Search results

VARIOUS steels, or even different heats of the same steel, with identical mechanical properties when determined by ordinary tests, vary considerably in behaviour in service; and such differences of performance are neither due to any variation in composition nor to any other known factors. That these differences exist is now known but their causes are still very much matters for metallurgical conjecture. It is known that steels tempered from the austenitic range and tempered to give a martensitic structure become increasingly ductile with rise of temperature. The ordinary tests, however, fail to give any indication of the variations in behaviour, on tempering, between even different low‐alloy steels, to say nothing of different heats of any one particular steel. The notched‐bar impact‐bend test is capable of revealing differences in impact properties among steels which have been tempered to levels of mechanical strength identical with the results obtained by ordinary tensile tests. The notched‐bar test is, however, highly complex, involving a certain amount of tension, compression, bending and shear, and its full significance is not yet clearly understood. Of its three characteristic features: high speed, notch, and bend action, the notch is the most potent embrittling factor. Recent investigations have shown that static notched‐bar tensile tests give more fully understandable results and evaluate metals in very much the same manner as impact tests.

In this article the author discusses various aspects of sacrificial corrosion. He refers to the relationship which exists between corrosion and electrolysis and draws attention to the considerable development of knowledge in this field since the war. He concludes by referring to the relationship which exists between atomic number, atomic weight and corrodibility.

THIS paper shows briefly the origins and development of a comparatively new and certainly important branch of engineering science. For many years the alloys of the light metals, particularly of aluminium and magnesium, have been developed, until the term “light alloys” has come to be generally accepted as indicating the alloys of the light metals or any metallic alloy having a density of less than about 3·8. Towards the other end of the density scale are now being developed alloys of the heavy metals, mainly tungsten and tantalum. The techniques of production and manufacture of these two groups are very different: whereas the light alloys are produced and manipulated mainly by melting, casting, annealing, and forging, the heavy alloys are produced by various processes of powder metallurgy, resulting in substances with densities of 15 or more.

WHILE considering the specification requirements of various steels, the possibility of graphically correlating the main factors occurred to the writer. At the first attempt, a correlation of ultimate tensile strengths with proof stresses produced, graphically, a sort of hyperbola; at the second attempt, by changing the vertical and horizontal scales, and working to average figures, the graph took the form of a straight line ending in a hyperbolic curve; at the third attempt the graph became a straight line with plotted points not exactly coincidental with the line; the fourth attempt produced the U.T.S./Proof Stress “curve” which is the subject of this paper.

The addition of aluminium to copper results in an improvement in the corrosion‐resisting properties of the metal; this article discusses why aluminium bronzes are noted for their performance in a number of industrial applications in which a wide range of corrosive materials—gaseous, liquid and solid—are encountered.

THE use of aluminium and aluminium alloys has grown to an enormous extent during recent years and there are few industries where aluminium docs not find a place. This paper is concerned with the welding of aluminium and its alloys by means of the oxy‐acctylene blowpipe flame.

FOR buyer and manufacturer alike today materials must satisfy recognized standards in their physical and mechanical properties. Thus, tests yielding comparative data are essential in determining the right material for any particular purpose.

EXAMINATION of the cross‐section of a tree‐trunk shows the following details of structure: Covering the trunk is the corky bark, the outer layers of which serve to protect the trunk from extreme variations of temperature and humidity, and from mechanical injury; the inner layers, called the bast, serve to conduct the food manufactured by the leaves to actively‐growing parts of the wood and to places of food‐storage in the tree. The bark and the bast together form the rind.

ALL ‘plastics’ are generally divided into two groups: the ‘thermoplastics’, which are formed by heating, can be re‐heated after forming, and re‐formed almost ad lib, such as celluloid, xylonite, rhodoid, cellophane, and perspex; and the ‘thermosetting plastics’, which are also formed by heating but cannot yet be re‐formed by the application of heat or any other means, probably the best‐known example of which is the thermosetting variety of bakelite.

FEW processes have made such an advance during the last two years as has the are welding of aluminium and its alloys. In the 1945 impression of the Second Edition of his Engineering Materials, Machine Tools and Processes (Longmans), W. Steeds states, on page 148: