scholarly journals A high-speed fatigue-tester, and the endurance of metals under alternating stresses of high frequency

1912 ◽  
Vol 86 (584) ◽  
pp. 131-149 ◽  
Keyword(s):  
High Speed ◽  
Early Stage ◽  
National Physical Laboratory ◽  
Fatigue Tests ◽  
General Nature ◽  
Wrought Iron ◽  
Physical Laboratory ◽  
The Subject ◽  
Algebraic Difference ◽  
The Mean

The deterioration of metals under the action of stress varying rapidly between fixed limits has keen the subject of much experimental investigation. It is found that the important factor in the rate at which this "fatigue" goes on is the algebraic difference of the limits between which the stress varies, usually called the "range of stress"; and that the absolute position of these limits matters little, provided, of course, that the mean stress is not too large. The number of applications of a given range of stress required to fracture the piece increases as the range is diminished, the general nature of the relation between the two being as shown in the curve (fig. 1), which represents the results of a series of tests made by Dr. Stanton on mild steel. In these observations the stress alternated between compression and tension, the ratio of the compression and tension limits being 1·09. The form of the curve suggests that a range of stress not much below 25 tons, which in an average specimen would just cause fracture alter a million reversals, could never break the bar, however often applied. One of the chief objects of the fatigue tests hitherto made has been to discover tins "limiting range." At an early stage in these investigations the question was raised whether the endurance by the material of a given cycle of stress is affected by the rate of repetition of the cycle. Besides its intrinsic interest, tins question is of importance because on the answer to it depends the possibility of reducing the excessive amount of time taken to carry out fatigue tests. The determination within a few per cent, of the limiting range requires several separate tests in which the cycle is repeated at least a million times, and even that number is not always sufficient to give a reasonably close approximation. Wöhler worked with 60 to 80 reversals per minute, and he found that the same wrought iron which could just sustain a million applications of a range of 23 tons broke after 19 million repetitions of a range of 17½ tons. The more recent machines have keen run at much higher speeds, and there is now a machine of the Wöhler type at the National Physical Laboratory which gives 2000 cycles of bending stress per minute. Even at this speed, which I believe is the highest yet reached under conditions admitting of accurate measurement, it takes eight hours to do a million reversals.

scholarly journals High-frequency fatigue tests

1925 ◽  
Vol 109 (749) ◽  
pp. 119-143 ◽  
Keyword(s):  
Mild Steel ◽  
High Frequency ◽  
High Speed ◽  
Fatigue Testing ◽  
National Physical Laboratory ◽  
Fatigue Tests ◽  
Research Committee ◽  
Engineering Research ◽  
Physical Laboratory ◽  
The Cost

The experiments on high-frequency fatigue in copper, Armco iron, and mild steel described in the following paper were carried out in the Engineering Laboratory, Oxford, for the Fatigue Panel of the Aeronautical Research Committee. The cost of the apparatus was defrayed by a grant from the Engineering Research Board of the Department of Scientific and Industrial Research. In 1911 Prof. B. Hopkinson called attention to the importance of ascertaining whether the fatigue limit of metals was dependent on the rate of alternation of stress. He designed and made an electric alternating directstress machine, and published the results of tests on mild steel carried out at about 7,000 periods per minute (116 per second), which was more than three times as fast as any tests made up to that time. The results at this speed were compared with those made by Dr. Stanton at the National Physical Laboratory on the same material at 2,000 periods per minute (33 per second). Prof. Hopkinson considered that the results showed that speed had a marked effect, but he did not consider that his tests were conclusive. In the light of the knowledge gained on fatigue testing since that date neither set of tests can be considered satisfactory. The question is of importance to the users of high-speed machinery. It is also of importance when comparisons are made between tests carried out at different speeds, and, finally, it has a bearing on the causes of fatigue failure. For these reasons it appeared to be desirable to make a more thorough investigation, and, if possible, to extend the tests to very much higher speeds.

A Critical Review of German Research on High-Speed Airflow

1946 ◽  
Vol 50 (432) ◽  
pp. 899-934 ◽  
Author(s):  
R. Smelt
Keyword(s):  
High Speed ◽  
Great Increase ◽  
National Physical Laboratory ◽  
High Speed Flow ◽  
Fundamental Study ◽  
Speed Flow ◽  
Physical Laboratory ◽  
Operational Problem ◽  
German Research ◽  
The Subject

Even before 1939 the problems of high-speed flow were receiving a great deal of attention in the German aeronautical world. Their leading aerodynamicists, Prandtl, Busemann and Schlichting among others, had contributed largely to the theory of compressible fluid flow, and basic experimental research in the high-speed field had begun both at Aachen and at Göttingen. The activity in Germany in this particular field before the war was, in fact, much greater than in Britain, where Mr. Lock and his co-workers at the National Physical Laboratory carried practically the entire responsibility for such work.The great increase in aircraft speeds during the war, and in particular the arrival of jet propulsion, completely changed our attitude to the subject in Britain. What had been an absorbing fundamental study became, quite suddenly, an important operational problem, looming large in every new fighter design.

scholarly journals The colorimetric properties of the spectrum

1931 ◽  
Vol 108 (759) ◽  
pp. 576-576 ◽  
Keyword(s):  
Distribution Curve ◽  
National Physical Laboratory ◽  
Group Of Seven ◽  
Physical Laboratory ◽  
Luminosity Functions ◽  
Direct Measurements ◽  
Energy Distribution Curve ◽  
The Mean ◽  
General Method

The paper describes an investigation carried out at the National Physical Laboratory to determine the colorimetric properties of a group of seven subjects as obtained from direct measurements of the trichromatic coefficients of the spectrum on a trichromatic colorimeter. The “spectral distribution curves of the primaries,” by means of which the colorimetric quality of a heterochromatic stimulus may be computed from its energy distribution curve, are obtained by combining the experimentally determined trichromatic coefficients with the International Standard visibility curve. This procedure is a simplification, applicable to the mean results of a normal group, of a general method by which the chromatic and luminosity functions of any subject or group of subjects can be determined from one set of observations. The general method is described in an Appendix.

scholarly journals V. An investigation of the flow of air an aёrofoil of infinite span

1926 ◽  
Vol 225 (626-635) ◽  
pp. 199-245 ◽  
Keyword(s):  
Unit Length ◽  
Lift Coefficient ◽  
National Physical Laboratory ◽  
Inviscid Fluid ◽  
Mean Velocity ◽  
High Lift ◽  
Physical Laboratory ◽  
The Mean ◽  
Definition Of ◽  
Stream Lines

1. A great deal of attention has been directed of late years to the development of a rational theory of the aёrofoil. Prof. L. Prandtl and others in Germany have applied the principles of the hydrodynamics of a perfect fluid to the aerofoil with remarkable results, whilst investigators in this country have extended this work and have verified experimentally many of the deductions of the Prandtl theory. The assumptions underlying the work of Prandtl are, however, of uncertain validity, and it has become a matter of great importance to add to existing experimental evidence of the fundamental characteristics of the motion of a viscous fluid round an aёrofoil. With this purpose in view an aerofoil section of fairly high lift coefficient was selected, and a model of it tested in the Duplex Tunnel at the National Physical Laboratory, the field of flow being thoroughly explored with a wind-velocity meter. At the same time the theoretical stream-lines corresponding to inviscid fluid flow were determined experimentally, as described in Part II of this paper. The case considered is that of an aerofoil of infinite span, the flow being two-dimensional. A comparison was made of the theoretical and experimental distributions of pressure over the surface of the aёrofoil, as well as of the two sets of superposed stream-lines. The work has provided an experimental verification of the law of Kutta and Joukowsky, that the product of the mean velocity and density of the fluid and of the circulation (according to the hydrodynamical definition of this term) around a contour enclosing the aerofoil is equal to the lift of the aёrofoil (per unit length). It has further shown that the circulation around the aёrofoil is constant within the limits of experimental error and independent of the contour of integration chosen, provided that the contour line does not at any part approach too near to the aerofoil, and also that it cuts the trailing “wake” approximately at right angles to its core. The lowest value of the circulation found (calculated for a contour as close to the aёrofoil surface as the observations permitted) was about 6½ per cent, less than the value corresponding to the lift coefficient; this is hardly outside the limits of experimental accuracy in the neighbourhood of the aёrofoil.

scholarly journals VIII. Gaseous combustion at medium pressures. Part I. —Carbon monoxide air explosions in a closed vessel. Part II. —Methane-air explosions in a closed vessel

1926 ◽  
Vol 225 (626-635) ◽  
pp. 331-356 ◽  
Keyword(s):  
Carbon Monoxide ◽  
National Physical Laboratory ◽  
Closed Vessel ◽  
Engineering Research ◽  
The Past ◽  
Physical Laboratory ◽  
Wide Range ◽  
The Subject ◽  
Temperature And Pressure ◽  
Air Explosion

During the past five years a programme of research involving air-fuel explosions in a closed vessel has been in progress at the National Physical Laboratory for the Engineering Research Board of the Department of Scientific and Industrial Research. Among the experimental results obtained, those relating to Carbon Monoxide and Methane were considered likely to be of interest to the Society, and form the subject of the present communication. Of the two investigations described, the first gives experimental data on the respective influences of hydrogen-air and water vapour on a carbon monoxide-air explosion, and the second relates to explosions of methane and air over a comparatively wide range of initial temperature and pressure.

scholarly journals John Edward Lennard-Jones, 1894-1954

1955 ◽  
Vol 1 ◽  
pp. 174-184 ◽  
Keyword(s):  
Royal Society ◽  
Trinity College ◽  
National Physical Laboratory ◽  
Grammar School ◽  
Atoms And Molecules ◽  
Lennard Jones ◽  
Physical Laboratory ◽  
The Subject ◽  
The University ◽  
University Of Manchester

John Lennard-Jones was born on 27 October 1894 in Leigh, Lancashire and was educated at Leigh Grammar School, where he specialized in classics. In 1912 he entered Manchester University, changed his subject to mathematics in which he took an honours degree and then an M.Sc. under Professor Lamb, carrying out some research on the theory of sound. In 1915 he joined the Royal Flying Corps, obtained his Wings in 1917 and saw service in France; he also took part in some investigations on aerodynamics with Messrs Boulton and Paul and at the National Physical Laboratory. In 1919 he returned to the University of Manchester as lecturer in mathematics, took the degree of D.Sc. of that university and continued to work on vibrations in gases, becoming more and more interested in the gas-kinetic aspects of the subject as his paper of 1922 in the Philosophical Transactions of the Royal Society shows. In 1922, on the advice of Professor Sydney Chapman, he applied for and was elected to a Senior 1851 Exhibition to enable him to work in Cambridge, where he became a research student at Trinity College and was awarded the degree of Ph.D. in 1924. At Cambridge under the influence of R. H. Fowler he became more and more interested in the forces between atoms and molecules and in the possibility of deducing them from the behaviour of gases.

The Thermal Rating of Worm Gearboxes

1944 ◽  
Vol 151 (1) ◽  
pp. 326-337 ◽  
Author(s):  
Harry Walker
Keyword(s):  
Temperature Rise ◽  
High Speed ◽  
Testing Machine ◽  
National Physical Laboratory ◽  
Worm Gear ◽  
Variable Load ◽  
Power Losses ◽  
Heating And Cooling ◽  
Physical Laboratory ◽  
Worm Gears

The paper deals with the factors affecting the temperature rise of totally enclosed self-lubricated gearboxes, with particular reference to worm gearboxes, and is based on observations obtained from a power circulating apparatus through worm gears which has provision for the accurate measurement of efficiency and temperature rise under variable load and speed. The theory underlying the heating and cooling of gearboxes is discussed, for gears running under continuous load and also under a repeated cycle of intermittent load. Temperature rise depends on the heat-dissipating capacity of the gearbox and the power losses within the box; heat-dissipating capacity is dealt with in relation to surface area of the box, speed of the gears, and artificial cooling by air fan; power losses are discussed under the headings of efficiency and oil drag losses. It is shown that gear speed and turbulence in the lubricant contribute considerably to heat-dissipating capacity, and that oil drag losses play an important part, particularly on large gears running at moderate or high speed. Cooling by air or other means is shown to result in an increase in power capacity (for a given allowable temperature rise) much more than in proportion to the increase in heat-dissipating capacity of the box, owing to a higher overall efficiency when transmitting heavier loads. Results of worm gear efficiency tests carried out in the past on the Daimler-Lanchester testing machine at the National Physical Laboratory on the author's design of worm gear, which gave the highest efficiency of any published tests carried out on this machine, are reconsidered in the light of recent work and it is contended that the National Physical Laboratory machine gives efficiency figures which are in general higher than the true efficiency.

scholarly journals Thomas Lydwell Eckersley, 1886-1959

1960 ◽  
Vol 5 ◽  
pp. 69-74
Keyword(s):  
Transmission Lines ◽  
Good Deal ◽  
National Physical Laboratory ◽  
Radio Waves ◽  
Thomas Henry Huxley ◽  
Physical Laboratory ◽  
University College London ◽  
The Subject ◽  
The University ◽  
Alternating Magnetic Fields

Thomas Lydwell Eckersley was born on 27 December 1886 in London. His mother was a daughter of Thomas Henry Huxley who was at one time President of the Royal Society. From the age of 2 1/2 to 6 Eckersley lived in Mexico where his father, who was a civil engineer, was engaged in building a railway. In his early life Eckersley was interested in engineering and in scientific devices and he had a desire to emulate his father and to build bridges. At the age of 11 he went to Bedales School where he came under the influence of an able teacher of mathematics who laid the foundations of his life-long interest in the subject. He left school at the early age of 15 and went to University College London, to read engineering, but he found he was not really as interested in the practical aspects of the work as he had at one time supposed, and he achieved only a Second Class degree. On leaving the University he went to the National Physical Laboratory where he found himself working under Albert Campbell on the behaviour of iron under the influence of alternating magnetic fields. Through this work he became interested in magnetic detectors for radio waves, and he did a good deal of experimenting with radio apparatus at his own house. His first paper was published, jointly with Campbell, on the effect of Pupin loading coils on waves travelling along transmission lines.

scholarly journals On the effect of the form of the transverse section on the frictional resistance to the motion of an elongated body parallel to its length through a fluid

1915 ◽  
Vol 92 (636) ◽  
pp. 144-157 ◽  
Keyword(s):  
Eddy Currents ◽  
Transverse Section ◽  
Practical Importance ◽  
Frictional Resistance ◽  
National Physical Laboratory ◽  
Cornell University ◽  
Physical Laboratory ◽  
Series Of Experiments ◽  
The Subject

1. The great increase in tire lengths of the parallel mid-bodies of recently constructed submarines and airships has raised into prominence the question of the frictional resistance of such elongated bodies moving parallel to their length through fluids, like air and water, whose viscosities cannot be neglected. This resistance increases as the length increases, and benefits comparable with the head and tail resistances, which for short bodies constitute nearly the whole resistance. In general, the problem of greatest practical importance is the determination of the frictional resistance when the motion is rapid enough to produce eddy currents in the fluid, but the difficulties in the way of a general theory of eddy current motion have presented a solution being reached. The simpler problem of the resistance offered by the walls of a circular pipe to the turbulent flow of viscous fluid through the pipe formed the subject of extensive series of experiments by Saph and Schoder, of Cornell University, and by Stanton and Pannell at the National Physical Laboratory.

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