bluuebunny/crossref_metadata_2025 huggingface dataset:
The Wear of Cross-Linked Polyethylene against Itself
Authors: Joyce T J , Ash H E , Unsworth A
Published: February 2007

Cross-linked polyethylene (XLPE) may have an application as a material for an all-plastic surface replacement finger joint. It is inexpensive, biocompatible and can be injection-moulded into the complex shapes that are found on the ends of the finger bones. Further, the cross-linking of polyethylene has significantly improved its mechanical properties. Therefore, the opportunity exists for an all-XLPE joint, and so the wear characteristics of XLPE sliding against itself have been investigated. Wear tests were carried out on both reciprocating pin-on-plate machines and a finger function simulator.

The reciprocating pin-on-plate machines had pins loaded at 10 N and 40 N. All pin-on-plate tests show wear factors from the plates very much greater than those of the pins. After 349 km of sliding, a mean wear factor of 0.46 × 10−6 mm3/N m was found for the plates compared with 0.021 × 10−6 mm3/N m for the pins. A fatigue mechanism may be causing this phenomenon of greater plate wear. Tests using the finger function simulator give an average wear rate of 0.22 ×10−6 mm3/N m after 368 km. This sliding distance is equivalent to 12.5 years of use in vivo. The wear factors found were comparable with those of ultra-high molecular weight polyethylene (UHMWPE) against a metallic counterface and, therefore, as the loads across the finger joint are much less than those across the knee or the hip, it is probable that an all-XLPE finger joint will be viable from a wear point of view.
Transmission of Rapidly Applied Loads Through Articular Cartilage Part 1: Uncracked Cartilage
Authors: Kelly P A , O'Connor J J
Published: February 2007

An elastostatic model of rapidly loaded articular cartilage is presented. It is assumed that the cartilage experiences little volumetric change or interstitial fluid flow while loaded instantaneously. Subchondral bone compliance and articular surface friction are incorporated. Integral representations of the stress distributions within cartilage are derived using Fourier transform techniques and the integrals are solved numerically. Localized tensile stresses are found and occur in regions close to the cartilage-bone interface as well as at the articular surface, outside the embrace of the load. The qualitative similarity between the results and those of previous investigations is explained by an elementary equilibrium analysis. The stress distributions suggest that the splits and cracks observed in diseased cartilage may be initiated, or propagated, by tensile stress.
Transmission of Rapidly Applied Loads Through Articular Cartilage Part 2: Cracked Cartilage
Authors: Kelly P A , O'Connor J J
Published: February 2007

A model of articular cartilage suffering rapidly applied loads and containing splits and fissures is presented. The possibility of cracks propagating through the cartilage collagen network is analysed using elastic fracture mechanics. Cracks are modelled using the distributed dislocation technique and the crack tip stress intensity factors are thereby evaluated. The mode I (tensile) stress intensity factors are generally much larger than the mode II (shearing) factors for cracks at the articular surface and close to, and at oblique angles to, the cartilage-bone interface, two regions where cartilage cracks have been observed. This suggests an opening, tensile mode of failure. The mode II factors are larger for cracks running along the interface. The rapidly loaded cracked cartilage model may explain the splits observed in osteoarthrotic cartilage.
Finite Element Analysis of a Total Knee Replacement by Using Gauss Point Contact Constraints
Authors: Mottershead J E , Edwards P D , Whelan M P , English R G
Published: February 2007

Finite element methods have been applied extensively and with much success in the analysis of orthopaedic hip and knee implants. Very recently a burgeoning interest has developed, in the finite element community, in how numerical models can be constructed for the solution of problems in contact mechanics. New developments in this area are of paramount importance in the design of implants for orthopaedic surgery. Modern techniques are described for finite element contact analysis and applied to two problems of stress analysis in a plastic tibial component. In the former, results are compared with a previous finite element analysis and with Hertzian solutions. In the latter, an estimate of the extent of convergence of the finite element solutions is provided.
Stress Distributions inside Intervertebral Discs: The Validity of Experimental ‘Stress Profilometry’
Authors: McMillan D W , McNally D S , Garbutt G , Adams M A
Published: February 2007

This paper evaluates a technique for measuring the distribution of compressive stress within cadaveric intervertebral discs. A strain-gauged pressure transducer, side-mounted near the tip of a 1.3 mm diameter needle, was inserted into cubes of disc tissue and into intact discs. Regardless of the position and orientation of the transducer within the tissue or disc, its output was found to be proportional to the compressive force applied to the specimen. The distribution of compressive stress was measured by pulling the instrumented needle through the specimen and the resulting stress profiles were reproducible to within 20 per cent. Profiles obtained at different applied loads showed a similar distribution of stress within the disc, suggesting that the compressive stress at any location and direction increased in proportion to the applied load. Since transducer output was also proportional to applied load, it was reasoned that it must be proportional to compressive stress within the disc. The average vertical compressive stresses acting on various regions within a disc were calculated from the stress profiles and multiplied by the cross-sectional area of each region: the resulting force was then compared with the known applied force in order to assess the calibration coefficient of the transducer. Agreement between the two forces was good, indicating that the calibration coefficient established in a saline bath was applicable to disc tissues also. However, artifactual stress peaks could be generated if the transducer was pulled across a bony asperity. It is concluded that the transducer measures the mean compressive stress acting upon it within disc tissues. Errors associated with the technique are small compared to differences in stress distributions which occur naturally, for example when intervertebral discs are loaded to simulate different postures in a living person.
Proximal Interphalangeal Joint Dimensions for the Design of a Surface Replacement Prosthesis
Authors: Ash H E , Unsworth A
Published: February 2007

The bones from 83 proximal interphalangeal joints (PIPJs) were dissected in order to determine the shape and size of the articular surfaces. The bones were modelled in acrylic dental bone cement and the original bones and replicas were then sectioned and shadow-graphed. Dimensions were taken from these shadowgraphs to be used in the design of a surface replacement prosthesis for the PIPJ.

It was found that the bi-condylar heads of the proximal and middle phalanges were circular in the sagittal plane as was the base of the middle phalanx. However, the radius of curvature of the middle phalangeal base was greater than that of the proximal phalangeal head indicating that the PIPJ is not a conforming joint. The alignment of the radial and ulnar condyles of the proximal phalangeal bones was investigated and it was found that the index and middle finger bones tended to have a more prominent ulnar condyle while the ring and little finger bones tended to have a more prominent radial condyle. This was due to a slight difference in diameters of the two condyles.

The proximal phalangeal bone lengths L ranged from 29–52 mm, maximum head widths W from 8.5–15.5 mm and maximum diameters D of the best-fit circles to the sagittal profile of the bone head from 6–11 mm. The middle phalangeal bone lengths ranged from 16–35 mm, maximum head widths from 8.5–12 mm and maximum diameters from 5–7.5 mm. The relationships and ratios between these dimensions for the proximal and middle phalanges have been calculated.
Time-Dependent Behaviour of a Force-Sensitive Resistor Plantar Pressure Measurement Insole
Authors: Pitei D L , Ison K , Edmonds M E , Lord M
Published: February 2007

Thin pressure-measuring insoles have enabled new clinical studies of in-shoe distribution of plantar pressure. One of these new devices, based on force-sensitive resistor (FSR) technology, exhibits time-varying behaviour due to the mechanical properties of the sensor materials. This has been variously attributed to initial bedding in, wear or time-dependency behaviour. Cyclic and sustained loading were used in laboratory conditions to investigate this phenomenon. The results show that the sensitivity of the sensor varies rapidly over the first minute of loading. There is also a slower long-term effect which reduces over time. From this information, procedures for optimal calibration and use are suggested.
Mechanistic and Morphological Origins of Ultra-High Molecular Weight Polyethylene Wear Debris in Total Joint Replacement Prostheses
Authors: Wang A , Stark C , Dumbleton J H
Published: February 2007

The mechanistic and morphological origins of microscopic wear debris generated from UHMWPE articular surfaces in total joint replacement prostheses are investigated in this study. It was found experimentally that the molecular chain structure at the articulating surface of UHMWPE undergoes a re-organization process due to strain accumulation caused by surface traction. This molecular re-organization process creates a fibre-like surface texture that exhibits an anisotropic behaviour similar to a unidirectionally reinforced polymer composite. This composite responds to stresses favourably if loaded along the fibre axis but unfavourably if loaded off axis. Due to the very complex multi-axial motion/loading nature at the articular surfaces in total joint replacements, the stress tensors applied to each localized asperity contact area continuously change their directions and magnitudes. These changes in the localized stress field create an off-axis loading situation at each localized contact zone with respect to the orientation of the molecular chains. Depending on the off-axis angle, failure of the molecular structure occurs in three different ways: tensile rupture at very small off-axis angles, shear rupture at intermediate off-axis angles and transverse splitting at large off-axis angles. These failure mechanisms all produce similar fibre-like wear debris. However, the failure stresses differ significantly among the three modes. According to this molecular wear theory, the preferred polymer microstructure for optimal wear resistance would be a three-dimensionally strong network connected by covalent bonds between molecular chains. For UHMWPE, a three-dimensional molecular network can be created by radiation induced cross-linking. Experiments conducted on both gamma irradiated and unirradiated UHMWPE specimens using a linear wear machine and multi-axial joint simulators confirmed the validity of the molecular wear theory.
Wear and Morphology of Ultra-High Molecular Weight Polyethylene Wear Particles from Total Hip Replacements
Authors: Campbell P , Doom P , Dorey F , Amstutz H C
Published: February 2007

The wear rate of ultra-high molecular weight polyethylene total hip replacement components is known to be influenced by various factors such as material and design. However, it is not known if these factors affect the size or morphology of the wear particles. The aim of this study was to compare the polyethylene wear particles from hip replacements of differing bearing materials and designs. Tissues were obtained at the revision surgeries of patients with surface replacements with titanium alloy or cobalt-chrome alloy femoral components up to 51 mm in diameter, and stem-type hip replacements with cobalt-chrome or alumina ceramic femoral components that were 28 or 32 mm in diameter. The polyethylene particles were isolated following tissue digestion and density gradient separation, and then studied by scanning electron microscopy. A computerized image analysis system was used to measure the diameter and length of the particles. The majority of wear particles were submicron in diameter. No systematic differences in size and morphology were found between the groups in this study. The similarity in size and morphology of the wear particles suggested that the same basic wear mechanisms were occurring in these components.
A Three-Axis Hip Joint Simulator for Wear and Friction Studies on Total Hip Prostheses
Authors: Saikko Vesa O
Published: February 2007

A three-axial, single-station hip joint simulator was designed and built for wear and friction studies on total hip prostheses. The design of the apparatus is described in detail. Continuous level walking is simulated. All three motion components, flexion-extension, abduction-adduction and internal-external rotation, are included. The motions are implemented electromechanically and the uniaxial load pneumatically. The load is measured continuously. For accurate measurement of wear, the apparatus has a loaded control joint, which also renders both the test and control joints self-centring, as they are loaded in series. The frictional torque of the test joint can be measured continuously throughout the wear test, which is an exceptional feature. Four tests of five million cycles each were completed using 32 mm diameter Co-Cr-Mo femoral heads and 5.6 mm thick, metal-backed, ultra-high molecular weight polyethylene acetabular cups as test specimens. Their wear and friction behaviour is described and discussed in relation to previous simulator studies and clinical observations. The lubricant was distilled water, maintained at body temperature. The wear of the cups was measured gravimetrically at intervals. The average wear rate was 3.9 mg/one million cycles, corresponding to 0.03 mm/year, and the average coefficient of friction was 0.01.
Estimation of Wear in Total Hip Replacement Using a Ten Station Hip Simulator
Authors: Brummitt K , Hardaker C S
Published: February 2007

The results of hip simulator tests on a total of 16 total hip joints, all of them 22.25 mm Charnley designs, are presented. Wear at up to 6.75 million cycles was assessed by using a coordinate measuring machine. The results gave good agreement with clinical estimates of wear rate on the same design of joint replacement from a number of sources. Good agreement was also obtained when comparison was made with the published results from more sophisticated simulators. The major source of variation in the results was found to occur in the first million cycles where creep predominates.

The results of this study support the use of this type of simplified simulator for estimating wear in a total hip prosthesis. The capability to test a significant number of joints simultaneously may make this mechanism preferable to more complex machines in many cases.
Effect of Counterface Material on the Characteristics of Retrieved Uncemented Cobalt-Chromium and Titanium Alloy Total Hip Replacements
Authors: Brummitt K , Hardaker C S , McCullagh P J J , Drabu K J , Smith R A
Published: February 2007

A number of total hip components explanted at revision with bearing surfaces in either cobalt-chromium-molybdenum alloy or titanium-6% aluminium-4% vanadium alloy were examined and compared to contemporaneously manufactured but unused items; particular attention was paid to the bearing surfaces which were examined visually, by low-power microscopy, scanning electron microscopy (SEM), confocal microscopy, white light interferometry, laser profilometry and conventional stylus profilometry. The cobalt alloy heads maintained their surface finish well over periods up to 12 years. The titanium implants became badly damaged over much shorter periods although even badly scratched heads continued to meet the current standards for titanium alloy heads. Analysis showed that the damage to the titanium alloy heads was not a random but a well-defined process of scarring of a consistent size created by abrasion with small particles of bone.

These damaged heads had the potential to wear the matching UHMWPE components rapidly creating large amounts of polymer debris. The finding that measurement of these damaged heads is within current standards raises concerns as to whether current standards incorporate fully the requirements for clinical performance.
An Investigation into the Origins of Time-Dependent Variation in Penetration Rates with Charnley Acetabular Cups—Wear, Creep or Degradation?
Authors: Isaac G H , Dowson D , Wroblewski B M
Published: February 2007

The total penetration of femoral heads into acetabular cups is achieved by a combination of long-term wear and early non-recoverable deformation or creep. The former is important in determining the total rate of production of polyethylene wear debris, recently implicated in the development of osteolysis and loosening, while the latter contributes to the overall penetration and the possibility of neck impingement in some designs of implants. Attention is drawn to the need to evaluate and to separate out these two physical processes in the assessment of clinical penetration rates. This is particularly important with more recent designs and combinations of materials, which are capable of operating with much reduced wear rates.

Measurements of the penetrations of metallic femoral heads into polyethylene acetabular cups in 87 explanted Charnley hip arthroplasties from 85 patients are reported and assessed. The vast majority of the acetabular cups had been sterilized by gamma irradiation and the established shadowgraph technique was used to determine the penetrations. The average implantation time was 8.75 years, with a range from 0.2–18.6 years and the average age was 55 years, covering the span 19–73 years.

The influence of sterilization procedure, implantation time and patient age are considered. Assessments of the relative magnitudes of wear and non-recoverable deformation are made by different statistical techniques and compared with previously reported data from clinical and laboratory studies.
Metal-On-Metal Articulation for Artificial Hip Joints: Laboratory Study and Clinical Results
Authors: Streicher R M , Semlitsch M , Schön R , Weber H , Rieker C
Published: February 2007

As wear is inevitable with artificial joint replacement, it has to be minimized to avoid possible aseptic loosening following osteolysis due to particle-initiated foreign body reaction. Co-Cr-Mo-C alloys have a long history with only minimum wear when articulating with themselves. This investigation shows that the choice of the alloy has an effect on the wear rate of this articulation couple. Tribological studies in a screening device, a pendulum apparatus and a hip joint simulator showed a marked influence of the environment as well as the diameter of the implants with metal-on-metal articulation. A wear-resistant combination with low friction characteristics has been developed by using a wrought Co-Cr-Mo-C alloy and reducing the implant diameter to 28 mm. Clinical wear rates are comparable with laboratory data and demonstrate the potential of the metal-on-metal articulation to solve the problem of wear-induced osteolysis of hip joint endoprostheses.
Dynamics of the Upper Limb during Performance of the Tasks of Everyday Living—A Review of the Current Knowledge Base
Authors: Buckley M A , Yardley A , Johnson G R , Cams D A
Published: February 2007

This paper provides a brief review of the published literature on the subject of kinematics and kinetics of the human arm and shoulder mechanism, specifically when performing the tasks of everyday living. Surprisingly, only a small number of papers covering functional analysis of the arm were found, and the majority of these were concerned only with the kinematics of the elbow and lower arm. Differences in experimental method and a lack of consensus as to how to model the joint axes of the human arm make the results difficult to compare. Results are normally only presented in the form of angular excursion of the arm segments, with only one paper providing data on angular velocities and accelerations. The results of the different analyses suggest that the human arm is adaptive (due to its inherent mechanical redundancy), showing the ability to perform the same tasks using differing kinematic strategies. Therefore, the principal interest for the designer of upper limb orthoses should be the work-space defined by the start and end points of the hand, and the maintenance of the desired hand orientation when performing these tasks.
The Biomechanics of Hip Protectors
Authors: Mills N J
Published: February 2007

The mode of action of one design of hip protector was investigated. A dummy femur surrounded by a flesh substitute was impacted from a range of heights while the forces on the trochanter and the surrounding flesh were measured. The protector doubled the estimated fall distance for fracture of the trochanter. The protection mechanisms are load transfer to the muscles of the thigh and energy absorption in the protector. Hip protectors could absorb more energy safely if they were thicker, or if the shell design was modified.
Mechatronics—Basics, Objectives, Examples
Authors: Schweitzer G
Published: February 2007

Mechatronics has developed world-wide into a very attractive research area. It combines in a synergetic way the classical engineering disciplines, mechanical and electrical engineering and computer science, leading to new kinds of products. How has this field emerged; in what way is it being developed in research and education; what are its objectives, its research challenges and new applications? The paper gives a survey and shows examples and typical applications.
Auto-Tuning of Low-Order Controllers by Direct Manipulation of Closed-Loop Time Domain Measures
Authors: Lawrence A J , Harris C J
Published: February 2007

Many controller tuners are based on linear models of both the controller and process. Desired performance is often predetermined or adjusted in a manner that is not directly related to the desired response. All physical processes contain non-linearities, commonly of the actuator saturating type, and many controllers contain heuristics for implementation in real systems, such as anti-integral wind-up in PID (proportional integral differential) controllers. For different processes a range of closed-loop response shapes are desired, often described by features of the response such as rise time, overshoot and settling time.

This paper investigates the possibility of basing controller tuning on closed-loop system response data such that desired performance is incorporated directly in terms of familiar time domain features or labels, thus eliminating the need for a mathematical process model and repeated tuning reformulations to achieve the desired performance. A controller tuning method named label-based neuro-tuning (LBNT) is developed and analysed by application to PID controller tuning for process models indicative of real process behaviour. Simulations and numerical investigation indicate that LBNT is a viable technique for the tuning of low-order SISO (single-input-single- output) controllers. Tuning is straightforward, flexible and copes well with process parametric changes and performance specification reformulation. The drawbacks are a complicated pretune phase, a limited selection of suitable labels and a difficulty in defining general classes of tuning problems for its application. The technique is not based on the assumption of process linearity, but due to the inability to characterize classes of input signals and operating points the types of process non-linearity are restricted. The controller may be non-linear, but must be structurally predetermined, and an input/output process model of arbitrary structure is required.
Matrix Quadratic Models
Authors: Whalley R , Mitchell D , Bartlett H
Published: February 2007

Process mechanical system models are considered and the techniques for analysis are discussed. A method for the investigation of system models which possess multiple degrees of freedom is outlined. To illustrate this general procedure the dynamical response of a pulp blender-beater, with dual impellers and five degrees of freedom, for paper and board manufacturing is computed.
Synthesizing Control Systems for Multi-Degree of Freedom Manipulators
Authors: Dalay B S , Medvedev V S , Romanova T A
Published: February 2007

Methods of analysing single input and single output control systems are well established (1). The same is not true of techniques for solving problems involving multi-inputs and multi-outputs. Such problems arise when controlling manipulators having many degrees of freedom. In this paper techniques of control system synthesis for manipulator mechanisms are considered. The method is based on locating the roots of the characteristic equation to give the desired dynamic properties for every link's servo system in the mechanism. Each link is treated independently. Simple examples to illustrate the method are presented.
Implicit Non-Linear Robust Control for an Electrohydraulic System with Uncertainties
Authors: Quintas M R , Richard E , Scavarda S
Published: February 2007

This paper deals with tracking the position of a linear cylinder moving a mass and controlled by a servovalve. The model of this system is non-linear with respect to state and input and has bounded uncertainties. Uncertainties are considered about the leakage flowrate of the servovalve and about the mass in movement. An implicit non-linear control with a robust term designed by the Corless-Leitmann approach is described step by step. Simulation results are shown in order to point out the advantages of this approach.
Output-Driven Minimal Controller Synthesis with an Adaptive Observer
Authors: Aziz K I , Thomson M
Published: February 2007

This paper describes how the minimal controller synthesis (MCS) algorithm is combined with the minimal observer synthesis (MOS) algorithm to produce an output feedback control structure in which no prior knowledge of plant state parameters is required. While the principal results relate to single-input single-output (SISO) systems, extensions to a particular class of multi-variable systems is discussed. Implementation and simulation examples are included to illustrate the effectiveness of the proposed scheme.
A Fuzzy Neural Controller Design for Use with a Non-Linear System
Authors: Chen Y-M , Gill K F
Published: February 2007

The control scheme presented utilizes both feed-forward and feedback controller elements. The former of the two elements comprises a neural network with both an identification and control role, and the latter is a fuzzy neural algorithm which is introduced to provide additional control enhancement. The feed-forward controller provides only coarse control, whereas the feedback controller can generate on-line conditional proposition rules automatically to improve the overall control action. To evaluate the performance of the controller, a simulated robot manipulator study was undertaken and the results show how well the proposed controller can minimize the error between an actual and desired end-effector trajectory.
Structure-Borne Noise Prediction in Liquid-Conveying Pipe Systems
Authors: Kwong A H M , Edge K A
Published: February 2007

This paper describes a method to predict fluid-induced structural vibrations in liquid-conveying pipe systems. A previously reported transfer matrix method has been extended to include predictions for long pipes. The length-diameter ratio of the simulated circuit has been increased from the previously reported value of 17.5 to 207. When compared to the experimental data from two different pipe configurations, excellent agreement was found between the measured and predicted resonant frequencies. However, at these resonant frequencies, the predicted oscillation levels were overestimated. This problem, which has been overlooked in previous fluid-structural coupling studies, can be resolved by the introduction of frequency-dependent viscosity in the fluid.
Non-Linear Robust Control Designs for a Remotely Operated Underwater Vehicle Depth Control System
Authors: Trebi-Ollennu A , White B A
Published: February 2007

This paper describes the heave and pitch control of a non-linear longitudinal model of a remotely operated vehicle (ROV) using three robust non-linear control techniques. The techniques are based on input-output (I/O) linearization, comprising basic I/O linearization control, I/O linearization with sliding mode control and I/O linearization with adaptive fuzzy systems.

Robustness of the designs is investigated by examining the closed-loop zero dynamics, which are shown to be bounded. The robustness of each control scheme is also investigated by varying the ROV hydrodynamic coefficients by 50 per cent. Simulation results are presented to compare the control schemes.
Partitioned Simulation of Fluid Power Systems—an Approach for Reduced Communication between Processors
Authors: Pollmeier K , Burrows C R , Edge K A
Published: February 2007

Parallel simulation of fluid power systems using the transmission line modelling method offers the benefit of increased speed of execution, but requires the system model to be partitioned on to individual processors. Fluid power systems are characterized by a transport delay in the pipelines connecting physical components, which allows component models to be decoupled; this leads to simulations involving frequent interprocessor communication and low computational performance. This paper describes a method that enables faster simulations by reducing the communication bottleneck. By adjusting the line impedance it is possible to use a larger time step for the communication between processors than the global time step. This approach requires a new filter for the approximation of frequency-dependent friction. Potential gains and the accuracy of the method are estimated. A hydraulic example circuit is partitioned in two subsystems and the new scheme leads to valuable reductions in run time without compromising accuracy.
The Influence of Forces Due to Electromagnetic Pick-Ups on the Performance of Small Turbine Flowmeters
Authors: Cheesewright R , Clark C
Published: February 2007

An analysis is presented of the influence of forces due to an electromagnetic pick-up on the calibration of small turbine flowmeters. The analysis shows how the forces can produce high starting flows. A comparison between the theory and the experimental results of calibrating a meter both with and without the electromagnetic pick-up suggests that the dominant effect of the pick-up is to produce an additional resisting torque which is almost independent of the rotational speed of the meter.
Moderated Reinforcement Learning of Active and Semi-Active Vehicle Suspension Control Laws
Authors: Frost G P , Gordon T J , Howell M N , Wu Q H
Published: February 2007

This paper is concerned with the application of reinforcement learning to the dynamic ride control of an active vehicle suspension system. The study makes key extensions to earlier simulation work to enable on-line implementation of the learning automaton methodology using an actual vehicle. Extensions to the methodology allow safe and continuous learning to take place on the road, using a limited instrumentation set. An important new feature is the use of a moderator to set physical limits on the vehicle states. It is shown that the addition of the moderator has little direct effect on the system's ability to learn, and allows learning to take place continuously even when there are unstable controllers present. The study concludes with the results of an experimental trial using vehicle hardware, where the successful synthesis of a semi-active ride controller is demonstrated.
Measurement and Modelling of Boundary Film Properties of Polymeric Lubricant Additives
Authors: Guangteng G , Smeeth M , Cann P M , Spikes H A
Published: February 2007

Experimental work using ultrathin film interferometry has shown that some polymer solutions in oil form much thicker films at slow speeds in rolling, concentrated contacts than predicted from elastohydrodynamic (EHD) theory. This behaviour can be interpreted as resulting from the polymers forming adsorbed, surface layers of enhanced concentration on the two solid surfaces. Such layers, which are typically 20 nm thick, would be significantly more viscous that the bulk solution and thus produce thicker EHD films. This concept has been supported by modelling the elastohydrodynamic point contact using control volume analysis with a layered surface viscosity. The film thickness behaviour predicted computationally using this technique is quite similar to that found experimentally using polymer solutions.
A Study of the Dependence of the Functional Properties of the Cylinder Liner Surface Layer on the Operating Conditions
Authors: Pawlus P
Published: February 2007

The paper presents results of the measurements of the surface roughness and physical properties of the outer layer of honed cylinders. The results of wear measurement of the cylinders and piston rings mating with them during running-in and during automotive engine operation under artificially increased dustiness conditions are presented and analysed. Interdependences among the state of the cylinder liner outer layer and operating parameters of the engines after running-in are also analysed. Additionally, the honed cylinder liners were used as specimens in wear resistance tests performed in the presence of lubricating oil with some amount of grinding particles. The results of the measurements of specimen and counter-specimen wear, as well as friction force and temperature at the friction surfaces during the test, are also presented and analysed. It was found that abrasive wear resistance of the honed cylinder liner depends on the operating conditions. During engine operation under increased dustiness conditions cylinder wear intensity depends mainly on the initial surface topography. Under conditions of low relative speed, low temperature and constant load, cylinder wear resistance in the case of large wear values depends on physical properties of the surface layer. However, when the amount of wear is smaller than the initial surface height, cylinder wear intensity in two studied cases depends mainly on its surface topography.
Single-Axial Groove Journal Bearings: Static Characteristics and a Temperature Prediction Technique
Authors: Pliakas P , Parkins D W
Published: February 2007

This paper describes measured data for the static characteristics of a plain hydrodynamic journal bearing with a single-axial oil supply groove located in the direction of the load vector. The journal centre static locus was measured for a variety of speed/load combinations with three values of length-diameter ratio. Full descriptions of the experimental procedures are given. Comparison is made with corresponding data from the appropriate ESDU data item. An extensive set of oil-film temperatures were also taken at each test condition.

Empirical equations were established from these measured temperature profiles. These were shown to reliably predict the complete temperature field, together with the maximum and its location, over the entire experimental range. Equations are formulated in a manner that is usable by the designer.
A Novel Variable Impedance Hydrodynamic Oil-Film Bearing: Part 2: Experimental Identification of the Steady State and Dynamic Characteristics
Authors: Ogrodnik P J , Goodwin M J , Fang Y , Roach M P
Published: February 2007

A novel form of hydrodynamic oil-film bearing has been examined experimentally to establish both steady state and dynamic characteristics. The novel bearing design is based on a 120° partial arc bearing but contains two recesses to which are attached accumulators. The facility to open or close a valve located between the accumulator and the recesses enables the engineer to effectively tune the bearing in situ. This bearing also has the benefit of being similar in cost to a standard bearing. The oil-film coefficients were obtained from the frequency response function obtained when the system was excited by a pseudo random binary sequence signal. The use of the generalized matrix inversion method to determine the oil-film coefficients from the frequency response function was found to be some 10 per cent faster than the least squares curve-fitting method. Both methods were shown to produce reliable estimates to extract oil-film coefficients.
Expressions for the Viscosity of Liquid/Vapour Mixtures: Predicted and Measured Pressure Distributions in a Hydrostatic Bearing
Authors: Saadat N , Flint W L
Published: February 2007

The present paper reports the correlation between the predicted performance and experimental data obtained from a hydrostatic thrust bearing under conditions designed to produce phase change due to viscous dissipation within the lubricant. The predicted values of pressure distribution indicate that the best correlation is obtained when the viscosity of a two-phase mixture is assumed to be the volume average of the viscosity of the individual phases.
Thrust Cone Lubrication: Part 2: Elastohydrodynamic Analysis of Crowned Rims
Authors: de Ling F dM Barragan , Evans H P , Snidle R W
Published: February 2007

In a companion paper it was shown that an elastohydrodynamic lubrication (EHL) analysis of purely conical thrust rims leads to the prediction of severe thinning of the oil film at the edges of the thrust tracks. This paper describes the results of an EHL analysis of thrust rims having a crowned geometry. It is found that the presence of crowning greatly reduces the edge thinning effect, particularly at heavy loads, with the further advantage of making the thrust rims much more tolerant to misalignment due to elastic deformation of the gears. This is at the cost of a reduction in the film clearance in the central region of the contact. Crowned geometry is proposed as the basis of a design method for thrust cones, which is to be presented in detail in a further paper.
Reproducing the Kinematic Conditions for Automotive Valve Train Wear in a Laboratory Test Machine
Authors: Bell J C
Published: February 2007

The positions of maximum wear on the surfaces of automotive cams and followers have been found to be characterized by low velocities of the point of contact over the surface in question, in combination with significant sliding velocities and thin oil films. The modelling of these critical conditions has now been extended to examine the significance of low contact velocities in two internationally accepted engine tests for the evaluation of the anti-wear properties of lubricants in valve train systems. Calculations of the contact dwell times and the corresponding sliding distances against the opposing surfaces indicate that the particular susceptibility to wear and surface distress in these systems arises from the extreme values of these parameters experienced by particular points on the surfaces during each rotation of the cam. The conditions on the follower surfaces appear to be more severe than on the cams in this respect. It is shown that kinematic conditions representative of the more severe parts of the operating cycles of the engine tests can be reproduced in a modified Amsler two-disc machine, thus enabling the use of small, flat test specimens, which are accessible to a wide range of advanced surface analysis instruments, to facilitate the study of lubricant anti-wear additive film formation.
The Effect of Engine Operating Temperature on Valve Train Wear: Mechanistic Understanding Through Used Oil Analysis
Authors: Shannon I , Bell J C , Cadu J
Published: February 2007

Analysis of used oils from a series of Peugeot TU-3 engine tests has been performed to investigate the effect of engine operating temperature on valve train wear in this engine. Iron content of intermediate and end-of-test used oil samples has been used as a monitor of valve train wear during the test and has indicated that a significant proportion of the wear occurs during the initial low-temperature phase of the test. Analysis of used oils using 31phosphorus nuclear magnetic resonance spectroscopy (3lP NMR) suggests that this is associated with low rates of zinc dialkyldithiophosphate (ZDTP) degradation during low-temperature operation, resulting in levels of extreme-pressure (e.p.)/anti-wear materials which are insufficient to provide the necessary wear protection.

Modification of the TU-3 test procedure, such that the high operating temperature phase precedes the low-temperature phase, results in very much lower observed levels of valve train wear.31 P NMR analysis indicates that this is associated with a much more rapid buildup of active ZDTP degradation products during initial high-temperature operation, which can then provide the necessary anti-wear protection during subsequent low-temperature operation.
Space Tribology in Japan
Authors: Kawashima N , Hiraoka N , Yoshii Y
Published: February 2007

This paper traces research and development in the field of lubrication technology for various mechanical elements. Japan is now in the process of developing the Japanese experimental module (JEM), one component of the US Space Station. This paper therefore emphasizes results relating to mechanical elements that will appear in JEM mechanisms. Methods of lubricating ball-bearings, sliding bearings, ball screws and gears for space use are described and some test results are given.
The Effect of Oil Supply and Sealing Arrangements on the Performance of Squeeze-Film Dampers: An Experimental Study
Authors: Levesley M C , Holmes R
Published: February 2007

This paper compares the effects on the damping capacity of a squeeze-film damper of (a) changing the number of oil-feed holes to the central circumferential oil supply groove, (b) changing the sealing arrangement from end-seals to piston-ring seals, and (c) changing the position of the circumferential supply groove. The conclusions are that much improved damping performance is achieved by the piston-ring sealed arrangement. Unlike the end-sealed arrangement it is very little adversely influenced by a reduction in the number of oil-feed holes. The damping offered by either sealing arrangement is influenced only marginally by repositioning the supply groove.
Elastoplastohydrodynamic Lubrication with Dent Effects
Authors: Xu G , Nickel D A , Sadeghi F , Ai X
Published: February 2007

A line contact elastoplastohydrodynamic lubrication (EPHL) model has been developed to investigate the effect of a dent on heavily loaded rolling/sliding contacts. The Jinite element analysis (FEA) was used to obtain the plastic deformation of the surfaces caused by the high-pressure spikes that occur in the contact due to the presence of a dent. The effects of various dent sizes on the pressure and film thickness were studied. The results indicate that by including the plastic deformation of the surfaces in the analysis, the pressure spikes that occur due to a dent in the contact are smaller than those of the purely elastic case, and local material yielding occurs, resulting in bumps at the edges of the dent. Effects of diflerent bump shapes at the dent edges were then studied in elastohydrodynamic lubrication (EHL) contacts and the results indicated that these bumps can reduce the magnitude of pressure spikes.
Solution of the Non-Newtonian Elastohydrodynamic Problem for Circular Contacts Based on a Flow Continuity Method
Authors: Holt C A , Evans H P , Snidle R W
Published: February 2007

The paper describes a numerical solution method for the point contact elastohydrodynamic lubrication (EHL) problem under non-Newtonian, isothermal conditions. The theoretical formulation of the non-Newtonian effect is general and may be applied to both shear thinning and limiting shear stress behaviour. The particular rheological model investigated in this work is the Eyring ‘sinh law’ relation. The numerical solution of the lubrication equations is based upon a control volume approach rather than the more usual methods that utilize a modified Reynolds equation. This new approach ensures that flow continuity is satisfied at the discretization level. Results are presented to show the effect of non-Newtonian behaviour on film thickness and pressure distribution in circular EHL contacts operating over a range of slide-roll ratios from 0 (pure rolling) to 1.5. Under conditions of pure rolling or low sliding there is found to be little effect of non-Newtonian behaviour, but at the highest degree of sliding the film thickness over the central, flattened area of the contact is reduced by up to 10 per cent at the highest rolling speed of 0.75 m/s.
Contact Pressure Fluctuations
Authors: Greenwood J A
Published: February 2007

This paper reintroduces an alternative plasticity index

where σm is the r.m.s. profile slope.
Lagrange Multipliers and Calmness Conditions of Order p
Authors: Yang X. Q. , Meng Z. Q.
Published: February 2007

In this paper, by assuming that a non-Lipschitz penalty function is exact, new conditions for the existence of Lagrange multipliers are established for an inequality and equality-constrained continuously differentiable optimization problem. This is done by virtue of a first-order necessary optimality condition of the penalty problem, which is obtained by estimating Dini upper-directional derivatives of the penalty function in terms of Taylor expansions, and a Farkas lemma. Relations among the obtained results and some well-known constraint qualifications are discussed.
Solution and Forecast Horizons for Infinite-Horizon Nonhomogeneous Markov Decision Processes
Authors: Cheevaprawatdomrong Torpong , Schochetman Irwin E. , Smith Robert L. , Garcia Alfredo
Published: February 2007

We consider a nonhomogeneous infinite-horizon Markov Decision Process (MDP) problem with multiple optimal first-period policies. We seek an algorithm that, given finite data, delivers an optimal first-period policy. Such an algorithm can thus recursively generate, within a rolling-horizon procedure, an infinite-horizon optimal solution to the original problem. However, it can happen that no such algorithm exists, i.e., the MDP is not well posed. Equivalently, it is impossible to solve the problem with a finite amount of data. Assuming increasing marginal returns in actions (with respect to states) and stochastically increasing state transitions (with respect to actions), we provide an algorithm that is guaranteed to solve the given MDP whenever it is well posed. This algorithm determines, in finite time, a forecast horizon for which an optimal solution delivers an optimal first-period policy. As an application, we solve all well-posed instances of the time-varying version of the classic asset-selling problem.
Variational Inequalities and Economic Equilibrium
Authors: Jofré Alejandro , Rockafellar R. Terry , Wets Roger J-B.
Published: February 2007

Variational inequality representations are set up for a general Walrasian model of consumption and production with trading in a market. The variational inequalities are of functional rather than geometric type and therefore are able to accommodate a wider range of utility functions than has been covered satisfactorily in the past. They incorporate Lagrange multipliers for budget constraints, which are shown to lead to an enhanced equilibrium framework with features of collective optimization. Existence of such an enhanced equilibrium is confirmed through a new result about solutions to nonmonotone variational inequalities over bounded domains. Truncation arguments with specific estimates, based on the data in one economic model, are devised to transform the unbounded variational inequality that naturally comes up into a bounded one having the same solutions.