Search Documents

By W. J. Taylor

It is, perhaps, more important to put on record the particulars of experiments that are derided failures than those that are successful, as those of the latter class are certain to live, while the former may be lost sight of in a short time, and repeated by others. TO this end, I propose to give the particulars of a straight or no-bosh furnace just tried at the Chester (New Jersey) works, which was such a decided failure as to leave no doubt of the plan being wrong, and determining the necessity of a bosh of some kind, as of old. Some experiences during the past year led me to suppose that the bosh or belly of a furnace was unnecessary, and that the contraction of the walls toward the bottom for the stock to wedge in, in its descent, facilitated dirty walls and scaffolding; hence, irregularity and high fuel. I concluded, however, that a very shallow bosh for a skew-back support to the stock would be necessary, and that the proper place for this was in the tuyere-section, beginning just below the tuyeres and ending just above them, where there is nothing in the solid state but fuel, which is consuming, and no slipping or travel of stock takes place. The cubical capacity of a furnace of this design would necessarily be much less than in the old style, unless it was made very much higher. But I assumed that the loss of room for reduction could be overcome by making the size of the ore and stone charged much smaller, so that the gases would act more quickly. The next point was, what should be the size of the shaft, crucible, tuyere-circle, and tunnel-head for a given quantity of air? My first design was 12 feet diameter of shaft for 7000 feet of air, with a 9-foot crucible and 8-foot toyere-circle. This I soon reduced to 8-foot shaft diameter, which I concluded was large enongh for economical work, if regular travel of the stock on the walls could be maintained. I consulted with a number of experienced furnacemen and furnace-engineers, and the plan was well thought of by many of them; and, as I had also some offers of financial aid from them toward the risk of trying the experiment, my firm concluded

Jan 1, 1885

By D. P. Harris

This paper surveys a few of the quantitative exploration models that might be of interest to an ex-plorationist seeking to apply methods of operations research to mineral exploration. A general development of each model is presented, and the model is evaluated relative to the exploration activity. Finally, a philosophy of exploration and mineral resources is presented, and a possible exploration strategy incorporating concepts of some of these models consistent with this philosophy is proposed. The high cost of conducting an effective exploration program has generated an increasing interest in methods of optimizing the allocation of the resources of a firm engaged in mineral exploration. As a step towards this, mathematical models have been formulated which are designed to quantify those variables of mineral exploration in such a manner that they can be integrated with all phases of the firm's operations so as to optimize its profit objective. QUANTITATIVE MODELS General: Exploration models express at least two concepts: mineral occurrence and effectiveness of search. In simplest terms, an exploration model might be formulated mathematically as follows: P(X) = F(X) . G(X), where P(X) = the unconditional probability of discovery of X deposits, F(X) = the probability of occurrence of X deposits, and G(X) = the probability of discovery of X deposits, conditional upon their existence in the search area. With these general models as a basis of reference, some of the specific exploration models are examined below. The Allais Model: DEVELOPMENT - M. Allaisl performed the first study in which a philosophy of exploration was formulated into a probability framework. His objective was to estimate the economic profitability of the exploration of the Algerian Sahara. Allais divided the Algerian Sahara into blocks of land (called cells) 10 km square and defined the random variable, X, as the number of mining districts per cell. Thus, F(X) would describe the probability of 1, 2, or n mining districts occurring within any cell of the search area. Allais reasoned that his best information as to the form of the distribution, F(X), was the number of mining districts per cell that had been found in well explored areas in the world, such as the Western States of the U.S. He found that the Poisson function produced a reasonably good fit to the distribution of districts in these explored areas: where? is a parameter, such as the average number of districts per cell. Thus, by determining the value

Jan 1, 1968

By A. J. Lyon

The stability and permanence of any structural material used in aircraft are of paramount importance. The spontaneous hardening, or age-hardening, which takes place in some of the aluminum alloys under ordinary conditions of temperature and atmosphere, is accompanied by an increase in tensile strength and proportional limit and a decrease in elongation or ductility. Within the last few years the introduction of a number of strong and ductile casting alloys led to a study by the Materiel Division, Air Corps, of the permanence of the physical properties in several of these alloys. It has been found that even though some alloys have good properties directly after casting or heat treatment, they are not satisfactory for stressed parts that require a combination of strength and ductility. It has also led to the conclusion that all alloys that can be hardened by artificial aging—heating in a temperature range below 170" C. (340" F.)—will harden spontaneously if allowed to stand for a sufficient length of time. It follows that, in aircraft work where the factors of safety are limited on account of the necessity of keeping the weight of the structures as low as possible consistent with their safe operation, the properties of the alloys in the stable or final condition should be used as a basis for design rather than the properties obtained on the material directly after casting. The work of Wilm in Germany, Hanson and Gayler at the National Physical Laboratory in England, and Merica, Jeffries, and others in the United States, has shown that the spontaneous hardening is characteristic to a greater or less extent in all aluminum-base alloys in which the solubility in the solid state of the alloying constituents decreases with the temperature. It has been shown that, by heating to a temperature as near as possible to the melting point of the material and soaking at that temperature for a sufficient length of time and then quenching or cooling rapidly, a maximum amount of the soluble constituents can be retained in solution and the condition of maximum hardening effect upon aging can be obtained. Also, in ordinary sand and chill castings, without heat treatment, a sufficient amount of the alloying constituents is held in solution to cause important changes in the final physical properties.

Jan 1, 1929

By M. R. Geer, H. F. Yancey

INTRODUCTION The maximum yield of washed coal and the required ash and sulfur contents are the only performance factors of direct, immediate interest to any operator. Yet since the turn of the century coal preparation engineers have repeatedly sought more sophisticated performance criteria that could be used to draw comparisons between different cleaning operations and to permit generalizations about types of cleaning equipment or kinds of coal. Proliferation of efficiency formulas resulted. Hardly a year goes by, and certainly not an International Coal Preparation Congress, without the introduction of some new formula or some new concept of an existing criterion. This is merely the usual quest for improvement, because the performance criteria available today, although highly useful, are imperfect. Moreover, they are not as widely understood as they might be. The First International Coal Preparation Conference, which was held in Paris in 1950, accomplished a great deal toward establishing uniformity in terminology and methods of expressing cleaning results; the proceedings of that conference provide a wealth of detailed information on the various performance criteria, their uses and their limitations. For ease of discussion, the various performance criteria can conveniently be classed according to the degree to which they are dependent on the density composition of the raw coal treated. Some are directly dependent, some are only indirectly dependent, and some are, under certain circum- stances, essentially independent. DEPENDENT CRITERIA The yield and ash content of a washed coal are directly dependent on the washability characteristics of the raw coal from which it is derived. Thus, they are manifestly unsuited to comparing the performance of different plants, because no two plant feeds are the same. In fact, yield and ash content, by themselves, are inadequate for even routine day-to-day control. The continuous variation that occurs in the amount of impurity in raw coal, and sometimes in the float ash, make it impossible to tell whether a reduction in yield or an increase in the ash content of the washed coal results from any malfunction or misadjustment of the cleaning equipment. Recovery Efficiency For many years the most popular performance criteria that are only indirectly dependent on the washability characteristics of the raw coal have been efficiency formulas. Of the many that have been proposed, the one advanced by Fraser and Yancey in 1923 has had the widest accept-

Jan 1, 1968

By D. U. Deere, F. D. Patton

Introduction A close relationship exists between the geologic investigation and the stability analysis of the slopes of an open pit mine. One significant result of this relationship is that the stability analysis is no better than the assessment of pertinent geologic factors that enter into the analysis. In some slope stability problems the engineering solution becomes obvious once the geologic framework is established. In other cases, establishing the geologic framework is only the first stage in the process of analysis. However, even in these cases the geology should not be neglected once the analysis is made. The geology should be periodically reviewed when new slopes are excavated. This will help ensure that the basic assumptions for the analysis have not changed and will permit changes when new conditions are encountered. In recent years improved methods of stability analysis have been accompanied by advances in laboratory testing techniques and new knowledge of the shear strength of rock discontinuities. At the same time there have been improvements in field geological descriptions. As more experience is gained in analyzing and predicting the stability of rock slopes, the importance of certain geologic factors has become more apparent. Some of these factors were described in a paper given at the Open Pit Mining Symposium in Johannesburg, South Africa in September 1970 (I). This paper includes many of the points covered at that meeting but with additional emphasis on the significance of the major geologic structures. Other papers given at the South African symposium also considered geological and hydrogeological factors in slope stability analysis (2) (3) (4) (5) (6). This paper first describes the approach to a slope stability problem including assessment of the relative roles of field geology studies, laboratory testing, stability analyses, and continued slope monitoring studies. Next, is described a framework which has been found useful for classifying or separating the several types of slope stability problems encountered in open pit mines. The principal geologic factors in slope stability problems in rock are discussed and brief comments are made on how these factors distinguish stability problems in rock slopes from those normally encountered in soil slopes. The over-riding control of major geologic structures, especially faults, in most slope stability problems is emphasized. In this regard the relative importance of statistical studies is contrasted with knowledge of the positions of key structural

Jan 1, 1971

Discussion Of the paper Of GEORGE K. BURGESS, J. J. CROWE, H. S. RAWDON, and R. G. WALTENBERG, presented at the Pittsburgh meeting, October, 1914, and printed in Bulletin NO. 93, September, 1914, pp. 2433 to 2437. ALBERT SAUVEUR, Cambridge, Mass.-The Bureau of Standards has once more rendered a public service. Manufacturers and consumers of steel rails alike should welcome the important results now laid before them by Dr. Burgess and his co-workers. Personally I welcome these results all the more that in the past, as some of the members may remember, I have never failed, when occasion arose, to call the attention of rail manufacturers to the importance of controlling the finishing temperature of their rails. The pioneer metallographic work conducted at the South Works of the Illinois Steel Co. in the early '90s clearly brought out the close relations existing between the manufacture, properties, and finishing temperature of steel rails and I think I may say without fear of being contradicted that the results of this early investigation had considerable influence in drawing the attention of manufacturers to the importance of finishing temperature and of heat treatment in general. The results now before us should be, it seems to me, of great value to rail manufacturers in their efforts to produce a better and, above all, a safer rail. It seems to be demonstrated in this paper that there is no difficulty in installing in rail mills pyrometric outfits, making it possible to record, without interfering in the mill operations, the temperature of the rails as they leave the finishing rolls, or of the ingots as they are withdrawn from the soaking pits, or at any intermediate point in the process of manufacture. The inference necessarily follows that manufacturers should see to it that such pyrometric installations are made, in order that they may actually know, instead of guessing at, the temperature of their rails;, and, for obvious reasons, rail consumers should insist upon such installations. In the rolling of heavy sections especially should care be taken to lower their finishing temperature, seeing that the present tendency is to finish them at higher temperature, whereas, owing to the slower cooling of their central portions, which makes for coarseness of grain, they should, if anything, be finished at a lower temperature than lighter rails.

Jan 4, 1915

By A. J. Lyon

The stability and permanence of any structural material used in aircraft are of paramount importance. The spontaneous hardening, or age-hardening, which takes place in some of the aluminum alloys under ordinary conditions of temperature and atmosphere, is accompanied by an increase in tensile strength and proportional limit and a decrease in elongation or ductility. Within the last few years the introduction of a number of strong and ductile casting alloys led to a study by the Materiel Division, Air Corps, of the permanence of the physical properties in several of these alloys. It has been found that even though some alloys have good properties directly after casting or heat treatment, they are not satisfactory for stressed parts that require a combination of strength and ductility. It has also led to the conclusion that all alloys that can be hardened by artificial aging—heating in a temperature range below 170" C. (340" F.)—will harden spontaneously if allowed to stand for a sufficient length of time. It follows that, in aircraft work where the factors of safety are limited on account of the necessity of keeping the weight of the structures as low as possible consistent with their safe operation, the properties of the alloys in the stable or final condition should be used as a basis for design rather than the properties obtained on the material directly after casting. The work of Wilm in Germany, Hanson and Gayler at the National Physical Laboratory in England, and Merica, Jeffries, and others in the United States, has shown that the spontaneous hardening is characteristic to a greater or less extent in all aluminum-base alloys in which the solubility in the solid state of the alloying constituents decreases with the temperature. It has been shown that, by heating to a temperature as near as possible to the melting point of the material and soaking at that temperature for a sufficient length of time and then quenching or cooling rapidly, a maximum amount of the soluble constituents can be retained in solution and the condition of maximum hardening effect upon aging can be obtained. Also, in ordinary sand and chill castings, without heat treatment, a sufficient amount of the alloying constituents is held in solution to cause important changes in the final physical properties.

Jan 1, 1929

By Ulick R. Evans

I Should like to commence by saying how much I appreciate the honor which the American Institute of Mining and Metallurgical Engineers has done me in inviting me to visit your country, and to deliver this lecture before you. In choosing a subject, and in deciding what to include and what to omit, I have endeavored to discuss as far as possible work carried out recently in Europe with which you may not be unduly familiar. It would be poor return for your hospitality, and a mistaken sort of compliment indeed, if I were to load the lecture with accounts of researches carried out in your own country—researches with which you are probably better acquainted than I. Not that I have in any way excluded work done on this side of the Atlantic from my survey; one would indeed find it difficult to write on this, or on any other branch of science, without mentioning American work. But I have endeavored as far as possible to concentrate on aspects of the case which will, I hope, be comparatively fresh to you, and I feel fairly certain that this will be in accordance with your own wishes. Films Produced at Elevated Temperatures If a strip of iron is heated strongly at one end, the other end remaining cold, there is produced over the heated portion a layer of oxide scale, the thickness of which diminishes steadily with the distance from the hot end. Somewhere in the middle of the strip, the thickness of the oxidized layer will become comparable to the wave length of light, and over this region the thin films give rise to a series of beautiful interference tints, commonly known as "temper colors." The colors are caused by the fact that two trains of light waves are reflected respectively from the outer and inner surfaces of the oxide film, and the possibility arises that the "crests" of one series of waves may coincide with the "troughs" of the other, thus diminishing the intensity of the light of some particular wave length. The state of affairs in this part of the strip is shown diagrammatically in Fig. 1, in which the film thickness is enormously exaggerated, of course, in comparison with the length of the strip; the

Jan 1, 1929

By Ulick R. Evans

I Should like to commence by saying how much I appreciate the honor which the American Institute of Mining and Metallurgical Engineers has done me in inviting me to visit your country, and to deliver this lecture before you. In choosing a subject, and in deciding what to include and what to omit, I have endeavored to discuss as far as possible work carried out recently in Europe with which you may not be unduly familiar. It would be poor return for your hospitality, and a mistaken sort of compliment indeed, if I were to load the lecture with accounts of researches carried out in your own country—researches with which you are probably better acquainted than I. Not that I have in any way excluded work done on this side of the Atlantic from my survey; one would indeed find it difficult to write on this, or on any other branch of science, without mentioning American work. But I have endeavored as far as possible to concentrate on aspects of the case which will, I hope, be comparatively fresh to you, and I feel fairly certain that this will be in accordance with your own wishes. Films Produced at Elevated Temperatures If a strip of iron is heated strongly at one end, the other end remaining cold, there is produced over the heated portion a layer of oxide scale, the thickness of which diminishes steadily with the distance from the hot end. Somewhere in the middle of the strip, the thickness of the oxidized layer will become comparable to the wave length of light, and over this region the thin films give rise to a series of beautiful interference tints, commonly known as "temper colors." The colors are caused by the fact that two trains of light waves are reflected respectively from the outer and inner surfaces of the oxide film, and the possibility arises that the "crests" of one series of waves may coincide with the "troughs" of the other, thus diminishing the intensity of the light of some particular wave length. The state of affairs in this part of the strip is shown diagrammatically in Fig. 1, in which the film thickness is enormously exaggerated, of course, in comparison with the length of the strip; the

Jan 1, 1929

By C. H. Mathewson, W. R. Hibbard, Robert Maddin

A satisfactory mathematical relationship between shear, elongation and change of orientation in the axial straining of a single crystalline rod or wire may be based on a simple model in which blocks, representing glide lamellae, glide over one another and rotate so as to maintain the original fixed position of the axis as the wire elongates.' Obviously such a model gives no information concerning strain-hardening or the atomic adjustments at the sliding surfaces and their influence on the internal structure of the blocks. Moreover such an operation could be conducted with rigid blocks only by using self-aligning grips or a flexible attachment which would permit the adjacent blocks to freely assume their changing orientations. There are many unsolved problems (see Andrade2) concerning the manner in which nature departs from the simple model in permitting the essentials of slip, rotation and elongation to occur along with strain-hardening and the appearance of glide lamellae of various dimensions and special characteristics, not fully appreciated at the present time. This paper describes part of an extensive investigation on the development and characteristics of glide ellipses in single crystalline alpha brass rods and is especially concerned with the observation of cross-slip in crystals oriented wholly within the range of slip on a single system according to the generalizations first presented by Taylor and Elam in 1923.³ Experimental Procedure Half-inch rods of alpha brass (nominally 70 pet Cu, 30 pet Zn)* were converted into single crystals by melting and gradual solidification in a graphite mold according to the Bridgman method.4 In order to remove any coring, the crystals were homogenized at 800°C for 16 hr and tested by etching with a 50 pet nitric acid solution. The back-reflection Laue technique as described by Greninger6 was used for determining the orientations of the crystals. Standard stereographic operations were employed to locate the specimen axis in a triangle of the Taylor and Elam3 projection so that the slip plane and direction could be predicted. The lineage structure reported by Buer-ger6 was present in the crystals used in this investigation. However, only crystals were used in which the internal differences in orientation did not exceed two degrees. Very little is known concerning the effect of the presence of a lineage structure on the detailed mechanism of plastic deformation.

Jan 1, 1949

By C. H. Mathewson, Robert Maddin, W. R. Hibbard

A satisfactory mathematical relationship between shear, elongation and change of orientation in the axial straining of a single crystalline rod or wire may be based on a simple model in which blocks, representing glide lamellae, glide over one another and rotate so as to maintain the original fixed position of the axis as the wire elongates.' Obviously such a model gives no information concerning strain-hardening or the atomic adjustments at the sliding surfaces and their influence on the internal structure of the blocks. Moreover such an operation could be conducted with rigid blocks only by using self-aligning grips or a flexible attachment which would permit the adjacent blocks to freely assume their changing orientations. There are many unsolved problems (see Andrade2) concerning the manner in which nature departs from the simple model in permitting the essentials of slip, rotation and elongation to occur along with strain-hardening and the appearance of glide lamellae of various dimensions and special characteristics, not fully appreciated at the present time. This paper describes part of an extensive investigation on the development and characteristics of glide ellipses in single crystalline alpha brass rods and is especially concerned with the observation of cross-slip in crystals oriented wholly within the range of slip on a single system according to the generalizations first presented by Taylor and Elam in 1923.³ Experimental Procedure Half-inch rods of alpha brass (nominally 70 pet Cu, 30 pet Zn)* were converted into single crystals by melting and gradual solidification in a graphite mold according to the Bridgman method.4 In order to remove any coring, the crystals were homogenized at 800°C for 16 hr and tested by etching with a 50 pet nitric acid solution. The back-reflection Laue technique as described by Greninger6 was used for determining the orientations of the crystals. Standard stereographic operations were employed to locate the specimen axis in a triangle of the Taylor and Elam3 projection so that the slip plane and direction could be predicted. The lineage structure reported by Buer-ger6 was present in the crystals used in this investigation. However, only crystals were used in which the internal differences in orientation did not exceed two degrees. Very little is known concerning the effect of the presence of a lineage structure on the detailed mechanism of plastic deformation.

Jan 1, 1949

By John K. Berry

The handling and disposal of mine water is a much larger problem than is apparent at first glance. Many more tons of water are removed from underground coal mines in the United States each year than tons of coal. In the old anthracite region of Pennsylvania the average was around 36 tons of water for each ton of coal produced, while bituminous mines average about 5 or 6 tons. Water encountered in the mines may come from several different sources. In mines with light cover and without a firm solid roof, rain may seep directly into the workings. This is also true of deeper mines where pillar falls have broken the roof to the surface. The top under creek beds is generally faulty and broken and water comes through the roof at this point. Deeper mines are frequently overlain by water-bearing strata and pillar breaks and faulty top can admit water, while places running to the dip often accumulate water which comes up through the bottom. In all cases, except where passing under a year-round stream, the amount of water made is usually pretty closely connected with the weather-more water during the rainy season, less in the dry, although the deeper a mine is, the longer it is before changes in rainfall are felt. Another source of water, not connected with seasonal changes, is old water, accumulated over a period of time in abandoned workings of the mine, or from flooded adjacent mines. Here the water filters through the coal, the parting, or comes up through cracks in the bottom. Similarly, core holes, drilled to prospect the property, can be a source of unexpected water and modern safety requirements for dust-allaying water at the working faces can turn a pleasant working area into a soggy mess over the weekend if the system is not properly maintained and operated. Why water must be disposed is obvious. If allowed to accumulate, sooner or later the mine will fill up, or at least it will become "roofed" in low places, blocking ventilation and traffic. But it must also be controlled long before it reaches this stage. Water standing in the working faces is unpleasant for the men who have to work there and also cuts down on the amount of work they can do, as they must watch where they step all the time. It is especially unpleasant in low coal.

Jan 1, 1973

By Herbert Haas

ChEap power is essential to large-scale mining and metallurgical operations, particularly where fine grinding of large tonnages has to be resorted to, as is the case with an increasing number of mines treating disseminated copper ores, or low-grade gold ores, in the grinding of which considerable power is consumed. A comparison of the cost of generating power with Diesel engines and steam turbines and a brief discussion of the different factors governing the profitable use of either type of prime mover may be timely in view of the importance of a cheap supply of power to the mining industry, and the prominence that has lately been given to Diesel engines in America. As many of our most important mines and largest producers of metals are located in sections where neither cheap coal nor water power is available, and the price of oil fuel is increased by long hauls, the Diesel engine will become a prime mover of increasing importance. This applies particularly to the Southwestern States, where an ample supply of cold water for condensing purposes is unusual and local climatological conditions interfere in securing the high vacua essential to high turbine efficiency. About 12 times as much water will be required for condensing purposes with steam turbines under general conditions as is needed for jacket-cooling of two-stroke cycle Diesel engines; four-stroke cycle Diesel engines require only one-twentieth of the cooling water. Another condition favoring the use of Diesel engines is the high load factor at which most mine power plants operate. The influence of load factor on the cost of generating power is shown in Tables 1. and 2 and in Fig. 1. The higher the cost of fuel and the load factor, the greater will be the proportion of the fuel to the other costs making up the total cost of generating power. Capital charges (interest and redemption), maintenance, operating labor, and lubrication are practically constant amounts regardless of the load-output of the station; the fuel consumption and its cost are practically the only variables with the load. The costs here given are based on conditions as generally found in the Southwestern States, and on Diesel engine operating experience in European countries, where this type of prime mover has reached a high state of perfection, units upward of 4,000 hp. having proved entirely successful in operation.

Jan 1, 1917

By R. F. Mehl, J. K. Stanley

THE recrystallization of cold-worked metals is studied ordinarily by determining the temperatures required for complete recrystallization to occur within a given arbitrary time period, usually within 15 min. to 2 hr. The results obtained are conventionally assembled in a three-dimensional diagram relating this temperature to the amount of cold-work (percentage deformation) and the resultant grain size, though sometimes other modes of representation are employed.1 Such three-dimensional diagrams are not complete, for the number of variables exceeds the number represented. The process of recrystallization is characterized by a time-rate, a fact that is not portrayed upon ordinary recrystallization diagrams. It is known that recrystallization consists in the formation of new nuclei and the growth of these nuclei, a process that continues until the matrix is completely consumed and the original set of grains entirely replaced by the new. This knowledge is old.2 Truly heterogeneous reactions invariably proceed by nucleation and growth; the decomposition of eutectoid solid solutions provides an example about which much is known,3 and freezing, originally studied by Tammann, provides the classic example. Although recrystallization is not a heterogeneous reaction within the orthodox meaning of the term, the mechanism of the process is the same. As in eutectoid inversion and freezing, it should be possible to study the rate of isothermal recrystallization as a function of time, and it should also be possible to analyze the isothermal reaction curve into the component rates of nucleation and growth that determine them.* Other methods, not employing the rates of nucleation and growth, have been used to represent the rates of such reactions, but these in general have been artificial and have not led to progress .4,5† The theory of recrystallization is not in advanced state; if recrystallization data were obtained in terms of the rate of isothermal recrystallization, and in terms of the rate of nucleation and the rate of growth of recrystallized grains, and in particular if the temperature coefficients of these rates were measured accurately, an adequate theory should be more readily developed .27 Such an effort requires proper experimental technique, but especially requires suitable methods of mathematical analysis to convert measurements made upon a surface of polish into values for the rate of nucleation and the rate of growth and to combine these into a rate of isothermal recrystallization. These methods are now

Jan 1, 1942

By C. H. Mathewson, Robert Maddin, W. R. Hibbard

A SATISFACTORY mathematical relationship between shear, elongation and change of orientation in the axial straining of a single crystalline rod or wire may be based on a simple model in which blocks, representing glide lamellae, glide over one another and rotate so as to maintain the original fixed position of the axis as the wire elongates.1 Obviously such a model gives no information concerning strain-hardening or the atomic adjustments at the sliding surfaces and their influence on the internal structure of the blocks. Moreover such an operation could be conducted with rigid blocks only by using self-aligning grips or a flexible attachment which would permit the adjacent blocks to freely assume their changing orientations. There are many unsolved problems (see Andrade2) concerning the manner in which nature departs from the simple model in permitting the essentials of slip, rotation and elongation to occur along with strain-hardening and the appearance of glide lamellae of various dimensions and special characteristics, not fully appreciated at the present time. This paper describes part of an extensive investigation on the development and characteristics of glide ellipses in single crystalline alpha brass rods and is especially concerned with the observation of cross-slip in crystals oriented wholly within the range of slip on a single system according to the generalizations first presented by Taylor and Elam in 1923.3 EXPERIMENTAL PROCEDURE Half inch rods of alpha brass (nominally 70 pct Cu, 30 pct Zn) * were converted into single crystals by melting and gradual solidification in a graphite mold according to the Bridgman method.' In order to remove any coring, the crystals were homogenized at 800°C for 16 hr and tested by etching with a 50 pct nitric acid solution. The back-reflection Laue technique as described by Greninger5 was used for determining the orientations of the crystals. Standard stereographic operations were employed to locate the specimen axis in a triangle of the Taylor and Elam3 projection so that the slip plane and direction could be predicted. The lineage structure reported by Buerger6 was present in the crystals used in this investigation. However, only crystals were used in which the internal differences in orientation did not exceed two degrees. Very little is known concerning the effect of the presence of a lineage structure on the detailed mechanism of plastic deformation.

Jan 1, 1948

By W. A. Backofen, B. C. Wonsiewicz

The Plasticity transition in magnesium was studied by plane-strain compression of single crystals and polycrystalline material at temperatures from about 20" to 307°C. Reduction of single crystals along the c axis was accommodated by twinning on {1011) and retwinning on (10 12}, followed by basal shear in the doubly twinned volume. Deformation in that mode can result in sufficient independent shears for arbitrary shape change. Fracture in c axis compression, below about 100°C, has been related to excessive shear caused by unloading from the stress for {1011} twinning (-50 ksi at 20°C) to that for slip within the twin (-3 ksi); ductility follows from heating because the stress difference is lowered and the twin volume, in which elastic strain energy is dissipated on unloading, is increased. The stress for (1011) twinning is strongly temperature-dependent but not given by a critical resolved shear stress law. The latter is attributed to the influence of stress concentration from prior intersecting shear on nonbasal planes, the former to the temperature dependence of the preliminary slip. THE basic symmetry of hcp crystals has the effect of limiting the number of independent slip systems and making twinning an important deformation mechanism. The general result in wrought polycrystalline aggregates is a more or less sharply developed texture (or preferred orientation) which underlies a strong anisotropy in mechanical behavior. Knowing how the one influences the other is essential background for the use of such materials. Magnesium was of interest in this work because of the unexplained plasticity transition that it undergoes somewhere in the neighborhood of 200°c.''~ At lower temperatures plastic deformation before fracture in polycrystalline material is limited, while at higher temperatures extensive deformation is possible. The transition temperature commonly determines the lower limit of the range in which magnesium is worked. The limited ductility can be traced to a lack of independent crystallographic shears. A minimum of five are required for arbitrary shape change.' Around room temperature, however, slip on all known systems provides only four.' In each case, the slip direction is in the (0001) basal plane so that slip does not allow strain along the c axis. With increasing temperature, more slip occurs on the ( 1011) pyramidal plane and the ( 1010) prism plane but without change in direction.'?' Thus, that development alone cannot explain the transition temperature.

Jan 1, 1968

By R. F. Mehl, J. K. Stanley

THE recrystallization of cold-worked metals is studied ordinarily by determining the temperatures required for complete recrystallization to occur within a given arbitrary time period, usually within 15 min. to 2 hr. The results obtained are conventionally assembled in a three-dimensional diagram relating this temperature to the amount of cold-work (percentage deformation) and the resultant grain size, though sometimes other modes of representation are employed.1 Such three-dimensional diagrams are not complete, for the number of variables exceeds the number represented. The process of recrystallization is characterized by a time-rate, a fact that is not portrayed upon ordinary recrystallization diagrams. It is known that recrystallization consists in the formation of new nuclei and the growth of these nuclei, a process that continues until the matrix is completely consumed and the original set of grains entirely replaced by the new. This knowledge is old.2 Truly heterogeneous reactions invariably proceed by nucleation and growth; the decomposition of eutectoid solid solutions provides an example about which much is known,3 and freezing, originally studied by Tammann, provides the classic example. Although recrystallization is not a heterogeneous reaction .within the orthodox meaning of the term, the mechanism of the process is the same. As in eutectoid inversion and freezing, it should be possible to study the rate of isothermal recrystallization as a function of time, and it should also be possible to analyze the isothermal reaction curve into the component rates of nucleation and growth that determine them.* Other methods, not employing the rates of nucleation and growth, have been used to represent the rates of such reactions, but these in general have been artificial and have not led to progress.4,5? The theory of recrystallization is not in advanced state; if recrystallization data were obtained, in terms of the rate of isothermal recrystallization, and in terms of the rate of nucleation and the rate of growth of recrystallized grains, and in particular if the temperature coefficients of these rates were measured accurately, an adequate theory should be more readily developed.27 Such an effort requires proper experimental technique, but especially requires suitable methods of mathematical analysis to convert measurements made upon a surface of polish into values for the rate of nucleation and the rate of growth and to combine these into a rate of isothermal recrystallization. These methods are now

Jan 1, 1942

By F. N. Rhines, T. E. Leonitis

The oxide scale that forms upon magnesium at elevated temperatures is non-protective in the sense that the rate of oxidation is constant and thus does not decrease with the growth of the scale as it does with other common metals. This generality was first stated by Pilling and Bedworth' and has been verified by Suzuki2 and by ScheiL3 Pilling and Bcdworth argued that the nonprotective characteristic could be predicted from the fact that magnesium oxide occupies less space than does the metal from which it springs, wherefore the scale is not expected to cover the metal so completely as to exclude all direct access to the atmosphere. Linear oxidation is thought by Scheil to be common to all cases where the reaction occurs at the oxide-metal interface. According to Suzuki," he product of high-temperature oxidation in the air is MgO contaminated with no more than traces of a nitride. When the metal is allowed to burn freely a fume composed of cubic crystals of Mg04 is given off. Delavaults observed that excrescences form upon liquid magnesium and alloys in thc course of oxidation. Beyond this it is known that the use of atmospheres containing small quantities of sulphur dioxide6 or carbon dioxide serve to retard the oxidation of solid magnesium and that beryllium' and calciums minimize the oxidation of molten magnesium exposed to the air. Many studies have been devoted to the nature and rates of "protective" oxidation, as exemplified by the cases of copper and iron, wherein the rate is characteristically parabolic. The theory of parabolic oxidation is well developed.~ Linear oxidation, on the other hand, has received but little attention and the theories proposed by Pilling and Bedworth and by Schcil have yet to withstand careful examination. There exists no comprehensive survey of the high-temperature oxidation of magnesium (or of any other metal that exhibits linear oxidation) over a broad range of temperature, under a variety of atmospheric conditions and covering a large group of alloys. It has been the purpose of the present investigation to provide such a survey, with the object of gaining a fuller understanding of linear oxidation, especially as applied to magnesium. Experimental Procedure and Results The experimental studies undertaken were of two kinds: (I) measurement of the rate of oxidation as influenced by the 6c

Jan 1, 1946

By Eugene F. Poncelet

Glass squares compressed on edge by steel jaws in poor contact with them developed jagged "partial-contact" cracks caused by the formation of local tensile stresses. Compressed by steel jaws in perfect contact, they developed smooth "release cracks" during release of the pressure, caused by the formation of local tensile stresses during the release of the pressure. All these cracks were parallel to the pressure. A Microflash photograph of a disintegrating specimen under sufficient pressure reveals a network of fractures roughly normal to each other, also "release cracks" and a disintegration cloud. The Griffith theory is amended to account for the formation of a first crack. A new theory, based on the theory of thermal agitation and wave propagation, is proposed to account for the progress, velocity and forking of cracks. The network of fractures is shown to have been caused by reflection at a free boundary of pressure pulses emanating from a first crack. Postulating equal distribution of energy in the pulses emitted on either side by a crack in particles, the smaller fragments are shown to continue fracturing preferentially while some of the coarser fragments remain as residual pieces. As comminution of the smaller fragments proceeds, the solid is reduced to a collection of residual particles of smaller and smaller sizes, accounting for the disintegration cloud. Experimental Procedure Apparatus A crushing device was built, consisting of a steel frame and two polished, hardened steel jaws to crush plate-glass samples. This device was placed between the plates of a hydraulic press (Fig. I). For centering the pressure, the upper jaw was guided vertically and provided with a rounded top. Later it was replaced by a steel jaw ground out of a 2½-in. steel ball, the lower surface being ground to an optical flat (Fig. 2). Four rollers were used to eliminate side thrust. Screws and centering blocks served to center the specimen in the crushing device. Hard steel shims placed under the shoulder of the upper jaw limited the "follow through'' of the jaw after failure of the specimen. Stress distribution was first examined with a polariscope mounted on an optical bench, using monochromatic light. It was found convenient to mount polaroid, quarter wave and monochromatic plates directly on the device itself. A Microflash unit* was used as light source for the photographs. A gold-paint pattern was fused on the plate-glass specimens and connected into the spark-

Jan 1, 1947

By Eugene F. Poncelet

Glass squares compressed on edge by steel jaws in poor contact with them developed jagged "partial-contact" cracks caused by the formation of local tensile stresses. Compressed by steel jaws in perfect contact, they developed smooth "release cracks" during release of the pressure, caused by the formation of local tensile stresses during the release of the pressure. All these cracks were parallel to the pressure. A Microflash photograph of a disintegrating specimen under sufficient pressure reveals a network of fractures roughly normal to each other, also "release cracks" and a disintegration cloud. The Griffith theory is amended to account for the formation of a first crack. A new theory, based on the theory of thermal agitation and wave propagation, is proposed to account for the progress, velocity and forking of cracks. The network of fractures is shown to have been caused by reflection at a free boundary of pressure pulses emanating from a first crack. Postulating equal distribution of energy in the pulses emitted on either side by a crack in particles, the smaller fragments are shown to continue fracturing preferentially while some of the coarser fragments remain as residual pieces. As comminution of the smaller fragments proceeds, the solid is reduced to a collection of residual particles of smaller and smaller sizes, accounting for the disintegration cloud. Experimental Procedure Apparatus A crushing device was built, consisting of a steel frame and two polished, hardened steel jaws to crush plate-glass samples. This device was placed between the plates of a hydraulic press (Fig. I). For centering the pressure, the upper jaw was guided vertically and provided with a rounded top. Later it was replaced by a steel jaw ground out of a 2½-in. steel ball, the lower surface being ground to an optical flat (Fig. 2). Four rollers were used to eliminate side thrust. Screws and centering blocks served to center the specimen in the crushing device. Hard steel shims placed under the shoulder of the upper jaw limited the "follow through'' of the jaw after failure of the specimen. Stress distribution was first examined with a polariscope mounted on an optical bench, using monochromatic light. It was found convenient to mount polaroid, quarter wave and monochromatic plates directly on the device itself. A Microflash unit* was used as light source for the photographs. A gold-paint pattern was fused on the plate-glass specimens and connected into the spark-

Jan 1, 1947