Simulation of Gas Transportation in Radial Shaft Seal With Model Surfaces

This paper describes an analytical study on gas transportation in radial shaft seal. A model is constructed in which seal surfaces with sinusoidal roughness, lubricant flow at the seal lip with gaseous cavity, dissolution of gas into and release of gas from the lubricant across double boundary films at gas-liquid interfaces, and convection of dissolved gas in the lubricant flow are considered. Polyalphaolefin as a lubricant, and helium, argon and carbon dioxide are assumed. The results demonstrate that the axial flow induced by surface roughness carries the gas, and that the gas flow through the lubricant film is proportional to the gas solubility coefficient, and the circumferential speed of the shaft, which agrees with the experimental finding for actual seals. The dependence of the gas flow on the axial flow of the oil and that on the boundary films are discussed.

Surface Integrity of Biodegradable Magnesium-Calcium (Mg-Ca) Alloy by Low Plasticity Burnishing

When a device is implanted into the body, into either hard or soft tissue, the body will respond. While the bulk material of the device is often important for integrity and mechanical success, the device surface is at the interface with biology. Major effort has been spent modifying a biomaterial surface in order to elicit or inhibit a biological response. Metallic biodegradable Magnesium-Calcium (Mg-Ca) alloys have attracted an increased attention for orthopedic fixation applications. This research focuses on low plasticity burnishing (LPB) as a novel surface modification technique that is added to the surface to control biodegradation as a biological response. The effects of burnishing pressure as an important process parameter on surface integrity characteristics such as surface roughness, surface topography, and residual stresses are investigated. Burnished surface roughness is smaller than the machined ones. However, some amount of waviness is observed which might be due to large diameter of the burnishing ball and sever plastic deformation. High compressive residual stresses are measured on the burnished surface.

A Brief Overview on High Temperature Friction and Wear

With the race for higher power and efficiency new gas turbines operate at ever increasing pressures and temperatures. Increased compression ratios and firing temperatures require many engine parts to survive extended service hours under large pressure loads and thermal distortions while sustaining relative vibratory motion. On the other hand, wear at elevated temperatures limits part life. Combined with rapid oxidation for most materials wear resistance reduces rapidly with increasing temperature. In order to achieve improved wear performance at elevated temperatures better understanding of combined wear and oxidation behavior of high temperature super alloys and coatings needed. In an attempt to aid designers for high temperature applications, this work provides a quick reference for the high temperature friction and wear research available in open literature. High temperature friction and wear data have been collected, grouped and summarized in tables.

Experimental Investigation of the Development of Cavitation in a Squeeze Film Damper

When cavitation takes place in the squeeze film damper (SFD), its types and extent affect the performance of the SFD significantly. Thus, a fundamental understanding of the incipience, formation and evolution of this phenomenon becomes important both for predicting the dynamic properties of the damper and for the practitioner designers. A test rig was set up to investigate the formation of the cavitation bubbles during the process of a steady-state operation. By adopting a crankshaft configuration, the SFD journal orbit can be fixed at a specified eccentricity. The journal position and its eccentricity are tracked by means of Bently proximity sensors. When cavitation takes place, its shape and evolution are recorded by a Photron APX-RS high speed camera. With the Dow Corning 200 lubricant, the gaseous bubbles form in a fern-leaf shape even at low whirling speed. The bubbles evolve to a miniature flattened shape and as the angular speed increases, the gaseous cavitation gives way or is joined by vaporous cavitation. With a further increase of whirling speed, the vaporous bubbles can be clearly seen to occupy a large area. The evolution of the cavitation can be explained by the Sommerfeld pressure curve as it relates to the gaseous and vaporous saturation pressure. The experimental results confirm the assumption made by these authors in the previous numerical simulations for the homogeneous cavitation models.

Friction and Wear Behavior of Polyetherimide(PEI) Filled With Polytetrafluoroethylene(PTFE)

The tribological performance of Polyetherimide (PEI) composites filled with different Polytetrafluoroethylene (PTFE) content was comparatively evaluated on MM-200 test rig in block-on-ring configuration under dry friction condition. The microstructures of worn surfaces, fractured surfaces and wear mechanisms of the PEI composite were examined under scanning electron microscope (SEM). The variations of elastic modulus and surface hardness with variation in composition were also investigated. The results showed that under conditions of dry friction the PTFE can lower the friction coefficient and reduce wear of the PEI composites. When filled with 10 wt. % PTFE, the composite had the lowest wear rate. For PEI filled with 5wt. % PTFE the friction coefficient was about 0.3 and remained comparatively stable with increase of the PTFE content.

Study of the Influence of Input Parameters on the Connecting Rod Big End Bearing Behavior

The present paper deals with the influence of functioning parameters on the connecting rod big end bearing behavior. The Design of Experiment (DOE) method is used to get the most of information from a given number of computations.

Molecular Dynamics and Multiscale Simulations of Nanoindentation and Nanoscratch

Three-dimensional molecular dynamics (MD) simulations have been performed to investigate behaviors of nanoindentation and nano-scratch. The first case concerns the effects of material defect on the nanoindentation of nickel thin film. The defect is modeled by a spherical void embedded in the substrate and located under the surface of indentation. The simulation results reveal that compared to the case without defect, the presence of the void softens the material and allows for larger indentation depth at a given load. MD simulations are then performed for nano-scratch of single crystal copper, with emphasis on the effect of indenter shape (sharp and blunt) on the substrate deformation. The results show that the blunt indenter causes larger deformation region and much more dislocations at both the indentation and scratch stages. It is also found that during the scratching stage the blunt indenter results in larger chip volume in front of the indenter and gives rise to more friction than the sharp indenter. The scope of the simulations has been extended by introducing a multiscale model which couples MD simulations with Finite Element Method (FEM), and multiscale simulations are performed for two-dimensional nanoindentation of copper. The model has been validated by well-consistent load-depth curves obtained from both multiscale and full MD simulations, and by good continuity of deformation observed in the handshake region. The simulations also reveal that indenter radius and indentation velocity significantly affect the nanoindentation behavior. By use of multiscale method, the system size to be explored can be greatly expanded without increasing much computational cost.

Effects of Grease Types on Vibration and Acoustic Emission of Defective Linear-Guideway Type Recirculating Ball Bearings

In this paper, vibrations and acoustic emissions (AEs) of defective linear-guideway type recirculating ball bearings under grease lubrication were measured. The experimental results show that the vibration and AE amplitudes (the pulse amplitudes, the RMS values) of both the normal and defective bearings have a tendency to be reduced when a grease with higher base oil viscosity is used. Under the same type of grease, the RMS values of the vibrations and AE of the defective bearings increase as the defect angle increases. However, the increases of the RMS values due to increased defect angle are reduced when a grease with higher base oil viscosity is used.

Clearance Effects on the Impact Behavior of Large Aspect Ratio Silicon Journal Microbearings

This paper investigates the effect of bearing clearance on the impact behavior of microfabricated silicon journal bearings. The design of a novel test apparatus to assess microbearing wear behavior is presented. Microbearing designs, microfabrication processes, and metrology characterization techniques are discussed. A dynamic impact model of the bearing system based on classical impulse-momentum relations is formulated in order to assess the effect of clearance on rotor speed. Coefficient of restitution values obtained over the range of kinematically allowable radial clearance specifications are found to agree well with previously published results for polysilicon microstructures.

Thermal-Mechanical Contact of a Sphere on a Layered Surface

The effect of coating thickness is investigated during transient thermal-mechanical contact between a sphere and a layered surface. The range of coating thicknesses studied was from 0.001≤t/R≤0.1, where t is the coating thickness and R is the radius of the contacting sphere. It was found that for the range of coating thickness and material properties investigated, the coating thickness has only a small effect on the mechanical deformation of the interface. On the other hand, the layer thickness has a large effect on the temperature rise of the interface.