An attempt is made here to explain the observed phenomena in the yielding and ageing of mild steel, described in two previous papers, in the general terms of a grain-boundary theory. On this hypothesis, a satisfactory explanation of the variation of the lower yield point with grain size may be developed. It is shown that strain-ageing must involve two processes: a healing of the grain-boundary films, coupled with a hardening in the grains themselves. A discussion of the possible nature of the grain-boundary film is also undertaken.
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J D Lawson 1957 Proc. Phys. Soc. B 70 6
Calculations of the power balance in thermonuclear reactors operating under various idealized conditions are given. Two classes of reactor are considered: first, self-sustaining systems in which the charged reaction products are trapped and, secondly, pulsed systems in which all the reaction products escape so that energy must be supplied continuously during the pulse. It is found that not only must the temperature be sufficiently high, but also the reaction must be sustained long enough for a definite fraction of the fuel to be burnt.
H Kolsky 1949 Proc. Phys. Soc. B 62 676
A method of determining the stress-strain relation of materials when stresses are applied for times of the order of 20 microseconds is described. The apparatus employed was a modification of the Hopkinson pressure bar, and detonators were used to produce large transient stresses. Thin specimens of rubbers, plastics and metals were investigated and the compressions produced were as high as 20% with the softer materials. It was found that whilst Perspex recovered almost as soon as the stress was removed, rubbers and polythene showed delayed recovery, and copper and lead showed irrecoverable flow. The phenomenon of delayed recovery is discussed in terms of the theory of mechanical relaxation and memory effects in the material.
E H Kerner 1956 Proc. Phys. Soc. B 69 808
In a continuation of a previous paper, it is shown here how the gross bulk and shear moduli of a composite material consisting of a suspension of grains or a compact of grains may be deduced. The grains are assumed to be perfectly bonded to the suspending medium or to each other, and are taken to be spheres in the mean. By using an averaging procedure due to Bruggeman, and analysing the effect of a uniform hydrostatic compression and of a uniform tension on an average grain, a pair of de-coupled equations for the gross moduli is found for suspensions. When the suspending medium vanishes and the grains are packed, these equations become coupled and there is exhibited a discontinuity in the gross moduli. The bulk coefficients of linear expansion of the two kinds of composites are found from an analysis of the dilatation and bulk stress for average spherical grains when the composite as a whole is subjected to some small temperature change. All results are free of any limitation on the number of components.
E A Owen and D Madoc Jones 1954 Proc. Phys. Soc. B 67 456
The paper gives an account of measurements made on the lattice parameter of cobalt when the material contained crystal grains of different sizes as found in fine dust, filings and annealed solid rod. The stable structure of cobalt was found to depend upon the grain size: between room temperature and about 450°c when the grain size is very small, as in cobalt sponge, the stable structure is face-centred cubic; when the grain size is larger, as in a solid rod, the stable structure is close-packed hexagonal; when there is a range of grain size, as in fine filings a mixture of these two structures is observed. At temperatures above 450°c cobalt sponge is still face-centred cubic, and the filings and rod also now show face-centred cubic structure with the same lattice parameter (3.5370kx at 18°c). The lattice constants of the hexagonal close-packed structure at 18°c are: a = 2.5003kx, c/a = 1.6322.
Different results were obtained according as the material was maintained and examined at elevated temperature or was quenched from elevated temperature and examined at room temperature. All specimens of cobalt, whatever the grain size, annealed at about 1000°c and quenched showed a mixture of the two structures although with cobalt sponge the amount of the hexagonal structure was very small compared with the amount of the cubic structure.
Combining these results with recent results by Newkirk and Geisler (1953) it is possible to present a fairly complete picture of the effects observed, between room temperature and 1220°c, with material examined at elevated temperature and with quenched material examined at room temperature. The main results fit the theory of the imperfect hexagonal structure put forward by Edwards and Lipson (1943).
A cubic face-centred structure with lattice parameter (3.5540kx) greater than that of the cubic lattice ordinarily found (3.5370kx) was observed with filings quenched from temperatures between about 600°c and 840°c. It is suggested that the material giving this lattice parameter is in a metastable state.
The thermal expansion of cobalt sponge is represented by a smooth curve the equation of which, for temperatures up to 650°c, is the quadratic at = α0(1 + αt + βt2), where a0 = 3.5362 kx; α = 12.297 × 10-6; β = 2.042 × 10-9. It shows no transformation such as is found at about 450°c with material in solid form. No other high-temperature transformation was observed.
T S Moss 1954 Proc. Phys. Soc. B 67 775
The data given on the optical properties of InSb are analysed and precise values for the position and temperature dependence of the absorption edge are given.
The variation of the position of the absorption edge with impurity concentration is explained by the very low effective mass of the conduction electrons, which is estimated by three methods to be about 0.03 of the free electron mass.
D Tabor 1954 Proc. Phys. Soc. B 67 249
The Mohs hardness scale consists of ten minerals arranged in increasing order of hardness such that each mineral will scratch the one on the scale below it, but will not scratch the one above it. Although these minerals are generally considered to be brittle, experiments show that under local indentation and during sliding their behaviour is primarily determined by the plastic properties of the minerals. This suggests that there should be some relation between the Mohs hardness and the indentation hardness of the minerals.
Experiments with metals show that in general a metal surface of indentation hardness Hs will be scratched by a point of hardness Hp if Hp gt-or-equal, slanted 1.2 Hs. Thus a scratch hardness scale can be constructed in which each standard has an indentation hardness at least 1.2 times greater than the preceding standard. The scratch hardness number is then proportional to the logarithm of the indentation hardness. Excluding diamond, which is anomalous, this type of relation is found to apply to the Mohs standards, and it is found that each standard is approximately 60% harder than the preceding one.
W Ehrenberg and R E Siday 1949 Proc. Phys. Soc. B 62 8
In view of mis-statements made in the literature, the origin of the refractive index in electron optics is discussed in some detail, and the uniqueness of an expression previously given is demonstrated. On this basis, some general properties of electron optics are investigated.
A relation between ray direction and wave normal is obtained. Whereas the refractive index is unique in terms of the magnetic vector potential A, this itself is arbitrary to some extent. It is shown that A must, for purposes of electron optics, be chosen so as to satisfy Stokes' theorem and that, if it does, no observable effects result from the arbitrariness of A. An expression for the optical path difference is given in terms of the magnetic flux enclosed. The results are applied to a number of questions, viz. the differential equations for trajectories, the focusing properties of an axially symmetric field and the interference pattern produced by two converging bundles of rays which enclose a magnetic flux.
E O Hall 1951 Proc. Phys. Soc. B 64 742
In this paper, some of the factors which influence the appearance of Lüders bands in mild steel are studied. It is shown that the Lüders band is adequately described by a uniform shear front, spreading over the specimen. In coarse-grained specimens, experiments indicate that this front becomes diffuse; diffuse bands are also present in strain-aged material, but here the diffuse fronts become sharper as the ageing becomes progressively longer.
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P T Landsberg 1957 Proc. Phys. Soc. B 70 1175
K D Bowers et al 1957 Proc. Phys. Soc. B 70 1176
J V Evans 1957 Proc. Phys. Soc. B 70 1105
A detailed investigation has been made of the rapid fading of radio echoes from the moon on a frequency of 120 Mc/s. This has shown that the conclusion reached in an earlier paper that the moon behaves as a uniformly bright reflector is in need of revision, and that metre length radio waves are reflected from the moon, largely by a region at the centre of the visible disc, which has a radius of about one third of the moon.
This result is supported by an investigation of the shape of the received echo using a receiver bandwidth 500 c/s and transmitter pulses of 10 and 2 msec. No lengthening of the transmitted pulse could be detected, indicating that the depth of the scattering region cannot be greater than about 1 msec. Range measurements show that the echo is returned from the front edge of the moon.
The effective scattering area of a moon reflecting in this manner has been calculated, and the theoretical and observed signal to noise ratios are now in good agreement, indicating that the power reflection coefficient of the lunar surface is 0.1. The effect of this type of scattering on a moon relay communications system is briefly discussed.
J P Llewellyn and T Smith 1957 Proc. Phys. Soc. B 70 1113
The variation with temperature of the unit cell dimensions of two samples of orthorhombic iron ditelluride FeTe2 00 and FeTe2 10, has been measured between 17°C and 550°C using the x-ray powder method. It is found that Gruneisen's relation between the volume expansion coefficient and specific heat is adequate for FeTe2 00, but Gruneisen and Goens' theory of the linear expansion coefficients is not satisfactory. A comparison between the expansion rates of FeTe2 00 and FeSb2 lends weight to the proposed existence of additional metalloid-metalloid bonds in the latter compound. The difference between the expansion curves of FeTe2 00 and FeTe2 10 cannot be explained in terms of additional covalent bonds and must be attributed to an increase in the ionic character of the bonds, which is associated with the vacancies present at the Te-rich composition.
R W Teale and G Rowlands 1957 Proc. Phys. Soc. B 70 1123
An expression is derived which relates associated magnetic and thermal changes for reversible rotation of the intrinsic magnetization or reversible domain wall motion. A coefficient in the expression depends upon the type of internal magnetic energy change which accompanies these processes, and hence experiments are proposed to differentiate between the various possible energy changes.
An effect arising from the second term in the magnetocrystalline energy expressions is predicted.