Proceedings of the Institution of Mechanical Engineers

An urgent plea for unity of purpose in engineering thought and action in a rapidly changing world is the underlying theme of this Address. An historical example forms the basis of the reflections and questions posed on the subject.

Experiments are described in which the pressure drop and pressure gradient were measured for air flowing through porous tubes with uniform extraction at the walls. A simple correlation is derived and is shown to be approximately consistent with the theoretical work of Silver (1)†. The results may be of particular interest to designers of condenser equipment in which pressure changes are important.

The use of the Reynolds flux to assess momentum transfer and pressure drop behaviour in condensation was a basic idea of a paper by Silver (1)†. In the present paper the same concepts are used with more consistent logic to develop a simpler and more satisfactory treatment. Experimental results of velocity profile measurements show that the assumptions made are permissible. The predictions from the improved theory are generally in accord with those previously given by Silver (1) and now confirmed by Wallis in the first of these two papers.

Owing to the nature of the stress system in a thick-walled cylinder it is possible to produce fatigue failures in such components after a relatively few repetitions of internal pressure, while still maintaining dimensional stability. This is particularly true for cylinders in which stress raisers are present, a situation of considerable practical importance.

The present paper covers in some detail the design and development of apparatus capable of repeatedly applying to cylinders internal pressures of up to 40 tonf/in². Results are presented for such tests on plain bored cylinders of two diameter ratios, 1.4 and 1.8, and on cylinders in which radial holes have been drilled, the latter having a diameter ratio of 2.25. The investigation has been confined to a 2 1/2 per cent nickel-chromium-molybdenum steel, with an ultimate tensile strength in the region of 58 tonf/in²; the results are intended to supplement the long life data obtained for this material by other investigators.

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.

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.

The screw feeder is considered as a measuring device for dry fragmental materials. Expressions are obtained for volume delivered and torque required, in terms of the dimensions and coefficients of friction involved. Limited confirmation has been obtained in experiments using coal. The cases where the tube is eccentric to the screw axis and where fine material can pass the wing-tip are examined. Improvement in screw feeder design appears possible.

The paper describes an experimental investigation arising out of theoretical work by one of the authors (1)^†, of the thermodynamic performance of a production opposed-piston compression-ignition engine under conditions of very high boost. By operating the engine with substantial internal cooling in the form of excess scavenge air, b.m.e.p.'s of the order of 230 lbf/in²-at a boost pressure ratio of 3/1 were achieved without imposing excessive thermal or mechanical loading on the engine, and at very high brake thermal efficiencies, exceeding 40 per cent in several instances.

The primary independent operating variables were: boost pressure ratio, trapped air/fuel ratio, scavenge ratio, engine speed and simulated compressor efficiency.

Very satisfactory agreement with predicted performance figures was obtained and, in addition, a promising correlation of aggregate heat transfer from the engine cylinders with the above operating variables has been devised.

The investigation is to be regarded as preliminary to a differential compound engine project, based on theoretical performance predictions by one of the authors (2), in which the engine is merely part of a power unit comprising, in addition, compressors, turbines and differential gearing.

The paper describes an investigation of high speed or ‘high energy-rate’ extrusion of cold metal billets. Preliminary trials were carried out with a small pilot machine which, with low explosive drive, could supply up to 430 ft lb per blow at a striking velocity of 132 ft/s. Main trials were subsequently completed using two ‘full-scale’ machines, one explosively driven and the other driven by compressed air, designed to be complementary to each other in such a way that a wide range of energies and striking velocities could be achieved, up to 10 000 ft lb and over 300 ft/s. The metals used were aluminium, copper and mild steel, all in the annealed state. In the main the experience gained was satisfactory and encouraging, and while it was concluded that impact velocities of the order of 50–100 ft/s are feasible, it appeared that the disadvantages of much higher velocities would outweigh the advantages.

Plant autocontrol systems are subject to failure; those occurring in autocontrolled nuclear reactors may necessitate a trip, with attendant economic penalties.

Such failures may be avoided by designing autocontrollers which comprise a number of identical subsystems.

The practical significance is discussed of some of the requirements for achieving high autocontrol reliability, and it is shown how these requirements have been translated into detailed design of hardware for a research reactor in which autocontrol of neutron flux and period is required.

The underlying theme is that autocontrol of the plant can continue in spite of subsystem failure, but that careful vigilance must be exercised over the duration of the failure.

Various devices are discussed which help to increase the efficiency of a redundant autocontrol system. Daily proof tests and passive monitoring devices can ensure that no relaxation of vigilance is allowed.

The author discusses some of the problems of failure-survival automatic flight control systems and suggests some basic ground rules as design criteria.

The advantages and disadvantages of some of the main types of system are discussed: duplex, triplex, triple component, duplicate-monitored and quadruplex systems being covered.

In particular, a quadruplex actuator is described which has been designed and developed mainly for automatic flight control system applications where a very high degrees of failure-survival capability is required.

A detailed failure analysis of the various systems is carried out and the importance of the electrical and hydraulic supply system configurations and failure rates is brought out.

The ‘Seacat’ missile has been adopted by the Royal Navy as the standard close-range ship-to-air weapon of the 1960's. When the specification was drawn up reliability requirements were nebulous in the extreme, but it was appreciated that with such a missile a ‘high’ reliability had to be achieved in spite of intense pressure to reduce weight, space, and cost to absolute minima, and in spite of some unusual operational requirements.

This paper reviews in retrospect some of the methods adopted both in the servo actuator design and in production procedures to meet these requirements. In addition the systematic reporting of tests carried out in depots of ships enables an assessment to be given of the reliability achieved in service.

It is concluded that, in the mechanical sphere, the cost of a full scale statistical exercise aimed at a prediction of reliability may well be exorbitant, and whilst assurance will be obtained, the contribution to the degrees of reliability may only be marginal. However, the systematic recording and analysis of experience in the field will enable maximum benefit to be derived for future projects.

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 10^3-10⁴/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.

It would be desirable to be able to predict the running characteristics of turbo-generators at the design stage. The paper describes tests on production generators and their component parts, directed at evaluating the relative contributions of these components to the dynamic behaviour of the complete system. Tests have shown that the contribution of the rotor alone may be estimated with some confidence, but that the present state of knowledge regarding the rotor supports, whose characteristics are shown to have a profound effect on the running behaviour of the machine, is inadequate. Theoretical techniques are presented which should rigorously solve any practical configuration provided the correct parameters are available.

In view of the importance of accurate measurement of flow rate at low Reynolds numbers, there have been numerous attempts to develop metering devices having constant discharge coefficients in the range of pipe Reynolds numbers between about 3000 and 200 and even below this latter value, and some of these attempts have achieved a reasonable degrees of success. Nevertheless, some confusion exists regarding the dimensions and range of utility of certain designs which have been recommended and further information is necessary in order that the situation may be clarified.

The aims of the present investigation, which is believed to be wider in scope than any published in this field in recent years, were to review and correlate existing knowledge and to make an experimental study of the properties of various types of orifice in the low range of Reynolds numbers. Arising from this it was hoped that a design might be evolved which not only had a satisfactorily constant discharge coefficient throughout the range but was also simple to manufacture and reproduce, even for small orifice diameters of the order of 0.5 in or less, and it is believed that some success in attaining this aim was achieved.

The first section of the paper contains a review of previous investigations classified into three main groups. In the second part of the paper, experiments with various types of orifice plate are described and it is shown that a properly proportioned single-bevelled orifice has as good a performance in the low Reynolds number range as that of any of the more complicated shapes.

The paper is a case history of the solution of a control problem in mechanical engineering. The system concerned, namely a pneumatic control system which regulated the leakage to the atmosphere of carbon dioxide through a rotating face seal, had exhibited the familiar symptoms of drift and hunting and had defied ad hoc methods to cure it. The difficulties stemmed from the fact that the gain of the element being controlled could assume indefinitely large values, whilst in addition, the loop contained one highly non-linear element.

The solution of the problem did not require highly sophisticated techniques. In contrast, a combination of frequency-response testing and the application of quite elementary servo theory enabled the causes of the malfunctioning of the system to be pin-pointed and indicated the modifications required.

Details are presented of the four phases of the investigation which comprised the initial frequency-response testing of the malfunctioning system, the theoretical analysis, laboratory tests on a simulator model of the system and final proving tests on the modified system at site.

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.

Work on the fatigue strength of thick cylinders subjected to repeated internal pressure described in earlier papers has been continued. Topics investigated include size effect, the effect of radial and tangential cross-bores, the improvement obtainable by autofrettaging such cylinders and the effect of the surface finish of the bores of the cylinders. The additional materials tested include 13 per cent chromium steel (En 56), 18 per cent nickel-cobalt-molybdenum maraging steel, 1 per cent chromium ball race steel, fully hardened (En 31), beryllium copper and tungsten carbide. Not all these materials could be obtained in a size large enough to make the previously used 1 in bore cylinders and a new head for the fatigue machine was designed to accommodate a variety of cylinder sizes and industrial high pressure components.

A dynamics analysis of a nuclear boiler based on a steam-generating, pressure-tube, heavy-water-moderated design is presented. In effect the plant is very similar to a La Mont recirculating cycle. A detailed mathematical model to represent plant dynamics (linearized, full power) is discussed with special reference to the boiling channel, steam drum, and recirculating loop. A simplified model is derived for analogue computer studies. Dynamic performance is discussed in terms of: (1) boiler only (no reactivity feedbacks): influence of pressure feedbacks, steam drum design, subcooling, recirculating delay; (2) complete plant (including reactor): as above but including influence of void coefficient.

The two most important results are: (1) the strong dependence of plant behaviour/stability on the degrees of float allowed to pressure; (2) the possibility of designing an inherently stable and self-regulating plant with a small positive void coefficient.

Finally, conclusions are drawn on the complete dynamic analysis under the heads: (1) optimal plant design; (2) control system design; (3) development of analytical/computing methods; (4) research into two-phase physics.

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 investigation reported here deals with the conditions of flow through a tangential fan. In order to gain a better understanding of the flow an experimental apparatus for testing the fan was designed. Detailed measurements of velocity and pressure through the impeller interior were carried out. The results indicate that a combined vortex is the main component of the flow, namely, a forced vortex, surrounded by a potential vortex (free vortex). The centre of the combined vortex lies inside the impeller and its location does not change with impeller speed.

A suitable theoretical model of the flow was developed and acceptable correlation was found between it and the measured flow field. It was found that the flow regime through the impeller interior could be controlled and that the location of the combined vortex centre and its strength would be regulated by the shape and location of a diffuser baffle.

A secondary flow perpendicular to the main flow, hitherto not mentioned, was found and an explanation of this phenomenon is offered.

Test results show that the fan efficiency increases with increasing impeller speed in the test range. Previous available works on the subject are reviewed.

In this paper the design of a spherical pressure vessel pierced by a radial cylindrical nozzle is discussed. The nozzles considered end flush with the inside of the vessel. Previous work on stress concentration factors, shakedown factors and limit pressure factors has been drawn together and presented in a compact form convenient for the use of designers. These results have been used to discuss the implications of designing to a certain stress concentration factor and to show that this procedure is very reasonable when a concentration factor of 2.25 is used.

The examination of a number of laboratory induced ‘wire wool’ type bearing failures and service failures has led to the conclusion that the steel slivers forming the wire wool, which are responsible for the often self-propagating nature of these failures, are produced by a process of spinning of the journal surface.

The friction force between 1/8, 3/32 and 1/16 in diameter, and the wear of 3/32 in diameter, specimens of En 1A steel sliding on a disc of S62 steel are measured at speeds between 93 and 655 ft/s, the normal load on the specimen varying between 0.2 and 4.5 lbf.

The coefficient of friction is shown to be dependent on sliding speed, normal load and specimen diameter, and to be a function of N^1/2U, where N is the normal load and U is the sliding speed.

It is suggested that the coefficient of friction is dependent on the specimen contact surface condition which is dependent on the specimen surface temperature. There is evidence to suggest a gradual change in the mechanism of sliding with increasing magnitude of N^1/2U from, (i) metallic abrasion and tearing of an oxide layer, (ii) to skidding on and shallow ploughing of an oxide layer, (iii) to gliding over and shearing of a soft surface layer.

It appears that the coefficient of friction is independent of, whereas specimen wear is dependent on, the disc surface condition. At low loads the material transferred from the specimen tends to form a continuous oxide layer on the disc., while at high loads there is the formation and tearing of a thick oxide layer, presenting a more abrasive surface to the specimen with a relative increase in wear. Generally specimen wear per sliding distance increases with N and decreases with U.

This paper describes work conducted on the passage of steam-water mixtures through standard sharp-edged orifices for the prediction of flow conditions.

When the stagnation enthalpy or alternatively the dryness fraction at the orifice is known, it is shown that the mass flow rate can be approximately determined.

For the case where a steam-water mixture passes through a pipeline to the atmosphere or to a low-pressure receiver so that critical flow occurs at the outlet, both the mass flow rate and the stagnation enthalpy may be approximately evaluated using an orifice meter in series with a pressure tapping located at the point of critical flow. In this case, a trial-and-error method is necessary.

The experimental results were within a range of dryness fractions from 1 per cent to 56 per cent, orifice pressures from 75 to 275 lb/in² abs., differentials from 15 to 780 mmHg under water and flow rates from 54 700 to 508 000 lb/h. Orifices of 5.591 and 6.615 in diameter were installed in 7.9-in diameter pipes which were equipped with radius (D and D/2) taps.

The method employs a correlation between the homogeneous dryness fraction x, and a corrected dryness fraction x _m necessary for evaluating the two-phase density used in the conventional single-phase meter equation.

Value analysis programmes in connection with the large scale production of two packaged liquid rocket engines are described. At the time of writing, costs in the order of $6.73 million had been removed from the total contract price of $70 million.

The fundamentals of the technique, organizational and motivational approaches and working examples are analysed and the implications reviewed. Value analysis is seen to exhibit no undesirable effects on fringe areas such as quality and reliability. It is concluded that a well structured value analysis programme is a most desirable management tool in carrying out the discipline of cost reduction.

In an earlier paper (1)^† the oil whirl of a rigid rotor was considered theoretically and compared with limited experimental findings. In this paper the comparison is taken further as a result of a fuller theoretical and experimental investigation.

This paper is divided into two parts and covers two aspects important to the military engineer. The first part argues the case for military development of construction equipment. Its basis is the recent change of emphasis in military doctrine from the concept of general war in Europe towards that of limited war in more remote parts of the world. This makes air portability the most important but not the only parameter, and from this follows the paramount need for equipment of light weight, easy to break down to loads suitable for transport by helicopter, and as easily reassembled under field conditions. Military development is necessary because of these special requirements and in some cases because no commercial equivalents exist. The paper outlines the advantages and disadvantages of the ‘military special’ equipment, and Ministry of Defence (Army) policy regarding development of Engineering Construction equipment. It also suggests ways in which the commercial designer and manufacturer might help to make this policy effective without detriment to their product, and without attempting to design specifically for the military market, which is not an economic proposition anyway.

The second part of the paper is the actual experience of its author in airborne engineer operations in Borneo. It discusses the equipment used, methods of getting it into and away from relatively inaccessible sites, and offers advice on training, packaging of ‘on-equipment’ spares, and aids to breaking down and reassembling plant for airlifted operations.

The results are given of an experimental investigation of the flow characteristics of a centrifugal compressor under non-steady flow conditions. The compressor delivered air against a rotary valve with a tee branch located in the pipe system between the compressor and the rotary valve. By varying the areas of a nozzle located at the branch end and orifices in the rotary valve a range of flow conditions could be explored. The tests showed that the surge point was displaced to a point of greater mass flow (thus reducing the flow range of the compressor); the magnitude of the displacement depended on the frequency and amplitude of the pressure pulses. Except for small fluctuations in pressure the overall compressor efficiency was reduced for all the test conditions. The flow characteristic of the compressor, as represented by the pressure-mass flow curves, were displaced under all conditions of pulsating flow, the greatest deviation from steady flow characteristics occurring with largest fluctuations in rotary valve area and at low frequencies.

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 paper describes the design and development of a new type of high energy-rate forming machine called ‘Petro-Forge’. This differs from other designs in that the energy required for the actuation of the ram is produced by a petrol combustion process. After describing the principle of operation, the design of the prototype machine, as well as its method of operation, is discussed. Extensive tests have been carried out with the aim of optimizing performance and determining the overall capabilities of the system. These results have led to the design of Petro-Forge Mark I, the essential features of which are also presented.

Mild steel (En 32B) and a 2 1/2 Ni-Cr-Mo steel in soft and heat treated conditions were subjected to reversed uniaxial strain cycling at 20°C and 450°C with continuous cycling at 2–10 c/min and also 10 min hold-times. The results are plotted in graphical form from which a number of empirical relationships are derived between plastic strain range, stable stress range, cycles to failure, strain energy, and true fracture ductility and strength. High temperature causes a marked reduction in strength for both materials, which is greater at the lower strain ranges, compared with room temperature cycling. There is little or no effect due to hold-time compared with continuous cycling at room temperature for En 25 (heat treated). There is only a slight reduction in strength at 450°C, but the situation is likely to be worse for longer hold-times.

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.

As a first stage in the development of a large, double-acting, petrol combustion actuated, high energy-rate forming machine, a compressed-air driven device was designed and constructed. This was intended to be a research vehicle for establishing general design principles, particularly as far as the structural configurations and the method of platen synchronization were concerned. The characteristic design features of this machine are discussed and an appraisal of the design is given.

Experiments were carried out with the aim of (1) determining the net energy output of the machine and (2) finding the maximum platen approach velocity for a range of values of the initial charge pressure. For the determination of the energy output of the machine, calibrated crush-gauges were used, the results being cross-checked by measuring the maximum relative velocity between the platens, and from this and the weight of the moving masses finding the maximum kinetic energy. For the determination of the maximum platen approach velocity, electric velocity transducers were used, the results being checked with the aid of a high-speed ciné camera. The maximum energy output of the machine was found to be 75 000 ft lb, which was attained with a maximum impact velocity of 80 ft/s, as aimed at in the design of the machine. Some typical examples of hot forgings produced with the machine are also presented.

The importance of establishing a realistic model of the title problem is stressed, and this is achieved by studying the process experimentally using ciné photography. Development of the discontinuous chip was traced carefully during the whole cycle of its formation and disposal, particular attention being paid to the extent and history of the plastic zone, and subsequent fracture and crack propagation.

It was interesting to observe that for the material considered, namely low carbon steel, the surfaces of the crack and chip were all sensibly straight, and cutting of the next chip began before separation of the one under consideration. It is suggested that discontinuous chip machining could perhaps be used as a method of evaluating strain rate dependencies in fracture mechanics in the same way that continuous chip machining offers possibilities for deriving stress-strain curves at high rates of strain.

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.

Apart from development testing and a few extreme conditions, a servo system spends most of its life dealing with small movements. These may be so small as to fall into the region of threshold conditions, where non-linearities become of the same order as command signals. In this paper an attempt is made to bring together some of the known facts associated with this region and the techniques used for improvement. It is hoped that this will stimulate further discussion in this interesting and rewarding topic.

In this investigation a theory is developed relating to the behaviour of the impact damper. The analysis is based on the assumptions that

(1)

two un-equispaced impacts per cycle occur in the steady state, and

Fourier series are used to represent the impact cycle and the differential equation of motion is derived. This is solved using the dynamic equations of impact to determine the boundary conditions. Three equations are developed to determine the variation of impulse, phase angle and vibrational amplitude with the change of the damper parameters.

Resonance curves are obtained and the theory is examined experimentally. The regions of validity of the above assumptions are studied both theoretically and experimentally. Non-linearity in the behaviour of this damper is very clear, especially in the range of its optimum behaviour. Two design curves are developed which can be used to determine the damper parameters necessary for a certain amplitude reduction.

A procedure is described for designing thermometer pockets having a good performance in rapidly changing steam conditions. For quick response, the bore diameter and tip wall thickness are minimized while, for safety reasons, the pocket is made conical: a low net error is achieved by choosing dimensions such that the positive and negative errors cancel out. The design theory, which takes account of the effects of fluid temperature gradients (on the assumption of fully developed turbulent flow) is discussed in detail and a practical guide is also given. Although the emphasis is primarily on steam pipes, much of the theory is of interest to the general field of fluid temperature measurement.

The use of prestrcssed concrete vessels to contain a nuclear reactor is not in itself novel, as the French in their G2 and G5 vessels at Marcoule had pioneered this form of construction, but the Oldbury vessels contained the first reactors of the integral type in which the core, boilers and gas circuit are contained within the same vessel. This type of reactor had been under consideration for some time by the author's company, and during the early part of 1960 a study had been completed which showed that this design was both feasible and economically attractive. The design formed the basis for the Oldbury Power Station, construction of which started in 1962.

The paper describes the experimental stress analysis of a range of rail sections and a fishplated joint carried out by means of a loading frame which accommodated a short length of track, hydraulic jacks with load cells, and electrical resistance strain gauges.

The most detailed test was that of the B.S. 110A rail which after being tested ‘as rolled’ was successively re-tested at states representing six stages of head wear, simulated by planing the rail head. The stress ranges determined under various loading conditions were compared with those for a bullhead rail planed to represent its known safe limit of wear and gave a guide to the permissible head wear of the B.S. 110A rail from stress criteria. The B.R. 116 lb/yd thick web rail was tested for comparison with the B.S. 110A, and rails representing three weights of the new B.S. A series were compared with three of the older B.S. R series rails of the same weights. From the test results various general conclusions have been drawn. The relationships between rail weight, head wear and fillet stresses, and the effect of different fastenings are discussed.

A fishplated joint for 60 lb/yd rail was tested. The fillet, bolthole and bending stresses on the rail end, and the bending and bolthole stresses on the fishplates were determined. Although this is a light rail by modern main-line standards, the stress distributions and the conclusions drawn are believed to be typical of joints in heavier rail also.

This paper puts forward anew theory on the operation of syphons. It proposes, and gives proof from test results, that the rising leg of a syphon can be greater than heretofore thought (i.e. it can be greater than atmospheric pressure expressed in feet of the fluid being used minus the friction loss). It also shows that the length of the down leg of a syphon has no limit. Test results are given using heated water in syphons; having residence time near the apex; using water supplied off pumps. Pressures and vacua throughout syphons are also tested.

It is shown that hydraulic gradient has no significance because the fluid stores energy in parts of some syphons; this matter is discussed in some detail. Other items discussed are friction factors to be used for syphons using water; noise in syphons; priming flows and parallel operation of syphons. It is shown that model tests for syphons have pitfalls. Lines for further investigation are indicated.

A measure, M, of the conformity or closeness of fit of gears is proposed and it is shown that there is a limit on its value; this limit is a function of the material properties and is about 2.5 times the value for involutes for gears of case hardened steel.

It is shown that no very large improvement in M can be had above that obtainable in known non-involute forms, specifically Wildhaber-Novikov gears.

A transducer has been developed to sense the variation of oil-film thickness in a thrust bearing by sweeping across the working face of the pads and ‘viewing’ them from the rotor. This device was used to compare the deflection of a circular pad with theory, and some degrees of correlation was found. The pads tested formed wedge-shaped films by elastic flexure and successfully carried considerable loads. A tentative explanation is provided for their means of starting to operate successfully.

By measurement of the unit-mass and the unit-time rates of exchange of energy between a flowing fluid and a heating or actuating source, the rates of mass flow can be directly determined, provided that certain thermodynamic properties of the fluid are known.

Various methods of application of this principle are described and an account of proving tests is given. In these tests special techniques of precision thermometry were used. The results obtained were very promising and warrant further laboratory and field investigations.

An alloy steel and a nickel-chromium alloy are shown to exhibit similar fatigue behaviour over a wide range of temperatures. Endurances tended to be time-dependent at elevated temperatures, and repeated-tension cycles were found to be more damaging than push-pull but less damaging than static-tension (creep). The behaviour was reversed at room temperature where failures tended to be cycle-dependent (number of cycles to failure independent of applied frequency) and creep loading was least damaging.

Rupture data for repeated-tension tests at approximately 10 c/min were analysed by a creep technique. For a wide range of temperature, the expressions fitted the experimental points encouragingly closely and the technique appears to be a useful method of describing this type of data. Tests at room temperature having more than 10⁴ cycles to failure were premature with respect to the analysed family of curves and this was attributed to failure occurring by a predominantly cycle-dependent mechanism. Fractures at higher stresses exhibited a ductile appearance attributed to a different fracture mechanism.

Time-dependent behaviour was enhanced by increase in the peak tensile stress, tensile mean stress, and temperature, or by decrease in cyclic frequency.

In the past, it has been a matter of concern to many people that natural gas which is available and sometimes flared to waste in desert places of the earth could not be conserved and economically transported as fuel to needy industrial countries.

To make such an operation possible, it is necessary to refrigerate the gas, which consists mainly of methane, to a temperature of — 260°F, under which condition it condenses to a liquid and shrinks to one-six-hundredth of its volume as a free gas. In this form and as a boiling liquid, it can be transported in insulated tanks built into ships specially designed for the purpose. Auto-refrigeration maintains the cargo at its boiling point and heat leakage through the insulation causes a small proportion of the cargo to boil off as gas. Such gas can either be re-liquefied by installing a refrigeration plant on board or be used as fuel in the ship's propulsion machinery.

The lecture describes the research and development work which led up to the full-scale trials in 1959 for the transportation of liquefied natural gas by sea in the Methane Pioneer. This is followed by a resume of the design requirements, building techniques and subsequent operating experience of the first two commercial ships which entered service in 1964 for the regular carriage of liquefied natural gas from Arzew in Algeria to Canvey Island in the Thames.

The design and engineering problems arising in these developments were unusual and varied, and they necessitated close co-ordination in the fields of cryogenics, metallurgy, chemical engineering and naval architecture. Not only were there problems associated with the physical properties of materials and insulants at low temperatures and the large contraction movements and strains induced by temperature change but there were problems of handling a boiling liquid continually releasing gas which, if trapped, could build up dangerous pressures. All these problems had to be faced on the large scale and assessed against the potential hazard of fire and explosion; in addition, they had to be superimposed on the somewhat unpredictable behaviour of a ship at sea whose design criteria were influenced more by experience and empiricism than by basic science.

The unusual and unprecedented nature of the project involving safety of life at sea, and affecting other users of rivers, ports and harbours, meant that from the outset there had to be close liaison and co-operation with Government Departments, Ministries, harbour and river authorities, regulatory bodies and local authorities. The successful conclusion of the project confirms the effectiveness of this co-operation and it affirms how the imagination, perseverance and technical skill of a team of engineers can be harnessed in endeavour and achievement.

In this lecture the author reports on the progress made in the development and application of creep-resisting steels over the last 20 years, with particular reference to research carried out at The Brown-Firth Research Laboratories. The properties of the more established steels are reviewed, along with those of a number of newer steels introduced during this period. These include the 12 per cent chromium variants specially ‘tailor-made’ for aircraft gas turbine discs, two improved austenitic steels and two non-stainless types: a 6 per cent chromium complex steel, and a 2 per cent chromium molybdenum vanadium aluminium nitriding type. Cast austenitic pipe steels are also discussed.

The author describes work being carried out with the object of improving the proof strength of austenitic steels, e.g. warm working and alloying with nitrogen.

Some information is also presented in respect of the creep ductility properties of a number of the steels mentioned in the paper, with special reference to weld heat effects.

The paper covers the factors which make balancing operations necessary, and outlines the principles and several methods of balancing used in factory practice. Some of the problems arising during balancing are mentioned, and methods used in overcoming them are given.

The industries of the North-east, to which mechanical engineering contributes so much, are to be seen against their historical background. Much of the developmental impetus came originally from the needs of the coal industry but the transformations wrought by technology have led to the present wide spread of industries among which coal, though vital, is no longer dominant. Notwithstanding the introduction of lighter industries, the mechanical engineer in the North-east is still mainly concerned with the heavier industries though in an almost unlimited variety of forms.