bluuebunny/crossref_metadata_2025 huggingface dataset:
An investigation of the hydrodynamic and mechanical behaviour of a soft nip rolling contact
Authors: Bohan M. F. J. , Lim C. H. , Korochkina T. V. , Claypole T. C. , Gethin D. T. , Roylance B. J.
Published: October 2002

A combined experimental and numerical investigation into the behaviour at the nip formed by the junction of a hard and soft elastomer covered roller is described. Experimental measurement of pressure at the film and elastomer-substrate interface are presented along with the speed differential due to microslip and thermal transients due to elastomer hysteresis. A unified finite element model of the nip is also presented where Newtonian behaviour is adopted to reflect the use of a gear oil as the lubricant in the experimental work. The system response was found to be dependent on engagement, contact width, surface speed and elastomer properties in particular. It was found that this contact type cannot be described accurately with a Hertzian model which has been adopted in all previous studies.
Contact length in grinding: Part 1: Contact length measurement
Authors: Qi H. S. , Rowe W. B. , Mills B
Published: October 2002

The nature of the contact behaviour between a grinding wheel and a workpiece in the grinding process was investigated by measurement and a model evaluation. In Part 1 of this paper measurement methods for assessment of contact length were investigated. The applied power source (APS) method was judged to give the most reliable measurement of contact length. The interpretation of contact length measurements is discussed. The contact signal can be distinguished in three stages which may correspond to the action of an active grain through the contact zone: cutting, ploughing and rubbing. The definition of contact length in grinding is discussed and it is found that it is difficult to use a single value to represent it. The measured results confirm that the measured contact length in grinding is considerably longer than the geometric contact length. There is considerable evidence that the measurements represent real contact phenomena.
Contact length in grinding: Part 2: Evaluation of contact length models
Authors: Qi H. S. , Rowe W. B. , Mills B
Published: October 2002

A non-linear curve fit method was used to identify model parameters for the prediction of contact length in grinding. The evaluation shows that the model based on a surface roughness factor demonstrates a high degree of correlation with experimental trends and behaviour. It was found that the roughness parameter R r is insensitive to depth of cut, speed ratio and material hardness, but is sensitive to the wheel-workpiece material combinations and whether grinding is conducted with or without coolant.
The behaviour of lubricants in elastohydrodynamic contacts
Authors: Moore A. J.
Published: October 2002

Difficulties once found in accounting for the tractional behaviour of lubricants in elastohydrodynamic (EHD) contacts have largely been resolved. A wealth of research stimulated by this problem has gradually unravelled the underlying rheological complexities and laid the basis for a coherent physical explanation. The understanding achieved and the problems that remain are briefly reviewed. Despite the advances made in rheological modelling, developments are not readily taken up by those engaged in theoretical investigations. Although computational complexity must inevitably rise when lubricants are modelled realistically, the penalty for not doing so must be clearly understood. The implications can be readily devined from previous research findings. Progress made in the exploration of EHD film thickness is also examined. Similarities and differences in film-forming behaviour in thick film (> 0.1 μm) and thin film (< 0.1 μm) regimes are identified and consideration given to the interpretational difficulties that may arise as EHD and boundary regimes begin to merge. Finally, a few observations are made on the value of EHD lubrication studies to automotive engineering.
Numerical prediction of the performance of gas-lubricated spiral groove thrust bearings
Authors: Yue Y , Stolarski T. A.
Published: October 2002

The objective of this paper is to develop an accurate numerical procedure for the analysis of nominally flat contacts with spiral grooves lubricated by gases. The numerical procedure, which is based on the control-volume method, enables the solutions of the non-linear Reynolds equation to be obtained without limitation in geometry and operating conditions. Satisfactory flow balance was achieved on the control volumes as well as on the whole boundary and the method was proved to be very accurate. Convergence of the method was quick for any compressibility number.

Three types of contact with spiral grooves were analysed. They were hydrodynamic bearings without interior chambers, hydrodynamic bearings with interior chambers and hybrid bearings. The effects of spiral angle, groove geometry (length, depth and width) and compressibility on performances were investigated for all possible designs.
GENSIM—a compact regression-based model for Coulomb torque in ball bearings
Authors: Todd M. J.
Published: October 2002

A computable model is described for estimating Coulomb (frictional) torque of a ball bearing under free rolling conditions. The model assumes complete microslip over the contact and makes use of precalculated polynomial regressions to approximate the roll and spin moments and the lateral traction force at each contact. Iterative solution of the force and moment balance equations (with only two unknowns) then allows the Coulomb torque to be found.

Use of regressions in this way makes the model compact and efficient at dealing with a wide range of rotational speeds and contact geometries. The range of validity of the model is discussed. From the so-far limited number of field trials, good agreement exists with other codes and experimental data.
Silicon carbide—;a potential material for magnetic recording sliders
Authors: Sharma V , Talke F E
Published: October 2002

The feasibility of using silicon carbide as a magnetic recording slider material is investigated using stiction tests with different dwell times, contact start-stop (CSS) tests and drag tests at different temperatures and humidities. The stiction and frictional properties of silicon carbide sliders are compared with standard Al2O3-TiC sliders and it is concluded that their tribological behaviour is superior to that of conventional Al2O3-TiC sliders. The results of this study show that silicon carbide is a promising material for magnetic recording sliders.
Layered flow in slider bearings
Authors: Nabhan M. B. W. , Ibrahim G. A. , Whomes T. L. , Anabtawi M. Z.
Published: October 2002

A procedure for solving the Navier-Stokes equations for the steady, one-dimensional flow of a binary water-based lubricant within an infinite slider bearing is described. The method uses an iterative process (Newton-Raphson procedure) to obtain the interface layer elevation between the liquid layers. The implementation of the Simpson rule integration technique into the equation set allows pressures along the bearing, drag on the moving bearing face, total flow into the bearing and the load-bearing capacity for a binary lubricant to be traced. Results are obtained for a range of non-linearity factors and lead to the conclusion that all the important indicators of bearing performance can be determined using the technique described.
Elastohydrodynamic film thickness for shear-thinning lubricants
Authors: Greenwood J. A. , Kauzlarich J. J.
Published: October 2002

Mineral oils and synthetic lubricants that are thickened by polymers of large molecular weight are being promoted for automobiles as well as aircraft gas turbines. These multiweight lubricants are found to have a complicated Newtonian and non-Newtonian viscosity depending upon shear rate in the bearing. In general, polymer-thickened mineral oil lubricants show a first Newtonian behaviour at a low shear rate, shear-thinning non-Newtonian behaviour at a higher shear rate and a second Newtonian behaviour at a very high shear rate, with a second Newtonian viscosity approximately equal to the base oil viscosity. Because of high shear thinning in the inlet region of rolling element bearings, predicting the film thickness using the low shear rate first Newtonian viscosity can be in error, in particular examples, by a factor of ½ for mineral oil plus 4% methacrylate thickener and 1/7 for mineral oil plus 20% polybutene thickener. The case of naturally shear-thinning silicone fluids is analysed and it is shown that the elastohydrodynamic (EHD) film thickness is nearly the same for silicones with widely varying first Newtonian viscosity.

A general EHD analysis for shear-thinning lubricants in pure rolling is presented and shown to agree with known special cases. A closed-form EHD equation for power law shear-thinning lubricants is derived, which gives very accurate results for a bearing where the inlet state of the rolling element falls in the region where the non-Newtonian viscosity is expected. A comparison with some published experimental results by Bair and Khonsari is presented.
A comprehensive study of the friction and dynamic motion of the piston assembly
Authors: Liu K , Xie Y. B. , Gui C. L.
Published: October 2002

A mixed lubrication model based on a two-dimensional average Reynolds equation is presented in this paper. It is developed for use in conjunction with a piston secondary motion analysis. The motion has been studied and the effects of structure parameters and different profiles of piston skirts on the motion are also investigated. The friction force and power loss consisting of piston skirt friction and the friction of the piston ring pack are also given.
Viscosity times density equations for five classes of lubricants
Authors: Kauzlarich J. J.
Published: October 2002

Viscometers based on wave mechanics measure absolute viscosity times density, λ = ηρ, and lubricant temperature. By using the ISO-VG (ASTM D2422) classification as a continuous (non-banded) system and fitting data for classes of lubricants at Patm, equations relating (a) absolute viscosity times density to (b) temperature and (c) ISO-VG number have been developed with good practical accuracy.

Five classes of lubricants have been correlated with ISO-VG numbers. They are paraffinics, naphthenics, PFPE (perfluoroalkylpolyether), diesters and polyol esters.
Gasoline engine valve train design evolution and the antiwear requirements of motor oils
Authors: Bell J. C.
Published: October 2002

The ability of motor oils to control valve train wear adequately is ensured by the evaluation of new formulations in a variety of standard industry tests. The most critical of these tests have single-overhead-cam valve train systems with pivoted (rocker- or finger-type) followers. Although many vehicles in service have these types of valve train, there is a strong trend towards the use of roller-follower and direct-acting tappet (DAT) systems in recently introduced passenger car engine designs. Roller designs virtually eliminate sliding between the cam and follower and in gasoline engines reduce wear and friction to low levels. Practical experience indicates that DAT systems also give lower wear and friction than pivoted systems do. The parameters affecting wear in the pivoted-follower valve trains of the Sequence VE and Peugeot TU-3 tests are analysed in comparison with equivalent DAT systems. The friction and wear benefits observed with DAT systems are shown to be inherent in the geometry and kinematics of this type of valve train. The consequences of this finding are discussed in relation to the requirements for antiwear protection provided by future motor oils.
Novel high wear resistant diamond-like carbon coatings deposited by magnetron sputtering of carbon targets
Authors: Jones A. H. S. , Camino D , Teer D. G. , Jiang J
Published: October 2002

A series of new diamond-like carbon (DLC) coatings has been produced by magnetron sputtering using in-house equipment. The new hydrogen-free pure carbon coatings were deposited by sputtering carbon targets in a pure argon atmosphere. With a metallic interlayer, they have shown improved tribological properties when compared with conventional hydrogenated DLC in pin-on-disc and reciprocating wear tests. The films have also shown the ability to perform in oil, water and dry environments, and to protect the counterpart. The method of ball cratering on wear tracks provided taper sections to allow the analysis of coating wear, interface condition and failure mechanisms. Wear rates as low as 3 × 10−17 m3/N m are shown for 100 N, 10000 cycle reciprocating wear tests in air and in water. Scratch tests have been used to assess coating adhesion with critical loads as high as 70 N. Results from nano-indentation, Raman spectroscopy, electron energy loss spectroscopy and X-ray diffraction are also reported.
Prediction of traction in elastohydrodynamic lubrication
Authors: Olver A. V. , Spikes H. A.
Published: October 2002

The prediction of traction (friction) in lubricated rolling-sliding contacts remains a challenging problem despite the development of the realistic Maxwell-Eyring-limiting shear stress model by Johnson and co-workers in the 1980s. This is largely because there is a strong coupling between the elastohydrodynamic traction and the film temperature. An added complication is that the heat conducted into the rubbing surfaces, as well as influencing traction directly, also determines the temperature in the inlet to the contact and hence the thickness of the elastohydrodynamic film.

In the present paper, the traction model of Johnson et al. is combined with a heat transfer analysis of the contacting bodies as well as the film thickness regression equation. In addition, the variations in the lubricant's rheological properties with temperature and pressure based upon the measurements of Muraki et al. have been included. The traction equation is expressed in dimensionless form and is solved using a simple iterative scheme, which in many cases allows estimation of the traction without the use of a computer. Closed-form equations for the friction are given for each of the traction regimes.
Effects of debris particles in sliding/rolling elastohydrodynamic contacts
Authors: Nikas G. K. , Sayles R. S. , loannides E
Published: October 2002

A theoretical simulation of the behaviour of debris particles in elastohydrodynamic (EHD) contacts is an effective means for obtaining information regarding the life and performance of lubricated machine elements compared with costly experimentation. The present work indicates that debris particles are often responsible for two failure modes: (a) scuffing caused by particle agglomeration in the inlet zone of an EHD contact and (b) local melting due to high heat produced by the friction of debris in sliding contacts. The present predictions are in agreement with experimental evidence in two ways: firstly, in that EHD contacts may fail because of scuffing if the lubricant becomes contaminated, where the failure due to inlet blockage by debris and eventually fluid starvation, and, secondly, in that sliding asperity contacts encounter high flash temperatures which may cause local melting and thus plastic deformations.
Observations on and the modelling of erosive wear of a long-radius pneumatic conveyor bend
Authors: Burnett A. J. , Pittman A. N. , Bradley M. S. A.
Published: October 2002

This paper describes the results of an experimental investigation of the erosive wear, and puncture, of a long-radius bend in a pneumatic conveyor when used to convey abrasive particles. Measurements were taken of (a) the local air pressure in the pipe bore (used to obtain values of the local superficial air velocity), (b) the mass of abrasive particles flowing through the pipe with time, (c) the reduction in the thickness of the bend wall and (d) the particle concentration distribution using a simple optical obscuration technique.

From analysis of the results it was deduced that an accumulation of the particles against the outside bend wall, and the shape of the pipe bore itself, caused the particles to rebound back towards the pipe bore centre-line after primary impact. This behaviour caused an intensification of particle impacts in the region where secondary impacts predominate, and this is where puncture was found to occur.

A simple empirical model is proposed for the prediction of the bend wear life. This is based upon an analogy between the particle dynamics in the bend and the optical aberration of a cylindrical mirror of similar dimensions to the pipe bore.
The influence of lubricant rheology and surface topography in modelling friction at concentrated contacts
Authors: Blencoe K. A. , Roper G. W. , Williams J. A.
Published: October 2002

The conventional picture of a boundary lubricant layer is of a film which exhibits mechanical properties more like a solid than a liquid. In this paper the influence that the form of the dependence of shear strength on pressure has on the overall friction coefficient of contacts exhibiting both model and measured surface profiles is examined quantitatively. The analysis can provide plots of coefficient of friction versus a service or load parameter which also includes some aspects of contact topography. The results indicate that variations in the macroscopic coefficient of friction which may occur as the load is varied have their roots in both the statistical nature of the surface and the mechanical response of the lubricating boundary film. The effect of running-in on friction and safe working loads can also be observed. The value of this analysis is that it attempts to combine the behaviour of films at molecular dimensions with the topography of surfaces measured at an engineering scale and so gives an indication of the full-size effects that can be achieved by chemical or molecular surface engineering.
Elastohydrodynamic solution for concentrated elliptical point contact of machine elements under combined entraining and squeeze-film motion
Authors: Jalali-Vahid D , Rahnejat H , Jin Z. M.
Published: October 2002

This paper presents numerical solution of isothermal elastohydrodynamic conjunction for concentrated contact of elastic bodies under the elliptical point contact condition. The solution includes the effect of squeeze-film motion that occurs under transient conditions due to the application of cyclic loads and/or oscillating motions in machine elements. It is shown that this time-dependent behaviour increases the load-carrying capacity of the contact which is largely responsible as a mechanism of lubricant film formation when the low speeds of entraining motion yield a low film thickness. An extrapolated oil-film thickness formula is also presented that can be employed under dynamic conditions.
Oil flow in plain steadily loaded journal bearings: Realistic predictions using rapid techniques
Authors: Martin F. A.
Published: October 2002

The aim of the paper is to produce a rapid calculation method for predicting lubricant flow in plain cylindrical journal bearings. Lubricant flow data, already available from rigorous solutions considering the effect of film reformation, are used together with experimental evidence to develop unique graphical aids and flow prediction equations. These equations, although developed from specific flow data, are of a general form and therefore will be applicable to a wide range of different bearing operating conditions.

Graphical aids, from which the flow equations are derived, give normalized actual flow as a function of normalized hydrodynamic flow for different groove geometries. The main input parameters, namely a hydrodynamic flow term Qh and a feed pressure flow term Qp, are easy to derive and have been in common use in bearing design techniques over many decades. The new design aids, in chart and equation form, give realistic flow predictions for bearings with an oil hole, a groove opposite the load line, an axial groove at the maximum film thickness position and the commonly used case of a bearing with two axial grooves. The flow prediction equations are supported by experimental data.
Use of computational fluid dynamics in hydrodynamic lubrication
Authors: Chen P. Y. P. , Hahn E. J.
Published: October 2002

This paper demonstrates the suitability of using computational fluid dynamics software for solving steady state hydrodynamic lubrication problems pertaining to slider bearings, step bearings, journal bearings and squeeze-film dampers under conditions of constant unidirectional or rotating loading. The relevance of the inertia and viscous terms which are neglected in the derivation of the Reynolds equation are briefly investigated for the above bearing and damper configurations and it is shown that the neglected viscous terms have negligible effect whereas the inertia effect predictions agree reasonably well with those reported in the literature.
Derivation of basic rheological parameters from experimental elastohydrodynamic lubrication traction curves of low-viscosity lubricants
Authors: Muraki M , Dong D
Published: October 2002

The rheological parameters characterizing the non-linear viscosity of lubricants having a low viscosity at a Hertzian contact were determined on an assumption of a parallel film, a Hertzian pressure distribution and the Eyring model expressing the relationship between the shear stress and the shear rate in an elliptical contact. Making a reasonable approximation and taking the variation in viscosity with pressure in the Hertzian contact into account, an approximate formula expressing the mean shear stress with shear rate was derived as a function of a viscosity-pressure coefficient and the representative stress determining the onset of non-Newtonian behaviour. Traction characteristics of two kinds of paraffinic mineral oil were determined with an elastohydrodynamic lubrication tester. Then, a regression analysis using a least-squares method with the proposed formula was applied to the traction measurements, from which the available rheological parameters and the effective pressure were obtained. The viscosity-pressure coefficients derived from traction measurements fall on the extrapolated line from the relation between the viscosity-pressure coefficient and the pressure in the pressure range from atmospheric pressure to 0.3 GPa obtained with a high-pressure viscometer.
Analysis of static and dynamic misaligned tilting-pad journal bearings
Authors: Monmousseau P , Fillon M
Published: October 2002

This analysis deals with the influence of misalignment (static and dynamic) of a tilting-pad journal bearing. Three different isothermal cases were compared: the initial bearing clearance and viscosity, the initial bearing clearance and effective viscosity deduced from a thermohydrodynamic analysis, and the operating bearing clearance and effective viscosity deduced from a thermoelastohydrody-namic analysis. It will be established that increasing the misalignment amplitude and dynamic load and decreasing the lubricant viscosity and clearance induce large changes in the bearing characteristics (the minimum film thickness, maximum pressure, axial flow and misalignment moment).
The effect of surface hardening on the elastic shakedown of elliptical contacts
Authors: Dyson I N , Williams J A , Kapoor A
Published: October 2002

The effect of varying both the aspect ratio and the coefficient of friction of contacts with elliptical geometry on their elastic shakedown performance has been examined theoretically for surfaces with two types of subsurface hardness or strength profiles. In stepwise hardening the hard layer is of uniform strength while in linear hardening its strength reduces from a maximum at the surface to that of the core at the base of the hardened layer. The shakedown load is expressed as the ratio of the maximum Hertzian pressure to the strength of the core material. As the depth of hardening, expressed as a multiple of the elliptical semi-axis, is increased so the potential shakedown load increases from a level that is appropriate to a uniform half-space of unhardened material to a value reflecting the hardness of the surface and near-surface material. In a step-hardened material, the shakedown limit for a surface ‘pummelled’ by the passage of a sequence of such loads reaches a cut-off or plateau value, which cannot be exceeded by further increases in hardening depth irrespective of the value of the friction coefficient. For a linear-hardened material the corresponding plateau is approached asymptotically. The work confirms earlier results on the upper bounds on shakedown of both point and line contacts and provides numerical values of shakedown loads for intermediate geometries. In general, the case depth required to achieve a given shakedown limit reduces in moving from a transversely moving nominal line load to an axisymmetric point load.
Molecular layering in thin-film elastohydrodynamics
Authors: Kato T , Matsuoka H
Published: October 2002

Liquid molecules take on a layered structure in the immediate vicinity of the solid surface and the effect of this structure on the tribological characteristics cannot be neglected when the lubricant film thickness between solid surfaces is less than several times the molecular diameter. The layered structure of liquid molecules is due to the non-uniform potential energy distribution of solid molecules. The molecular layering increases the strength of the film owing to the solid-like, ordered structure of liquid molecules and increases the liquid film thickness. In addition, the layering exerts a force (structural force or solvation force) on the solid surfaces. Although this force is small, namely comparable with the van der Waals force, the surface deforms elastically and the amount of deformation is of the order of the film thickness. This work examines the layering effect in a contact lubricated with a very thin film and shows the elastohydrodynamic (EHD) calculation in which the solvation force is involved.
Amplitude reduction of small-amplitude waviness in transient elastohydrodynamically lubricated line contacts
Authors: Venner C. H. , Morales-Espejel G. E.
Published: October 2002

By means of numerical simulations the amplitude reduction of waviness in a transient elastohydrodynamically lubricated line contact is investigated as a function of slip, under conditions representative of a highly loaded (piezoviscous) situation.

Firstly, the case of waviness on one of the surfaces is investigated. It is shown that the behaviour of the deformed amplitude as a function of the sliding velocity can be traced back to the variations in the mass flow induced by the waviness (which are forced by the squeeze term oscillations). The results are compared with recent theoretical work, showing excellent agreement. In particular, the peculiar effect of (significant) amplification of the amplitude (instead of reduction) for short wavelengths under conditions of sliding predicted in this work is confirmed by the presented results. However, for similar conditions it is almost absent if lubricant compressibility is taken into account.

Secondly, waviness was assumed on both surfaces. The magnitude of the film oscillations in the centre of the contact has been monitored as a function of the sliding velocity and amplitude ratio. Again the behaviour can be traced back to the squeeze term and mass flow variations. Furthermore, it is shown that, for the conditions considered here, accurate predictions can be obtained on the basis of the results obtained for single-sided waviness. A simple formula is presented.
Kinematics of two-sided surface features in elastohydrodynamic lubrication
Authors: Morales-Espejel G. E. , Félix-Quiñonez A
Published: October 2002

A Newton-Raphson scheme is used to solve the transient elastohydrodynamic lubrication line-contact problem with two-sided features and waviness for moderate loads. Surface features such as dents, bumps and waviness are studied; pressure and film thickness distributions in time are presented for each case. The analytical solution of Greenwood and Morales-Espejel for transient one-sided waviness is extended for two-sided waviness and the results compared with numerical simulations; they show again that the transient solution is made of two steady state components (one from each surface) travelling with each surface velocity and two propagated waves coming from the inlet (pumping-up effect from each surface) travelling with the average velocity of the lubricant. The results are in good agreement with theoretical predictions; they also establish the importance of the complementary function's shift of phase to determine the distributions of the pressure and the film thickness with time for a fixed location.
Passive magnetic bearings: The conic-shaped bearing
Authors: Bassani R , Villani S
Published: October 2002

An analytical and numerical method, based on the equivalent surface current density theory for magnetic field modelling has been used for characterizing the behaviour of some basic configurations of axially and radially magnetized ring-shaped magnetic bearings, also superimposed in a conic shape. The forces and stiffnesses versus the geometric and magnetic characteristics of rings have been calculated also in relation to the possible stability of conic bearings.
Theory of lubrication of elastomeric rotary shaft seals
Authors: Salant R. F.
Published: October 2002

Current knowledge of the principles of rotary lip seal operation is assessed through a review of the experimental foundation and the key theoretical models. Studies of the existence of the lubricating film, the load support mechanism, the sealing mechanism, the thermal effects and the followability are described.
Design aspects of modern rotary shaft seals
Authors: Johnston D. E.
Published: October 2002

Rotary shaft seals, or alternatively rotary lip seals, made from synthetic elastomers are used in a wide range of applications under very varied conditions. They provide an economical means of sealing against rotating shafts, preventing the system lubricant from leaking out and also external contamination from entering. When designing the seal to run under specified conditions, there are many factors to take into account. In this paper it is not possible to cover all the aspects of seal design nor can a comprehensive catalogue of the options available on the market be given. Instead, the reader is presented with some salient facts and guidelines on current technology and made aware of the functional problems facing the designer.
The application of plastics in dynamic seals
Authors: Duhring B , Iversen G
Published: October 2002

The employment of plastic-faced seals in reciprocating and rotary service is reviewed. Functional principles are described with applications and service parameters.
The modelling and simulation of vehicle handling Part 3: Tyre modelling
Authors: Blundell M V
Published: October 2002

This is the third in a series of four papers (Parts 1 to 4) looking at the application of computer-based analysis methods to model vehicles and simulate vehicle handling. The material contained in these papers is based on a study carried out in order to investigate the influence of suspension and tyre modelling on the outputs predicted by vehicle handling simulations. The papers deal with analysis methods, vehicle modelling (both in the previous Issue), tyre modelling and handling simulation.

In this paper an overview of the use of tyre models in vehicle dynamics is provided. This is followed by a more detailed description of three tyre modelling approaches that can be used for handling simulations. A description is also provided of a computer-based modelling system where FORTRAN routines represent the various models and a computer model of a tyre test rig is used to interrogate the models and data before integrating these into a full vehicle handling simulation. The use of this system to compare the accuracy of the tyre models under consideration is also presented. The examples used to illustrate the concepts explained throughout this series of papers have been generated using the ADAMS (Automatic Dynamic Analysis of Mechanical Systems) program.
Rolling bearing damping for dynamic analysis of multi-body systems—experimental and theoretical results
Authors: Dietl P , Wensing J , van Nijen G C
Published: October 2002

The present paper deals with the measurement and calculation of the damping capability of rolling element bearings. Rolling bearing damping is strongly influenced by the lubricated contacts between rolling elements and raceways. A theoretical model for calculating lubricant film (elasto-hydrodynamic lubrication) damping is briefly described in the first part of this paper. Furthermore, a relationship for estimating damping due to other dissipative mechanisms in the bearing is suggested. In the second part, two experimental approaches for measuring rolling bearing damping are discussed. The first (more ‘classical’) approach is based on conventional frequency response measurements and was used to verify the developed damping model regarding the influence of bearing lubrication, speed and preload. Finally, a new experimental approach for identifying rolling bearing damping is presented, eliminating some of the drawbacks of the ‘classical’ approach.
The contact and friction problem in the rolling process
Authors: Lee J D , Shen S
Published: October 2002

In this work, a new generalized non-Euclidean friction law is proposed. This friction law allows the friction coefficients in the tangential and axial directions of the roll to be different. A three-dimensional, large-strain, non-steady state elastic-plastic finite element analysis has been performed for the flat rolling process. The contact and friction problem at the interface between the workpiece and the rolls is treated rigorously. The finite element procedures are based on the updated Lagrangian virtual work equations in incremental form. The solution at each time step is accepted only if the equilibrium of nodal forces, the calculation of which is an exact treatment, is reached pointwise. The numerical results, including the interfacial normal and shear stresses, are presented and discussed.
A geometric method for determining joint rotations in spatial mechanisms
Authors: Fischer I S
Published: October 2002

An iterative procedure has been developed where the rotational displacements of a spatial mechanism are determined by a geometric method. The technique mimics the way a person would determine the rotations by making a trial assembly of the links of the mechanism and then adjusting the displacements so that links close up to form a loop. The procedure has been found to be practical and can be applied to complicated spatial mechanisms for which the mathematics are overly involved, and is particularly useful for situations when a good initial guess adequate for a successful Newton-Raphson solution is unavailable.
Real-time dynamics simulation of a closed-chain robot within a virtual reality environment
Authors: Isnard F , Dodds G , Vallée C , Fortunéa D
Published: October 2002

In this paper, an implementation of the dynamics of chain systems in a virtual reality (VR) environment is presented. The approach permits real-time dynamic robot workplace simulations as well as user immersion provided by VR. It is then demonstrated with a number of practical examples on a standard VR package. A new method for building the dynamic equations, which is developed from a linear geometric model; is presented. This method is particulary well suited to managing closed-chain systems. A tool to allow dynamic interactions between a robot and the user is then developed. The implementation is also described and the approach is validated by giving examples of robot simulations.
The UK 8 MW facility for gear noise and vibration research
Authors: Haigh J , Fawcett J N
Published: October 2002

A fully instrumented power circulating test rig is described for the study of the dynamic behaviour of large gears. The circulating torque can be varied while the rig is in operation. Instrumentation is provided for measuring dynamic transmission error, dynamic bearing force variation, vibration levels, mesh alignment and the orbits of the shafts within their bearings. The rig has a maximum pinion speed of 6000 r/min and a maximum power of 8 MW. Typical results are presented.
Transient high-frequency elasto-acoustic response of a vehicular drivetrain to sudden throttle demand
Authors: Vafaei S , Menday M , Rahnejat H
Published: October 2002

This paper presents an experimental investigation of the high-frequency structural response of vehicular powertrain systems when subjected to sudden surge in output torque demand as in throttle tip-in from coast to drive condition. The lightly damped drivetrain system has many lash zones represented by low stiffness components and thin shell elements with large modal densities. The high-frequency noise and structural dynamic modes excited under impact conditions through low lash rate zones are of short transitory nature but a major concern to vehicle drivers and other road users alike. An investigation of the root cause of these transitory events requires state-of-the art signal processing techniques at reasonably high sampling rates. This paper presents the results of an investigation into the driveline clonk problem and establishes the relationship between this phenomenon and the low-frequency shuffle of the vehicle.
Simulation of multi-body dynamics and elastohydrodynamic excitation in engines especially considering piston-liner contact
Authors: Offner G , Krasser J , Laback O , Priebsch H H
Published: October 2002

The computational simulation of the vibrational behaviour of running engines at the design stage is one of the most challenging targets in the present design analysis work of automotive engineers. In order to describe oil-lubricated body contacts (piston-liner, shaft-bearing) a detailed model of the geometrical and physical properties of the contact area is necessary. This paper presents a comprehensive simulation tool for modelling multi-body dynamics. The concept is based on dividing the non-linear mechanical system into subsystems with linear elastic behaviour and with non-linearities occurring only at the connections between these subsystems. Therefore, in the simulation model, linear elastic bodies, e.g. piston and liner, and highly non-linear connections, e.g. oil film at the inner liner wall, are distinguished. The paper describes the mathematical modelling of body structures and the calculation of the non-linear connecting forces resulting from elastohydrodynamic contacts between these bodies and outlines the methodology of the simulation procedure. Results of parametric studies, e.g. the influence of piston surface profile on the contact mechanism between piston and liner, are shown. Future aspects of the application of this method to support noise optimization of internal combustion engines as well as minimization of frictional losses and wear are discussed.
Cosimulation of multi-body-based vehicle dynamics and an electric power steering control system
Authors: Liao Y G , Du H I
Published: October 2002

Increasing use of electric power steering (EPS) systems, which affect vehicle dynamic behaviour, has prompted the need for a more effective method of analysing control systems coupled with detailed vehicle models. This paper develops an integrated simulation of an EPS control system with a full-vehicle dynamic model. Using a cosimulation technique, a multi-body-based full-vehicle dynamic model interacting with the EPS control algorithm is concurrently simulated on a single-bump road condition. The effects of EPS on the vehicle dynamic behaviour and handling responses resulting from steer and road input are analysed and compared with proving ground experimental data. The comparisons show reasonable agreement on tie rod load, rack displacement, steering wheel torque and tyre centre acceleration. This cosimulation capability may be useful for EPS performance evaluation and calibration, as well as for vehicle handling performance integration.
Design optimization of multi-body systems under impact loading by response surface methodology
Authors: Kurtaran H , Eskandarian A
Published: October 2002

Design optimization of multi-body systems is challenged by the highly non-linear and computationally expensive (for large-scale systems) nature of many multi-body responses. In this paper, a sequential approximate optimization method is presented in order to achieve accurate and efficient design optimization of multi-body systems under impact loads. The sequential approximate optimization method is obtained by coupling a conventional optimization algorithm with a statistical model building technique, response surface methodology (RSM). In this method, a multi-body optimization problem is approximated as a series of simpler subproblems, using RSM and a genetic algorithm, before it is solved by a numerical optimization algorithm. The approximate optimization method is applied to several multi-body impact problems. These include a linear impact absorber and lumped-mass systems representing simplified vehicle-barrier and vehicle-vehicle frontal impacts. The effect of the choice of various approximation methods is also addressed. The results demonstrate that the use of RSM coupled with conventional optimization methods leads to efficient and effective design tools for multi-body systems under impacts.
Control of an actively constrained robotic joint for passive deployment applications
Authors: Reedman A V C , Bouazza-Marouf K
Published: October 2002

The design and control of an actively constrained revolute joint with backlash cancellation for passively deployed devices is presented in this paper. The drive mechanism consists of two motor-driven worms coupled to a single worm wheel. A mathematical model of the system is used in order to develop a backlash cancellation strategy and computed-torque motion control algorithm. Experimental results show that the position of the joint can be successfully controlled to track a trajectory generated from a user-input force command signal while cancelling backlash at the gear interface.
On the effects of bearing settings on the dynamic performance of a three-bearing machine tool spindle assembly
Authors: Rahman A K , Aini R , Gohar R
Published: October 2002

An analytical investigation of the response characteristics of a spindle unit supported by three angular contact ball bearings is presented in this paper. A general system of equations is presented utilizing the Hertzian equation for representing the non-linear elastic deformation of the rolling elements. The system of non-linear ordinary differential equations is integrated using the Runge-Kutta Fehlberg technique in Matlab. The model is used to study the effects of bearing settings and preload on the variable-compliance vibrations. The study shows that a three-bearing spindle is characterized by a beat-type mode of response with families of sidebands around the main frequency components. The modulations of the carrier and the spacing of the sidebands are shown to be affected by change in the bearing settings. This type of response is not evident in the conventional two- or four-bearing spindle units.
Torsional damping of a back-to-back gearbox rig: Experimental measurements and frequency domain modelling
Authors: Drew S J , Stone B J
Published: October 2002

This paper is concerned with the experimental measurement and modelling of the torsional damping levels of a back-to-back gearbox rig. The aims of the investigation were to experimentally measure and analyse modal damping levels for the first nine torsional natural frequencies; to optimize damping parameters for modelling and to assess any limitations of the models for future work. Standard signal processing methods were used to determine modal damping levels from measured torsional frequency responses, with good confidence in the results. A damping sensitivity analysis for the two frequency domain receptance (FDR) models was used to determine optimum damping parameter values. Damping levels for six of nine natural frequencies were well matched with the experimental data. Discrepancies at other frequencies were attributed mainly to torsional-transverse coupling, present in the rig but not the model. Analysis of results for the ninth natural frequency determined a very low level of damping for the gearbox. It was also concluded that the model parameters may be used with confidence in a time domain receptance model for future investigations related to the test gearbox damping.
Improved model of chatter in grinding, including torsional effects
Authors: Hesterman D , Stone B
Published: October 2002

To date the effect of torsional vibration on grinding chatter has been largely ignored. Recent research on cylindrical plunge grinding has shown, however, that the torsional characteristics can signi. cantly modify system behaviour and in certain circumstances may stop chatter from occurring. In order to investigate this in more detail, both frequency and time domain solutions have been developed for a cylindrical grinding model. A description of these solution methods and a comparison of their results are presented in this paper. The potential for tailoring the torsional characteristics of the system to improve or eliminate chatter in cylindrical grinding is con. rmed by both models.
Externally pressurized gas bearings in a mixed configuration
Authors: Cazan A , Gohar R , Safa M M A
Published: October 2002

This paper analyses the stabilityof an externally pressurized gas bearing (EPB) in a series-parallel arrangement. This mixed con. guration is an alternative to the rigidly mounted single bearing with no external damping, yielding, as one extreme, a high stiffness, but a low whirl threshold speed. The other extreme is a series bearing arrangement with a full-length externally pressurized sleeve between the journal and the housing, yielding a lower stiffness but a higher whirl threshold speed. The paper shows that a mixed con. guration allows for an increase in whirl threshold speed above that for an equivalent rigidly mounted single bearing but below that for a series arrangement. However, the mixed con. guration is stiffer than the series arrangement.
Forward kinematic calibration and gravity compensation for parallel-mechanism-based machine tools
Authors: Ota H , Shibukawa T , Tooyama T , Uchiyama M
Published: October 2002

This paper describes a newly developed forward kinematic calibration method for parallel mechanisms, which identifies the kinematic parameters using the positioning data measured by a Double Ball Bar (DBB) system. This method enables precise calibration with easy measurements, which improves the static accuracy reduced by kinematic parameter errors. This paper also describes a new gravity compensation method, in which the kinematic parameters are updated gradually according to the travelling plate position. This provides real-time motion control with compensation. These methods are applied to the parallel-mechanism-based milling machine, named HexaM, and their validity is verified by simulation and experiment.
Characterization of PKM dynamics in terms of system identification
Authors: Wiens G J , Shamblin S A , Oh Y H
Published: October 2002

This paper presents a study on the dynamics of parallel kinematic mechanisms (PKMs), and the determination of which dynamics terms are candidates for identification. Using D'Alembert's method, the dynamics equations of motion are derived with inclusion of the strut masses. These equations are used to solve for the required actuator forces that are grouped according to inertial and gravitational components. Comparative observations are made using Euclidean norms and sample trajectory-based characterizations. Detailed results are presented for the University of Florida Special 6-6 PKM and two geometric variants. Observations of the Hexel PKM machine tool and Ford PKM vehicle simulator's dynamics are also presented to further demonstrate shifts in the dynamics effects. Experimental validation substantiates the simulation-based results and highlights the measurement difficulties as well as delineating a need for an iterative methodology for full dynamic system identification implementation.