bluuebunny/crossref_metadata_2025 huggingface dataset:
A Performance-Based Design Methodology for Glass-Reinforced Plastic Pipework and Fittings
Authors: Eckold G C
Published: February 2007

This paper is concerned with the development of a design methodology for glass-reinforced plastic (GRP) pipework and fittings. As the use of GRP material becomes more widespread procurement is being increasingly carried out on a performance basis against specified pressure ratings. This is analogous to schedules in metallic piping systems. However, there are, as yet, no design methods available that are able to relate the test data obtained in the measurement of long-term performance under simple internal pressure conditions to the wider requirements of pipe components in service. The most significant outstanding issue is the effect of material anisotropy and the need to cater for the wide variety of possible loading situations present in a typical piping layout. In this paper a rationale is presented based on a simple analysis which employs a limited range of measured data to derive an allowable design envelope. This is then used to develop a qualification procedure which can be used to establish pressure ratings and takes into account the behaviour of GRP materials under likely imposed loads.
Vibratory Stress Relief—An Investigation of the Underlying Processes
Authors: Walker C A , Waddell A J , Johnston D J
Published: February 2007

The use of vibration to reduce residual stress levels in fabrications is potentially an attractive alternative to thermal annealing. The application of the process has hitherto been limited by the lack of coherent theory of operation. In this study, residual stresses were introduced into a low-alloy steel EN3b by rolling. It was shown that prolonged low-amplitude vibration at 100 Hz induced a stress relaxation of as much as 40 per cent, where the original level was close to yield. A model has been developed to explain the diverse effects resulting from low-amplitude vibration; the model involves the motion of dislocations under the influence of the combined residual and external cyclic stress fields. This model, which has been validated by detailed X-ray line profile analysis and elasticity measurements, is an extension to the currently available explanation for VSR (vibratory stress relief). The standard model, which assumed the need to exceed the local yield stress, only comes into operation at the higher levels of applied stress amplitude. The development of accurate and validated methods for the application of VSR may now be contemplated.
Analysis of the Mechanics of Die Drawing Polypropylene Through Strain Rate Controlled Dies
Authors: Ulas I , Craggs G
Published: February 2007

The die drawing of polymers in the solid state is now an established process for achieving molecular orientation in drawn products and an enhancement of their mechanical properties. A mechanics analysis is presented of the drawing of polypropylene through strain rate controlled dies, where the strain rate is either constant, increasing at a uniform rate or decreasing through the die. The stress in an element of material being drawn is determined from equilibrium considerations and application of the Tresca yield criterion. Flow stress data are deduced from uniaxial stress-strain-strain rate tests and applied to the problem using equivalent stress-strain concepts.

Results are presented of axial stress, flow stress and die wall pressure throughout the dies and show that polypropylene can prematurely leave contact with the die wall, particularly in decreasing strain rate dies at high drawing speeds. Increased friction of the die wall and increased drawing speed cause this ‘loss of contact’ point to move progressively downstream in all die cases. Theoretically predicted drawing loads show acceptable agreement with experimental test results when low values of friction coefficient are assumed.
The Dependence of Power Consumption of Pneumatic Conveying Systems upon Bulk Material Properties, Pipeline Bore and Routing, and Mode of Flow
Authors: Schuster T , Bradley M S A , Reed A R
Published: February 2007

In this paper the dependence of the power consumption of pneumatic conveyors upon conveyed materials, pipeline route and bore, and mode of flow has been examined. The findings are that, with different materials and modes of flow, not only is the amount of power consumed very different but it varies in different ways with pipe bore and routing. Additionally it has been found that, for any given conveying system, the choice of air mover also has a strong influence on the power requirement.
The Monitoring and Control of a Retail Food Container Filling Machine
Authors: Zeng Z , Whalley R , Hull J B
Published: February 2007

This paper details the development of a monitoring and control system for level regulation in bottles during filling operations. The dispensing system used is a multi-fill carousel employing vacuum filling of up to 16 bottles simultaneously. Normal production rates are around 400 bottles per minute. In the scheme proposed, ultrasound technology and computer control are used to regulate fluid level in order to achieve a rapid response system that is flexible and highly accurate. Further industrial applications of the technology are indicated.
The Approximate Location of Damage through the Analysis of Natural Frequencies with Artificial Neural Networks
Authors: Kaminski P C
Published: February 2007

An effective and reliable damage assessment methodology is a valuable tool for the timely determination of damage and the deterioration stage of structural members as well as for non-destructive testing (NDT). In this work artificial neural networks are used to identify the approximate location of damage through the analysis of changes in the natural frequencies. At first, a methodology for the use of artificial neural networks for this purpose is described. Different ways of pre-processing the data are discussed. The proposed approach is illustrated through the simulation of a free-free beam with a crack whose natural frequencies were obtained experimentally.
FRC Tanks, Vessels and Pipework—2
Authors: Misty J
Published: February 2007

The second seminar on ‘FRC tanks, vessels and pipework’ was held at the Headquarters of the Institution of Mechanical Engineers in London on 10 April 1995.
Phenolic Composites—Novel Developments in Products and Processing
Authors: Orpin M R
Published: February 2007

Recent developments in the nature of phenolic resins and catalysts (for example, Cellobond FRP range from BP Chemicals Ltd) for the production of fibre-reinforced composites are presented. These are shown to be making significant steps towards meeting the needs of both fabricators and end-user markets such as the rail industry. In addition, novel phenolic composite products are discussed which may be of value in the production of future rail vehicles where fire safety and weight reduction are becoming increasingly important.
Design for the Alleviation of Transportation Fatality Risk by the Implementation of New Light Rail Transit
Authors: Huston R , Cardimen P , Halperin K
Published: February 2007

There is a tendency for each engineering community to think of safety only in the context of its own system. Rail engineers think of the safety of the existing rail system and road engineers of the existing road systems. The important safety, however, is that of the entire population. And that safety is considerably higher on rails than on roads. The research question then arises as to whether it is possible to correct an existing road safety problem by design of a rail system. Given the human lives at stake, it is a question worth answering.

A design is presented for correction of the highest death rate road in a particular urban area by installation of a light rail system. The road is a 2.6-mile (4.2-km) stretch of urban arterial that has had 18 fatalities in the past thirteen years. The light rail system is shown to be a possible solution to the problem, both from the standpoint of design and from that of economics. It is predicted that the new design should prevent 1.25 fatalities per year.
Vertical Interaction between Train and Track with Soft and Stiff Railpads—Full-Scale Experiments and Theory
Authors: Fermér M , Nielsen J C O
Published: February 2007

The vertical dynamic interaction between a running freight wagon and a tangent railway track has been investigated experimentally and numerically. Standard solid wheels without and with wheelflats were instrumented for measurement of transient vertical wheel/rail contact forces. Accelerations and strains in the track structure were measured in parallel. The location of the instrumented wheelset in relation to the instrumented portion of the track was determined at each instant of time. A portion of the track was equipped with railpads considerably stiffer than the soft ones used as standard in Sweden. The influence of train speed and axle load on dynamic responses was studied and compared for the two test sites. Track parameters determined at the test site were used as inputs to a mathematical model. Numerical results show reasonable agreement with measured responses. In the presence of wheelflats, measured dynamic contact forces were largely affected by pad stiffness and axle load. For some of the loading cases investigated, it was observed that soft pads did not always lead to lower contact forces. Maximum dynamic responses generally increased with increasing train speed.
Prediction of Railway Disc Brake Temperatures Taking the Bearing Surface Variations into Account
Authors: Dufrénoy P , Weichert D
Published: February 2007

For several years, increasing velocities and loads on modern trains have pushed the braking materials more and more to their limits. The temperatures reached by disc brakes are very difficult to predict locally because of the discontinuous contact surface between disc and pads and because of the non-uniform pressure distribution on this surface. This contact problem may also vary rapidly with time during a single braking and from one braking to the next one. The present work proposes a two-dimensional numerical approach calculating the evolution of the bearing surface between disc and pad, with an impact-contact analysis coupled with a thermomechanical resolution. The distribution and the evolution of the temperatures are calculated and compared to experimental measurements. The method can be used to assess the performance of braking systems and gives valuable indications for braking design.
Tiger—a Study in International Collaborative Helicopter Engineering
Authors: Humphrey G
Published: February 2007

A number of European procurement programmes of defence equipment are undertaken as international collaborative ventures. It might be imagined that the inherent management complexities of such undertakings would create overpowering temptation to settle for technically unimaginative solutions, but nothing could be further from the truth. The Eurocopter Tiger helicopter, which is under development for the French and German governments, and is also being offered to the British Ministry of Defence, is a good example of a ‘high tech’ programme. The author reviews the management arrangements and provides a few examples of the advanced engineering that have been incorporated in this new helicopter.
Evolution of Aviation and Propulsion Systems: The Next Fifty Years
Authors: Allen J E , Armstrong F W , Denning R M
Published: February 2007

The prospects for the longer-term evolution of aircraft and their propulsion systems are explored, taking a fifty year time-frame. It is considered that the most likely global scenario features continued economic development, aided by the introduction of fuel from alternative sources to offset a progressive shortfall in the availability of oil from relatively accessible fields. Pollution and other environmental problems are foreseen as exerting an increasing influence on decision making.

Assuming such a scenario, the aviation fuel prospect is considered. It is concluded that the most likely alternative fuel for aviation in the next fifty years is some form of manufactured liquid hydrocarbon resembling current aviation kerosine, rather than liquid hydrogen, which is a candidate for later introduction. An assessment is offered of the classes of flight vehicle that will be required for civil and military purposes in the time-frame under review. The implications with regard to propulsion systems are then considered, with a discussion of design objectives, technological challenges and research requirements.
The Application of Scanning Laser Doppler vibrometry in Aero-Engine Development
Authors: Hancox J , Staples B C , Parker R J
Published: February 2007

The integration of a laser Doppler vibrometer with computer controlled scanning mirrors provides a versatile system for vibration measurement. Such an instrument has been developed at Rolls-Royce, with the objective of using it for vibration measurement in both the laboratory and in a hostile environment such as an engine test cell. This paper describes this system together with a number of examples of its application to vibration testing in aero-engine development.
A Method of Strain and Stress Analysis for Failure Prediction in Laminated Composites
Authors: Ardiç E S , Bolcan C , Kayran A
Published: February 2007

In this study, a method of strain and stress analysis is developed to predict the failure initiation in laminated composites containing two or more different kinds of laminae. In principle, the method developed in this study is similar to non-local elasticity, but the long-range interactions are considered on the strains instead of material moduli, and the method is developed and applied as a realistic and practical one. Firstly, the strain fields in each layer are determined separately and then these strain fields are used as input in-layer strains to obtain the strains and stresses in fibres and matrix in each layer individually. The principal strains and stresses in fibres and matrix are calculated in order to predict failure initiation. The method is applied to a sample problem and numerical results are presented as well as a comparison of the layer stresses with the results from the classical plate and shell theory.
The Tearing of Petalled Holes in 2014–T651 Aluminium Alloy Produced by Explosions and its Possible Contribution to the Loss of Aircraft by Sabotage
Authors: Edwards M R , Owen C L
Published: February 2007

Petalled holes were formed in thin 2014–T651 aluminium alloy sheet by blast, explosively formed projectiles and shaped charges, as well as by explosives placed directly on the sheet. Tensile testing of the sheets containing the various holes showed no macroscopic plasticity. Analysis of the lengths of petalled cracks produced by 1.26 g charges of an RDX-wax explosive in direct contact with a sheet, acting as a diaphragm in a canister, showed that these were increased by 50 per cent if the canister was pressurized to 0.6 MPa (6 bar), indicating that the length of petalled cracks produced by an explosion was affected by the stress applied to the thin sheet. Calculations showed that the strain energy in the diaphragm was 17.5 J, while the energy required to produce the extra cracking was estimated to be 57 J, assuming that the work required to extend the crack is 0.1 MJ/m2. This suggested that the energy stored in the gas, as well as that elastically stored in the diaphragm, was used to extend the cracks. The lengths of petalled cracks produced by 55 g charges of the RDX-wax explosive at 400 mm stand-off were substantially less than those produced by the 1.26 g charges placed in contact with the sheet, indicating the beneficial effect of the attenuation of the blast wave by stand-off and the greater damage caused by the presence of explosives in contact with or very close to the sheet.
New Large Aircraft
Authors: Travers Captain P O C
Published: February 2007

This is a review of the operational and commercial requirements that affect the design and hence the operating costs of the next generation of new large aircraft.
A New Approach to the Design of the Large Turbofan Power Plant
Authors: Wilde G L
Published: February 2007

The lower direct operating costs of the Big Twin subsonic transports encourage the building of ever larger turbofan engines installed on the wings. The steadily improving reliability of the turbofans and the good safety statistics of twin-engined aircraft over many years encourages this trend.

Fuel economy is still the dominant factor in determining the design layout of turbofan engines. It requires the combination of the highest possible thermal efficiency of the gas generator core of the engine with optimum propulsion efficiency of the power plant as a whole in cruise flight, allowing for engine nacelle drag and nacelle to wing interference drag. High thermal efficiency and high propulsion efficiency together, lead to relatively small volume flow rate gas generators and high volume flow rate propulsion fans. The resulting geometrical mismatch between the compressors and turbines of the principal turbomachinery components within the engine, introduces losses that penalize the performance gains expected from theoretical considerations of thermodynamics cycle and component efficiencies alone.

The paper presents two possible turbofan design layouts intended to overcome the limitation of current turbofan power plant designs. The aim is to design a power plant with the highest thrust per unit frontal area combined with the highest air miles per gallon in cruise flight.
An Engineer'S Viewpoint on Design and Analysis of Aircraft Structural Joints
Authors: Hart-Smith L J
Published: February 2007

The design of structurally efficient joints in aircraft fuselage structures and wing skin splices is addressed. It is contended that the joints should be designed first and the gaps in between filled in afterwards, taking pains not to optimize the basic structure first and then discover that it either cannot be assembled or that, when it is assembled, it is full of weak-link fuses. Both adhesively bonded and mechanically fastened joints are covered. Analogies are drawn between the characteristics of both classes of joints. The aspects of static joint strength and fatigue lives are included. The work is applicable to metallic as well as composite structures, and covers both high-load wing joints which have already been tested and new ideas for fuselage splices which have not. The effects of flaws and defects are associated with the need for damage tolerance, particularly in fuselage structures.
Rapid Method for Spacecraft Sizing
Authors: Cuerno-Rejado C , López-Díez J , Sanz-Andrés A
Published: February 2007

In this paper, a rapid method for spacecraft sizing is presented. This method is useful in both the conceptual and preliminary design phases of scientific and communication satellites. The aim of this method is to provide a sizing procedure similar to the ones used in the design of aircraft; actually by determining the mass of all the spacecraft subsystems. In the Introduction, the importance of an accurate initial mass budget in the design of satellites is emphasized. Literature about this topic is not very extensive and most of the existing methods have been recapitulated. The methodology followed in the proposed procedure for spacecraft mass sizing is based on these methods. Data from 26 existing satellites have been considered to obtain correlations between each subsystem mass and the mass of the whole spacecraft.
An Evaluation of the Energy Absorption of Laminated Composite Plates
Authors: Lavoie J A , Morton J , Jackson K
Published: February 2007

The energy absorption characteristics of continuous fibre reinforced laminated plates made from three material systems: APC-2 (graphite/PEEK), AS4/3502 (graphite/epoxy), and a hybrid AS4/Kevlar-49/3502 composite, have been investigated. The effects of geometric scaling of specimen size, ply-level and sublaminate-level scaling of the stacking sequence, and trigger mechanism on the energy absorption capability in edgewise compression were evaluated. Scaling method and matrix material were found to influence the preferred crushing mode and energy absorption efficiency of the composite plates. Energy absorption and crushing modes where found to be similar to that of composite tubes.
Minimum Induced Drag of a Three-Surface Ultra High Capacity Aircraft
Authors: Ruiz-Calavera L P , Martínez-Val R , Gómez-Blanco R
Published: February 2007

The aerodynamic properties of a particular three-surface ultra high capacity airplane are determined by means of a hybrid vortex-lattice/panel method model. The study includes effects of aerodynamic and structural design limitations. It is shown that stable or slightly unstable configurations are compatible with low values of induced drag, and that the main design constraints are the maximum allowed lift coefficient of wing sections and the canard surface loading.
Superplastic Forming and Diffusion Bonding of Aircraft Structures
Authors: Bottomley I E
Published: February 2007

The diffusion bonding (DB)/superplastic forming (SPF) manufacturing process, for titanium 6A1/4V material, has been developed within British Aerospace for the manufacture of military aircraft components. Diffusion bonding of titanium alloys offers the potential for parent metal joint strengths, and when combined with SPF, complex aircraft components offering significant cost and weight savings can be manufactured. This paper briefly describes the DB/SPF development programme and the manufacture of the Tornado heat exchanger ducts and European Fighter Aircraft (EFA) foreplane components.
Active Control of Surge in Multi-Stage Axial-Flow Compressors
Authors: Escuret J-F , Elder R L
Published: February 2007

Non-linear simulations of a surge model with and without control are investigated using a Runge-Kutta scheme. This shows how some non-linearities in the flow model can affect the normal operation of a linear controller and the problem of actuatop sensor locations. Also, the amplitudes and frequency response required of the actuator to retain stability can sometimes be found to exceed the practical limitations.
European Civil Aviation Safety Regulation—an Update of the Joint Aviation Authorities
Authors: Ashford R
Published: February 2007

The paper reviews airline safety in recent years and argues the case for a need to ensure a continuing improving trend. The role of the European Joint Aviation Authorities (JAA) is described and the need for the JAA and the United States agency, the Federal Aviation Administration (FAA), to harmonize their safety regulations is explained. The approach to new technology and the case for the application of some of the latest requirements to derivative' aircraft are discussed. Some recent controversial issues related to new technology are described and general conclusions drawn.
Actuation System Requirements for Advanced Short Take-Off and Vertical Landing Powerplants
Authors: Northcott A J
Published: February 2007

Most of the powerplant concepts currently being studied for advanced short take-off and vertical landing ASTOVL) aircraft require significantly more actuation than conventional powerplants. This paper highlights the challenge being faced by the powerplant and acuation system designers to produce an acceptable solution. Typical concepts and their operation are described, and using this as a basis, it is shown that the actuation system will impact significantly on the viability of the concepts. Most of the actuated features are flight safety critical in the jet-borne flight regime, and considerable care will be needed to achieve a safe system without unacceptable penalties on cost, weight and reliability. The projected timescale of the ASTOVL aircraft (entry into service in 2010) means that there is time for radical solutions to be developed and work to achieve these solutions is already underway.
The Application of Level II Reliability Theory
Authors: Langley R S , Ribas C S
Published: February 2007

Level II reliability theory provides an approximate method whereby the reliability of a complex engineering structure which has multiple strength and loading variables may be estimated. This technique has been applied previously to both civil and offshore structures with considerable success. The aim of the present work is to assess the applicability of the method for aircraft structures, and to this end landing gear design is considered in detail. It is found that the technique yields useful information regarding the structural reliability, and further it enables the critical design parameters to be identified.
Lateral and Directional Stability and Control in Air-to-Air Refuelling
Authors: Bloy A W , Jouma'a M
Published: February 2007

Application of a wake roll-up method coupled with the vortex lattice method and approximate expressions for the receiver fuselage effect have been used to determine the induced loads on a Hercules receiver aircraft behind a KC10 tanker. The induced loads depend strongly on the vertical position of the receiver wing and fin relative to the tanker wing wake. In the case of steady sideslip there is a large decrease in the directional stability of the receiver as quantified by the gradient of the rudder angle versus sideslip. This is due mainly to the combined effects of the yawing moments due to bank, yaw and side displacements. Minimum directional stability corresponds to the tip of the receiver fin intersecting the tanker wing wake. The associated aileron angle is two to three times the value in free air in agreement with flight test data. Solution of the linearized equations of motion gives three lateral characteristic oscillations for the air-to-air refuelling case. These include the usual Dutch roll oscillation, a highly damped rolling oscillation and a divergent oscillation involving mainly bank and side displacements.
Contact Pressure Prediction in Total Knee Joint Replacements Part 1: General Elasticity Solution for Elliptical Layered Contacts
Authors: Jin Z M , Dowson D , Fisher J
Published: February 2007

A general elasticity contact theory has been developed, to predict the contact area and the contact pressure in total knee joint replacements with elliptical contacts where the thickness of ultra high molecular weight polyethylene (UHMWPE) is similar or less than the contact half width. The interfacial boundary condition between the UHMWPE component and the underlying metal substrate has been considered to be either perfectly bonded or perfectly unbonded in the model. Poisson's ratio for UHMWPE has been assumed to be 0.3 or 0.4. The effect of the thickness of the UHMWPE layer on the contact area and the contact pressure has been examined. The predictions of the maximum contact pressure and the contact area have been presented in non-dimensional forms and can readily be applied for typical design configurations of current total knee joint replacements. Furthermore, the present results can readily be applied to design considerations for total knee joint replacements to reduce contact stresses within the UHMWPE component.
The Influence of Geometrical Distortions of Three-Dimensional Finite Elements, Used to Model Proximal Femoral Bone
Authors: Vander Sloten J , van der Perre G
Published: February 2007

A realistic three-dimensional finite element model of the proximal femur requires the use of irregularly shaped elements to represent this geometry, unless the geometry is considerably simplified. The authors have investigated the influence of different types of element distortions upon the accuracy of two stresses which are relevant in the proximal femur: the bending stress and the tangential (hoop) stress. While most angular and geometric distortions did not influence the bending stress significantly, the position of the middle node on the edge of a quadratic element was very critical, as were some types of element skewness. The hoop stresses can only be calculated accurately if the geometry is modelled as well as possible by a cylinder, and not by a cone.
Geometrical Properties of the Ovine Tibia: A Suitable Animal Model to Study the Pin-Bone Interface in Fracture Fixation?
Authors: Finlay J B , Hurtig M B , Hardie W R , Liggins A B , Batte S W P
Published: February 2007

To determine whether dimensional scaling (relative to the human) is necessary for screwed pins used in externally applied fracture fixation studies on sheep, geometrical data were determined for six ovine tibiae. Each tibia was potted relative to a lengthwise reference axis and sectioned at 5 per cent length intervals over its central 80 per cent. Enlarged (280 per cent) images of each cross-section were digitized at 1 mm increments around the periphery of the periosteal and endosteal surfaces, the data were digitally filtered, and geometrical properties were computed to include cross-sectional area A, maximum and minimum second moments of area (Imax and Imin), polar second moment of area J, and effective polar second moment of area Jeff. Proportional scaling of geometrical properties with respect to bone length (L2 for A, and L4 for second moments of area) significantly (p < 0.01) decreased the coefficient of variation in data by an average 36 per cent. From 30–90 per cent distal, J eff for the ovine tibia is smaller but within 7 per cent of J—in stark contrast with the human tibia, where Jeff has been reported as 70–80 per cent of J over the same tibial length. While previous ovine studies involving external fixator pins have employed the same diameter of pin as has been used in humans (that is 5 or 6 mm), a ‘first-order’ approximation of the data for A, Imax, Imin and Jeff suggests these pins should be scaled down to 4 mm and 4.75 mm respectively for use on the ovine tibia over the range 25–80 per cent distal along its length.
The Influence of Manufacturing Methods on the Function and Performance of a Synthetic Leaflet Heart Valve
Authors: Leat M E , Fisher J
Published: February 2007

There is considerable interest in polyurethane synthetic leaflet heart valves for both ventricular assist devices and direct implantation in the body. Two different manufacturing methods, thermal forming, and dip casting, of the leaflets have been investigated. There were only small differences in the hydrodynamic function of the valves made by the two methods. However, the durability of dip cast valves was far superior to the thermally formed film fabricated leaflets, with all of the dip cast valves reaching 160 million cycles without failure. This study indicates that a correctly designed and manufactured polyurethane synthetic leaflet heart valve has the potential for long-term implantation in the body.
Cushion form Bearings for Total Knee Joint Replacement Part 2: Wear and Durability
Authors: Auger D D , Dowson D , Fisher J
Published: February 2007

Cushion knee prostheses have been designed and constructed to produce larger initial contact areas and thicker theoretical film thicknesses than a conventional UHMWPE (ultra-high molecular weight polyethylene) joint. The compliant bearing had a flat tibial component which imposed fewer biomechanical constraints and allowed greater range of movement. Wear tests were performed in a knee joint simulator and creep tests were carried out in a servo-hydraulic apparatus. Various failure modes of cushion joints that require further study were identified. However, the results showed that adequate durability was achieved from a 20 MPa polyurethane material in joint simulating tests carried out over 0.5, 1.0 and 5.0 million cycles. Most importantly, during these tests, no detectable wear debris was generated. It is believed that this is the first time that the full potential of cushion bearings has been demonstrated in a joint simulator over periods corresponding to about five years of service in vivo.
Determination of the Curvatures and Bending Strains in Open Trileaflet Heart Valves
Authors: Corden J , David T , Fisher J
Published: February 2007

The leaflets of trileaflet artificial heart valves manufactured from polyurethane, gluteraldehyde-treated porcine aortic valves and pericardial tissue are subject to cyclic stresses and strains which can reduce the lifetime of the implanted valves through leaflet calcification and fatigue failure. A detailed knowledge of the stress state within a valve leaflet throughout a cardiac cycle is desirable in order to improve the geometry of the valve leaflets and ultimately improve the valve performance. An experimental method to evaluate the radius of curvature at the free edge of the open valve leaflet is presented. The technique has been applied to polyurethane trileaflet heart valves manufactured within the authors' laboratory and to commercially available bioprosthetic valves in the fully open position under steady and pulsatile flow conditions. Simple bending theory has been applied to the polyurethane valves to calculate bending stresses and strains at the free leaflet edge based on the measured curvature. The results showed that in the fully open position the highest curvatures occurred at the commissural regions for all the valves analysed. Additional areas of high curvature were present along the free leaflet edge. Average curvatures as high as 0.85 mm−1 were observed at the leaflet commissures for the polyurethane valves with a resultant bending stress of 0.72 MPa. The porcine bioprosthetic valves showed average curvatures as high as 2.5 mm−1 which also occurred at the leaflet commissures. The results of the study have been compared to values of stress obtained from numerical analysis of closed polyurethane valve leaflets reported in the literature. The highest stresses in the closed position also occurred at the valve commissures and were of the same magnitude, but greater than the stresses predicted in this experimental study of polyurethane valves in the open position.
A Measurement System for the Recognition of Arm Gestures Using Accelerometers
Authors: Harrington M E , Daniel R W , Kyberd P J
Published: February 2007

This paper describes a strategy to measure arm movements using accelerometers for the computer recognition of arm gestures. Gesture recognition is being investigated as an alternative method of computer input for people with severe speech and motor impairment; the emphasis is on the needs of people with athetoid cerebral palsy who have difficulties with existing computer input devices. An initial model-based approach to estimate the kinematic motion of the arm from acceleration measurements is given, followed by the chosen measurement scheme. The current system considers the forearm as a rigid body and uses two data streams derived from four linear accelerometers. By treating these signals as outputs from postulated mechanical models, the data are reduced to two series of step inputs that are appropriate for pattern classification and recognition. Although this does not in any way model the arm, the concepts used are based on the type of driving signals expected in the control of arm gestures. Initial experimental results show that the information content of gestures is preserved by this data parameterization.
Forces Generated in Guide-Wires when Drilling Human Bone
Authors: Shuaib I , Hillery M
Published: February 2007

In orthopaedic surgery guide-wires are extensively used for the drilling of pilot holes in human bones to allow further drilling, reaming and screw-tapping to take place in the repair and reconstruction of fractures. The guide-wires are generally 1.5 to 2.5 mm in diameter and have a three-faceted point with or without a screw thread. This paper describes drilling tests carried out using both types of guide-wire and these are compared with results obtained from a two-faceted geometry developed during this research. Tests were performed on the heads of femurs which had been removed during hip arthroplasty. A variable speed drilling machine together with a very sensitive drilling dynamometer were used for measuring the torque and thrust during the experimental stage of the research. This equipment was developed as part of an overall research programme into the mechanics of drilling of human bone. The indications are, firstly, that little advantage is gained by using a threaded-point guide-wire. In fact using a thread on the guide-wire can be a disadvantage. Secondly, the thrust cutting force is dependent on the spindle speed and feed. An optimum set of speeds of between 800 and 1400 r/min is recommended for 2.5 mm diameter guide-wires.
Finite Element Analysis in the Design and Characterization of an Absorbable Cement Restrictor
Authors: Wilson S F , Ochoa J A , Rogers L L , Lancaster R L , Ritchie A
Published: February 2007

The benefit of using a cement restrictor to achieve cement pressurization during total hip arthroplasty is well established. An absorbable cement restrictor design has been developed with the use of a finite element model. The non-linear axisymmetric model was used to optimize specific parameters so as to perform within acceptable limits when tested over a specified range of medullary canal sizes. The results achieved from a hybrid experimental/analytical design methodology allowed for a shorter development cycle for the initial size and each additional size in the design family thereafter. The resulting cement restrictor design was compared to and exceeded the performance of currently clinically accepted devices in resisting migration.
Roentgen Stereophotogrammetric Analysis for Assessing Migration of Total Hip Replacement Femoral Components
Authors: Kiss J , Murray D W , Turner-Smith A R , Bulstrode C J
Published: February 2007

A new Roentgen stereophotogrammetric analysis system, using a biplane technique, has been developed to determine the migration and rotation of total hip replacement (THR) femoral components in three dimensions. Stainless steel marker balls were injected into the femur during the operation. The patients stood within a calibration frame during the X-ray. The two exposures were taken consecutively allowing radio-opaque shutters to be moved in front of the films to prevent fogging.

Studies with a model demonstrated that the system was capable of measuring the position of an implant to better than 0.11 mm (2 SD)w. In vivo measurements demonstrated that the migration rate of the different parts of the femoral component could be determined with an accuracy of 0.25 to 0.50 mm/year. By considering the accuracy determined in different ways, methods for improving the system have been identified.

The migration and rotation rate of 58 Hinek cemented femoral components was studied for four years. Migration was three to five times greater (p < 0.001) during the first year than subsequently. The prosthesis head moved the most during the first year (0.94 mm). A better understanding of the cause of implant failure could be obtained by studying the early migration of different types of prosthesis and comparing this with their clinical results and design features.
Assessment of Mechanical Stability of a Parallel Wire Bone Transport System for use with an Ilizarov Frame
Authors: Wilkes R A , Harrison A , Atkins R M
Published: February 2007

A novel fine wire bone transport system for use with Ilizarov frames has been used in Bristol. It uses parallel wires instead of crossed wires. Its stiffness has been tested and compared with a crossed wire construct. In its basic form it is not as stiff to bending and shear loading, however, by modification it can be made at least as stiff. A parallel wire construct does not transfix as much soft tissue as a crossed wire construct when used in the leg. This is advantageous, because soft tissue transfixion causes pain and limb swelling, which impair patient mobilization.
An Appraisal of the Paper by O'Carrol et al. (1990)
Authors: Strozzi A , Unsworth A
Published: February 2007

The paper by O'Carrol et al. (1), which addresses the problem of an elastomeric disc indented by a spherical punch, has been evaluated. The sources of disagreement between linear elastic numerical predictions and experimental measurements noted in this paper have been critically examined in the light of finite element forecasts obtained with a package which incorporates finite elasticity effects and incompressibility.
Experimental and Theoretical Study of the Contact Mechanics of Five Total Knee Joint Replacements
Authors: Stewart T , Jin Z M , Shaw D , Auger D D , Stone M , Fisher J
Published: February 2007

The tibio-femoral contact area in five current popular total knee joint replacements has been measured using pressure-sensitive film under a normal load of 2.5 kN and at several angles of flexion The corresponding maximum contact pressure has been estimated from the measured contact areas and found to exceed the point at which plastic deformation is expected in the ultra-high molecular weight polyethylene (UHMWPE) component particularly at flexion angles near 90°. The measured contact area and the estimated maximum contact stress have been found to be similar in magnitude for all of the five knee joint replacements tested.

A significant difference, however, has been found in maximum contact pressure predicted from linear elasticity analysis for the different knee joints. This indicates that varying amounts of plastic deformation occurred in the polyethylene component in the different knee designs. It is important to know the extent of damage as knees with large amounts of plastic deformation are more likely to suffer low cycle fatigue failure. It is therefore concluded that the measurement of contact areas alone can be misleading in the design of and deformation in total knee joint replacements. It is important to modify geometries to reduce the maximum contact stress as predicted from the linear elasticity analysis, to below the linear elastic limit of the plastic component.
Measurement of Wear in Retrieved Acetabular Sockets
Authors: Hall R M , Unsworth A , Craig P S , Hardaker C , Siney P , Wroblewski B M
Published: February 2007

Twenty-eight standard Charnley sockets were retrieved at revision surgery. The penetration angle with respect to the cup coordinate system, β, and penetration depth, d, of the sockets were measured using both the traditional shadowgraph technique and by analysing data obtained from a coordinate measuring machine (CMM). In addition, d was deduced radiographically from pre-revision X-rays. Limits of agreement between the three methods of measuring d were of the order of ±0.5 mm. Using the data obtained from the CMM it was possible to deduce the wear volume Vmeas directly. It was found that, in general, values of the wear volume calculated from d and β using equations cited elsewhere (1, 2) were both imprecise and inaccurate. The direct measurement of the wear volume using the CMM depends on the location of reference points external to the wear surface. If such surfaces were damaged, then it was concluded that the shadowgraph technique provided the most suitable method for measuring the dimensional changes in the retrieved socket, due to its relative ease of use.
In Vitro Determination of the Curvatures and Bending Strains Acting on the Leaflets of Polyurethane Trileaflet Heart Valves During Leaflet Motion
Authors: Corden J , David T , Fisher J
Published: February 2007

Leaflet tears originating from the free leaflet edge and calcification around the commissural region are common modes of failure exhibited by explanted bioprosthetic trileaflet heart valves. These may be a result of the cyclic bending and high levels of curvature that affect the leaflets within these areas during normal valve operation. These high leves of curvature occur in a short time period (approximately 20 ms) during rapid leaflet opening and to a lesser degree during leaflet closure. The curvatures that occur at the free leaflet edge of two designs of polyurethane trileaflet heart valve were determined in vitro at various stages during a cardiac cycle using a high-speed video camera (1000 frames/s). Significant deformations at the free leaflet edge were observed and bending radii as low as 0.55 ± 0.125 mm (mean ± standard deviation) were present during leaflet opening, 0.76 ± 0.24 mm during leaflet closure and 1.01 ± 0.27 mm while the valve was fully open during peak systole. The values of curvature were used to determine the values of bending strain and bending stress acting at the free leaflet edge using thin shell bending theory. The calculated values of bending strain were a maximum during the leaflet flexure associated with valve opening. These high levels of bending strain, which occur for short periods of time, are likely to be an important determinant of the valve's durability. It has been shown that the method of manufacture significantly influenced the level of bending strain in the valve leaflets. Valves manufactured using a dip-casting technique resulted in open leaflet bending strains up to 31 per cent lower than valves manufactured from solvent-cast sheets of polyurethane.
An Automatic Technique for Micro-Drilling a Stapedotomy in the Flexible Stapes Footplate
Authors: Brett P N , Baker D A , Reyes L , Blanshard J
Published: February 2007

This paper describes a technique for controlling the drill bit breakthrough during low-speed micro-drilling of a flexible bone element The research reported focuses on the penetration of the stapes footplate at the boundary of the middle and inner ear where there is a need to minimize the penetration of the drill bit through the medial surface. The bone is of unknown thickness and compliance, and the efficiency of cutting is variable between specimens. An automated system is presented that is able to determine these unknowns, to detect the onset of breakthrough and to control drill protrusion beyond the medial surface. The methods used to determine and control the level of protrusion on breakthrough are described. It is reported that the drill bit protrusion beyond the medial surface is achieved to within 0.02 mm of the ideal position.
Eigenstructure Assignment: A Survey
Authors: White B A
Published: February 2007

This paper surveys the field of eigenstructure assignment literature from the early 1960s to the present. The eigenstructure assignment problem is first defined as the assignment of eigenvectors within an eigenspace associated with each eigenvalue. Four broad approaches to eigenstructure assignment are identified: the protection method, the parametric method, the projection method and the orthogonal eigenvector method. The major papers for each method are described in a common nomenclature and the techniques discussed. Recent developments such as parameter uncertainty robustness and hybrid eigenstructure assignment/H∞ control are examined in the recent literature, together with some suggestions for future research. The survey includes over 140 important references.
Real-Time Finite Difference Simulation of a Single-Link Flexible Manipulator System Incorporating Hub Inertia and Payload
Authors: Tokhi M O , Azad A K M
Published: February 2007

This paper presents an investigation into the real-time simulation of a flexible manipulator system. A single-link flexible manipulator incorporating hub inertia and payload mass which can bend freely in the horizontal plane and is stiff in vertical bending and torsion is considered. A fourth-order partial differential equation (PDE) model of the system obtained through the utilization of the Lagrange equation and the modal expansion method is considered. A finite-dimensional simulation of the flexible manipulator system is developed using a finite difference discretization of the dynamic equation of motion of the manipulator. The algorithm proposed allows the inclusion of distributed actuator and sensor terms in the PDE and modification of boundary conditions. The real-time processing requirements of the algorithm are investigated by implementing the algorithm on several digital processing domains. Finally, simulation results verifying the performance of the algorithm in characterizing the behaviour of the manipulator under various loading conditions are presented and discussed.