Strength of materials

“ In all structures the materials have to support their own weight, and therefore their available strength is to be estimated by the excess of their absolute strength above that degree of strength which is just sufficient to support their own weight. ”

“ At exceedingly high temperatures much greater pressure, and therefore much greater density, can be attained without liquefaction or solidification. And, in considering the effect of pressure on the materials of a solid globe, we must not fall into the mistake of supposing that the strength of such solid materials can protect the material from compression and its effects. We must extend our conceptions beyond what is familiar to us. ”

“ Metallurgical and ceramic engineers test and evaluate the strength, durability, and other characteristics of materials to be used in the fabrication of equipment, and they produce new materials for specific jobs. ”

“ Also it permits better dimensional control of the product, lessened sensitivity to physical characteristics of starting materials, and allows powder to be driven to higher densities than with cold pressing, resulting in higher strength. ”

“ Turning now to the physical properties of the several classes of iron and steel mentioned above, it may be noted, first, that strength may be subdivided into strength against rupture by direct pull, or tensile strength ”

“ Every department of human industry is represented, from the quarrying and the cutting of the stones, the mining and smelting of the ores, the conversion of iron into steel by the pneumatic process, to the final shaping of the masses of metal into useful forms, and its reduction into wire, so as to develop in the highest degree the tensile strength which fits it for the work of suspension. Every tool which the ingenuity of man has invented has somewhere, in some special detail, contributed its share in the accomplishment of the final result. ”

“ Even now, using iron and steel and steam, we can concentrate power until we can match the energy of a bird; but, by the substitution of aluminum, possessing equal strength and weighing only a third as much as steel, why should we not hope to do much more than that? ”

“ Steel (Bessemer, Siemens-Martin, open hearth, etc.) contains more carbon than wrought iron, possesses both strength and hardness, and is used for rails, structural material, machinery, tools, wire rope, sheet steel, etc. Its hardness may be increased by tempering. ”

“ The importance of the chemical laboratory to a tool-steel plant cannot be over-estimated. Every heat of steel is analyzed for each element, and check analyses obtained; also, every substance used in the mix is analyzed for all impurities. The importance of using pure base materials is known to all manufacturers despite chemical evidence that certain detrimental elements are removed in the process of manufacture. ”

“ Although the application of chemical knowledge to the manufacture of malleable iron cannot fail to produce beneficial results, the quality of the metal depends more upon the mechanical than the chemical processes.... ”

“ But I may tell you that I have found an alloy that is unequalled in the known world for strength, durability and lightness. It weighs a little more than pure aluminum, but has a thousand times its tensile strength. ”

“ The tensile strength of steel, as is well known, is the result of an admixture of carbon with the iron, varying between one tenth and two per cent, and the nature of this combination of carbon with iron is a matter of great interest both from a theoretical and practical point of view. ”

“ It governs the transformation of the salts, minerals and humus of our fields and the components of the air into corn, wheat, cotton and the innumerable other products of the soil; it governs no less the transformation of crude ores into steel and alloys, which, with the cunning born of chemical knowledge, may be given practically any conceivable quality of hardness, elasticity, toughness or strength. And exactly the same thing may be said of the hundreds of national activities that lie between the two extremes of agriculture and steel manufacture! ”

“ Technical knowledge and skill were developing with an extraordinary rapidity, and to an extraordinary extent measured by the progress of any previous age. Far less conspicuous at first in everyday life, but finally far more important, was the extension of man’s power over various structural materials. Before the middle of the eighteenth century iron was reduced from its ores by means of wood-charcoal, was handled in small pieces, and hammered and wrought into shape. It was material for a craftsman. ”

“ There are published in many transactions and technical periodicals thousands of tests giving elastic and ultimate strength, ductility, etc., so that every engineer can find easily what has been done to guide him as to what he can get. ”

“ In the weighing of large masses of coarse material, such as grain, coal, cotton seed, and the like, machines have been constructed which automatically weigh such materials and at the same time register the weight. ”

“ The strength of a compound spring formed of two metals may, by the application of heat, be increased to any given power. Rationale.—Iron possessing an expansive power of 1/95, and brass being only 1/60, the weaker metal will be bent by that whose power of expansion is greater, and the impulse of the spring increased in an equal ratio. ”

“ With the larger employment of metal in all industries the need for handling it easily is increased. Much greater [62] accuracy generally distinguishes metal as compared with woodwork. "In turning a piece of work on the old-fashioned lathe, the workman applied and guided his tool by means of muscular strength. ”

“ The Most Tenacious Metal.—Steel has the greatest tenacity of all metals, and lead the least. In proportion to weight, however, there are many substances which have this property in a higher degree. Cotton fibers will support millions of times their own weight.
There is one peculiar thing, that tenacity varies with the form of the body. A solid cylindrical body has a greater strength than a square one of the same size; and a hollow cylinder more tenacity than a solid one. ”

“ I allude to the mixture of certain kinds of mineral oil with an oil that has a tendency to dry. Even a small percentage is asserted to entirely check this tendency and the resulting mixture is said to have the property of not in any way acting on or damaging the metal to which it is applied. The thickness, or 'body,' is made to vary according to the pressure to which the oil is subjected. * * * * Would it be oversanguine to hope that some such mixture, prepared from perfectly pure materials, might help even the chronometer maker to secure more uniform rates? ”

“ I do not mean merely practical discoveries made empirically, but the chief part of this progress is attributable to the highest theoretical conceptions of the positive sciences. Thus all the modern industries of metals, stones, wood, work in materials of every sort, rest upon the general discoveries of chemistry and mechanics. ”

“ Where a very great deal of power is needed for the making of an article or material of comparatively small weight and bulk proportioned to its value—such for instance as calcium carbide or aluminium—the immediate vicinity of the source of natural power will offer superlative inducements. ”

“ From an engineering point of view the structural merit of a material, especially when variable loads and possible shocks have to be sustained, depends not only on the strength but also on the extent to which the material will bear deformation without rupture. ”

“ The steel, after having been forged, is soft, like iron, and to give it the requisite degree of strength under the uses to which the tools or instruments are to be exposed, it is hardened. The process by which this is effected is called tempering, and the degree of hardness or strength to which the steel is brought is called its temper, which is required to be higher or lower, according to the use which is to be made of the particular instrument. ”

“ As the rubber joist sags between its ends, we observe that its upper half is compressed, and its lower half extended, the two effects though small being quite measurable. As we approach the central line, A B, this compression and tension gradually fall to zero; it is clear that only the uppermost and undermost layers [10] fully call forth the strength of the material, the inner layers doing so little that they may be removed with hardly any loss. ”

“ Iron, steel, and other metals have their surfaces easily reduced and smoothly or coarsely granulated, according to the force and abrasive powder used. The abrasive need not be harder than the metal to which it is applied. ”

“ In engineering, for example, there are questions as to the durability of steels and other building materials, which when investigated would yield rich harvests to every practicing engineer on the globe. ”

“ In his preliminary chapters he describes the behavior of materials under the several kinds of stress, the matter here given being designed to supplement that usually contained in text-books on applied mechanics. A second division of the work, which the author intends to be read by engineering students if they do not get the information in other ways, deals with the manufacture and general properties of cast and wrought iron, steel, and other metals, lime, cement, brick, and timber. The attention given to the structural properties of wood is a feature of the work. ”

“ The methods of producing varieties of the metal suitable to the requirements of the engineer, foundryman and mechanician are described so that the worker may learn the history of the material he is handling. ”

“ The ultimate tensile strength, therefore, of malleable iron is four times greater than that of cast iron, but the crushing strength of cast iron is between three and four times greater than that of wrought iron. ”

“ Between the molecules of a solid, however, the forces of attraction are strong, as is shown by the fact that a solid often requires a great force to pull it apart; some, as steel and iron, show this property in a superlative degree, a high-grade steel rod 1 cm. ”

“ The more solid, dry or compact bodies, such as stones, wood and metals, admit of much less, and indeed scarcely any perceptible compression or expansion, but escape by breaking, slipping forward, or other efforts; as appears in bending wood, or steel for watch-springs, in projectiles, hammering and many other motions, all of which, together with their degrees, are to be observed and examined in the investigation of nature, either to a certainty, or by estimation, or comparison, as opportunity permits. ”

“ They are simple and strong in construction, of high capacity with comparatively small consumption of power, and furnish a good, uniform product, the size of which ranges from fine powder to coarse granules, according to the screens used and the class of material treated. ”

“ Specifications must therefore be drawn with care to insure that the requirements can be met by satisfactory materials. But certain properties, such as specific gravity, may vary greatly among materials equally satisfactory for construction purposes. One should not be misled by apparent differences in the characteristics of materials, because these may simply be natural peculiarities which have no bearing on the usefulness of the material. ”

“ Even the general character of the material is important, those of soft, earthy consistency being much easier to treat, and the cost of preparation smaller, than if the raw material be hard, tough and crystalline. ”

“ The reason for this lies in the fact that the maximum strength of the material used in one and the same engineering structure, or in a tree, being a known constant, it is evidently of the greatest economic advantage to make the specific stresses throughout as uniform as possible. ”

“ In getting up a surface of considerable extent, it is necessary to take into account the strain which the metal suffers from its own weight, and the length of time required to produce the full effect on the external form. ”

“ Transparency becomes universal, and they are all elastic. They now form but one set of substances, and the varieties of density, hardness, opacity, color, elasticity and form, which render the number of solids and fluids almost infinite, are now supplied by a few slight variations in weight, and some unimportant shades of color. ”

“ In the first place, the quantity of materials being always very great in metallurgy, requires corresponding adaptations of apparatus, and often produces peculiar phenomena; in the second place, the agents to be employed for treating great masses, must be selected with a view to economy, as well as to chemical action. In analytical chemistry, the main object being exactness of result, and purity of product, little attention is bestowed upon the value of the reagents, on account of the small quantity required for any particular process. ”

“ It must happen in some cases that the component materials are mixed in such proportions as to prepare them readily to enter into chemical union, and form new minerals; while in other cases the mass may be more homogeneous, or the proportions less adapted for such union. ”

“ By these modern improvements wonderful materials were placed at the disposal of the industries. The hardness of steel has been so increased that for safety vaults and safes an alloy is made which can neither be drilled nor exploded nor cut by the oxy-hydrogen flame. ”

“ The proper allowance for a forced fit depends upon the mass of metal surrounding the hole, the size of the work, the kind and quality of the material of which the parts are composed and the smoothness and accuracy of the pin and bore. ”

“ The impurities in iron and steel are just what are needed to hold the particles of iron together, and to make them valuable. By regulating the amount of carbon, phosphorus, etc., manufacturers can make different grades and qualities of iron or steel. ”