. An experimental setup is designed and developed to investigate the performance characteristics of proposed concept of hybrid bearing. Minimum film thickness, oil flow rate, and temperature rise are recorded at various speed- and load- conditions. Results are plotted to demonstrate the behavior of hybrid bearing arrangement.

Fretting Behavior of Coated and Treated Titanium Alloy Using an Open-Loop System

Titanium alloys are well known to present poor sliding behaviour and high wear values. Various coatings and treatments have been tested to prevent such an occurrence under fretting conditions at high frequency of displacement (100 Hz). An original test apparatus, using an open-loop system instead of a classical imposed displacement simulator, has been performed to directly display the phenomenon of seizure, defined as the stopping of the relative motion between the contacting elements. A classification of the tested coatings has been proposed on the basis of their capacity to maintain full or partial sliding conditions, to present low wear rates and to prevent seizure.

Vapor Deposition of Composite Organic-Inorganic Films

Results on the thermal and immersion stability of ultra-thin composite films created by a deposition method call MVD™ (Molecular Vapor Deposition [1]) are reported. It is observed that these composite films were denser and more stable in thermal and immersion applications when compared to traditional self-assembled monolayer (SAM) films. These improved films were created by a special “sequential” or “layered” deposition process sequence. The MVD™ composite coatings can be deposited at room temperature on a variety of materials such as polymers, fibers, metals, alloys and other materials which normally do not allow films to form with complete surface coverage.

Micro/Nano-Tribological Behavior of Octadecyltrichlorosilane on Silicon as a Coating for MEMS

Despite progresses achieved in the technology of MEMS, the tribological problem continues being an unresolved matter. Wear and stick-slip phenomena are many times the origin of failure of these devices. The application of self-assembled monolayers (SAMs) in liquid phase seems to be a solution to this problems. SAMs of octadecyltrichlorosilane (CH3(CH2)17SiCl3, OTS) were attached to Si(100) oxidized in liquid phase. Contact angle measurements were used for characterizing the grade of hydrophobicity. The topography of the coating was obtained with an Atomic Force Microscopy (AFM) in semicontact mode. The images showed the presence of particles related to the polymerization of the precursor molecule during the formation process of the SAMs. Creating the film of lubricant in vapour phase would avoid this undesirable effect. Tribological tests were carried out with a microtribometer in linear reciprocating movement with a ball of 2 mm of diameter (100Cr6 and Si3N4) and load of some milinewtons. Results were compared with those obtained for silicon oxidized without any coating. The coefficient of friction (COF) and wear (substrate and ball) were studied under different test conditions.

Packing Structure of OTS on Silicon Surfaces: A Computational Approach

Optimal packing structure of Octadecyltrichlorosilane (OTS) self-assembled monolayer (SAM) adsorbed on a SiO2 surface with a Si (100) substrate was studied performing molecular dynamics (MD) computational simulations. Molecular substitution, substitution pattern and molecular orientation of the OTS molecules on the SiO2 (100) are the main factors studied in order to determine the optimal packing structure taking into account energetic balance. We have used the optimal packing structure to study other properties usually used to characterize SAMs as molecular and system tilt angles, film thickness and gauche defects. These properties and monolayer stability were studied performing MD simulations in a temperature range from 100 K to 600 K and we found that results obtained agree with those from experimental measurements. We found that OTS films are stable up to 500 K. The optimal structure obtained could be used in further MD simulations studies in order to determine tribological properties of OTS-SiO2 systems.

PVD-Based Microstructuring Surface Techniques for Tribological Applications

Combined techniques of Physical Vapour Deposition (PVD), laser ablation and UV-Photolithography have been set up to produce well defined surface textures able to increase the seizure resistance of high loaded lubricated systems. Using these new techniques, different predefined surface textures, following rectangular grid and zigzag stripped patterns have been generated. The microstructured surfaces developed have been characterised with confocal microscopy, optical and scanning electron microscopy. Ball-on-disc tribological tests under progressively increased load have been carried out using mineral oil as lubricant to determine the influence of surface microtextures on seizure resistance. The influence of shape and size of texture patterns on the tribological performance of the surface have been also studied.

Passive Magnetic Bearings: Low Instability and Possible Stability

Permanent magnet bearings and systems offer negligible friction and no wear, but static instability too. Nevertheless, spaces of low static instability exhist, and stability may be possible in non static conditions.

Thermo-Elasto-Hydro-Dynamic Modeling of Hydrostatic Seals in Reactor Coolant Pumps

The French energy company EDF has experienced in the last years some problems in managing reactor coolant pumps (RCP) seals in operation. That’s why a thermo-elasto-hydrodynamical model of the seal has been developed. The present model is a steady two-dimensional approach so as to characterize the normal operating mode of the seal. Numerical results are successfully compared to experimental results of leak-flow rate. The influence of pressure drop and injection temperature is described. The influence of the conicity of the faceplates is underlined. The friction is introduced in the model in order to reproduce the hysteretic behavior of the seal. The development of this model leads to a better knowledge of the behavior of a critical component.