bluuebunny/crossref_metadata_2025_split huggingface dataset:
The role of inhomogeneous deformation in high-temperature ring compression testing
Authors: Nanneh M , Dunne F P E 
Published: October 2002

Elastic-viscoplastic constitutive equations that enable the modelling of rate effects, temperature effects and dynamic recrystallization are employed to model the ring compression test at high temperatures. The effects of strain rate and temperature on the calibration curves, used widely to characterize frictional behaviour in forging, are investigated. Both strain rate and temperature are found to influence the calibration curves obtained, and it is found that the influence derives from the dependency of dynamic recrystallization processes on strain rate and temperature. The coupling between the deformation and the recrystallization process is found to lead to the establishment of significantly different strain fields with different strain rates, and it is this that leads to the dependency of the calibration curves on strain rate and temperature. A methodology has been presented for the determination of friction calibration curves for hot forging of high-performance materials, which accounts for strain rate effects, temperature effects and recrystallization processes. The method is likely to be useful to industries involved in the high-temperature processing of high-performance components.
Modelling void nucleation and growth in axisymmetric extrusion
Authors: Lim L G , Dunne F P E 
Published: October 2002

Elastic-viscoplastic constitutive equations, with kinematic and isotropic hardening, are employed to model the deformation behaviour of an aluminium alloy in extrusion. Constitutive equations are also employed for void nucleation and growth, which are fully coupled with the deformation behaviour. The material model is employed to investigate the roles of void nucleation and growth in extrusion defect formation. It has been shown that central bursting is a void growth controlled process. The existence of nucleated voids only leads to central burst formation with the existence of appropriate stress states which lead to void growth. The results obtained show excellent agreement with well-established limit diagrams, obtained analytically and experimentally. The results also show that for a given combination of area reduction and semi-cone die angle, the introduction of friction tends to inhibit the formation of central bursting, but increases the likelihood of surface tearing/cracking. The tendency to inhibit central burst formation with increasing friction results from the reduction in the levels of tensile hydrostatic stress, which therefore reduce the rate of void growth. A comparison of the results obtained using kinematic and isotropic hardening in the extrusion process showed that significantly different residual stress fields are obtained for the two cases. This is of importance, for example, in the case of multipass extrusion or where the residual stress field is to be used subsequently in design analysis.
Self-assessment: Methods, management and process
Authors: Teo W F , Dale B G 
Published: October 2002

Self-assessment is a method for reviewing the activities and performance of an organization. This paper reports the findings of a study in four organizations of their management of this process. Each company followed the key self-assessment stages of planning, developing awareness, implementation and review but carried out the process in a different manner. The level of total quality management (TQM) maturity, available resources and organizational culture were the main factors for the differences. The key to successful self-assessment is effective management and the use of a team to manage the process. The most important activities were identified as: selection of a suitable model, appropriate approach(es) for the assessment, provision of appropriate training, monitoring the progress of improvement actions, establishment of a ‘closed-loop’ structure for the improvement cycle and integration of improvement with the strategic business plan. It is also pointed out that self-assessment is not without difficulties, including scarcity of time, overemphasis on scoring and scores, failing to follow-up improvement actions and lack of communication.
Procedures for effective implementation of simultaneous engineering in small to medium enterprises
Authors: Hindson G A , Kochhar A K , Cook P 
Published: October 2002

Simultaneous engineering (SE) has been developed by large multinational companies working in consumer oriented industries. This has meant that the implementation methods, tools and techniques have been geared towards these industries. 600 Lathes is a medium-sized company engaged in the manufacture of a variety of machine tools. The application of an SE approach in such environments requires the adaptation of its generic principles. The initial use of SE on a new machine tool, the Tornado lathe, indicated the need for procedures to institutionalize this new method of working. A critical analysis of SE identified four generic principles that were used as a framework for product introduction. Procedures were developed drawing on organizational communication theory and involving the users. The aim was to create procedures with company-wide acceptance that were user friendly and worked. These procedures were used for the introduction of a second range of lathes, named Alpha. Their effectiveness was studied as a crucial part of the Alpha project review. This evaluation showed that procedures based on practical experience are readily adopted. Each procedure was necessary and integral to SE. Any company wanting to implement SE must tackle similar issues. The generic principles of SE are proposed as the method for developing effective procedures.
Direct experimental evidence of lubrication in a metal-on-metal total hip replacement tested in a joint simulator
Authors: Dowson D , McNie C. M. , Goldsmith A. A. J. 
Published: October 2002

The purpose of the study reported in this paper was to investigate experimentally the conditions of lubrication and contact between a metallic femoral head and a metallic acetabular cup in a hip joint simulator. An electrical resistivity technique previously developed for engine tribology studies was used to detect the extent of surface separation throughout a cycle of dynamic loading simulating walking conditions. A metal-on-metal total joint replacement was tested in a single station of a ten-station hip joint simulator in the presence of five different lubricants. Two proteinaceous serum-based fluids of concentrations 25 and 100 per cent were used as well as three lubricants devoid of protein but of quite different viscosities. It was observed that surface separation developed with both the protein-based fluids during the swing phase of the articulation and that an equilibrium cyclic pattern of contact and separation was established after running the simulator for some minutes. Furthermore, there was at times some evidence of separation during the severe conditions encountered during the stance phase. Silicone fluid failed to promote surface separation, while water and the more viscous carboxymethylcellulose solution yielded only modest periods of separation during the swing phase. It was deduced from experimental and analytical features of the study that the mode of lubrication was mixed, with some periods of very effective surface separation and others of metal-to-metal contact. While the presence of protein was necessary for effective lubrication, the cyclic pattern of separation appeared to be determined by elastohydrodynamic action. The bond strength of the protein to the metals appeared to be weak. The partial film of lubricant between the boundary lubricating layers provided significant enhancement to the combined protective action in this mixed lubrication system. The simple, cheap and effective electrical resistivity technique has revealed important new information on the tribological conditions in metal-on-metal hip joints which determine friction and wear. It can readily be adopted on most forms of total joint simulators. The technique and the findings reported here further advance the development of criteria for lubricants to be used in laboratory studies of the performance of total replacement joints.
A validation study on mathematical models of speed and frequency dependence in seakeeping
Authors: Du S. X. , Hudson D. A. , Price W. G. , Temarel P 
Published: October 2002

An extensive theoretical validation exercise is presented into the speed and frequency dependent solutions associated with surface piercing vessels travelling in waves. The basis of the study lies in the formulation of the Green's function satisfying the traditionally posed linearized boundary value problem of an oscillating ship with forward speed and the development/implementation of appropriate numerical schemes of study for solution. Two widely different mathematical models in formulation and numerical algorithm, denoted as methods A and B, are discussed and employed to predict hydrodynamic coefficients, wave loads and responses of a Series 60 form and an NPL monohull. Only a selection of results are shown, but great care was taken in the overall investigation to verify and validate intermediate steps within the separate calculation procedures as well as to compare final predicted values. The extensive qualitative and quantitative agreement of comparable results from methods A and B provides a measure of confidence that the presented findings are solutions to the posed seakeeping problem. The influence of speed and frequency dependence within the context of this study are discussed as well as a preliminary study into their influence in the occurrence of irregular frequencies in the numerical schemes.
The effect of diametral clearance, motion and loading cycles upon lubrication of metal-on-metal total hip replacements
Authors: Smith S L , Dowson D , Goldsmith A A J 
Published: October 2002

A study of surface contact and separation of 36mm diameter metal-on-metal joints was undertaken in 25 per cent bovine serum using a hip simulator. A range of diametral clearances from 130 to 170 μm was tested and each joint was subjected to two different dynamic motion and loading walking cycles. One simulation used physiological motion and loading cycles as described by Paul [I], while the other used simplified motion cycles, as described by Barbour et al. [2], and simplified loading. An electrical resistivity technique was used to detect the extent of surface separation throughout a complete walking cycle. The proportion of surface separation per cycle was generally greater in the simplified than in the physiological walking cycle. The latter cycle thus appears to present a more severe condition than the simplified cycle as far as joint lubrication is concerned. No surface separation was observed, for either cycle, with the largest diametral clearance of 170 μm. All of the remaining joints, with smaller diametral clearances, showed surface separation for at least a portion of each walking cycle. The proportion of surface separation per simulated walking cycle generally increased as the diametral clearance decreased.
New developments in the design and generation of gear drives
Authors: Litvin F. L. , Fuentes A , Demenego A , Vecchiato D , Fan Q 
Published: October 2002

Design, generation and simulation of the meshing and contact of gear drives with favourable bearing contact and reduced noise are considered. The proposed approach is based on replacement of the instantaneous line of contact of tooth surfaces by point contact and on application of a predesigned parabolic function of transmission errors that is able to absorb linear discontinuous functions of transmission errors caused by misalignment. Basic algorithms for analysis and synthesis of gear drives are presented. The developed theory is applied for design and generation of the following gear drives with modified geometry: (a) spur and helical gears, (b) a new version of Novikov-Wildhaber (N-W) helical gears, (c) asymmetric face gear drives with a spur pinion, (d) formate-cut spiral bevel gears. Generation of the tooth surface of a worm gear is presented as the formation of a two-branch envelope. The discussed topics are illustrated with examples.
Design optimization of large-scale structures with sequential linear programming
Authors: Lamberti L , Pappalettere C 
Published: October 2002

Design optimization of complex structures entails tasks that oppose the usual constraints on time and computational resources. However, using optimization techniques is very useful because it allows engineers to obtain a large set of designs at low computational cost. Among the different optimization methods, sequential linear programming (SLP) is very popular because of its simplicity and because linear solvers (e.g. Simplex) are easily available. In spite of the inherent theoretical simplicity, well-coded SLP algorithms may outperform more sophisticated optimization methods. This paper describes the experience obtained in the design optimization of large-scale truss structures and beams with SLP-based algorithms. Sizing and configuration problems of structures under multiple loading conditions with up to 1000 design variables and 3500 constraints are considered. The relative performance and merits of some SLP-based algorithms are compared and the efficiency of an advanced SLP-based algorithm called ILEAML (improved linearization error amplitude move limits) is tested. ILEAML is also compared to the sequential quadratic programming (SQP) method, which is considered by theoreticians as probably the best theoretically founded optimization technique.
On the coupling of the elastohydrodynamic problem
Authors: Elcoate C D , Evans H P , Hughes T G 
Published: October 2002

The paper presents the results of an investigation of methods of mathematically coupling the equations of elastohydrodynamic lubrication (EHL) that define the EHL line contact problem. The objective is to develop numerical solvers for use in the study of thin-film/rough surface contacts such as found in gears. It has been found that deformation behaviour of the surfaces is a dominant effect and that full rather than partial coupling is necessary for stable solutions. For cases considered using a Newtonian lubricant a first-order formulation of the Reynolds equation is required at high loads in the high-pressure part of the contact. The fully coupled method is also applied to contact between a moving smooth surface and a stationary rough surface. The significant changes brought about by non-Newtonian oil behaviour are demonstrated, together with the ability of the method to provide solutions for cases where the λ ratio (of film thickness to surface roughness) is as low as 0.1.
Stokes flow in a double-lid-driven cavity with free surface side walls
Authors: Gaskell P H , Gürcan F , Savage M D , Thompson H M 
Published: October 2002

Stokes flow is considered in a rectangular double-lid-driven cavity with free surface side walls, aspect ratio A and speed ratio S= U1/ U2, where U1 and U2 are lid velocities, as an idealized model for two-dimensional viscous flow in the ‘bead’ of a two-roll, meniscus coating system. For S ≤ 0 (> 0) there is one (two) large eddy (eddies) within the cavity with one (two) stagnation points on the centre-line between the free surfaces. Various transformations of flow structure arising as a result of flow bifurcations at these stagnation points are identified as the two control parameters A and S are continuously varied. In the case of symmetric flow, S= -1, reducing A from A = 2.5 produces a sequence of pitchfork bifurcations at which a stagnation-saddle point changes to a centre (or vice versa) with the generation of two additional stagnation points. As A → 0 and the number of stagnation points increases, it is shown that the flow structure consists of a series of nested separatrices, each contained within the central section of the previous one. In the case of asymmetric flow, S ≠ -1, S < 0, the above pattern of behaviour is repeated as A is reduced from A = 2.5, apart from an initial saddle-node bifurcation at which a saddle and a centre annihilate each other. When the lids move in the same direction ( S > 0) bifurcations may arise separately or simultaneously in each of the two large eddies. Again as A → 0 with S constant, nested separatrices appear in both eddies. The key results are displayed via bifurcation curves in an ( S, A) control space diagram.
A systematic approach to profile relief design of low and high contact ratio spur gears
Authors: Yildirim N , Munro R G 
Published: October 2002

This is the first of a series of papers on the design of the tooth profile relief of both low and high contact ratio spur gears and its effects on transmission error (TE) and tooth loads. A systematic approach to profile relief design is introduced. The process of profile relief analysis is based on a number of simplifying assumptions to ease the understanding of the relief design. Useful relief cases determined during the simplified analysis are further investigated, with realistic parameter values such as variable stiffness, manufacturing tolerances and so on, in other papers of the series. Experimental validation of the cases proven to be good are also given in forthcoming papers. In the present paper, the systematic approach is applied to low contact ratio (LCR) spur gears first with some design regions and to high contact ratio (HCR) spur gears with some new and promising design regions and rules. Several smooth transmission error curves at different loads are shown to be possible for the relief designed, hence allowing a range of loads with uniform motion transfer. The advantages of HCRG over LCRG in terms of smooth TE curves and tooth load values are noted.
Transonic fan and compressor design
Authors: Calvert W. J. , Ginder R. B. 
Published: October 2002

Transonic fans and compressors are now widely used in gas turbine engines because of their benefits in terms of compactness and reduced weight and cost. However, careful and precise design is essential if high levels of performance are to be achieved. In this paper, the evolution of transonic compressor designs and methods is outlined, followed by more detailed descriptions of current compressor configurations and requirements and modern aerodynamic design methods and philosophies. Current procedures employ a range of methods to allow the designer to refine a new design progressively. Overall parameters, such as specific flow and mean stage loading, the axial matching between the stages at key operating conditions and the radial matching between the blade rows are set in turn, using one- and two-dimensional techniques. Finally, detailed quasi-three-dimensional and three-dimensional computational fluid dynamics (CFD) analyses are employed to refine the design. However, it is important to appreciate that the methods all have significant limitations and designers must take this into account if successful compressors are to be produced.
The validation of a two-dimensional transient catalyst model for direct injection two-stroke applications
Authors: McCullough G , Douglas R , Cunningham G , Foley L 
Published: October 2002

This paper describes the detailed validation of a computer model designed to simulate the transient light-off in a two-stroke oxidation catalyst. A plug flow reactor is employed to provide measurements of temperature and gas concentration at various radial and axial locations inside the catalyst. These measurements are recorded at discrete intervals during a transient light-off in which the inlet temperature is increased from ambient to 300°C at rates of up to 6°C/s. The catalyst formulation used in the flow reactor and its associated test procedures are then simulated by the computer and a comparison made between experimental readings and model predictions. The design of the computer model to which this validation exercise relates is described in detail in a separate technical paper. The first section of the paper investigates the warm-up characteristics of the substrate and examines the validity of the heat transfer predictions between the wall and the gas in the absence of chemical reactions. The predictions from a typical single-component CO transient light-off test are discussed in the second section and are compared with experimental data. In particular the effect of the temperature ramp on the light-off curve and reaction zone development is examined. An analysis of the C3H6 conversion is given in the third section while the final section examines the accuracy of the light-off curves which are produced when both CO and C3H6 are present in the feed gas. The analysis shows that the heat and mass transfer calculations provided reliable predictions of the warm-up behaviour and post-light-off gas concentration profiles. The self-inhibition and cross-inhibition terms in the global rate expressions were also found to be reasonably reliable although the surface reaction rates required calibration with experimental data.
A theoretical investigation of a prototype active roll control system
Authors: Darling J , Ross-Martin T. J. 
Published: October 2002

This paper describes a simulation study conducted as part of the development of a hydraulic active roll control suspension. The system is based upon roll bars with integral closed loop position controlled hydraulic rotary actuators supplied with flow by a single proportional valve. A theoretical analysis of the fundamental characteristics of the system is presented together with the simulation implementation. System performance is examined, parameter sensitivity studies are undertaken and a number of practical measures to enhance performance are considered. The roll control system was largely insensitive to hydraulic system changes, control valve bandwidth being the most important parameter. Speed dependent gain scheduling of the forward path actuation system roll moment controller was shown to partially overcome the problem of vehicle dynamics which change with forward speed. A comparison of actuator displacement and actuator differential pressure feedback systems demonstrated that while the roll control performance of the former system was superior, the ride performance was inferior.
An experimental and theoretical investigation into the design of an active suspension system for a racing car
Authors: Purdy D. J. , Bulman D. N. 
Published: October 2002

The well-established quarter car representation is used to investigate the design of an active suspension system for a racing car. The work presented is from both a practical and theoretical study. The experimental open-loop and passive responses of the suspension system are used to validate the model and estimate the level of damping within the system. A cascade control structure is used, consisting of an inner body acceleration loop and an outer ride height loop. Comparisons are made between the experimental results and those predicted by the theory. During the 1980s and early 1990s a number of Formula 1 teams developed active suspension systems to improve the performance of cars. Little detail was published about these systems because of the highly competitive nature of the application. Some of these systems were very sophisticated and successful. Because of this, speed increased considerably and because of the costs involved, the difference in performance between the lower and higher funded teams became unacceptable. For this reason, the governing body of motor sport decided to ban active suspensions from the end of the 1993 racing season. Both authors of this paper were involved with different racing teams at that time, and this paper is an introduction to the very basic philosophy behind a typical active system that was employed on a Formula 1 car.