Hydrodynamic Pressure of Thrust Step Bearings

Step bearings are frequently used in industry for better load capacity. Analytical solutions to the Rayleigh step bearing and a rectangular slider with a finite width are available in literature, but none for a fan-shaped thrust step bearing. This study starts with a known solution to the Laplace equation in a cylindrical coordinate system, which is in the form of infinite summation. An analytical solution to pressure is derived in this paper for hydrodynamic lubrication problems encountered in the fan-shaped step bearing. The presented solutions can be useful for designers to maximize bearing performance as well as for researchers to benchmark numerical lubrication models.

A Coupled Approach for Modelling Rolling Contact Fatigue Cracks Under Elastohydrodynamic Lubrication

In this paper we present a coupled method for modelling fluid-solid interaction within a crack generated in rolling contact fatigue (RCF) in the presence of lubrication. The technique describes the fluid flow in the contact area and within the crack and explores how this affects the elastic deformation of the solid while the moving load traverses the cracked region. It is argued that this approach sheds light on the instantaneous response of the system, therefore providing a more physically-accurate description of the phenomenon under investigation.

Abrasive Wear Behavior of Permanent Moulded Toughened Austempered Ductile Iron

Laboratory abrasive wear tests have been reported on permanent moulded toughened austempered ductile iron. The influence of austempering temperature on the abrasive wear behavior have been studied and discussed. The results indicate that with increase in austempering temperature from 300°C to 350°C, the abrasive wear resistance increased, and as the austempering temperature increased to 400°C, there was reduction in the abrasive wear resistance. These results have been interpreted based on the structural features and graphite morphology.

Fretting Wear of CMSX4 at Blade Tip Interface With and Without Coating

Fretting wear is a complex phenomenon that occurs at component interfaces that are subjected to low amplitude oscillation under high contact pressure. In turbomachinery fretting occurs also at the blade tip interfaces where shrouds, that have the aim to reduce the blade resonant vibration amplitude, are machined. To diminish the fretting damage coatings are applied to the blade tips. The aim of this study is to compare the fretting wear behaviour of single crystal CMSX-4 superalloy interfaces with and without plasma sprayed T-800 coating. Experiments have been conducted with hemispherical surface in contact with a flat surface of the same materials at temperature of 800 °C. The hysteresis cycles have been measured through the experiment. The comparison of the hysteresis cycles shown that the tangential contact stiffness of the coated surfaces is greater then that of the surfaces without coating. At the end of wear process, the mating surfaces have been characterized by three-dimensional optical interferometry and SEM analysis. After 10×106 wear cycles, the uncoated surfaces show a large change in the contact parameters and fretting cracks on the flat surface. On the other hand, the coated surfaces do not shows a measurable change in the contact parameters while the coating damage on the flat surface leads to predict an incipient catastrophic wear.

Energy Harvesting With Piezoelectric Nanobrushes: Analysis and Design Principles

The development of self-powered electronic devices is essential for emerging technologies such as wireless sensor networks, wearable electronics, and microrobotics. Of particular interest is the rapidly growing field of piezoelectric energy harvesting (PEH), in which mechanical strains are converted to electricity. Recently, PEH has been demonstrated by brushing an array of piezoelectric nanowires against a nanostructured surface. The piezoelectric nanobrush generator can be limited to sub-micron dimensions and thus allows for a vast reduction in the size of self-powered devices. Moreover, energy harvesting is controlled through contact between the nanowire tips and nanostructured surface, which broadens the design space to a wealth of innovations in tribology. Here we propose design criteria based on principles of contact mechanics, elastic rod theory, and continuum piezoelasticity.

Frictional Characteristics of IF-WS2 Nanoparticles in Simulated Engine Conditions

The effect of inorganic fullerene-like (IF) WS2 nanoparticles added to mineral oil which has a potential to reduce engine friction was investigated using a reciprocating piston ring - cylinder bore bench test system. The test system simulates actual engine conditions controlling oil temperature, speed, and normal load. Frictional characteristics of various IF-WS2 nanoparticle concentrations in mineral oil were experimentally analyzed. After a certain period of running in mixed lubrication regime, a significant reduction in friction coefficient was observed when the IF-WS2 formulated oil was used. This reduction remains to some extent with the reference mineral oil even after solvent cleaning. The results show that a thin tribofilm gradually forms on the piston ring and the cylinder bore surfaces that reduce the coefficient of friction in mixed lubrication regime. The effects of lubrication regime, load, speed, temperature and surface roughness on tribofilm formation were also discussed.

Quantification of Friction Force for Dual-Axis Probe Friction Force Microscope

Conventional friction force microscopes (FFMs) had the disadvantage of low force sensitivity due to mechanical interference between torsion caused by friction force and deflection by normal force. In order to overcome disadvantage, we developed a dual-axis micro-mechanical probe, which measures the lateral force by the double cantilever and the vertical force by the torsion beam. However, the calibration method of the lateral force has not been established. In this study, we present a new calibration method using a step-structure.

A Study of Real Area of Contact for Tire/Road Interface

This paper investigates some of the modeling techniques available for predicting the real area of contact between two surfaces. These models are then applied to an idealized case of a rubber block in contact with a rough surface representing a tire on the road. A description of how the models work is presented. The various contact models are compared and analyzed. Qualitatively the models compare very well. Several models also compare well quantitatively.

An Energy Approach for Helping the Selection of Solid Lubrication Coatings Under Fretting Conditions

Employing friction reduction coatings is one of the most effective methods to palliate the fretting damage. However, facing numerous available coatings, how to compare them and select the optimum one for a specific application is still a challenging task. In this paper, based on the investigation of the fretting behaviors of several bonded solid lubricant coatings, an energy approach in terms of “initial maximal dissipated energy density” was suggested to compare the tribological response of coatings. According to test results, the lifetime of each coating under different test parameters can be fitted by one master curve. The definition of this master curve for a given coating may be used for the prediction of the coating lifetime only by knowing the initial energy dissipated in the contact. The comparison of different master curves for different coatings can be employed to help the coating selection.

Nanostructured Diamond Coatings for Dry Drilling

In this study, nanostructured diamond (NSD) films were grown, by microwave plasma assisted chemical vapor deposition (MP-CVD) technology, on WC-Co drills for performance enhancement in dry drilling of A390 alloys. Surface cobalt was removed by a well-controlled precision etching process. H2/CH4 gas mixture with a small amount of N2 was applied to produce NSD films. Moreover, slight hone was applied to the cutting edges prior to the NSD deposition to relieve residual stresses generated by thermal mismatch in depositions. The results show feasibility of dry drilling of A390 alloys by NSD coated drills, substantially outperforming carbide drills.