bluuebunny/crossref_metadata_2025_split huggingface dataset:
Caustic Cracking: Stress-Corrosion Tests in Sodium Hydroxide Solutions at Elevated Temperatures
Authors: Weir C. D. 
Published: October 2007

The paper describes a series of tests carried out using an apparatus specially designed for stress-corrosion investigations at high temperatures. The specimens, which were of hollow form, were inserted into the base of an autoclave and loaded by means of a lever system, through a push rod inserted in the specimen. This arrangement permitted the production of accurate notch-forms on the external surface in contact with the sodium hydroxide solutions. It was found possible to produce failure of notched specimens rapidly and consistently, but homogeneously stressed specimens were immune. The fractures were intercrystalline and typical of those occurring in practice. Dilute solutions, though not entirely impotent, were found to be very much less effective than those of high concentration. The presence (or absence) of silica in the solutions exerted no appreciable influence. Neither the addition of tannin nor the use of fine-grain steels was completely effective in preventing intercrystalline failure, though in the case of the latter, increased resistance was noted in some cases. Cathodic polarization was found to be protective while anodic polarization did not prevent, and possibly hastened, failure.
Recent Developments of the Mechanism of the Hydraulic Variable-pitch Aircraft Propeller
Authors: Milner H. L. 
Published: October 2007

After briefly outlining the main features of the variable-pitch propeller, this paper proceeds to describe the development of the piston-engined hydraulically operated propeller as a brake, both in the air and on the ground. Examples are given of the magnitude of the braking effort of a propeller when windmilling under controlled conditions and when in reverse pitch under power. The advent of the gas turbine, originally intended as a means of jet propulsion, opened up a new field of application for the variable-pitch propeller and this application with its attendant problems and their solution is discussed. Three types of gas-turbine power plant, together with the appropriate propeller arrangements are reviewed. These are: (1) the direct-connected turbine; (2) the compound-compressor turbine; and (3) the free-propeller turbine. Each engine requires a plurality of controllable pitch stops peculiar to the engine type, and these are described. The necessity for powerful controlling forces in maintaining the blades at any given pitch angle is made clear by consideration of the centrifugal action of a blade element, and an example of the magnitude of these forces is given for a specific case. Brief reference is made to developments in blade bearings, followed by an illustrated description of a contra-rotating propeller.
A Theoretical Investigation of Roll Flattening
Authors: Bland D. R. 
Published: October 2007

A method of finding the distortion of the roll surface when subject to a known pressure distribution is described. This method is then combined with a plastic-flow theory of rolling to determine the shape of the arc-of-contact and the pressure distribution over it when neither of these are known beforehand. Apart from the assumptions inherent in the theory of plastic flow, two assumptions only have been made: that the roll is in a state of plane strain and that the shape of the arc-of-contact is independent of the distribution of the balancing forces. The accuracy of the results is estimated to be 20 per cent. This paper shows that: first, it is not necessary to assume a parabolic pressure distribution to obtain a quantitative result; secondly, Hitchcock's solution (Hitchcock 1935)† is within the limits of error of the more fundamental solution and remains the most suitable method, for practical purposes, of allowing for roll flattening; thirdly, the main feature of the arc-of-contact is the depression in the region of peak pressure and the compensating greater curvature at both ends. This is a theoretical confirmation of Orowan's experiments (Orowan 1943).
Gear-Tooth Stresses at High Speed
Authors: Tuplin W. A. 
Published: October 2007

If the maximum stress in a gear tooth is less than the fatigue limit for the material, the tooth should not fail even after indefinitely prolonged running. Fatigue data collected in the conventional way suggest that the number of stress cycles required to cause failure of a given material under any particular stress is independent of the time-rate of repetition of stress. It should therefore be permissible to stress any gear, regardless of its speed, up to the fatigue limit for its material, although this suggestion may need modification because of the difference between the impulsive nature of the application of load to a gear, and the more gradual fluctuation of stress in a fatigue-test specimen of the Wöhler type. Where high-speed gears have failed under stresses apparently lower than the fatigue limit, it becomes necessary to consider whether the actual stress was as low as had been supposed. Errors of pitch and profile in gear teeth may cause actual stresses to be higher than nominal stresses by an amount that increases with speed in any particular installation, up to a limit that would not be exceeded even at infinite speed. The nominal permissible stress (corresponding to the mean transmitted torque) should therefore take account of probable errors in the teeth. High tooth-loads may also be induced by running a geared system in a condition approaching that of resonance with some type of vibration. In general, this danger is more likely in high-speed installations than in others, and it is not always wise to follow the usual practice of ignoring its possibility.
The Variation of the Coefficient of Static Friction with the Rate of Application of the Tangential Force
Authors: Parker R. C. , Farnworth W. , Milne R. 
Published: October 2007

The coefficient of static friction has been measured for a number of different materials under impact conditions. An analysis of the conditions of impact, derived from collision between solid bodies, and from a suitable hydraulic system, showed the latter to be the more convenient and equally effective method of applying tangential force. The method adopted consisted of feeding oil at a constant rate into an oil cylinder, the piston of which constituted the striking head. The friction members were so arranged that the struck member was in the form of a bar that was clamped between two massive plates. The normal force was applied hydraulically and the tangential force was measured by wire resistance strain-gauges. The static friction was measured for rates of application of the axial force up to 103 tons per sec. Under dry conditions the friction increased with the rate of applied force, an effect more pronounced between a non-metal and a metal than between metals. Lubrication with oil diminished the variation of friction with rate of application of force for all combinations of materials tested. The magnitude of this effect was sufficient to explain a type of failure commonly encountered with safety clutches, and similar mechanical devices.
Overall and Stage Characteristics of Axial-flow Compressors
Authors: Howell A. R. , Bonham R. P. 
Published: October 2007

Axial compressors, particularly near design conditions are, on the whole, amenable to analytical treatment, and usually a good estimate of their performance can be made before they are run. Away from the design points, the performances are conveniently thought of in terms of the overall characteristics of pressure-rises, temperature-rises, and efficiencies plotted against mass-flows. For these performance estimations the aerodynamicists must have knowledge of the stage and overall characteristics of previous compressors and of methods of predicting such characteristics. Obtaining the overall characteristics from a stage-by-stage calculation is a lengthy process, but, fortunately, simplified methods can often be used. In this lecture we have indicated some of the methods that are employed to obtain and predict the overall characteristics and their associated stage characteristics. Reference is made to test-results from various National Gas Turbine Establishment research compressors, one of which uses water instead of air as the working fluid, and also to published information on other compressors. The importance of blade and test errors on performance and analysis work is also emphasized. In our simplified method of analysis and prediction of overall characteristics we have reduced the individual overall characteristics at each speed to what are, in effect, mean stage characteristics plotted relative to their maximum-efficiency-point conditions. Then the maximum-efficiency-point conditions at the different speeds are plotted and considered separately.
Form Grinding by Mechanical and Optical Methods
Authors: Cooke E. A. 
Published: October 2007

Methods of producing profile tools and gauges remained for many years particularly conservative and often expensive in the use of highly skilled toolroom labour. Up to comparatively recent times it was not uncommon to find high-class machine tools, such as jig boring machines, applied to the task of marking out centres of radii and so on, because they embody accurate means of measurement. The early introductions of special-purpose machines for this work were mainly continental, and the advantages normally to be expected from the use of such machines were not altogether realized as the result of designs based inherently upon the use of master copy. Later, machines were developed intended to be independent of copy to a very large extent, and this was facilitated by a trend of component design based upon the use of geometric and definable shapes wherever possible. The application of optics to this class of machine, mainly in the form of microscopes or projection systems, is now fairly common, and in its application to engineering the optical projector perhaps reaches its highest standard of definition and accuracy of reproduction. The incorporation of optical and electrical measuring devices has also helped greatly in providing an accurate and versatile machine tool. The object of the paper is to reveal aspects of design more peculiar to this type of machine, particularly the association of optics and mechanical linkages, and is therefore mainly confined to the copying and generating mechanisms. It also indicates the development trend of this class of design. Methods of forming and truing the grinding wheel are not considered.
On the Solution of Beam-on-elastic-foundation Problems by Means of a Mechanical Analogue
Authors: Wells A. A. 
Published: October 2007

The equation d4 y/ dx4- f(x)y + g(x) = 0 may be solved by means of the differential analyser, but only straightforwardly when the four boundary conditions are specified at one point. When the equation is associated with beams on elastic foundations, or elastic shells, the boundary conditions are more often specified at two points, and a quicker method of solution is desirable. In the analogue, direct use is made of the beam in the form of an elastic wire, supported at intervals in cradles on which weights may be made to simulate the terms f(x)y and g(x); the wire takes up a transversely deflected form which may be measured, and boundary conditions are imposed where they are required. A specific problem is examined and the results are shown to agree reasonably with the solution by calculation. A disadvantage when d2 y/dx2 is required is the inaccuracy inherent in differentiating by finite differences, but for engineering calculations the simplicity of the method may have its advantages. The solution of a typical pressure-vessel problem, by means of the analogue, is described.
Screws and Screwing
Authors: Eatough C. 
Published: October 2007

The paper describes the various commercial methods of producing screw threads by cutting, rolling, grinding, and milling. The operating principles on which the several processes depend are dealt with and their advantages and limitations are discussed. A workshop method of determining the torque required for tapping and for threading is described, and a chart based on the results gives figures suitable for determining the power of machines to undertake the tapping or screwing of a wide range of work. A mathematical treatment of the clearance between the flanks of a tool and a screw thread is given. This permits the investigation of clearances at any point on the tool profile or flank, and enables relief and tilt angles to be chosen to suit various conditions of lead, thread profile, and diameter for both internal and external threads. For design purposes, a simple formula is available which gives clearance angles in relation to the portions of the tools most subject to interference.
Mechanical Handling
Authors: Roebuck A. , Carnegie H. S. , Taylor E. G. 
Published: October 2007

The authors of this paper were members of the team appointed by the Anglo-American Council on Productivity to study and report on materials handling in industry in the United States of America. The purpose of the paper is to focus attention on certain aspects of the report, “Materials Handling in Industry”, which contains the findings, conclusions, and recommendations of the team, with particular reference to the application of mechanical handling inside factories. The importance and advantages of applying modern techniques in materials handling and also the need for more extensive use of known methods and equipment already available in Britain, are points particularly stressed by the authors. The opinion is expressed that better materials handling offers a greater opportunity to cut production costs and to increase productivity than any other single factor. The paper enlarges on some of the conclusions listed in the report, such as those relating to applications of methods and newer techniques, periodic reviews, layout and design, team work, and use of small power tools.
On the Calculation of Forces in Power-Shovels
Authors: Jenike A. W. 
Published: October 2007

A power-shovel is essentially a revolving crane mounted on a self-propelled carriage and equipped with a digging device. The paper describes the process of calculation of forces for the stage of digging, that is, for the time when the dipper is in contact with the excavated face, and the influence of forces arising during slewing on the boom and the handle. It is shown that the maximum values of the main forces acting in the shovel are governed by the maximum values of the bail-pull and of the braking torque of the crowd-motion. In view of the fact that the handle and boom form a toggle arrangement, the induced forces will reach destructive values unless the governing forces are controlled. Equations relating the forces are established and, as an example, a cu. yd. power-shovel, weighing 17·3 tons is analysed. The main forces are evaluated and presented graphically for the area of action of the dipper after which the critical loading conditions are specified.
The Training of Craftsmen
Authors: Loxham John 
Published: October 2007

The author outlines a plan to secure for each engineering apprentice the best possible development of his natural aptitudes and abilities as a potential craftsman, technician, or fully trained technologist. This plan calls for the close co-operation of all the agencies concerned with education and with the organization of labour, including the responsible ministries, universities and technical colleges, professional institutions, local education authorities, and, perhaps most of all, the employer. Emphasis is given to the best possible provision of facilities, both in works and in colleges, for those who show capacity for training as highly skilled craftsmen. The importance of the contribution of such men to the national economy is examined, and regret expressed at the relatively inadequate provision made, both in works and in colleges, for the training of those whose primary interests are in actual manufacture. The bearing of recent changes in legislation affecting the structure of secondary education, and the availability of technical courses in their relationship to the age, quality, and outlook of recruits entering the engineering industry, is discussed in some detail. The possibility of setting up new national awards in craftsmanship, with the co-operation of all the agencies concerned, is foreshadowed.
Steam Piping for High Pressures and High Temperatures
Authors: Bailey R. W. 
Published: October 2007

Consideration of the following matters is made important by recent progress to high operating steam pressures and temperatures: the changing and more favourable distribution of stress in a pipe, the accompanying creep, and their application to the rational and economical design of steam piping; the determination of permissible working stress; differences in American and British procedures and consequent differences in stress magnitudes; the influence of operating fluctuations of pressure and temperature and the choice of a design temperature at rated pressure to provide for them; tentative considerations of behaviour of ferritic and austenitic steels; the action of creep at operating pressure and temperature in reducing and removing the initial thermal expansion loading of a pipe-line, and in imposing it fully when cold. In these connexions some consideration should be paid to bolted, or otherwise removable, joints at terminal or other special positions; the problem of making a joint between ferritic and austenitic steel piping and components; the factors of materials and corrosion; promised adequacy of existing ferritic steels for present requirements, and application of the principles operative at very high temperatures to piping for less advanced conditions, and economy arising therefrom.
Creep under Complex Stress Systems at Elevated Temperatures
Authors: Johnson A. E. 
Published: October 2007

During the last few years a programme of creep tests under general stress systems at elevated temperatures has been carried out at the National Physical Laboratory (N.P.L.), using four metallic alloys (a cast 0.17 per cent carbon steel, an aluminium alloy—RR. 59, a magnesium alloy containing 2 per cent aluminium, and a nickel-chromium alloy—Nimonic 75) chosen as representative of basic groups of materials used in practice, and tested at temperatures lying within their normal working range. In this paper an effort is made at a general comparison of the complex stress creep characteristics of the materials, and such generalizations as appeared possible. Appendices are provided, dealing respectively with: experimental data for one of the materials (data for the others having been published elsewhere); the effect of hydrostatic stress on complex stress creep, and specific examples of application of the data.
Problems in Design and Research on Condensers of Vapours and Vapour Mixtures
Authors: Colburn Allan P. 
Published: October 2007

The theoretical background is outlined for condensation of pure and mixed vapours in conditions of a film-type condensate. The effect of vapour velocity is important for both pure vapours and those mixed with non-condensable gases. On the basis of the fundamental mechanism of condensation involved, approximation procedures are developed which are particularly useful for designers who wish to have quick methods for use in estimating and rough checking. It is concluded that there is great need at present for testing theoretical and approximate methods against full-scale performance data.
Friction Losses in Turbulent Pipe-flow
Authors: Prosser L. E. , Worster R. C. , Bonnington S. T. 
Published: October 2007

Significant developments in the theory of turbulent flow in smooth and rough pipes are reviewed to establish a rational basis for the commonly accepted logarithmic laws for pipe friction. The Prandtl (1932)‡ smooth-pipe law, , where f is the friction coefficient in the formula , agrees with measured results on smooth pipes up to Reynolds numbers of at least 3 × 106. With rough pipe walls and sufficiently high Reynolds numbers, viscosity (and hence Reynolds number) ceases to have any direct effect and the friction coefficient depends on wall roughness and pipe size only. Almost all practical cases of water flow in commercial pipes lie between these two extremes of completely smooth and fully rough conditions, where the friction coefficient varies with both Reynolds number and roughness. Exponential flow formulae of the Manning type— V = *** Am1xiy—can be rearranged into a more rational form f = B( Re) p( k/d) q*** relating f to Reynolds number and relative roughness for a given class of pipe carrying a fluid of given viscosity. A detailed study is made of published test data on wrought-iron and steel pipes which generally operate in the transition zone, and an exponential formula is derived which agrees with these results. This is found to be similar to that given by Blair for this class of pipe. The relative merits of these exponential formulae, and of the Colebrook-White transition function, are discussed and it is concluded that, for most practical cases of water flow in pipes, the simple formulae are no less reliable.
Load Distribution in Riveted and Spot-welded Joints
Authors: Williams D. 
Published: October 2007

It is known that a spot weld is a much more rigid connexion between two sheets than a rivet, and that this is likely to have some bearing on the relative strengths of the two types of joint. A recent test has emphasized this point. A spot-welded box, identical with a riveted box except that spot welds replaced rivets, failed at about two-thirds of tie failing load of the riveted box in spite of the fact that the shear strength of an individual spot weld was nearly twice that of a rivet, as determined by tests. In this paper the problem is examined theoretically on the basis of experimentally obtained stress-strain curves for riveted and spot-welded joints in shear. The theoretical treatment takes account of the plastic, as well as the elastic, part of the stress-strain curves, and examples are given of the relative behaviour of the two types of joint in certain simple structural elements. A multi-row lap joint is the first example chosen, and the second is a stringer reinforced panel in which there is appreciable shear-lag. In each example the riveted specimen gives the higher failing load (assuming the fastenings fail and not the connected members), although the experimental failing load of the individual rivet is less than half that of the spot weld. For lower loads, curves are shown which indicate the radical change that takes place in the distribution of shear among the rivets and welds, as more and more of them are loaded beyond their yield points. While such changes are of only incidental interest so far as the ultimate failing load of the structure is concerned, they are of paramount interest when assessing the life of the structure under repeated loading at loads that may be small compared with the ultimate load, for the distribution of shear among the fastenings is then clearly an important consideration. The shear-lag case is of interest as showing how the difference between rivet and weld shear flexibility tends to be masked by that of the sheet panel connecting the booms and stringers. It is therefore a useful example for emphasizing that the character of the structure must be taken into account, as well as the individual properties of the fastenings, when comparing the likely behaviour of rivets and welds.