bluuebunny/crossref_metadata_2025 huggingface dataset:
Highly Accurate Automated 3D Measuring and Data Conditioning for Turbine and Compressor Blades
Authors: Holtzhausen Stefan , Schreiber S. , Scho¨ne Ch. , Stelzer R. , Heinze K. , Lange A.
Published: February 2010

The measurement of compressor or turbine blades is very interesting for quality control and inspection checks. Especially for mechanical wear valuation it is important to inspect the whole geometry of a blade with main focus on the airfoil. This 3D measurement task, which involves many identical components, and high accuracy, as well as high point density in the airfoil edge regions, demands detailed planning of the appropriate 3D-measuring machine, measurement planning, reproducibility as well as analysis and provision of measuring values for the user. Preliminary investigations were carried out to select an appropriate measuring method providing both a complete geometric and as automatic as possible acquisition of blade geometries. Another constraint was that the technique had to make efficient use of time and be accurate. A data processing routine using software developed at TU Dresden is used for automated analysis and provision of measuring values for the user. The approach to linking automated complete 3D data acquisition by means of strip projection with automated analysis of measuring data opens up the option of using it as an efficient 3D-measuring machine for high accuracy requirements and higher quantities. The method shown can be transferred to other objects that need to be scanned in larger quantities.
Thermohydrodynamic Analysis of Bump Type Gas Foil Bearings: A Model Anchored to Test Data
Authors: San Andre´s Luis , Kim Tae Ho
Published: February 2010

The paper introduces a thermohydrodynamic (THD) model for prediction of gas foil bearing (GFB) performance. The model includes thermal energy transport in the gas film region, and with cooling gas streams, inner or outer, as in typical rotor-GFBs systems. The analysis also accounts for material property changes and the bearing components’ expansion due to temperature rises and shaft centrifugal growth due to rotational speed. Gas inlet feed characteristics are thoroughly discussed in bearings whose top foil must detach, i.e., not allowing for subambient pressure. Thermal growths determine the actual bearing clearance needed for accurate prediction of GFB forced performance, static and dynamic. Model predictions are benchmarked against published measurements of (metal) temperatures in a GFB operating without a forced cooling gas flow. The tested foil bearing is proprietary; hence its geometry and material properties are largely unknown. Predictions are obtained for an assumed bearing configuration, with bump-foil geometry and materials taken from prior art and best known practices. The predicted film peak temperature occurs just downstream of the maximum gas pressure. The film temperature is higher at the bearing middle plane than at the foil edges, as the test results also show. The journal speed, rather than the applied static load, influences more the rise in film temperature and with a larger thermal gradient towards the bearing sides. In addition, as in the tests conducted at a constant rotor speed and even for the lowest static load, the gas film temperature increases rapidly due to the absence of a forced cooling air that could carry away the recirculation gas flow and thermal energy drawn by the spinning rotor, Predictions are in good agreement with the test data. A comparison of predicted static load parameters to those obtained from an isothermal condition shows the THD model producing a smaller journal eccentricity (larger minimum film thickness) and larger drag torque. A rise in gas temperature is tantamount to an increase in gas viscosity, hence the noted effect in the foil bearing forced performance.
A New Concept of a Two-Dimensional Supersonic Relative Inlet Mach Number Compressor Cascade
Authors: Sonoda Toyotaka , Olhofer Markus , Arima Toshiyuki , Sendhoff Bernhard
Published: February 2010

In this study, a numerical shape optimization method based on evolutionary algorithms coupled with a verified CFD solver has been applied to the ambitious target of a shock free 2-D supersonic inlet Mach number compressor cascade. The study is based on the DLR-PAV-1.5 supersonic compressor cascade designed by the pre-compression blading concept. The DLR cascade airfoil has been optimized using a verified CFD code. A superior performance of the optimized supersonic cascade with about 24% reduction of the total pressure loss coefficient compared to the original cascade has been realized. The flow mechanisms observable around the blade with improved performance and the resulting design concept are discussed in this paper.
Turbocharger Design for a 1.8 Liter Turbocharged Gasoline Engine Using an Integrated Method
Authors: Chen Tao , Zhuge Weilin , Zheng Xinqian , Zhang Yangjun , He Yongsheng
Published: February 2010

Turbocharging is playing an increasingly vital role in the development of gasoline engines to reduce fuel consumption and CO2 emissions. Turbocharger design is a key technique used for improving the gasoline engine’s performance. In this study, a new turbocharger design method is proposed by integrating a turbocharger through-flow model with a gasoline engine model for better turbocharger matching. The integrated method was applied to design a new turbocharger according to the performance requirements of a 1.8L turbocharged gasoline engine. Compared to the original prototype, the engine with the new turbocharger designed with the integrated method can achieve a better power and torque curve with about a 4% reduction of fuel consumption at the rated engine speed.
Modeling Thermo-Mechanical Relaxation of Shot Peening Induced Residual Stresses During Engine Operation
Authors: Huang Min , Potdar Yogesh K. , Akkaram Srikanth
Published: February 2010

Shot peening is widely used to improve the fatigue life of engine blades and rotors by inducing compressive residual stress. However, the residual stresses can relax due to exposure at high service temperature and mechanical loading. A physics-motivated analytical solution was developed to predict the residual stress relaxation at high temperature and under mechanical loading. In this thermo-mechanical relaxation model, the plastic strains in shot peening layer and substrate are obtained analytically by using linear kinematic hardening materials law, and then the plastic strain evolution at high temperature is modeled by using a recovery strain term. The final stress as a function of time, temperature and mechanical loading is obtained analytically by combining this recovery strain with equilibrium and compatibility conditions. The whole method can be implemented into Microsoft (MS) Excel, and is easy to use and validate. As a special case, an analytical closed-form solution to predict pure thermal relaxation of shot peening residual stress is developed. The model predictions agree satisfactorily with published experimental data.
2D Viscous Aerodynamic Shape Design Optimization for Turbine Blades Based on Adjoint Method
Authors: Li Haitao , Song Liming , Li Yingchen , Feng Zhenping
Published: February 2010

Since the adjoint method can perform the quick and exact sensitivity analysis and save large computational resources, it has been the highlight in aerodynamic shape design optimization field. The purpose of this work was to extend the adjoint method into turbomachinery applications for viscous and compressible flow and to improve the aerodynamic performance. Being considered as the cost function, the minimization of entropy generation rate was applied to the direct design. The adjoint boundary conditions of the corresponding cost function were derived in detail, by using non-slip boundary condition on the blade wall and neglecting the viscous effect on the cascade inlet and outlet. Numerical techniques used in CFD were employed here to solve the adjoint linear Partial Difference Equations (PDEs). With the solved adjoint variables, final expression of the cost function gradient with respect to the design variables was formulated. Combined with quasi-Newton algorithm, the aerodynamic design approach for turbine blades was presented, which was independent of the Navier-Stokes (N-S) solver being used. Finally, to validate the present optimization algorithm, an aerodynamic design case of transonic turbomachinery blade was performed and analyzed.
An Accelerated 3D Navier-Stokes Solver for Flows in Turbomachines
Authors: Brandvik Tobias , Pullan Graham
Published: February 2010

A new three-dimensional Navier-Stokes solver for flows in turbomachines has been developed. The new solver is based on the latest version of the Denton codes, but has been implemented to run on Graphics Processing Units (GPUs) instead of the traditional Central Processing Unit (CPU). The change in processor enables an order-of-magnitude reduction in run-time due to the higher performance of the GPU. Scaling results for a 16 node GPU cluster are also presented, showing almost linear scaling for typical turbomachinery cases. For validation purposes, a test case consisting of a three-stage turbine with complete hub and casing leakage paths is described. Good agreement is obtained with previously published experimental results. The simulation runs in less than 10 minutes on a cluster with four GPUs.
On the Effects of Unsteadiness on the Condensation Process in Low-Pressure Steam Turbines
Authors: Fakhari Keramat
Published: February 2010

The condensation process in a turbomachine is in reality an essentially random and unsteady phenomenon. On a time-averaged basis, the condensation zone is spread over a much greater distance in the flow direction than a simple steady-flow calculation would indicate. The droplet growth rate also shows different characteristics which are observed in experiments measured in real low-pressure steam turbines. These differences are mainly introduced by the large-scale temperature fluctuations which are caused by the segmentation of blade wakes by successive blade rows. Furthermore, the additional losses by condensation have to be reconsidered for an unsteady simulation. This paper describes a time-accurate Eulerian/Lagrangian two-phase model which is implemented within the DLR in-house code TRACE [1]. The phases are coupled through appropriately generated source terms for heat, mass and momentum. For the subcooled thermodynamic properties of steam the local formulation of IAPWS-IF97 [2, 3] is used. The implementation has been validated in a previous publication of the author [4] using one and two-dimensional experiments of Laval nozzles and a cascade blade from literature. The focus of this work is on the unsteady Phenomena which are investigated in a stage of an industrial low-pressure steam turbine.
An Experimental and Computational Study of the Erosion in Submersible Pumps and the Development of a Methodology for Selecting Appropriate Protective Coatings
Authors: Hadjiyannis Stavros , Charalambous Nicolas , Tourlidakis Antonios , Michaelides Kristis
Published: February 2010

Solid Particle Erosion is one of the major problems in pump industry, since operation in erosive environment could cause performance alterations of pumps with consequent increased maintenance and running costs, mainly due to the lower efficiency. The research work aimed to study the erosion phenomenon in vertical multistage submersible pumps and develop new coatings as means to prolong their operating life through the reduction of the erosion rate. The mechanical properties of various coatings were examined using nano-indentations, impact tests, 3D-surface topography and Finite Element Analysis. Following a computational performance analysis of a pump stage using CFD software was completed and the experimental results were utilized to calculate the erosion factor k which has been introduced in the Finnie Erosion Model to computationally determine the erosion rate of the pump stage.
Aeroelastic Instability of Fan Blades at High Altitudes
Authors: di Mare Luca , Vadati Mehdi , Mueck Bernhard , Smith Nigel H. , Birch Nigel
Published: February 2010

This paper describes a computational study into non-integral fan assembly vibration due to excitation from boundary layer transition. In large-diameter fans, the transition location is usually well ahead of the shock, even at high altitudes. In smaller machines, however, a laminar boundary layer is present at the foot of the passage shock. The resulting flow is intrinsically unstable and can create excitation frequencies close to assembly natural frequencies. The present study applies a heuristic model to determine the transition location and aims at assessing changes in transition-driven excitation amplitude and frequency as functions of fan speed and pressure ratio for a given altitude. The basic aspects of the unsteady flow are described and the computed excitation spectrum is compared to available test data. The proposed methodology is relatively simple to apply, shows good correlation with available measured data and offers the possibility of assessing the risk of non-integral response on fan blades at an early stage during development.
Radial Forces in a Centrifugal Compressor Equipped With Vaned Diffusers
Authors: Jaatinen Ahti , Backman Jari L. H. , Turunen-Saaresti Teemu
Published: February 2010

A non-uniform pressure distribution in a volute of a centrifugal compressor causes a radial force on the impeller and the rotating shaft. The diffuser preceding the volute determines how the flow field entering to the volute, and affects the radial forces that are caused by the volute towards the impeller. The radial forces were measured for three different vaned diffuser geometries and one vaneless diffuser with a pinch. The force measurements were made for each assembly with the same compressor using active magnetic bearings. The impeller forces were found to be the smallest near the design flow and higher at choke and at stall for all configurations. The radial forces on the impeller were higher with the vaneless diffuser than with the vaned diffuser. The force distributions with the vaned diffusers were uniform and clearly different from those of the vaneless diffuser. In addition, the radial forces were estimated using static pressure distributions measured at the impeller outlet. The radial force determined from the pressure measurements verified the measured forces obtained in the magnetic bearing measurements.
A Method for Evaluating the Aerodynamic Stability of Multi-Stage Axial-Flow Compressors
Authors: Nakano Tsuguji , Breeze-Stringfellow Andy
Published: February 2010

A new simple engineering parameter to evaluate the stability of multi-stage axial compressors has been derived. It is based on the stability analysis for a small circumferential disturbance imposed on the steady state flow field. The analytical model assumes that the flow field is two dimensional and incompressible in the ducts between blade rows although the steady state density is permitted to change across the blade rows. The resulting stall parameter contains terms that relate to the slope of the pressure rise characteristic of the blade rows and the inertia effects of the fluid in the blade rows and ducts. The parameter leads to the classical stability criteria based on the slope of the overall total to static pressure rise coefficient in the limit where constant density and constant blade rotational speed are assumed across the compressor. The proposed stall parameter has been calculated for three different multi-stage axial flow compressors and the results indicate that the parameter has a strong correlation with the measured stability of the compressors. The good correlation with the test data demonstrates that the newly derived stall parameter captures much of the fundamental physics of instability inception in multi-stage compressors, and that it can be a good guideline for designers and engineers needing to evaluate the stability boundary of multi-stage machines.
CFD Analysis of a Canned Pump Rotor Considering an Annular Fluid With Axial Flow
Authors: Untaroiu Alexandrina , Dimond Timothy W. , Allaire Paul E. , Armentrout Richard
Published: February 2010

Instability in rotor-bearing systems can lead to high levels of vibration, that can ultimately result in the destruction of rotating machines or lost production due to reduced speeds and flow rates. Thus, accurate characterization of instability drivers is vital in prediction of the stability of rotor-bearing-structural systems, allowing for design changes to reduce deleterious effects. These changes include alteration of the system component causing instability and alteration of the bearing design to improve the overall system stability. A source of destabilizing forces in vertical canned motor pumps arises from fluid-structure interaction (FSI) forces between the rotor can and the stator. In this paper, the FSI forces are modeled using an analysis of a long annular fluid filled region with an axial flow component. The model includes the effects of pre-swirl of the fluid entering the annulus. The rotor center static operating position is eccentric to the stator center due to manufacturing tolerances. The fluid forces are calculated using computational fluid dynamics (CFD) and are expressed in terms of equivalent stiffness, damping and fluid inertia (added mass) rotordynamic coefficients. The rotordynamic coefficients are identified using CFD by simulating non-synchronous perturbations of the rotor position and velocity around the static operating point. A separate set of simulations, which does not consider the effects of axial flow on the rotordynamic coefficients, are performed to facilitate direct comparison between the CFD predictions and the dynamic coefficients calculated using the bulk-flow method developed by Fritz.
Analysis of the Unsteady Flow in an Aspirated Counter-Rotating Compressor Using the Nonlinear Harmonic Method
Authors: Guidotti Emanuele , Turner Mark G.
Published: February 2010

A multistage frequency domain (Nonlinear Harmonic) Navier-Stokes unsteady flow solver has been used to analyze the flow field in the MIT (rotor/rotor) aspirated counter-rotating compressor. The numerical accuracy and computational efficiency of the Nonlinear Harmonic method implemented in Numeca’s Fine/Turbo CFD code has been demonstrated by comparing predictions with experimental data and nonlinear time-accurate solutions for the test case. The comparison is good, especially considering the big savings in time with respect to a time accurate simulation. An imposed inlet boundary condition takes into account the flow change due to the IGV (not simulated in the computational model). Details of the flow field are presented and physical explanations are provided. Also, suggestions and recommendations on the use of the Nonlinear Harmonic method are provided. From this work it can be concluded that the development of efficient frequency domain approaches enables routine unsteady flow predictions to be used in the design of modern turbomachinery.
Numerical Analysis of Point Contact EHL on Coated Substrates
Authors: Wang Zhan-jiang , Hu Yuan-zhong , Wang Wen-zhong , Wang Hui
Published: February 2010

Performances of point contact EHL on multilayered or coated substrates have been analyzed in this paper via computer simulations, with emphasis on comparing the effects of Newtonian and non-Newtonian lubricants. The lubrication system consists of a rigid ball in contact with a smooth coated flat. The coating is perfectly bonded to an elastic substrate and it has a uniform thickness. The rigid ball has surface velocity U relative to the contact point. The hydrodynamic pressure p is governed by a generalized Reynolds equation in which the non-Newtonian effects of lubricants are characterized by two factors whose values are determined based on lubricant rheology. The Papkovich-Neuber potentials were employed to get the response functions in frequency domain for layered contact problems, and the influence coefficients relating pressure to surface displacements and stresses can be obtained via invert Fourier transform. The surface deformation was then calculated in terms of the pressure-displacement influence coefficients and the DC-FFT method was used to speed up the computation. The distributions of pressure, film thickness and subsurface stress have been analyzed for lubricants with different rheological behaviors, from which pressure and film thickness profiles along the rolling direction are calculated for Newtonian and Non-Newtonian lubricants. The central film thickness become thicker for stiffer coatings in the case of Newtonian lubricants, but the trend is reversed for Non-Newtonian lubricants. The surface stresses along the rolling direction show a spike corresponding to the pressure, which is more significant with stiffer coatings in the Newtonian case, but the spike is less visible for Non-Newtonian lubricants.
Recent Research and Future Challenges in the Simulation of Hydraulic Seals
Authors: Salant Richard F. , Yang Bo , Thatte Azam
Published: February 2010

Recent numerical simulation results of hydraulic rod seals are reviewed. These include steady-state simulations of U-cup seals. Challenges for future research are discussed.
Tribological Properties and Applicability of Thermo-Reversible Gel-Lubricants
Authors: Ohno Nobuyoshi , Mia Sobahan , Masuhara Kazuo , Sonoda Kentaro , Yamashita Yuji , Tamura Yoshitaka , Morita Shigeki , Shitara Yuji
Published: February 2010

The tribological properties of a new unique thermo-reversible Gel-Lubricant (TR Gel-Lube) were investigated. TR Gel-Lube which includes 10–40% of amide type gel agent in base fluid, is repeatedly able to change from gel-state to liquid-state at the melting point of its gel agent. High-pressure rheological tests were performed in order to characterize the behavior of base oil and TR Gel-Lube as a function of pressure and temperature. The effect of TR Gel-Lube on ball bearings fatigue life was carried out by systematic tests using thrust ball bearings. The results of L10 life tests of TR Gel-Lube showed a longer life than the conventional greases. This result was investigated from oil film formation. It was found that gel agent played a key role in the lubricating properties. Some mechanisms such as adsorbed film formation and solid like formation are proposed.
Effect of Surface Topography on Mixed Lubrication Film Under Transient Conditions
Authors: Krupka Ivan , Hartl Martin , Svoboda Petr
Published: February 2010

Surface topography plays an important role in the efficiency of lubricated contacts formed between highly loaded machine parts. Gears, rolling bearings, cam and followers etc. subjected to high loads and/or slow speeds are operated under mixed lubrication when lubrication film is not able to completely separate rubbing surfaces. Such an effect becomes even more serious under transient conditions that bring the risk of the surface damage because of asperities interactions. This paper focuses on the effects of both artificially produced and real roughness features on mixed lubrication film formation during start up motion of non-conformal contacts operated under rolling/sliding conditions. The observation of the effects of surface dents artificially produced on the ball surface helped to understand better the behavior of real surface topography. It was found that the presence of shallow surface features can help to separate mixed lubricated rubbing surfaces more efficiently than it could be suggested from the results obtained with smooth surfaces.
Design of Damped Air Bearings at Head Disk Interface
Authors: Li Jianhua , Xu Junguo , Shimizu Yuki , Honchi Masayuki , Ono Kyosuke
Published: February 2010

Small perturbation and modal-analysis methods were employed to systematically study a damped slider’s dynamic characteristics. We found that a design with grooves distributed on a trailing pad effectively improved the slider’s damping at higher frequencies, and the damping ratio was dependent on the number of grooves, their depth, location, width, length, distribution, orientation, and types. A higher damping ratio could be obtained by optimizing these parameters. The femto slider with distributed damping grooves on a trailing pad had a higher damping ratio in the third mode, and hence, its responses to disk parallel and wavy motion were greatly reduced. This new design for the damped slider was an effective solution reducing the slider’s modulation.
Effects of Texture Modification on Bearing RCF Life
Authors: Kang Young Sup , Hager Carl H. , Cao Dongbu , Evans Ryan D.
Published: February 2010

Highly localized tribological contacts can modify the surface texture of rolling element bearing surfaces. The evolution of the surface texture generates modified subsurface stress fields within the contact and subsequently may alter the bearing rolling contact fatigue (RCF) life. In this present study, relationships between bearing surface topography and subsurface stress states are examined for their effects on bearing RCF life in the limiting case of boundary or dry contact. Results show that seemingly minor changes to surface topography may influence the stress distribution enough to affect RCF life under heavily loaded conditions.
The Role of Fragility in EHL Entrapment
Authors: Martini Ashlie , Bair Scott
Published: February 2010

EHL entrapments are known to be highly dependent on the lubricant viscous characteristics. One such property is fragility, whose significant effect on entrapments we investigate here for the first time. We employ both experimental measurements and a numerical transient EHL simulation. We find that fragility is an extremely important property and, at least for low viscosity lubricants, must be included in high pressure EHL calculations for accurate prediction of physical behavior.
Spherical Indentation of an Elastic–Perfectly Plastic Half-Space: Deformation Map and Evolution of Plasticity
Authors: Song Z. , Komvopoulos K.
Published: February 2010

A finite element analysis of the indentation of an elastic-perfectly plastic half-space by a rigid sphere was performed for a wide range of material properties. The post-yield deformation behavior was found to consist of four deformation regimes, namely linear elastic-plastic, non-linear elastic-plastic, transient fully-plastic, and steady-state fully-plastic deformation. The boundaries of these deformation regimes were determined numerically in terms of elastic-plastic material properties. The deformation behavior in different regimes was examined in the context of finite element results showing the evolution of subsurface plasticity for different material properties.
Performance Optimization of Thermal Nano-Actuator for Fly Height Control in Disk Drives
Authors: Tan Haisan , Liu Bo , Zhang Mingsheng , Yu Shengkai
Published: February 2010

Slider with thermal fly height control (TFC) uses a thermal heater to produce localized thermal protrusion and adjust the vertical position of the read/write head. This paper reports authors’ efforts in exploring large protrusion stroke with minimal heater power input whilst preserving heater robustness in the TFC slider, with an optimized thermal nano-actuator design. Effects of both heater line width and line spacing on TFC slider performances are investigated. A novel ‘Stream-River’ heater design approach is proposed. Simulation results conclude that the “Stream-River” approach is of both high power-protrusion efficiency and high heater robustness.
Multibody Dynamics of Rolling Element Bearings With Faults
Authors: Nakhaeinejad Mohsen , Bryant Michael D.
Published: February 2010

A detailed bondgraph model of rolling element bearings with direct correspondence between parameters of the model and physical system components was developed as multibody systems, with vector bondgraphs to represent dynamics. The model incorporates gyroscopic and centrifugal effects, contact elastic deflections and forces, contact slip, and bearing faults. The model clearly defines how a healthy or faulty bearing behaves. Dents and pits are modeled through changes in surface profiles. Simulation results in form of time/frequency domain data, orbit plots and Poincare maps show the effectiveness of the multi-DOF bearing model in fault detection.
End Effect Attenuation in Tapered Roller Contacts
Authors: Diaconescu Emanuel
Published: February 2010

The end effect attenuation in finite length line contacts is mainly approached for cylindrical bodies. Multi-radius crowning may remove end effects in tapered roller contacts. Another method for leveling maximum pressure in these contacts is the use of polynomial generatrix. This paper investigates the effect of this generatrix in tapered roller contacts. An improved pressure distribution is obtained. This has a nearly flat maximum value along most of contact length.
Influence of Surface Treatment of High Carbon Steel on the Reciprocating Wear in Comparison With the 316 Stainless Steel
Authors: Gulhane U. D. , Roy Manish , Sapate S. G. , Mishra S. B. , Mishra P. K.
Published: February 2010

Diffusion treatments such as chromising and aluminising of high carbon steel results in the formation of Cr and Al rich layers on the surface. These layers will be responsible for formation of protective Cr2O3 and Al2O3 scale on exposure to corrosive environment. In view of extensive application of 316 Stainless Steel in biomedical engineering, present work is undertaken to examine the influence of diffusion treatment of high carbon steel on the reciprocating wear in Hank’s solution and to compare the same behavior with that of 316 SS. In order to achieve the above mentioned objectives, the wear rates of 316 SS, 304 SS, high carbon steel in aluminised and chromised condition have been evaluated. Though the general characteristics of the wear behavior, such as higher wear rate at higher load and at higher reciprocating speed, for all the materials are similar, aluminised and chromised high carbon steel exhibited best wear resistance especially at high and intermediate load. In simulated body fluid condition, 316 SS exhibited two different material removal mechanisms. In the first case, which is observed at higher load, material loss is by nucleation and propagation of crack. In the second mechanism which is prevalent at low and intermediate load, wear takes place by deterioration of composite layer formed on the surface by mixing the corrosion product and the substrate. Consequently it is noted that wear rate decreases with increase of hardness at higher load. At intermediate and at low load wear rate is less dependent of hardness.
Abrasive Wear Behavior of Permanent Moulded Toughened Austempered Ductile Iron
Authors: Uma T. R. , Simha J. B. , Narasimha Murthy K.
Published: February 2010

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.
Experimental Structural Stiffness and Damping in a 2nd Generation Foil Bearing for Increasing Shaft Temperatures
Authors: San Andre´s Luis , Ryu Keun
Published: February 2010

Demonstrated gas foil bearing (GFB) operation at high temperature is of interest for gas turbine applications. The effects of (high) shaft temperature on the structural stiffness and damping parameters of a foil bearing must be assessed experimentally. Presently, a hollow shaft warmed by an electric heater holds a floating 2nd generation FB that is loaded dynamically by an electromagnetic shaker. In tests with the shaft temperature up to 184°C, the measurements of dynamic load and ensuing FB deflection render the bearing structural parameters, stiffness and damping, as a function of excitation frequency and amplitude of motion. The identified FB stiffness and viscous damping coefficients increase with shaft temperature due to a reduction in the FB clearance. The bearing material structural loss factor, best representing mechanical energy dissipation, decreases slightly with shaft temperature while increasing with excitation frequency.
Tribology Issues in the Operation of a Microswitch: A Tutorial
Authors: Adams George G.
Published: February 2010

Microswitches have the potential to be used in numerous applications [1]. Microswitches are slower and currently less reliable than semiconductor switches. However they have the advantage of reduced power consumption, less insertion loss, and better isolation. The operation of a microswitch involves many interesting phenomena which will be reviewed. In an electrostatically actuated switch a voltage difference is applied between the beam and the gate. The resulting electrostatic force pulls the beam toward the gate such that its tip contacts the drain and completes the circuit. However the momentum of the beam causes it to deflect further, even after the tip is in contact with the drain. This stored elastic energy can be sufficient to cause the tip to separate from the drain resulting in what is often referred to as “contact bounce” [2]. Contact bounce causes several problems. First the switch cannot be used until the bouncing has stopped, thus increasing the effective time-to-closure. Second the tip and drain are subjected to more mechanical open-close contacts than are intended. Third the impact force between the tip and drain can be several times greater than the force in the closed position. These last two phenomena can prematurely degrade the contact surfaces. Attempts have been made to tailor the actuation voltage in order to reduce both the impact force and contact bounce [3]. Switches can fail in either of two failure modes. In one mode the contact resistance decreases with cycling. This behavior, while seemingly not a problem, is symptomatic of the contact being cleaned due to repeated contacts (i.e. “contact scrub” as it is known in the industry). As the resistance decreases the force of adhesion increases between these clean metal-to-metal contacts, eventually causing the switch to stick shut when the restoring force in the beam is insufficient to pull the contacts apart [4]. Another failure mechanism is a steady increase in contact resistance until the point at which the switch is no longer useable. These failures are attributable to the growth of contamination in the form of a friction polymer on the contacting surfaces [5]. Another measure of switch performance is intermodulation distortion which quantifies the distortion of a pair of harmonic RF signals with nearly equal frequencies. The beating between two such components causes the power to vary relatively slowly, i.e. at the beat frequency. This beat frequency may be sufficiently close to the thermal response time of the switch leading to distortion and false signals in the frequency range of interest [6].
Frictional Characteristics of IF-WS2 Nanoparticles in Simulated Engine Conditions
Authors: Gullac Burak , Akalin Ozgen
Published: February 2010

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.
Energy Harvesting With Piezoelectric Nanobrushes: Analysis and Design Principles
Authors: Majidi Carmel , Haataja Mikko , Srolovitz David J.
Published: February 2010

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.
Hysteresis Damping in Vibration Response of a Block in Elastic-Plastic Rough Surface Contact
Authors: Sepehri A. , Farhang K.
Published: February 2010

The differences in load and unload paths in an elastic-plastic contact of a rough surface and a flat leads to hysteretic energy loss. The nonlinear normal vibration response of the block is examined when subject to an external compressive load. The vibration response corresponds to the application of a constant compressive external It is shown that vibration decay rate is constant as opposed to the exponential decay rate for the linear vibrating systems. Closed form equations relating contact damping and contact natural frequency to the surface parameters are given.
An Indirect Boundary Element Formulation for the Solution of Coupled 2D Contact Problems
Authors: Zografos Angelos , Dini Daniele
Published: February 2010

An indirect boundary element scheme is employed for the first time to solve two-dimensional, frictional contact problems in the presence of coupling between normal and tangential tractions due to material mismatch and/or geometrical characteristics of the problem under investigation. A fully incremental contact algorithm is used which accounts for changes in the contact regime and the deformed shape of the bodies. The developed algorithm is first validated against the analytical solution obtained for a rigid flat and rounded tilted punch indenting an elastic finite body. The extension of the formulation to treat surface and subsurface cracks, wear and large deformations is also discussed.
A FEM Based Multiple Asperity Deterministic Contact Model
Authors: Megalingam A. , Mayuram M. M.
Published: February 2010

Knowledge of contact stresses generated when two surfaces are in contact play a significant role in understanding most mechanisms of friction and wear. Most of present contact models are based on the Greenwood-Williamson (GW) single asperity contact model and a statistical approach is adopted to calculate the real contact area for the entire surface based on the assumption that all the summits have uniform radius of curvatures and their heights vary randomly. But in real cases, the asperity radii vary. For a clear understanding about those aspects, a multiple asperity contact model, based on 3-D rough surface generated is analyzed using a commercial FEM package. Salient aspects of the present model are presented here and results are compared with a single asperity contact model.
Friction Characteristics of Porous Rubber Under Wet Conditions
Authors: Kosugi Yutaro , Iwai Tomoaki , Shokaku Yutaka , Amino Naoya
Published: February 2010

In recent years, porous rubber has been used as a tread matrix for studless tires. It is said that the pores in the tread rubber remove water between the tire and the wet road surface; however, the water removal is not sufficiently well understood. In this study, a rotating rubber specimen was rubbed against a mating prism to observe the contact surface. The friction force was also measured simultaneously with observation of contact surface. The water entering the pores was distinguished by the continuity method. As the result of these experiments, the coefficient of friction for rubber having pores on the surface was found to be larger than that of rubber without pores. Moreover, the difference in the coefficient of friction for rubber specimens with and without pores tended to be larger at lower sliding speeds. No water entered pores 3mm or less in diameter at any sliding speed in this experiment. An experiment to make the rubber specimen collide with the mating prism was conducted since actual tires seem to be deformed by the vehicle weight, such that the tire surface might contact the road collisionally. In the resulting collision experiment, the water did enter pores 3mm in diameter.
Quantification of Friction Force for Dual-Axis Probe Friction Force Microscope
Authors: Amakawa Hiroaki , Fukuzawa Kenji , Shikida Mitsuhiro , Zhang Hedong , Itoh Shitaro
Published: February 2010

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.
Film Forming Characteristics of Oil-in-Water Emulsions in Elastohydrodynamic Contacts
Authors: Hili J. , Reddyhoff T. , Olver A. V. , Pelletier C. , Jacobs L.
Published: February 2010

Oil-in-water emulsions are the most widely used lubricants in metal rolling, as they provide a combination of cooling and lubricating properties. These avoid severe metal-to-metal contact by forming a separating (elastohydrodynamic) film between the metal strip and the rolls so as to prevent scuffing, limit wear and control friction.
Bearing Wear Due to Mechanical Stresses and Electrical Currents
Authors: Srinidhi S. , Tiwari Mayank , Burra Rajni , Gowda Hombe , Siemers Paul A.
Published: February 2010

Passage of current through moving conductive contacts results in electrical discharge and then melting of the material, which leads to wear. Such kind of bearing wear is common in electrical machines. There are however certain patterns which are unique to this kind wear. This wear pattern is called ‘fluting’, which are repetitive in nature. Electrical discharge can create higher surface roughness. Also the thermal and rheological properties of the lubricant play a big role in the film thickness formation. The passage of current through the lubricant also changes this and is determined by the electrical properties of the lubricant. In this work effect of bearing currents on a 7204 angular contact ball bearing is studied. This is tested with and without different cage materials with an axial load and no radial load, rotating at 2700 rpm. Four experiments were done at different-level of voltage, lube and cage material. Type of lubricant was seen to play a significant role in fluting.
Automated Structural Health Monitoring of Bolted Joints in Railroad Switches
Authors: Afshari Mana , Marquie´ Thomas , Inman Daniel J.
Published: February 2010

Current switch bolt inspection on rail systems is a labor intensive and sometimes unreliable approach to maintaining the switch integrity. Recent rail accidents in the United Kingdom (Potters Bar in 2002 and Grayrigg in 2007) underscore the need for routine inspections of the switch mechanisms. From the Grayrigg report of 23 February 2007 the main causes of the accident were found to be the loosening and, as a result, the initiation and growth of cracks, and, eventually, rupture of the bolts of the switch bars, especially the one maintaining the switch rails at a correct distance apart. Such findings also resulted from the 2002 crash report but unfortunately frequent visual inspections were not forthcoming. In this paper, an effective method for monitoring the loosening of the switch bolts is described. As the loosening of the bolts further causes the crack formation in the bolted joints, it seems valid to say that the early detection of loosening of bolted joints in railroad switches will be of great importance in eliminating the need for frequent visual inspection by totally automating inspection of the switches’ mechanical condition. The first part of the present paper focuses on the use of smart materials and structures for the health monitoring of bolted joints in railroad switches. It is shown that using the piezoelectric transducers and the impedance-based structural health monitoring technique, the loosening of the bolted joints are detectable. The accuracy in loosening detection is as high as 25 ft-lbs which corresponds to merely 1/10th of a bolt turn. Being able to detect the loosening of the bolted joints in railroad switches, the concept of self-healing bolted joints is applied in the next part in order to automatically retighten the loosened bolts to their prescribed functional conditions.
Collision Safety Improvements for Light Rail Vehicles Operating in Shared Right of Way Street Environments
Authors: Bocchieri Robert T. , Kirkpatrick Steven W. , Navarro-Northrup Claudia , MacNeill Robert A. , Peterson Brian D. , Gough Glenn
Published: February 2010

The majority of fatalities that occur from light rail vehicle (LRV) operations are occupants of automobiles that are struck by the LRVs. Recent developments of crashworthiness standards for LRVs by the American Society of Mechanical Engineers (ASME) Rail Transit Vehicle Standards Committee included consideration of a wide variety of crash scenarios including collisions between LRVs and street running automobiles. The requirements included in the standard are primarily to create an enclosed front end geometry where the struck vehicle will not be entrapped or overridden. A smooth enclosed front end profile is a primary requirement for improving the compatibility of LRVs colliding with automobiles. More recently, a study has been initiated by the Federal Transit Administration (FTA) to develop LRV front end features that further improve the crash compatibility with automobiles. The approach depends on results from computer simulation modeling of vehicle collisions across a wide variety of LRV bumper designs, some with and some without energy absorbers. Results of the study and the design of the energy absorbing bumper system are presented.
Brake Shoe Force Variation
Authors: Cummings Scott
Published: February 2010

The Wheel Defect Prevention Research Consortium (WDPRC) has conducted a review and analysis of existing literature and existing data related to brake shoe force (BSF) variation in freight car brake rigging. This work was conducted to explore the sources of BSF variation, define the expected amount of BSF variation, and describe some of the existing brake system designs that may help reduce the amount of BSF variation. Wheel temperature is related to BSF due to the use of the wheel tread as a brake drum. Variation in BSF within a given railcar is one potential source of elevated wheel temperatures and thermal mechanical shelling (TMS) damage to the wheels. At elevated temperatures, wheels become less resistant to fatigue damage due to changes in the material mechanical properties and relief of beneficial residual stresses. Data recorded by a wayside wheel temperature detector shows that eliminating wheel temperature differences within individual cars could reduce the number of wheels reaching temperatures of concern for TMS by a factor of eight.