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By R. V. Ramani, R. M. Mishra, Y. J. Wang

The validity of the concept of mine resistance in ventilation systems is examined. Mine resistance is the proportionality constant relating the head generated by a fan and the quantity flowing through it when the fan is connected to a mine circuit. It is the total effect of all branches in the mine ventilation circuit. Its importance lies in the fact that for new mine projections, and in the extensions of existing mines, ventilation calculations are usually based upon adjustments of the mine resistance. In ventilation circuits with regulation, and/or with multi-fans, simple adjustments of the mine resistance curve do not lead to correct solution. A ventilation system consists of several interconnected subsystems where one subsystem behavior affects that of the others, and the total system. Through a series of simple but realistic examples, the authors demonstrate the importance of the systems concept in mine ventilation, and its practical application to coal mine ventilation planning. Starting from an initial system with no leakage and one fan, more complex ventilation networks with several leakages, sections and fans, are analyzed to show that ventilation system design on the basis of total systems approach is the correct procedure.

Jan 1, 1979

EXECUTIVE COMMITTEES OF LOCAL SECTIONS New York LOUIS D. HUNTOON, Chairman. ARTHUR S. DWIGHT, Vice-Chairman. THOMAS T. READ, Secretary, Woolworth Bldg., New York, N. Y. E. MALTBY SHIPP. Treasurer. GEORGE F. KUNZ, W. DE L. BENEDICT. Boston ROBERT H. RICHARDS, Chairman. ALBERT SAUVEUR, Vice-Chairman. AUGUSTUS H. EUSTIS, Secretary-Treasurer, 131 State St., Boston, Mass. TIMOTHY W. SPRAGUE, HENRY A. WENTWORTH. Columbia F. A. THOMSON, Chairman. GEORGE W. RODDEWIG, Vice-Chairman. LYNDON K. ARMSTRONG, Secretary-Treasurer, P. O. Drawer 2154, Spokane, Wash. R. S. McCAFFERY. S. H. RICHARDSON.

Jan 3, 1914

By George E. Kruger, William F. Butler

The less developed nations maintaining a free enterprise economy (to which this chapter is addressed) have real and substantial opportunities to lay a foundation for general economic progress by using their mineral resources. Most of these nations have mineral resources which could be developed. By seizing these opportunities, nations seeking rapid economic development can secure a source of foreign exchange earnings to finance the imports needed for growth and, at the same time, increase the technical knowledge and well-being of an important part of their population. History clearly shows the manner in which most of the currently industrialized nations have used mineral resources to support their development. Indeed, few nations have managed to achieve a high level of income without a firm base of mineral resource development. The main exceptions appear to be the Netherlands, Switzerland, Denmark, and New Zealand, and the last two have based their prosperity on a highly efficient agriculture. Economic growth in the United States, the United Kingdom, Canada, France, Germany, and Russia was importantly based on the use of indigenous mineral resources. Despite this record of accomplishment through mineral development, many of the currently less developed nations are not taking advantage of the opportunities available in the mineral field. Restrictive laws or practices in many such nations operate effectively to prevent development of mineral resources. This failure to grasp real opportunities for development is based on a series of arguments that the mineral field offers few substantial and attainable advantages. Among these, the following propositions appear the most important:

Jan 1, 1964

By Eugene H. Cowles

Now that a determined public effort is being made on this side of the Atlantic to create a steel ship-building industry, the materials that are demanded for this purpose assume a new interest to the American metallurgist. In the past, the uses of metals in this country have been almost exclusively connected with the land, while in England their application to marine purposes has been equal in importance to that on shore. In the future the same should be the case here. This is the reason for bringing a somewhat nautical or rather naval topic before a body the chief interests of which are supposed to lie in the mines and mountains of the interior of the country. A modern war-ship or " ocean-grayhound" (like the City of Paris) is an epitome of philosophy and human skill. In her graceful lines we have, as Ruskin might quaintly say, a " builded geometry ;" while in her wonderful machinery for motion, offensive and defensive, we have the summation of the ideas of a host of students who have, at one time or another, during the course of a hundred years of her evolution, contributed their intellectual mites to render her a thing of beauty and of power. Notwithstanding her present perfection, the modern ship contains room for further improvement. One of the most important things about her is the propeller. This active member is of more impor-

Jan 1, 1890

By C. D. Gilpin, Franklin Moeller

The application of electric power for driving mine hoists handling heavy loads at high speeds has recently been extended by the installation of what is probably the largest electrically driven hoist in this country at the Granite Mountain shaft of the North Butte Mining Co., Butte, Mont. While the weight of rock which is hoisted by this machine is not the largest now being handled by electric mine hoists, the speed of hoisting is so, and the combination of the high speed with the heavy load has resulted in a machine of considerable interest to all those actively engaged in mining. Aside from mere considcration of size, this installation deserves attention because of the careful attention given, not only to the question of economy of operation, but to the details of construction and installation of the entire equipment. The conditions to be met in this installation were as follows: Weight of rock to be raised per trip, 7 gross tons........... 15,680 1b. Weight of skip.......................................... 8,000 1b. Weight of cage.......................................... 1,800 1b. Maximum depth of hoisting.............................. 4,000 ft. Diameter of rope.......................................... 15/8 Total weight suspended on one rope from drum............. 42,000 1b. Normal hoisting speed.................................... 2,700 ft. per minute. Maximum hoisting speed.................................. 3,000 ft. per minute. Desired capacity-200 tons per hour from 4,000 ft. depth. The ore is mined in several levels and hoisting is carried on from the 800-ft. level down to the 2,700-ft., which is at present the maximum depth from which the ore is raised regularly. Development is proceeding and a depth of 2,900 ft. has already been reached. The rock is handled underground in cars holding % ton, and about 10 cars are the usual load for a skip. All of the ore is dumped into underground bins, which are of diffcrent capacities varying up to 250 tons. From the bins the ore is fed into the skips without passing into measuring pockets. At the surface the

Jan 1, 1916

By Dewitt T. Ring

Reliable and detailed data covering the enormous number of wells drilled and the long historical production of the state, many of which were never recorded until recent years, render it impossible to gather statistical material suitable for the Institute's standardized form. The total production of crude oil in Ohio for the year was 3,654,503 bbl., which is less than the total production in the United States for the peak day of August 1937. For a period of eight years, from 1895 to 1902 inclusive, Ohio produced more oil than any other state. During the year, 1271 tests were drilled in the state, or 114 more than in 1936. Of these, 317 were oil wells, with an initial production of 7088 bbl., an average of 22.3 bbl. per well; 503 were gas wells, with an initial open flow of approximately 222,441 M cu. ft., or 443 M cu. ft. per gas well drilled; 451 were dry holes, that is, 35 per cent of the total completions. A number of factors account for the steady decline of oil production in Ohio. In the state, at the close of thc year, there were fewer than 28,122 producing oil wells. In 1936, there were 30,150 operated oil wells with an average yearly production per well of 126 bbl. The production for 1937 averaged 130 bbl. per well. During the year, 2028 oil wells were abandoned. In other words, old wells are being abandoned more than six times faster than new ones are being drilled. Since the inception of the oil and gas industry in Ohio, between 150,000 and 160,000 wells have been drilled in the state; new potential territory, offering desirable locations for either oil or gas, is becoming increasingly more difficult to find; the dry-hole percentage will continue to increase. Prices Another factor directly affecting the crude situation during the year was the matter of price and proration of Pennsylvania grade oil. The posted price for Pennsylvania grade in Ohio on June 7 was $2.37 per barrel; at the close of the year, it was $1.70 per barrel, or a reduction of 28 per cent in price. In addition to this price cut, a 50 per cent pro-

Jan 1, 1938

By F. P. Bullen

Empirical relationships between fracture stress, orientation angle, and diameter of crystal have been determined at 77°K. Orientation ranges of markedly different behavior were found—a law of constant normal stress&apos; of value a (diameter)-1/2 for the fracture of ductile crystals, and a condition of shear stress (or strain) for more brittle crystals. The observations are not consistent with current theories. An interpretation is advanced which is also applicable to observations on the effect of prestrain at room temperature on the subsequent fracture stress at 77°K and to the effect of cyclic stressing on the cleavage strength.&apos;&apos; The law of constunt normal stress&apos; and the brittle ductile transition are also explained. The interpretation is more consistent with the initiation of cracks by intersecting dislocations than with theories based on stress -concentration by dislocation arrays. ZINC single crystals are particularly suited to the study of cleavage because fracture occurs on the basal plane over a wide range of crystal orientations. Analysis of the conditions of stress and strain at fracture in crystals of different orientations should indicate which parameters control the cleavage process. Unfortunately, controversy has arisen over the correct empirical relationship between tensile fracture stress and orientation. Schmid&apos;s observations1,2 favored a &apos;law of constant normal stress&apos;, as observed in other materials.2 For zinc, however, the observed values are far below the theoretical strength and cannot represent the true limit of cohesion between neighboring atomic planes. Hence, the interpretation of such a &apos;law&apos; is not straightforward. Deruyttere and Greenough3,4 found a complex variation between tensile fracture stress and orientation; this variation did not agree with a &apos;law of constant normal stress&apos;. Two theories have been advanced to account for their observations: a) the propagation of cracks from low-angle boundaries,5 and b) the release of energy from piled-up dislocations during crack-propagation.4 The present work resolves the apparent discrepancy between the observations and shows that neither of the above theories are applicable to the tensile fracture of zinc single crystals. A phenomenological explanation, along the lines suggested by Gilman,&apos; is advanced and successfully applied to previously unexplained effects. EXPERIMENTAL DETAILS &apos;Crown Special&apos; redistilled zinc was used, except for one comparison series op tests using &apos;Tadanac&apos; electrolytic zinc. Crystals of 1 mm diam, subsequently called &apos;1 mm crystals&apos;, were grown from the melt in vacuo in precision-bore Pyrex tubes internally coated with graphite. Several specimens 1 in. long were cut from each crystal and chemically polished. Jigs were used to minimize handling strains, and crystals were mounted in the Polanyi machine the day prior to testing to allow recovery from any such strains. One-mm crystals were chemically polished for long periods to obtain 0.1 mm (approx) crystals. One-mm crystals were cemented into miniature gimbals by &apos;Araldite&apos; casting resin. The Appendix gives the reasons for using gimbals and the results obtained by other methods. More complete details of all techniques are given elsewhere.7 The symbols and terminology used are as follows: X = orientation angle (angle between tensile axis and line of greatest slope in the basal plane). T = tensile stress (on true cross-section) S,N = shear and normal stress (components of T with respect to the basal plane) ? = shear strain D = crystal diameter. The subscript &apos;f&apos; will be used to denote values at fracture. PART I-ANNEALED CRYSTALS EXPERIMENTAL OBSERVATIONS One-mm crystals were used to establish the variation of fracture stress at 77°K with orientation at fracture (Xf), Fig. 1. For 18 deg = Xf = 55 deg, a &apos;law of constant normal stress&apos; was observed. For Xf > 55 deg, the fracture condition approximated to a constant shear stress. At Xf< 18 deg, twinning occurred before fracture so that the results were not typical of homogeneous single crystals,4,8— such specimens will not be considered herein. The dependences of fracture stress upon Xf were of similar type for 6 mm,* 1 mm, and 0.1 mm crystals,

Jan 1, 1963

By Franklin Moeller

THE application of electric power for driving, mine hoists handling heavy loads at high speeds has recently been extended by the installation of what is probably the largest electrically driven hoist in this country at the Granite Mountain shaft of the North Butte Mining Co., Butte, Mont. While the weight of rock which is hoisted by this machine is not the largest now being handled by electric mine hoists, the speed of hoisting is so, and the combination of the high speed with the heavy load has resulted in a machine of considerable interest to all those actively engaged in mining. Aside from mere consideration of size, this installation deserves attention because of the careful attention given, not only to the question of economy of operation, but to the details of construction and installation of the entire equipment. The conditions to be met in this installation were as follows: Weight of rock to be raised per trip, 7 gross tons 15,680 1b. Weight of skip 8,0001b. Weight of cage 1,8001b. Maximum depth of hoisting 4,000 ft. Diameter of rope 153 in. Total weight suspended on one rope from drum 42,000 1b. Normal hoisting speed 2,700 ft. per minute. Maximum hoisting speed : 3,000 ft. per minute. Desired capacity-200 tons per hour from 4,000 ft: depth. The ore is mined in several levels and hoisting is carried on from the 800-ft. level down to the 2,700-ft., which is at present the maximum depth from which the ore is raised regularly. Development is proceeding and a depth of 2,900 ft. has already been reached. The rock is handled underground in cars holding ¾ ton, and about 10 cars are the usual load for a skip. All of the ore is clumped into underground bins, which are of different capacities varying up to 250 tons. From the bins the ore is fed into the skips without passing into measuring pockets. At the surface the

Jan 2, 1916

By Thomas W. Dawson

THE H. C. Frick Coke Co. has used belt conveyers for handling coal for the last eighteen years but, until recently, only for small tonnage and over short distances. The first installations were outside the mines for distributing coal to various parts of plants. A belt conveyer was put in service at Colonial No. 4 Mine in November, 1906, to carry coal from the main hoisting shaft to a storage bin serving two blocks of beehive ovens on the other side of the valley; it was in constant service until the Colonial No. 4 ovens were abandoned less than a year ago. This conveyor was in an overhead gallery that spanned our sidings and yard tracks and the main line of the Pennsylvania Railroad. It was a crude installation, from the viewpoint of present conveyor engineering practice. It had no mechanical feeding device, the coal simply ran through a gate in the side of a bin on to the belt; but one belt on this conveyor lasted eleven years. This conveyor is about 300 ft. long center, to center of pulleys. It operated at a speed of 250 ft. per min. and carried about 400 tons per day. On this basis, the belt life of eleven years means that not over a million and a quarter tons were carried by the belt. While this is not a large tonnage, the cost per ton was much less than by any previous method in use for supplying coal to ovens located at a distance from the main shaft. The next belt conveyor was installed at Bridgeport Mine in 1907. It carried about the same daily tonnage as the first, delivering from the hoisting shaft to a coke-oven bin. Very few data were kept on this conveyor. It also operated until the coke ovens at the plant were put out of blast and the coal taken to the Clairton byproduct plant by river. In 1916, work was started to equip the Bridgeport, Palmer, Gates, and Ronco mines to load their entire output on, the river for transportation to the Clairton byproduct plant, which was then being built. These mines were all operating at that time and had a large area of coal available for river shipment. The Monongahela Railroad was located between the hoisting shaft and the river at each of these plants and,, therefore, had to be crossed at each location to deliver coal to the river.

Jan 6, 1925

By Howard Talbot

THE history of the development of the strip in- dustry, mentioned in this paper, was covered in considerable detail by Stephen Badlam in his paper presented. before the American Iron and Steel Institute at its meeting in New York last October. The description of progress in rolling strip there out-lined will be found good reading by anyone interested in the subject. Quoting from Mr. Badlam&apos;s paper, "For practically thirty years, we find no record of the use of the backing-roll principle, until in 1916 the Lukens Steel Co., Coatesville, Pa., put in a 206-in. plate mill of the four-high type. This was a reversing mill with two 32-in. working rolls and two 50-in. backing rolls and is today making the widest and heaviest plate made anywhere in the world." The functioning of this mill, though rolling hot plate, is, on account of the extreme width and thinness of plate rolled, quite comparable to the rolling of wide strip either hot or cold and was a considerable factor in demonstrating the marked advantages available with the four-high or backing-roll mill for thin accurate rolling. As the writer has brought out, a demand for a product, the rolling of which required the character-istics of the backing-roll mill, was broached by the In-ternational Nickel Co. This resulted in an inquiry of March, 1924, for the building of a mill capable of cold-rolling wide nickel and monel metal sheets or strip, as mentioned. It may be of some interest to note, that whereas the .six-roll cluster mill with plain bearings was built for this installation, the mill designed by the United En-gineering and Foundry Co. for this inquiry was of the four-high type with roller bearings on the backing-roll necks, being essentially the same design as the four-high roller-bearing mill built in 1925 for the Rome Brass & Copper Co. This Rome mill, to quote again from Mr. Badlam&apos;s paper, "fulfilled every requirement, and was the model on which succeeding mills of this type were built."

Jan 5, 1928

By E. C. W. Perryman

IN spite of the large amount of work which has been carried out on the recrystallization of aluminum and its alloys, there has been no complete investigation of the recrystallization characteristics of A1-Mg alloys. The most complete investigation is that reported by Bungardt and Osswald&apos; who, working with commercial-purity materials, found that the temperature both of beginning and of complete recrystallization increased with magnesium content up to about 2 pct Mg, then decreased with a further increase in magnesium up to 5.0 pct, and thereafter increased again. Michaud and Segolz working with 99.93 pct A1 also found the temperature of beginning of recrystallization to decrease as the magnesium content increased from 2.13 pct to about 4.5 pct. Chossat3 using aluminum of 99.99 pct purity found that 0.12 pct Mg had no effect but that 0.4 pct Mg increased the recrystallization temperature by about 30°C. That no effect was found for 0.12 pct Mg does not agree with the later results reported by Demer and Beck4 who found that 0.025 pct Mg in 99.99 pct A1 increased the time for complete recrystallization and furthermore increased the activation energy for the recrystallization process. Kratz" using 99.997 pct A1 found that 0.5 pct Mg increased both the temperature of beginning and of complete recrystallization by 100°C. Chadwick and Hooper" working with commercial-purity material found that 1 pct Mg increased the temperature of complete recrystallization by about 40 °C for cold reductions in the range 17 to 72 pct. With smaller amounts of cold work produced by stretching (10 pct strain), they found no significant effect of magnesium. The latter result agrees with that obtained by Williams and Eborall&apos; who found no effect of 2 pct Mg on the recrystallization temperature of commercial-purity aluminum strained 10 pct or less by stretching. Experimental Procedure Material Used: The chemical analyses of the materials used throughout this investigation are given in Table I. Fabrication: The alloys were cast in iron molds which had been washed thoroughly with alumina. After scalping, the ingots were annealed for 16 hr at 450°C, pressed, annealed at 450°C for 16 hr and hot rolled to 0.25 in. After hot rolling, the slabs were alternately annealed and cold rolled to 0.036 in. Cold-rolling reductions between intermediate anneals were kept at about 30 pct and a high intermediate annealing temperature of 450°C was used so as to obtain, as nearly as possible, similar starting grain sizes for the different materials. All intermediate anneals were done in a salt bath and were followed by cold-water quenching so as to retain all the magnesium in solid solution. The final cold reductions investigated were 20, 30, 40, 50, 60, and 80 pct. The initial grain sizes, that is, the grain size before the final cold reduction, were all very similar. Annealing Procedure: Specimens, 1 in. sq, were cut from the 0.036 in. sheet and annealed in a salt bath, the temperature of which was controlled to k2"C. Separate specimens were annealed for different times at 350°, 375", 400°, and in one or two cases at 415°C and after annealing were quenched in cold water. The time taken for a specimen to reach temperature was approximately 5 sec. Metal-lographic examination after annealing showed that no precipitation of Mg+413 occurred during cooling. Procedures Used for Determining Recrystallization Characteristics: All specimens were electrolyti-cally polished and etched by the method described previously1° and polishing was continued until about 0.002 in. had been removed from each side of the specimen. Using this technique, the smallest recrys-tallized grain which could be observed with cer-

Jan 1, 1956

By H. S. Coe, G. H. Clevenger

Engineers have long recognized the desirability of correlating the data obtained from small-scale slime-scttling tests with commercial work as carried on in large tanks. This need, though most apparent in designing new installations, frequently arises also in existent plants, since a large range of experimental work can be performed without interfering with regular operation. General Settling Phenomena In order to develop rational methods of laboratory testing, it becomes necessary to study the general phenomena of settling. Since it was desired to give the public the benefit of these methods at as early a date as possible, together with the knowledge of the general principles of slime settling necessary for a clear understanding of the laboratory tests, we have ventured to discuss the subject in so far as brought out by the work which we now have under way. We realize that certain of our preliminary conclusions may be subject to modification, but it seems probable that, with but few exceptions, the general laws enunciated will cover the settling behavior of all pulps encountered in metallurgical plants. However, it must be recognized that there is still a vast amount of work to be done upon certain phases of the subject; therefore, at this time we will attempt only a discussion of the behavior of ore pulps during the process of settling or dewatering, under certain given conditions. The laws and principles controlling these conditions are not fully established, so that a complete discussion of them will not be attempted in this paper. In metallurgical practice, slime pulp consists of water, finely divided sand

Jan 1, 1917

In 1970, the federal Clean Air Act was passed, promulgating limits on the emissions of sulfur dioxide (SO2) from large stationary sources that would affect local air quality. The brunt of this regulation was felt by the electric utility industry, especially those units generating electricity with coal-fired boilers. The law hastened development of a new industry, flue gas desulfurization (FGD), which is composed of three major segments: the electric utility, the FGD equipment suppliers (the scrubbing modules), and the scrubbing chemical suppliers. Dravo&apos;s experience suggested the equipment end of the business, but market analysis recommended investigating the chemical processes involved in the removal of the SO2 gas. This resulted in the formation of Dravo Lime Co. to manufacture and market reagents to the FGD industry. This paper will briefly describe the Thiosorbic lime scrubbing process and review Dravo&apos;s innovative mine and calcining facility.

Jan 1, 1982

EXECUTIVE COMMITTEES OF LOCAL SECTIONS New York LOUIS D. HUNTOON, Chairman. ARTHUR S. DWIGHT, Vice-Chairman. THOMAS T. READ, Secretary, Woolworth Bldg., New York, N. Y. E. MALTBY SHIPP, Treasurer. GEORGE F. KUNZ. W. DE L. BENEDICT. Boston ROBERT H. RICHARDS, Chairman. ALBERT SAUVEUR, Vice-Chairman. AUGUSTUS H. EUSTIS, Secretary-Treasurer, 131 State St., Boston, Mass. TIMOTHY W. SPRAGUE, HENRY A. WENTWORTH. Columbia F. A. THOMSON, Chairman. GEORGE W. RODDEWIG, Vice-Chairman. LYNDON K. ARMSTRONG, Secretary-Treasurer, P. 0. Drawer 2154, Spokane, Wash. R. S. McCAFFERY, S. H. RICHARDSON.

Jan 4, 1914

EXECUTIVE COMMITTEES OF LOCAL SECTIONS New York LOUIS D. HUNTOON, Chairman. ARTHUR S. DWIGHT, Vice-Chairman. THOMAS T. READ, Secretary, Woolworth Bldg., New York, N. Y. E. MALTBY SHIPP. Treasurer. GEORGE F. KUNZ, W. De L. BENEDICT. Boston ROBERT H. RICHARDS, Chairman. ALBERT SAUVEUR, Vice-Chairman. AUGUSTUS H. EUSTIS, Secretary-Treasurer, 131 State St., Boston, Mass. TIMOTHY W. SPRAGUE. HENRY A. WENTWORTH. Columbia F. A. THOMSON, Chairman. GEORGE W. RODDEWIG, Vice-Chairman. LYNDON K. ARMSTRONG, Secretary-Treasurer. P. O. Drawer 2154, Spokane, Wash. R. S. McCAFFERY. S. H. RICHARDSON.

Jan 5, 1914

By William P. Blake

Postscript to the paper read by Prof. William P. Blake at the Lake Superior meeting, September, 1904. POSTSCRIPT.*-Since the publication of my paper upon the blackening of the surface of rocks in desert regions, I have noted that similar views of the origin of superficial discoloration in the case of certain rocks from the Salt Lake basin of Utah have been expressed by Prof. George P. Merrill. In the pamphlet, he described the brown-coated weathered boulders from Tooele county, reaching the conclusion that the discoloration was due to the solution of the manganese and iron compounds &apos;in the interior of the boulder, while they were in the water, and the gradual bringing of this material to the surface through capillarity and its oxidation when exposed.

Mar 1, 1905

By H. F. Gossenberger, J. J. Tietjen, J. J. Gannon, C. J. Nuese

External quantum efficiency measurements at 300" and 77°K are presented for vapor-grown GaAs and GaAs1-xPx electroluminescent diodes as a function of junction depth and doping. In GaAs, external efficiencies are found to decrease exponentially with increasing junction depth, defining an average absorption coefficient of 900 cm-1 at 300°K and 350 cm-1 at 77°Kfor epitaxial layers of p-type GaAs. It is shown that photon absorption losses dominate at room temperature and, in fact, account for most of the external efficiency degradation between 77° and 300°K. Healever, the internal (&apos;junction) quantum efficiency is also found to decrease by a factor of 3.5 between 77" ALTHOUGH rapid progress has been made in recent years with GaAs, Gap, and their alloys for use in electroluminescent diodes, there are still important unknown factors related to the performance of these de- and 300°K. The dependence of GaAs efficiencies on donor and acceptor concentrations is presented, illustrating best efficiencies at donor concentrations of 1.5 to 2x 1018 cm-3 . External efficiencies are found to be independent of acceptor concentrations less than 3 x 1019 cm-3 but to degrade at higher doping. The fabrication of GaAsi-xPx electroluminescent diodes is briefly discussed. External efficiencies here for planar uncoated diodes are about 0.035 pct at 300°K and 0.4 pct at 77°for x = 0.42. A brightness of about 8500 ft-Lamberts is attained at 77°K and of 315 ft-Lamberts at 300° K. for curvent densities of 10 amp per sq cm. vices. For example, although the external efficiency is known to decrease by factors of typically 10 to 30 between 77°K and room temperature, the exact causes of this are still uncertain. Experimental results of ill&apos; and carr2 with zinc-diffused electroluminescent diodes suggest that this external degradation is almost entirely due to increased absorption losses at room temperature, with a relatively temperature-independent internal efficiency; recent calculations by Gonda et al.3 corroborate this hypothesis. In contrast, Pilkuhn and Rupprecht4 find the internal efficiency of solution-grown GaAs laser diodes to degrade from 100 to 66 to 40 pct as the temperature is increased from

Jan 1, 1969

YEAR OF ELECTION 1913. FRANK DAWSON ADAMS, Montreal, Canada. 1921. WILLIAM CUTHBERT BLACKETT Sacriston, Durham, England. 1923. GELASIO CAETANI Rome, Italy. 1920. HENRY STURGIS DRINKER Merion Station, Pa. 1933. KARL EIKERS NEW YORK, N. Y. 1922. FEDERICO GIOLITTI Torino, Italy. 1906. SIR ROBERT A. HADFIELD London, England. 1928. JOHN HAYS HAMMOND New York, N. Y. 1921. FRANK WILLIAM HARBORD London, England. 1917. HERBERT HOOVER Washington, D. C. 1905. HENRI LECHATELIER Paris, France. 1931. WALDEMAR LINDGREN Cambridge, Mass. 1921. C. McDERMID London, England. 1913. EZEQUIEL ORDONEZ Mexico City, Mexico.

Jan 1, 1934

By T. H. Alden

In several recent studies of fatigue fracture in single-phase metals, tests have been made using the condition of essentially constant plastic strain amplitude.1-4 This procedure departs from the more common practice of holding the amplitude of stress constant. From these studies have emerged two important generalizations about the behavior of metals during cyclic straining. First, measurements of the stress amplitude, required to impose the fixed plastic strain amplitude, have shown that the rate of cyclic strain hardening in annealed metals is rapid in the early cycles but decays quickly to a very low value.1"5 This behavior is displayed particularly for a range of strain amplitudes below about 2 pct and at low and high temperature. Frequently, the hardening rate becomes so low that one can determine a "saturation" stress. This stress increases with strain amplitude. In addition, an experimental relation between fracture life and plastic strain amplitude was obtained by Coffin and Taternelli,&apos; namely N 1/2 ep = constant. For several metal:;, this equation has been shown to hold down to a strain amplitude of 0.1 pct. Whether it also holds in the "low amplitude" range (lives of more than about 105 cycles) has not been established. The importance of the saturation stress level (a value derived from strain hardening measurements) to the question of fracture life (the usual quantity of interest of fatigue testing) lies in the observation that cracks start to form when the cyclic hardening rate is essentially zero, and not before.4"5 This point suggests immediately a means of relating tests at constant stress and constant strain amplitudes. When making comparison, the stress in a constant stress test is to be identified with the saturation stress in a constant strain test. If these ideas are correct, then it should be possible, using the relation between fracture life and strain amplitude and experimental curves of saturation stress versus strain amplitude, to predict the fracture life as a function of stress, i.e. predict the S -N curve, for low stress fatigue. Saturation stress amplitude-plastic strain amplitude data, obtained in tension-compression, exist only for a few metals and for relatively high amplitudes of strain. Comparable S -N curves (push-pull loading) were known by the author only for OFHC copper. Values for this metal taken from Ref. 2 are shown in Fig. 1. The strain amplitudes, the lowest

Jan 1, 1962

By W. K. Tony Seiler

Further development of mechanical boring machines for hard and abrasive rocks will be effected by the development of more efficient rock cutting tools or the evolution of entirely new rock excavating principles. Presently the cutting tools suitable for extremely hard rocks and successfully and economically used with raise and tunnel boring machines are tungsten carbide insert big hole cutters. This paper explains the design, rock cutting principles, and actual boring operations to illustrate the capabilities and applications of tungsten carbide (TC) insert cutters. While the rate of borehole advance may fall short of the rapid excavating results achieved with soft rock boring machines, the cutter described in this paper may prove to be the most suitable tool in hard rock excavation for many years to come. DEFINITION OF HARD ROCK Existing bored excavations in hard abrasive rocks are proof of the economic application of new methods and mechanical rock boring in the mining industry. Most of the experience in cutting hard to extremely hard rocks has been gained in raise boring where relatively short and small diameter openings are bored. This poses a lesser risk regarding cutter cost than a long and large diameter tunnel and has therefore promoted the testing of various cutter products. Many types of rocks and geologic conditions were en- countered and actual test data was recorded in materials of up to 100,000 psi uniaxial compressive strength. To clarify the term hard to extremely hard, a 1970 interpretation of rock strength which was recently used is adopted and expanded in this paper.

Jan 1, 1971