bluuebunny/crossref_metadata_2025 huggingface dataset:
An artificial neural network based approach to fault diagnosis and classification of fluid power systems
Authors: Le T T , Watton J , Pham D T
Published: October 2002

In this paper, multilayer perceptron (MLP) type neural networks are used to detect leakages in an electrohydraulic cylinder drive. Both single-leakage and multiple-leakage type faults are investigated. The performance of MLPs is examined relating to the level of leakage flowrate and it was found that MLPs perform well for line leakages but for across-cylinder seal leakages they could only detect leakage over 1.01/min. The generalization tests on non-training leakage flowrate and working temperature are also included. A novel feature is the use of system state variables for network training, including additional terms to accelerate convergence. The approach has also made a significant contribution to multiple-fault detection, particularly for the complex three-fault case.
Evolving inherently fault-tolerant systems
Authors: Thompson A
Published: October 2002

Artificial evolution can integrate fault tolerance considerations into the automatic design process, producing inherently fault-tolerant designs without explicit redundant parts. Population dynamics can give rise to some level of fault tolerance ‘for free’. Requirements for fault tolerance can also be incorporated into the fitness function. The practicalities of these methods are investigated, grounded in the study of a real-world evolved electronic control system for a robot.
The control of fluid power systems-responding to the challenges
Authors: Edge K A
Published: October 2002

A review of recent and current research on the control of fluid power systems is presented. Strengths and weaknesses of different schemes for control at both the component and system level are identified. It is argued that the selection and tuning of the controller is a critical part of system design and that simulation has an essential role to play in this process.
Generic parametric controller design using output feedback eigenstructure assignment
Authors: Liu G P , Patton R J
Published: October 2002

This paper is concerned with generic parametric controller design via output-feedback eigenstructure assignment for linear multivariable systems. A new parametric expression of closed-loop eigenvectors and generalized eigenvectors is developed for both real eigenvalue and complex-conjugate eigenvalue cases. It also considers the case where the closed-loop eigenvalues are multiple and/or the same as the open-loop ones so that the system to be designed can be uncontrollable and/or unobservable. The controller designed via output-feedback eigenstructure assignment is expressed by new proposed parameter vectors. The freedom provided by output-feedback eigenstructure assignment is used to optimize a performance function which is used to measure the sensitivity of the closed-loop system matrix.
Examination of flow behaviour of electrorheological fluids in the flow mode
Authors: Wolff-Jesse C , Fees G
Published: October 2002

The use of electrorheological (ER) fluids in hydraulic systems has been demonstrated in detailed investigations at the Institute of Fluid Power Transmission and Control (IFAS) [1]. The flow behaviour of this fluid cannot be described reliably. A detailed knowledge of this flow behaviour would enable better ER component design and produce basic information for simulation models. It is therefore important for the practical applications of ER fluids.

A detailed comparison is made between existing rheological models, e.g. the Bingham model, and measured values in flow mode to confirm these models and, if possible, to define a material property constant. In addition, a simple model describing the flow behaviour of an ER fluid in the flow mode with the help of a geometrical dependent variable is presented. This variable is derived from measured values and reflects the influence of the gap height and the gap length. A comparison between this function and real measured values gives a very good agreement within the defined sphere and therefore it is a good tool for the design of electrorheological flow resistors.
Design of smart machinery installations to reduce transmitted vibrations by adaptive modification of internal forces
Authors: Long T , Brennan M J , Elliott S J
Published: October 2002

There is a requirement to isolate machinery from their surroundings to reduce the transmission of noise and vibration. Reducing the input disturbance of a system can reduce vibration levels, but this is not always a feasible option. One of the simplest ways to overcome these problems is to retrofit a vibration attenuation device. The method used for vibration isolation discussed in this paper is semi-active control and involves using tunable resonators at the mounting positions. These resonators operate by continually adjusting their characteristics such that a large force is generated, achieving vibration attenuation over a range of varying operating conditions. In this paper, the resonators are tuned such that the natural frequency of the resonator is equal to the excitation frequency. Open-loop control is used to roughly tune the resonator, with a precise algorithm changing the characteristics of the resonator such that the host structure and resonator are in quadrature. Using multiple resonators increases the complexity of the system as interaction is possible between the resonators. The interaction between well-coupled resonators is modelled and examined experimentally. A simple control algorithm is developed and implemented which demonstrates that the resonators can be tuned independently, irrespective of the dynamic coupling between them.
Application of learning to high-speed robotic manipulators
Authors: Kirecci A , Gilmartin M J
Published: October 2002

When a desired signal is applied to a servo system it responds in a characteristic fashion and follows the required trajectory with an error. The physical features of the actuators and the gain setting of the controller are the main parameters that determine the response of the system. Controllers with fixed gain values are effective for many conventional processes using slow-speed manipulators. However, there are several cases where the precise tracing of a fast trajectory under different payloads requires more advanced control techniques. When the motion is cyclical, learning control is one advanced technique which is appropriate to use. Depending solely on measurements of data from the preceding cycle, its implementation in real time is both fast and efficient. In practice, however, it has been observed that learning can induce high-frequency ripples on the tuned command curve which with increasing iterations result eventually in the saturation of the system's actuators. In this study, the use of on-line learning control techniques is discussed and a new approach using digital filters is implemented to prevent actuator saturation from occurring when learning is applied. A planar robotic manipulator has been designed and built to investigate the practical problems of learning control, particularly when the system runs at high speeds.
A bifurcation-based procedure for designing and analysing robustly stable non-linear hydraulic servo systems
Authors: Kremer G G , Thompson D F
Published: October 2002

A critical evaluation of current hydraulic servo system analysis methods indicates a need for alternative methods better able to quantify robust stability. One promising method recently developed for analysing large-scale power systems determines stability robustness in a high-dimensional parameter space by computing the distance to the ‘closest’ Hopf bifurcation (which corresponds to the birth of a limit cycle oscillation). In this paper a procedure is developed for applying closest Hopf bifurcation theory in the design and analysis of robustly stable hydraulic servo systems. The procedure addresses practical implementation issues such as the impact of an inhomogeneous parameter space and the choice of a metric that yields a meaningful quantitative measure of stability robustness. Results from the new procedure applied to a common position control system compare favourably with published describing function results and new simulation results. Additionally, the new procedure is easier to apply and produces results which are easier to interpret and use. As a demonstration of the design procedure's ability to handle non-linear systems with high-dimensional parameter spaces, a hydraulic servo system with an inhomogeneous seven-dimensional parameter space is designed to meet a robust stability requirement.
Robustness enhancement of an optimal fuzzy control electrical position servo system by a novel model-following approach
Authors: Li G , Tsang K M , Ho S L
Published: October 2002

In this paper, an optimal fuzzy model-following control (OFMFC) scheme for position servo systems is presented. A fuzzy model controller (FMC) is used to generate an optimal reference output trajectory and a proportional-integral-derivative adaptation mechanism is included to force the plant output to follow the optimal model output. Both design of the FMC and that of the PID adaptation mechanism are addressed. Numerical results illustrate that the proposed OFMFC scheme can retain optimal system performance even in the presence of significant parameter variations and load disturbance. The comparison between an OFMFC system and an optimal fuzzy control (OFC) system shows that the OFMFC scheme is much more robust than the pure OFC scheme.
On-line optimization of unknown non-linear systems using a correlation-integration method
Authors: Liu G P , Daley S
Published: October 2002

This paper addresses a novel on-line optimization control strategy for unknown nonlinear systems. The Volterra series is used as a non-linear operator for the representation of unknown non-linear systems, which maps one function to another with a specific form. Based on this nonlinear operator, the correlation-integration method is proposed using on-line measured input and output data. This method has the following properties: system model free, strong rejection to disturbances, good robustness and on-line adaptation. Some examples are used to demonstrate these properties.
Feedback linearization for acceleration control of electrohydraulic actuators
Authors: Plummer A R
Published: October 2002

Accurate control of acceleration is important in several fields: prime examples are flight simulator motion and vehicle active suspensions. In both these applications hydraulic actuation is normally found to be most appropriate, despite certain non-linear characteristics. This paper describes a feedback linearization technique for controlling the acceleration of electrohydraulic actuators, compensating for the main non-linear characteristics of the valve and cylinder. Two versions are simulated and compared with conventional linear controllers. The first version requires velocity, acceleration and pressure feedback; the second dispenses with the need for acceleration measurements. Significant performance improvements are achieved over conventional methods.
Simulation of fluid power circuits using artificial network models: Part 1: Selection of component models
Authors: Watton J , Xue Y
Published: October 2002

Consideration is given to the transient analysis of fluid power circuits based solely upon a variety of artificial networks rather than the conventional mathematical modelling approach. Networks, trained using data from practical tests, are developed for an axial piston pump and filter, a proportional pressure relief valve, a lumped volume and a subsystem containing a proportional flow control valve driving an axial piston motor with its integral load assembly. A variety of networks are considered ranging from the linear-regression type, BARMAX, the self-organizing group method of data handling (GMDH) using nonlinear regression theory to multilayer perceptron (MLP) networks by the back propagation algorithm. Part 2 (1) then shows how the network models may be linked with the aid of additional steady state network models to predict the behaviour of a motor speed control system.
Implementation of non-linear tracking control schemes for a serial/parallel topology robot
Authors: Yao L , Spurgeon S K
Published: October 2002

Results of the application of an advanced non-linear controller to the problem of joint motion control for a robot are presented. For a class of desired state motions a control strategy is expounded which ensures that the system asymptotically tracks the desired motion to any desired degree of accuracy. The results are applied to a three-degree-of-freedom tetrahedral robot. Simulation results and experimental studies are described.
A real-time expert system for the condition monitoring of hydraulic control systems in a hot steel strip finishing mill
Authors: Gale K W , Watton J
Published: October 2002

This paper describes the evolution of an expert system for the condition monitoring of hydraulic control systems in a hot steel strip finishing mill. This intelligent management information system integrates real-time LabVIEW data acquisition with the Gensym G2 expert system, running on a Windows NT client-server computer network. The software architecture for building the predictive maintenance application is based on a conceptually new signal-conditioning technique for detecting vibration in roll stack assemblies. The design of the graphic user interfaces incorporate plant data models, where real-time feature extraction algorithms classify the failure mode and effects relating to the operational control of the mill. The use of object-oriented software methodologies for data analysis and system modelling are discussed including the identification of condition-monitoring variables and the fault classification procedures.
Multivariable system regulation with minimum control effort
Authors: Whalley R , Ebrahimi M
Published: October 2002

Linear multivariable time-invariant system models, controlled by proportional regulators, are considered. Selection of the regulator gain elements so that a specified polynomial function is generated, to provide improved closed-loop properties, is advocated. The effect on the characteristics of the closed-loop system model is assessed using conventional frequency domain techniques. Control effort minimization is achieved by optimizing the gain ratios. An illustrative example is provided to demonstrate effectiveness. Simulated transient characteristics are computed, completing the design exercise thereby.
Force as a flow variable
Authors: Fairlie-Clarke A C
Published: October 2002

The paper stems from an assessment of the suitability of bond graphs for modelling mechanical systems. Although mathematically rigorous, difficulties arise with intuitive interpretation of bond graphs. The source of the difficulty is the semantics commonly adopted and the way that they relate to traditional interpretations of mechanical system dynamics. Bond graphs represent dynamic systems as energy manipulators with the flow of energy given by the product of two power variables, commonly described as the flow and effort variables. In the mechanical domain, velocity is commonly described as the flow variable, and force as the effort variable. The physical interpretation of mechanical systems and the analogies across systems domains are much improved if force is adopted as the flow variable and the second power variable (i. e. velocity) is called the potential variable. Force can be represented as the flow of a mechanical charge, where the total charge stored in a mass is equal to its momentum. It displays all the properties of a flow variable. Mass is then analogous to electrical capacitance, and mechanical compliance is analogous to electrical inductance.
Two-dimensional flow of a non-Newtonian lubricant
Authors: Greenwood J. A.
Published: October 2002

The traction coefficients predicted in an elastohydrodynamic contact with a Newtonian fluid are impossibly large, so that methods of analysing the behaviour of a non-Newtonian fluid are essential. Except for one-dimensional flow, no convenient exact method is known. Two approximate methods of treating the flow of a non-Newtonian lubricant, proposed by Ehret et al. and Hooke respectively, are examined by comparing their predictions for a particular non-Newtonian fluid for which an exact solution may readily be obtained. While there is no reason to believe that any real fluid exhibits this behaviour, it is not too different from Eyring behaviour, so that the conclusions are believed to be applicable to real fluids.

A method of obtaining an exact solution for a general non-Newtonian lubricant is investigated, although it appears to involve too much computation for use in an elastohydrodynamic lubrication (EHL) solver. A limited number of full solutions obtained for an Eyring fluid support the conclusions deduced using the model fluid, namely that the approximations will be quite adequate for the analysis of EHL of smooth surfaces and may be good enough for wavy or rough surfaces.
Film thickness predictions for elastohydrodynamic elliptical contacts over a wide range of radius ratios with consideration of side starvation
Authors: Sharif K. J. , de Ling Fd M Barragan , Martin M. J. , Alanou M. P. , Evans H. P. , Snidle R. W.
Published: October 2002

The paper presents numerical solutions obtained for a wide range of elliptical elastohydrodynamic lubrication (EHL) problems. The conditions considered encompass relative principal radii of curvature ratios from 20:1 with entrainment in the minor axis direction, to 50:1 with entrainment in the major axis direction. The problems considered derive from investigations of practical machine elements where the width of contact (perpendicular to entrainment) is limited by the extent of the metal surfaces on either side. Two sets of results have been obtained: one with the width of the lubricated contact approximately twice that of the Hertzian dry contact, and the other where the ratio of these widths is 1.2. Taken as a whole the results present a complete range of conditions obtained using the same numerical model throughout. The film thickness predictions are compared with those given by well-known published formulae and design charts.
Wear debris and associated wear phenomena—fundamental research and practice
Authors: Roylance B. J. , Williams J. A. , Dwyer-Joyce R
Published: October 2002

The effect and consequences of wear on the present-day operation and maintenance of industrial machinery are considerable and far reaching in terms of the performance, cost and underlying business environment. One of the ways open to maintenance engineers to keep track of the wear occurring is to monitor the condition, or ‘health’, of critical items of machinery by either measuring or capturing representative samples of wear products, primarily the debris that is generated in the contact which is subsequently released and transported away from the source by the lubricant behaving as a carrier fluid.

Commencing with a brief description of some wear-related failures of critical components, such as bearings and gears, the different manifestations of wear debris are reviewed with particular regard to the methods employed to measure or capture the debris and how their characteristics are determined. Of particular importance is the need to establish and single out those morphological features which relate to the underlying wear mechanisms involved which led to their generation. The manifestation of wear phenomena and the causal effects are to be addressed by examining the mechanisms in the light of current fundamental research in which the links between wear and the generation of the associated debris are reviewed and discussed.
Recent thermohydrodynamic analyses and designs of thick-film bearings
Authors: Tanaka M
Published: October 2002

This paper is a state-of-the-art report on recent thermohydrodynamic analyses and designs of journal and thrust bearings. Recent papers published in journals and proceedings on tribology mostly in the 1990s are referred to. Bearings not only for turbomachinery but also for automotive engines are covered.
Optimum initial axial compression due to preload in an arrangement of two tapered roller bearings Part 2: Application to the transfer shaft of an automobile automatic transaxle
Authors: Bercea I , Nélias D , Cretu S
Published: October 2002

A method to determine the optimum value of the initial axial compression or preload between two tapered roller bearings has been described in Part 1 of this paper. The optimization consists in maximizing the fatigue life of the bearing arrangement. The method is applied here to the transfer shaft of an automobile automatic transaxle, and the results are analysed.

Numerical results show the importance of an adequate axial compression to ensure a maximum bearing arrangement reliability for a complex cycle of operating conditions in terms of load and speed.
Comparisons of contact pressures of crowned rollers
Authors: Ju S. H. , Horng T. L. , Cha K. C.
Published: October 2002

The present work determines the contact pressure and stress concentration between the crowned roller and the raceway by using three-dimensional finite element analysis. A number of crowned profiles with various dimensions were examined. Fine meshes and node-to-Hermit-surface contact elements were used along the contact surface in order to obtain accurate analysis results. A table was generated to show the stress concentration near the roller edge for various crowned profiles and dimensions. This table indicates that the exponential profile is the optimal crowned profile to eliminate stress concentration.
A study of the mechanism of crack initiation on a mandrel bar for mandrel mill rolling in a seamless tube
Authors: Akiyama M , Tsubouchi K , Tsumura M , Hori H
Published: October 2002

An investigation was carried out on the mechanism of crack initiation on a mandrel bar used for the mandrel mill operation in seamless tube manufacturing. Close observations of the mandrel bar surface suggested that crack initiation may be induced by a thermal shock. In order to check the validity of this hypothesis, laboratory tests mainly based on cyclic temperature treatment were then carried out in a laboratory and a method was proposed to improve the mandrel bar life. After the estimation of the temperature on the mandrel bar surface both by numerical analysis during rolling and stripping and by an experimental approach during the stripping operation, an acceleration test using a corrugated mandrel bar was carried out on the mandrel mill to verify the validity of the proposed method (to improve the mandrel bar life).
Comprehensive design methodology for an engine journal bearing
Authors: Hirani H , Athre K , Biswas S
Published: October 2002

The trend towards high power output, high speed and low power loss in engines requires a better understanding of bearing behaviour. Research in this area is directed more towards different aspects involved in bearing analyses, rather than providing a comprehensive guideline on design of bearing. This effort compiles the design methodology for selection of diametral clearance and bearing length by limiting the minimum film thickness, maximum pressure and temperature. The design procedure is summarized on the basis of the existing rapid bearing analyses for evaluation of the journal trajectory, minimum film thickness and maximum pressure and simplified thermal analysis. A flow chart is provided for step-by-step bearing design. Finally, two case studies of engine bearings are described: one investigates the VEB bigend connecting-rod bearing for a large industrial reciprocating engine and the other a main crankshaft bearing for an automotive engine.

The methodology translates into easy-to-use expressions and the overall procedure is outlined, using practical data to demonstrate how this can be employed effectively by users.
Failure analysis of laser-textured surfaces
Authors: Chilamakuri S , Zhao X , Bhushan B
Published: October 2002

Friction/stiction behaviour of ultrahigh-density magnetic disk drives can be controlled by controlling the size and shape of the laser bumps. Tribological behaviour of laser-textured disk surfaces depends on the size and shape of the laser bumps, bump density and operating conditions. In this study, theoretical and experimental analyses have been carried out on nine different laser-textured disk surfaces. Stiction and friction experiments have been carried out on sombrero, V-type and W-type laser-textured disks and these results are compared with theoretical results. A good correlation is obtained between experimental and theoretical results. The effect of laser bump uniformity on critical number of bumps required to prevent plastic deformation and stiction has also been studied.
Wear behaviour and surface form evolution of a novel titanium carbide implanted surface under lubricated conditions
Authors: Fletcher D. I. , Kapoor A , Steinhoff K , Schuleit N
Published: October 2002

Tribological behaviour (friction and wear) of heavily loaded lubricated surfaces is found to be influenced by the presence of very small scale surface textures. The Indirect Structuring process, which is described here, is a new method of surface texture production through implantation of a surface with wear-resistant regions. During use a surface texture is developed and maintained because, at a given wear rate, the wear-resistant regions can sustain higher contact pressures than can the substrate.

Indirect Structuring of a tool steel surface was carried out by laser implantation of the surface with titanium carbide implants, and rolling contact experiments were conducted under elastohydrodynamic and mixed-lubrication regimes. It was found that the indirect structuring process produces a surface structure which fulfils the design requirements for textured tool surfaces, and which is insensitive to the load applied to the surface. The mechanisms found to steer the development of the surface texture may be used to develop design methods for application of the Indirect Structuring process.
The effects of surface defects on the fatigue of water-and oil-lubricated contacts
Authors: Gao N , Dwyer-Joyce R. S.
Published: October 2002

A study into effects of surface defects on the rolling contact fatigue of brass and rail steel has been undertaken on a twin-disc rolling-sliding test machine with both oil and water lubrication. Furrows and dents were artificially introduced into the disc surfaces, and surface microcracks and pits were monitored by means of surface replication. The results showed that artificial dents only reduce the fatigue life of the contact with oil, but not water lubrication. With oil lubrication the fatigue failure initiates at the surface defect. However, with water as a lubricant the whole of the surface undergoes cracking with the defect having no preferential effect. The possible mechanisms behind this behaviour are discussed in this paper.
A new model for thin-film lubrication
Authors: Qu Q. W. , Meng L. X. , Chai S , Niu S. T.
Published: October 2002

Based on adsorption theory, an equivalent viscosity model is derived. Under the condition of different film thicknesses, the thickness of adsorption layers hardly changes, but the load capacity of the oil film will increase rapidly as the oil-film thickness decreases. When the clearance is in the nanometre range, the pressure change will be more obvious. When this equivalent viscosity model is applied to calculate the bearing properties, the calculation results are consistent with Reynolds equation calculations in the thick-film range and in agreement with reports and experiments in the thin-film range
Magnetic and tribological evaluation of metal particle and metal-evaporated tapes in a linear tape drive
Authors: Topoleski J. J. , Bhushan B
Published: October 2002

Improving the performance of computer tape drives is an ongoing process that has recently involved the utilization of metal-evaporated (ME) tapes. The magnetic and tribological performance of the current metal particle (MP) tape and a new dual-magnetic-layer ME tape were evaluated in a Quantum DLT 4000 linear tape drive. Head output, drop-outs and head-tape interface friction were monitored during high-tension (1.7 N) high-speed (4 m/s) short-pass (10 m) shuttling tests without stepping the head. The severe MP test never showed signs of failure, but wear of the head's outriggers is believed to impact the stability of the head output signal. MP tape significantly outperformed ME tape; ME even performed poorly at nominal tension (0.8 N) and speed (2.5 m/s) conditions. ME tape lubricant was stripped away by corners on the DLT head, resulting in increased friction, wear and exposure of the relatively brittle diamond-like carbon layer. A high-tension high-speed MP test with head stepping was also performed to evaluate the effect of stepping; it failed far sooner than the non-step MP test. The nominal ME test and severe MP head step test are both believed to have failed because of the drive's inability to overcome high (wear-induced) static friction experienced during changes in tape direction. Modifications to the existing head or a new head design could improve the performance of ME tape in the DLT 4000 linear tape drive.
Measurements of real non-Newtonian response for liquid lubricants under moderate pressures
Authors: Bair S
Published: October 2002

A thorough characterization of all viscous flow properties relevant to steady simple shear was carried out for five liquid lubricants of current interest to tribology. Shear stresses were generated to values significant to concentrated contact lubrication. Two types of non-Newtonian response were observed: shear-thinning as a power-law fluid and near rate-independence. Functions and parameters were obtained for the temperature and pressure dependence of the viscosity and of the time constant for the Carreau-Yasuda equation. Results are consistent with free volume and kinetic theory, but directly contradict many assumptions currently utilized for numerical simulation and for extracting rheological properties from contact measurements.
Observation of Kaneta's dimples in elastohydrodynamic lubrication contacts
Authors: Ehret P , Bauget F
Published: October 2002

The formation of Kaneta's dimples are investigated under different sliding conditions using a high-speed video camera. Of interest is the observation of an unstable regime in which trains of dimples are formed and propagate throughout the high-pressure conjunction at regular intervals while the running conditions are steady. This study shows that such a situation can be associated with a type of stick-slip phenomenon in which adherence at the wall is periodically lost. A simple time-dependent model is developed to validate this concept. The model extends the consideration of interfacial slip previously proposed and accounts for a periodic variation in slip with time. The results reveal that such a condition effectively allows trains of single dimples to move throughout the conjunction. A refined modelling of the conditions at the wall/lubricant interface is, however, required in the future if a better understanding of the conditions which trigger such instabilities is to be obtained.
Implications of cavitation in individual grooves of spiral groove bearings
Authors: Broman G. I.
Published: October 2002

The pressure distribution in a flat spiral groove thrust bearing obtained from a straightforward solution of the Reynolds equation includes subatmospheric pressure in part of the grooved area. This is masked in the common theory based on the assumption of an infinite number of grooves. Furthermore, the negative contribution to the load capacity from this area is usually small, which may explain why the presence of subatmospheric pressure has not been given much attention in connection with these bearings.

Subatmospheric pressure is, however, necessary for liquid-lubricated flat spiral groove thrust bearings of conventional design to work at all at low numbers of grooves, which in turn requires a non-zero cavitation pressure. Cavitation within individual grooves implies non-linearity in, for example, the relation between load capacity and rotational speed of the bearing and limits the obtainable load capacity. This is more pronounced and important to consider at low numbers of grooves (wide grooves) than at high numbers of grooves (narrow grooves), and it is difficult to determine for what number of grooves that reliable prediction of bearing performance can be expected. It depends on the actual value of the cavitation pressure and other parameters that are usually unknown or difficult to account for.

To avoid this disadvantage a modified design of liquid-lubricated flat spiral groove thrust bearings is suggested.
On the conical whirl instability of hydrodynamic journal bearings lubricated with micropolar fluids
Authors: Das S , Guha S. K. , Chattopadhyay A. K.
Published: October 2002

A linear analysis of conical whirl instability of an unloaded rigid rotor supported on hydrodynamic journal bearings with micropolar lubrication has been presented. In self-excited conical whirling motion, the rotor has 2 degrees of freedom with hydrdynamic film pressure distribution in the bearing clearance. The hydrodynamic film pressure distribution has been obtained by solving the modified Reynolds equation based on the theory of the micropolar lubrication satisfying the appropriate boundary conditions. With the help of the components of dynamic tilting stiffness and damping coefficients, stability characteristics are obtained. The effects of various parameters, namely the non-dimensional micropolar characteristic length, coupling number, clearance ratio and slenderness ratio on the conical stability parameter have been investigated.
Dynamic behaviour of rolling bearings: Simulations and experiments
Authors: Stacke L-E , Fritzson D
Published: October 2002

Rolling bearings have been very common machine elements for more than 100 years. During this time, vast experiences about their steady state behaviour, e.g. their load-carrying capacity has been accumulated. Fatigue life predictions have been refined to handle clean and contaminated bearings. The understanding of the dynamic behaviour of rolling bearings has not reached the same level of maturity. Still most phenomena that occur in rolling bearings, under both normal and unacceptable operation, are dynamic in nature. These dynamic phenomena have to be studied with dynamic tools. One such tool is the bearing simulation tool, called BEAST. BEAST is based on multi-body techniques, with special focus on contact problems. It allows for studies of the dynamic behaviour of all bearing components under general loading conditions, e.g. the forces on and motions of the cage, skew and tilt behaviours of rollers and skidding of balls. A description of the most important aspects of the BEAST model and some examples of comparisons with experiments, are given in this paper.
Influence of surface topography on friction, film breakdown and running-in in the mixed lubrication regime
Authors: Lugt P. M. , Severt R. W. M. , Fogelströ J , Tripp J. H.
Published: October 2002

The influence of surface topography on the lubricant film build-up ability and the friction characteristics of potential rolling bearing surfaces has been investigated by experiments on two-disc rigs. Traction-friction torque measurements were made for a variety of surface combinations, together with measurement of the electrical resistance between the discs as an indication of surface separation. For all disc combinations, running-in of the surfaces under load at any slide-roll ratio led eventually to full film separation. Contrary to results reported in the literature, film breakdown did not always increase with slip but depended on certain aspects of the surface structure. Friction torque measurements in the mixed lubrication regime also confirmed that friction is not determined simply by an Ra value. By suitable modification of the surface topography, keeping Ra constant, friction can be varied by as much as 10 per cent.
The shear rheology of thin compressed liquid films
Authors: Bair S
Published: October 2002

Thin liquid films at elevated pressures have a unique property. A sufficiently high shear stress can be generated in steady shear without encountering the thermal softening limit or interfacial slip that it is possible to observe, in low molecular weight liquids, various non-Newtonian effects ordinarily thought to be reserved for high polymers. These include shear thinning, viscoelasticity and cohesive failure. The relevant rheology literature is reviewed. Only the properties of the continuum are addressed here, omitting near-surface effects.

Within the last 10 years in particular, both experiment and molecular simulation have shown that many analogies may be made between lubricants and liquid polymers when allowance is made for the much shorter relaxation time of the low molecular weight liquid. Shear thinning, elasticity and liquid failure are all aspects of the shear response of thin films of low molecular weight liquids at elevated pressures.
Analysis of lubrication and friction for a complete piston-ring pack with an improved oil availability model: Part 2: Circumferentially variable film
Authors: Ma M-T , Smith E. H. , Sherrington I
Published: October 2002

A model of piston-ring pack lubrication and friction which is capable of analysing non-axisymmetric conditions has been developed by the authors. Part 1 of this paper describes how the influences of relative ring locations, oil accumulation and mixed/boundary lubrication are modelled in a ring pack. An attempt has been made to validate the model by comparing its predictions with measurements from Hamilton and Moore's experiments. Results obtained from a computer simulation of a modern automotive ring pack in a circular bore, based on this model, have also been presented and discussed. In this part of the paper, a description of a bore geometry model and an approximate approach for evaluating the ring conformability are presented. In addition, two methods for determining the oil availability in a distorted bore are described. Finally, the results obtained from simulating the operation of a full ring pack in a non-circular bore under a range of conditions are presented and discussed. The results show that bore distortion can considerably reduce the power loss, but will also dramatically increase the net quantity of oil transported into the combustion chamber, when the bore out-of-roundness is excessively large.
Loss of lubricant from oil-lubricated near-starved spherical roller bearings
Authors: Wikström V , Jacobson B
Published: October 2002

The time to lubricant film breakthrough in an oil-lubricated spherical roller bearing has been measured using SKF Lubcheck for various settings of bearing load, outer ring temperature, shaft speed and oil type and viscosity. The bearings were lubricated once and then run to film breakthrough with the aim of estimating the lubricant losses under different conditions. The result of the experiments supports the theory of lubricant replenishment, and it is shown that high speed combined with high lubricant viscosity will shorten the time to film breakthrough.
The hydrodynamic phase of gearbox synchromesh operation: The influence of radial and circumferential grooves
Authors: Paffoni B , Progri R , Gras R , Blouët J
Published: October 2002

An earlier brief phenomenological study (1) allowed the authors to divide the period of synchronization into three distinct stages of operation. Each stage corresponded to different types of friction. Expressions establishing estimations of pressure, axial stress, torque and coefficient of friction were made for the case of a smooth synchromesh ring. These all depend upon the film thickness and angular velocities whose variations in time are unknown. The dynamical study presented here permits the solution to this problem. The influence of circumferential and radial grooves on different parameters (distribution of pressure on the contact area, the load borne by the film, torque transmitted by viscous friction and coefficient of friction) is presented and a comparison of the efficiencies of these two types of grooves is made. This study allows the determination of the initial values necessary for the study of the second stage, which takes place in the presence of a variable friction.
Degradation of perfluoropolyether lubricants on magnetic recording disks during sliding
Authors: Li Y , Bhushan B
Published: October 2002

Degradation of perfluoropolyether lubricants (Fomblin Z-Dol and Fomblin AM 2001) on the magnetic recording thin-films disks are studied during sliding with an Al2O3-TiC slider under high vacuum. Gaseous products generated from the head/disk interfaces are detected and monitored as a function of sliding distance using a quadrupole mass spectrometer. Effects of overcoats and surface roughnesses of disks on degradation of lubricants and coefficient of friction were also studied. Experimental results show that the gaseous products generated from Z-Dol and AM 2001 lubricants during sliding are quite similar. Degradation of both lubricants is found to take place from the beginning of sliding, and the evolution rate of decomposition fragments decreases with the sliding distance. Removal of the lubricants is accompanied by a rapid rise in the coefficient of friction of the interfaces, followed by gaseous products from the tribochemical reaction of the overcoat material. Surface roughness of the disk has an effect on the sliding distance to failure, but little effect on the decomposition of lubricant.
Full-field interferometric measurement of head-tape contact spacing
Authors: Swain R , Baugh E , Talke F E
Published: October 2002

Interferometry is the preferred measurement method for the contact spacing of the head-tape interface, due to its ease of use and high accuracy. Full-field techniques provide spacing data at all points in the field of view as opposed to a single measurement point. Dynamic interferometric measurement necessitates the use of a strobed illumination source, and thus prohibits the alteration of the fringe field to resolve the ill-constrained nature of the analysis problem. In addition, the head-tape contact problem is further complicated by the low phase gradient in the region of head-tape contact, which is often large in comparison to the field of view.

In this paper two algorithms are compared which do not require alteration of the fringe field and therefore can easily be applied to the dynamic head-tape interface. The first technique is a two-dimensional implementation of a biquadratic fit to the fringe extremes, while the second is a pseudo-spatial heterodyne technique using the two-dimensional Fourier transform. Theoretical implementation and results are presented.
Effect of environmental humidity on the friction/stiction and durability of lubricated magnetic thin-film disks
Authors: Zhao Z , Bhushan B
Published: October 2002

Drag and CSS (contact start and stop) tests were conducted to study the effects of the degree of chemical bonding of the lubricant and environmental humidity on the friction/stiction and durability of the head-disk interface. Disks with untreated, partially bonded and fully bonded films of a polar perfluoropolyether lubricant were tested at different levels of humidity. Static friction is low for unlubricated disks and disks with a fully bonded lubricant film as compared to disks with untreated and partially bonded lubricant films. Static friction gradually increases with an increase in the relative humidity and the effect of humidity at high humidity values is more pronounced in the case of disks with untreated and partially bonded lubricant films. At high humidities, durability is low for all lubricated disks but is high for unlubricated disks, as compared to that at low humidities. At low humidities, durability in drag tests is more sensitive to the degree of bonded fraction than that in the CSS tests. In general, partially bonded lubricant films are desirable for low friction/stiction and high durability and lubricated disks perform best at low to moderate humidities. Operation at high humidities must be avoided.
Friction and durability of ceramic slider materials in contact with lubricated thin-film rigid disks
Authors: Xu J , Bhushan B
Published: October 2002

Slider materials with improved static and kinetic friction and durability of the head-disk interface are required for minimum separation between the head slider and magnetic medium and miniaturization of sliders. Mn-Zn ferrite, calcium titanate, Al2O3-TiC and SiC sliders were used in drag tests, stiction tests and contact start-stop (CSS) tests. The SiC slider exhibits the best tribological performance at all humidities as compared to other sliders. Relevant mechanisms are revealed with measurement of the contact angle of perfluoropolyether (PFPE) lubricants on slider materials, lubricant transfer tests, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and Fourier transform infra-red (FTIR) analyses on the slider surfaces before and after tests. Best friction and wear performance of SiC is attributed to lubricant transfer from the lubricated disk to the slider surface and formation of tribochemical films. A lubricant layer on the slider surface protects the slider from wear and also increases the contact angle with the water film, resulting in a low meniscus contribution leading to low stiction. The tribochemical reaction forms a gel-like hydroxide layer on the SiC slider surface which performs as a boundary lubricant, leading to a low coefficient of friction and low wear.
Friction, wear and magnetic performance of metal evaporated and particulate magnetic tapes
Authors: Patton S T , Bhushan B
Published: October 2002

Metal evaporated (ME), metal particle (MP) and barium ferrite (BaFeO) magnetic tapes are leading candidates for ultra-high-density magnetic tape recording applications. Using a commercial video cassette recorder as a magnetometer and the Wallace equation, changes in the r.m.s. head output level were correlated to changes in head-to-tape spacing as tape wear occurred during play/rewind cycling tests. Interface stability and recording performance at a 0.6 μm recording wavelength were measured to bit level resolution using a drop-out counter. Some pause mode testing was done for comparison with streaming mode experiments. Methodologies to measure head and tape wear were developed and applied to worn specimens. Development of the experimental apparatus with nanometer vertical and submicrosecond temporal resolutions has enabled unprecedented understanding of the interplay of friction, wear and surface topography in a sliding contact. Waviness of ME tape and high roughness of BaFeO tape led to poor high-density recording performance as compared to the excellent performance of the flat MP tape. Interface stability generally improved as the tapes were used and worn smooth by the rotary heads, and head-to-tape spacing was reduced by about 10 nm over 1000 play/rewind cycles for the tapes. ME tape showed the least durability of all of the tapes, and damage areas initiated at high points or bumps on the tape surface were connected by lateral cracks (driven by longitudinal tension) across the tape width at tape failure after about 800 play/rewind cycles. MP tape performance improved gradually through 1000 play/rewind cycles. High asperities on the virgin tapes were severed off the tapes during the record pass, and those that remained on the tape surface increased friction force and tape wear by three-body abrasion early on in play/rewind cycling tests. Lower friction and virtually no wear were observed later in cycling tests when loose wear debris were no longer on the tape surface and the wear mechanism was adhesive. The wear coefficient in the streaming mode was larger than that in the pause mode due to abrasive particles in the contact interface in the streaming mode. MP and BaFeO tapes caused head stains on the metal core and glass surfaces of composite metal-in-gap heads. Anisotropic high tape stiffness led to asymmetrical head wear and head contours with large radii of curvature.