bluuebunny/crossref_metadata_2025_split huggingface dataset:
Electromagnetic Metal Forming
Authors: Baines K. , Duncan J. L. , Johnson W. 
Published: October 2007

Some results of an experimental and theoretical investigation of the dynamic forming of thin-walled tubes and flat circular diaphragms by the electromagnetic metal forming process are given. The paper is divided into two parts. Part 1—The magnetic forming process is described and its use as a production technique is discussed. The process is a high strain-rate technique suitable for forming relatively light gauge material; the forces causing deformation result from the interaction of the current in specially constructed coils and the resulting eddy currents induced in the workpiece. The source of energy is a capacitor bank which can be discharged rapidly through the work-coil. The experiments described were performed using a specially constructed 16 kj discharge unit. The method of constructing work-coils and the failures experienced with these coils in service are described. Thin-walled copper and aluminium tubes were expanded by means of internal solenoidal work-coils of various lengths. The strain distribution and forming efficiency is presented, together with results showing the variation of process efficiency with changes in the primary circuit parameters. The strain distribution for a circular aluminium alloy diaphragm bulged by means of a flat spiral coil is given. Typical primary current waveforms are given and the changes in waveform and discharge current frequency due to different workpiece materials and changes in primary circuit parameters are indicated. Part 2—An attempt is made to determine theoretically the forces acting on one of the aluminium alloy tubes expanded and described in the work of Part 1. The currents in the work-coil and workpiece are calculated using the experimentally determined current waveform and the calculated value of workpiece inductance. A rudimentary method is developed for relating pressure on the workpiece to the primary and secondary currents and, using this, the radial motion of the tube is predicted. Although the analysis involves the use of a number of simplifications and approximations, the theoretical results obtained are of the same magnitude as would be expected by reference to other high-rate forming processes.
Burst Strength of Rotating Discs
Authors: Waldren N. E. , Percy M. J. , Mellor P. B. 
Published: October 2007

The rotating discs in the aircraft gas turbine engine are components in which the requirement for high strength/weight ratio and the complex stress produced by rotation have a significant influence on material strength and ductility and the study of material behaviour under these conditions has been the subject of numerous investigations. The opportunity to examine the most promising theories for predicting the plastic deformation and fracture of rotating discs arose when a large number of model discs in vacuum melted steel, having near uniform properties, became available for evaluation by burst testing. Fully ductile behaviour of a rotating disc is manifested in the instability phenomenon and correlation between theory and experiment shows that the rotational speed at which instability occurs may be predicted from a knowledge of the true stress-strain curve for the material in simple tension using the Hencky deformation theory. However, due to complex stress resulting from centrifugal loading, fracture in a rotating disc may precede the instability condition and it is not possible to assume fully ductile behaviour in a real material. The plastic stress analysis of model discs in which burst has resulted from fracture prior to instability shows that the materials tested favour a maximum principal stress criterion of fracture and good correlation has been achieved with the maximum true stress at fracture in the tensile test piece. The important influence of strain-hardening on the strength of a rotating disc is demonstrated by the theoretical analysis and by the burst results. For materials exhibiting low strain-hardening the average tangential burst stress in a disc agrees reasonably well with the tensile strength of the material and confirms the simple burst criterion. High strain-hardening materials, however, may be required to exhibit exceptional ductility to allow a disc to achieve a burst strength consistent with the tensile strength and in practical examples relatively low burst strengths have resulted.
Dynamic Indentation of Copper and an Aluminium Alloy with a Conical Projectile at Elevated Temperatures
Authors: Mahtab F. U. , Johnson W. , Slater R. A. C. 
Published: October 2007

The dynamic indentation of copper (B.S. 1433) and an aluminium alloy (B.S. 1476 HE 10) has been investigated, using cylindro-conical projectiles fired from an air-actuated gun. The experiments were performed with impact velocities varying between 1000 and 2500 in/s and at elevated temperatures up to 600°C for the copper and 550°C for the aluminium alloy. The magnitude of the corresponding range of mean strain rate was then 103-104/s, depending upon the material; impact velocity and temperature (see Appendix I). For the range of impact velocities investigated no consequential transition temperature † was encountered. The dynamic temperature coefficient† thus remained constant throughout the test temperature range for each material. This dynamic temperature coefficient was found to be equal to the static temperature coefficient corresponding to the sub-transitional temperature range for the respective materials. The mean effective dynamic indentation pressure is shown to decrease with temperature but the ratio of this dynamic pressure to the static indentation pressure increases with temperature. Strain rate effects for both materials were negligible for sub-transitional temperatures but become important at super-transitional temperatures. It was observed that the parameters on which the strain rate effect depends are in some way related to the absolute melting point of a pure metal.
A Platform with Six Degrees of Freedom
Authors: Stewart D. 
Published: October 2007

This paper describes a mechanism which has six degrees of freedom, controlled in any combination by six motors, each having a ground abutment. It is considered that by its particular arrangement, this mechanism may form an elegant design for simulating flight conditions in the training of pilots. Unlike most simulators, it has no fixed axes relative to the ground, and therefore within the limits of amplitude of the design it can truly simulate the conditions of banking by carrying the simulation of control surfaces into the axes of the new attitude. Variations in control arrangements are described and their respective design merits considered. Other possible uses for this mechanism are mentioned, including automation of production.
An Introduction to the Dynamic Pressure Exchanger
Authors: Azoury P. H. 
Published: October 2007

The historical background and operational principle of the Dynamic Pressure Exchanger (DPE) are outlined. The basic aerodynamic processes of cell-emptying and cell-filling are analysed by the ‘method of characteristics’ for air and for no temperature discontinuities in the unsteady flow pattern. The results of the analysis are then used to generalize performance qualitatively for overall pressure ratios up to the sonic threshold. It is shown that, for pressure wave effects to be fully utilized, a DPE rotor should run such that 8 is of the order of or less than 0.5, where δ is the ratio of the time taken to open or close a cell to the time taken for a sound wave to travel a cell length at the thermodynamic stagnation state of the primary or secondary fluid. In the case where the thermodynamic properties of the fluids vary considerably, it is suggested that 8 be referred to the gas which yields the highest sonic speed. In general, the extent to which the performance is affected by a change in δ, within the range 0 < δ < 0.5, is inappreciable. It is also shown that the use of a transfer passage may be expected to yield a significant improvement in performance and an increased range in overall pressure ratio. A number of applications are described and some recent developments are reviewed. It is also indicated that the main sources of loss can be incorporated within the method of characteristics used in the prediction of performance.
The Performance and Quality Control of Diesel Engine Components
Authors: Towell R. 
Published: October 2007

This paper outlines methods developed to control the quality of incoming materials and finished components with emphasis on the performance that is ultimately required from them. The examples given are taken from diesel engineering but the basic ideas apply to all industries whose final products consist of an assembly of components which are complete in themselves. The quality control of materials and components fills an important role in ensuring that the technical requirements written into a specification by a designer are met by suppliers. The author outlines various techniques developed in his company to achieve this. The paper has two main sections: ( a) quality control of incoming materials, and ( b) performance control of components. The first part deals with the controls established for cast-iron components of various sizes ranging from bedplates and columns weighing about 20 tons to piston rings weighing less than one pound. Ultrasonic testing is briefly discussed as also is the material specification for white metal bearings. The second part of the paper gives examples of performance testing of a number of diesel engine components together with brief details of some of the test rigs that have been developed to carry out the tests. Some of the components discussed in this section are piston rings, crankshafts, camshafts, cams, and fuel injection equipment.
The Large Signal Response of a Loaded High-Pressure Hydraulic Servomechanism
Authors: Nikiforuk P. N. , Westlund D. R. 
Published: October 2007

This paper describes the closed-loop response of a loaded, valve-controlled, high-pressure, hydraulic servo-mechanism to large-amplitude sinusoidal and transient input signals. Oil compressibility and leakage are included in the analysis. The system is of conventional constant-supply-pressure, d.c, position-control configuration. It consists of an electronic amplifier, a two-stage electrohydraulic transfer valve, and a ram-type actuator. The load is comprised of a mass, viscous damping, and Coulomb friction. Load loci and the describing- function technique are used to evaluate the closed-loop frequency response. Load loci and piecewise linearization are used to determine the closed-loop transient response. Experimental verification of the analytical work is included.
Elevated Temperature Yield and 0·2 per cent Proof Stress Properties of Carbon Steel Plates, with Particular Reference to the Values Specified in B.S. 1501: 1964
Authors: Glen J. , Johnson R. F. 
Published: October 2007

The results of some 5000 elevated temperature yield or proof stress tests on steels conforming to the new series of B.S. 1501 carbon steel plate specifications are reported. The data are discussed in relation to the levels of yield and proof stress specified in B.S. 1501: 1964 and the various factors causing variations in the elevated temperature properties are outlined. The effect of differences in testing technique and in methods of deriving ‘guaranteed’ properties (i.e. minimum values which the steel in question will always meet) are considered in relation to the draft International Boiler Code and it is suggested that discrepancies in design thicknesses of approximately 10 per cent can arise owing to these differences.
Oil Hydraulic Spool Valve Operating Times
Authors: Lorenz M. H. , Stringer J. D. 
Published: October 2007

This paper concerns oil hydraulic spool valves of the on-off type and describes an investigation into the time taken for such valves to open or to close. Operating times depend upon the forces acting on a spool as it slides along the bore and the balance of these axial forces has been both analysed and studied experimentally. Operating times were first estimated from a simplified equation neglecting forces due to fluid flow. Experiments were then made on two solenoid operated valves to measure actual times and to discover the reasons for differences between calculated and measured values. Measurements of the sliding friction force between spool and bore indicated that the spools were never concentric in their bores but were displaced radially at all times. Measurements and analyses were also made of the forces due to fluid flow through the test valves. These suggested that it is important to take account not only of momentum changes (1)† and fluid acceleration effects (2) but also of fluid friction in the valve chamber. The influence of fluid flow on operating times was found to be significant unless flow rates were small. Another equation incorporating flow effects was then developed and shown to give a realistic indication of the behaviour of a valve. It is concluded that a simple form of equation may be adequate for approximate predictions of valve operating times, but that a more satisfactory method is to use the complete equation based on the work reported in this paper.
Analysis of the Rigidity of the Grinding Wheel-Workpiece-Grinding Machine System
Authors: Kaliszer H. , Singbal P. D. 
Published: October 2007

The purpose of the paper is to establish a relationship between the vibration marks generated on the work-piece periphery and the rigidities of the grinding wheel-workpiece-grinding machine systems. To investigate the problem several static and dynamic methods of determining the rigidity are analysed. Based on experimental results the grinding machine is assumed to consist of two separate sub-systems: the wheel-head-body system and the workpiece holding system, both coupled together by the grinding wheel. To check the correlation between various methods of determining rigidity, differential equations of motion have been introduced and solved with the aid of a digital computer. In order to consider all forces taking part during grinding an effective force factor has been analytically defined and applied to determine the rigidities. To find the relationship between rigidity established in static conditions and during grinding, coefficients of static and dynamic rigidity have been proposed.
First Paper: An Analytical Study of the Tilting Pad Gas Lubricated Journal Bearing
Authors: Pitts G. 
Published: October 2007

Presented in this paper is an analytical method of producing design curves for tilting pad gas journal bearings, with dimensionless parameters chosen in such a way that a single set of curves may be used for any size of bearing with any length to diameter ratio. An analytical solution to the compressible Reynolds equation, based on the linearization by Ausman, is presented in detail. Comparisons are made between the analytical results, numerical results, and experimental findings on the author's rig at Southampton University. Included in the paper is a sample design curve, together with equations for constructing additional curves. The author concludes by briefly outlining his proposed extension of this work.
The Use of Numerical Methods for the Investigation of Flow in Water Pump Impellers
Authors: Wood M. D. , Marlow A. V. 
Published: October 2007

The paper describes the development of a digital computer method for predicting the streamlines and vane surface velocities in mixed flow impellers. The flow is assumed to be axisymmetric and reversible. However, even with these simplified assumptions, it is shown by examples that valuable information can be obtained for design purposes. No attempt is made to describe computer flow diagrams or to list machine orders. The paper is concerned rather with the fundamental and practical difficulties encountered in getting the program to work and with the techniques finally devised to produce meaningful numerical results.
The Thirty-Ninth Thomas Lowe Gray Lecture: Offshore Drilling, with Particular Reference to the North Sea and the ‘Sea Quest’
Authors: Avery R. G. S. 
Published: October 2007

The origins of offshore drilling work and the development of structures used at sea are traced. Comparison of the various types illustrates the advantages and disadvantages of each. Tables show the numbers in operation, being built, and the apparent liability of each type to damage. Typical bore-hole structures are illustrated, the need for undersea well-heads explained and their development into a sea-bed completion is discussed. Much more research is necessary before this can be considered a practical proposition. The design of drilling barge equipment is compared with typical land rigs and the development of drilling equipment, including the sophisticated electric drive and turbo-drill, discussed. Rigs in various types of barge are compared. Fire precautions and other safety equipment are described. The problems associated with control by the driller lead to complications of motive power layout. The lecture describes in some detail the design of the semi-submersible drilling barge Sea Quest, illustrates the weight problems and their effect on floating stability and indicates the need for management decisions on the degree of resistance to damage. This is measured by the variable deck load of drilling equipment that can be held on board and the degree of weather deterioration that can be tolerated before disengaging the drill from the hole. The need for, and extent of, diving is discussed, with some comparison between diving vehicles. Weather too is an essential factor of work in the North Sea and both pre-surveys and day-to-day reporting are described.
The Third John Player Lecture: Progress in the Manufacture of Large Forgings
Authors: Sully A. H. 
Published: October 2007

Difficulties in the production of large steel forgings stem from the metallurgical and physical heterogeneity of large ingots, the extent of which increases with the size of ingot. The production of large forgings will be discussed with special reference to the manufacture of large mono-bloc rotor forgings for electrical generating plant, the size of which has increased progressively. These rotors are required to meet extremely high standards and must have uniform mechanical and creep properties. Manufacturing processes are reviewed in relation to steelmaking (the advantages of vacuum treatment of the liquid steel are discussed), forging (involving upsetting operations in a forging press of very large capacity), metallurgical control of properties in components of great metal thickness; and in relation to inspection, involving refined ultrasonic techniques. Recent developments and improved techniques offer the possibility of producing sound unbored rotors with guaranteed creep properties and consequent design advantages to turbine engineers. Future developments in the production of large forgings are speculated on, and the significance is discussed of the influence of electroslag welding which opens up new possibilities through its ability to join sections of large thickness.
Graphical Analysis of the Step Response of Hydraulic Servomechanisms
Authors: McCloy D. 
Published: October 2007

The closed loop hydraulic servomechanism is analysed graphically. The fluid is assumed to be incompressible. Electrical and mechanical feedbacks are considered and the effect of feedback on the system step response is demonstrated. Viscous and Coloumb friction forces and inertia and spring loads are considered. A non-linear valve area-displacement characteristic is shown to have a considerable effect on the response.
First Paper: Sliding Friction between Lubricated Rollers
Authors: Jefferis J. A. , Johnson K. L. 
Published: October 2007

The design and development of a power circulating rolling contact disc machine is described. Each disc is mechanically coupled to a separately excited d.c. electrical machine whose armatures are connected electrically. When the discs develop traction, power circulates by one machine acting as a motor and the other as a generator. In this way controlled traction with a stepless variation of sliding speed can be maintained between the rolling discs. Dawson has shown that the pitting fatigue life of steel discs depends inversely upon the ratio of surface roughness to oil-film thickness. The disc machine has been used to measure the sliding friction between rolling discs under conditions similar to Dawson's fatigue tests. Large variations in surface roughness and film thickness resulted in relatively small changes in friction force. It is concluded that the effect of surface roughness and film thickness upon pitting life cannot be accounted for by changes in the friction force transmitted between the discs. The insensitivity of the observed friction to variation in the surface roughness of the discs is explained in terms of the shear behaviour of the lubricant film at high contact pressures.
Fatigue Strength of Small Pinned Connections Made from Alloy Steel Fv 520B
Authors: White D. J. 
Published: October 2007

Published work on pin-loaded lugs is reviewed, particular attention being given to photoelastically determined stress distributions and to results of fatigue tests for the purpose of identifying those factors that affect fatigue strength. Fatigue tests have been conducted on lugs of width 1 [Formula: see text] in made from alloy steel FV 520B and loaded by means of a [Formula: see text]-in diameter pin. A systematic investigation was made of pin fit for both clearance and interference and the effect of various treatments was investigated; these included cadmium plating the lug bore and pin, applying the ‘Sulfinuz’ process to the lug and overstraining the lug bore. Two conditions of mean stress were investigated, namely, pulsating or repeated tension and 15 tonf/in2 mean tension. Strength comparisons are based on the fatigue strength at 108 cycles, for the appropriate mean stress, of untreated lugs with exact-fit pins, these showing the lowest strength of all the lugs tested. It was found that clearance-fit pins and interference-fit pins were beneficial and with the larger values of clearance and interference tested the fatigue strength was almost doubled. Cadmium plating was ineffective while both Sulfinuz treated lugs and lugs with overstrained bores gave strength ratios of at least 1.6. An increase in mean stress from pulsating tension to 15 tonf/in2 mean tension, significantly reduced fatigue strength in most cases. On the basis of the present experimental results, the design method proposed for lugs with interference-fit pins in Royal Aeronautical Society Data Sheet A.05.02, amended by Engineering Sciences Data No. 67012, may sometimes prove to be unsafe and caution is warranted in interpreting the safe loads predicted.
Simulation of an On-Off Pneumatic Servomechanism
Authors: Burrows C. R. , Webb C. R. 
Published: October 2007

This paper describes an analogue computer simulation of an on-off pneumatic servomechanism comprising a polarized relay with dead zone and hysteresis, power relays, and an on-off four-way spool valve supplying air to a cylinder driving an inertia load acted upon by viscous damping and Coulomb friction. The effect of varying the amount of friction and of position, velocity, and acceleration feedback is studied. The effect of the addition of stabilizing tanks is also considered.