Search Documents

By Robert Bosworth

THE liability for damages to the surface caused by subsidence is an ever present threat in all underground mining. In ordinary lode mining, this threat rarely materializes into an action, due to the method of mining metaliferous ores, the dip of the veins, and the nature of the ground itself. In the mining of coal, however, this threat is very real. The coal frequently lies close to the surface, in beds underlying large areas of land the surface of which is suitable for agricultural or urban development. Furthermore, the coal is generally mined by the "room and pillar" method and when the pillars of coal are removed, the subjacent support is destroyed. This question of the duty of surface support has now become a very live one in Colorado. What was waste prairie land a few years ago, has become valuable agricultural land dotted here and there with growing towns. Frequent references. will be made here to Colorado conditions and adjudicated cases, but those conditions and cases and the conclusions to be drawn therefrom are equally applicable to all coal-mining states. Briefly stated, the question: is "Does the owner of the substrata or underlying mineral owe any duty of surface support to the owner of the superjacent strata or surface?" There is no absolute duty of support owed by the mineral owner and this assertion is made with full knowledge of numerous expressions to the contrary by courts of Pennsylvania, Illinois, Colorado and other coal-mining states. Whether or not any duty exists depends upon the circumstances surrounding each case, and since in the nature of things those circumstances are rarely identical, there can be no absolute rule.

Jan 1, 1927

By R. R. Spencer, C. A. Campbell, R. J. Marcotte, A. S. Kromer, P. H. Ostlender

Calumet Div. of Calumet & Hecla Inc. is engaged primarily in mining, milling, and smelting the native copper ores of northern Michigan. The copper occurs in fragmental tops of lava flows and in certain interbedded felsitic conglomerates of Pre- Cambrian age. The most famous native copper ore- body in world history is the Calumet conglomerate, which outcrops between the villages of Calumet and Laurium for a distance of about 2 miles. The Osceola lode parallels the conglomerate lode and is mineralized for about 3 miles. Horizontal distance between the two is 750 ft. In 1932 the price of copper dropped to 54 per lb. Coupled with the high cost of obtaining copper from extreme depths, this low price made the venture un- profitable, and the mining unit was abandoned. After the shaft pillar copper was removed from several of the conglomerate shafts in a retreating operation, the mine was allowed to fill with water. In post-depression years, when the price of copper stabilized at about 12¢, Calumet Div. found it profitable to operate its remaining mines on other lodes, as well as its tailings reclamation plants.

Apr 1, 1956

Until a comparatively few years ago, interest in tantalum was limited almost wholly to its scientific investigation, but its extreme resistance to the action of even the strong mineral acids, its great avidity for the common gases, hydrogen, oxygen and nitrogen, and its capacity for transforming alternating to direct current are winning for it a place in our industrial life. Tantalum is not attacked by any single acid except hydrpfluoric, nor is it affected by solutions of alkalies. Aqua regia, which readily dissolves both platinum and gold, has no action on it. This resistance to the common corrosive agents is an outstanding property of tantalum and accounts for many of the applications to which it has been put. When heated, tantalum reacts readily with oxygen and nitrogen and absorbs large volumes of hydrogen, 740 volumes being taken up at a dull red heat. This capacity for absorbing gases is being utilized to an increasing extent in the manufacture of vacuum tubes, in which tantalum is used for the metal parts, especially for grid wire. It is said to be a superior metal for this purpose, particularly in power and sending tubes, because of its low secondary emission. The use of tantalum in the manufacture of electrodes, dishes, spatulas and other laboratory apparatus appears to be fairly steady. There has been some development in its use for dental instruments, surgical tools, pen points, hypodermic needles and acid-proof pumps. Recently it has been used in the manufacture of spinnerets for the rayon industry, of nozzles for the manufacture of artificial casings for sausages and of lining for plant equipment. Tantalum in Electrolysis It has been known for some time that certain substances permit the passage of an alternating current in one direction more readily than in the other. Tantalum possesses this property to a marked degree.' When an alternating current is passed through a cell with tantalum electrodes and sulfuric acid electrolyte, a thin film is soon formed at the

Jan 1, 1930

By D. I. Cameron

A graphical method has been developed and tested for separating the effects of grain boundary and lattice diffusion in polycrystalline materials. The method is based on the assumptions that for unidirectional diffusion from a plane source of radioactive material, the penetration of activity far into the specimen from the source is due solely to grain-boundary effects, and 2) pure grain-boundary penetration is described by a linear plot of log activity vs the perpendicular distance x from the source. The former is based on the fact that at any temperature the grain-boundary diffusion coefficient is always very large relative to the lattice diffusion coefficient; and the latter is based on the derivation of Fisher.1 Using these criteria along with appropriate penetration data (in this case, data for the diffusion of Cb95 in pressed and sintered UO2) one first plots the data as log activity vs x2 and as log activity vs x, as shown by curves 1 and 2, respectively, in Fig. 1. A tangent line to curve 2 for large x (curve 3) is then transferred to the x2 plot as curve 4. The subtraction of curve 4 from curve 1 yields curve 5 which represents only lattice diffusion and may therefore be related to the diffusion coefficient by using the appropriate solution to Fick's second law. It should be noted that the method has inherent inaccuracies for small and large values of x2 and only the subtraction at intermediate values can be used. For the illustrated specimen the calculated diffusion coefficient is 3.4 X 10-11 sq cm per sec at 1445°C while data using a single crystal of UO2 at the same temperature yielded a value of 2.9 x 10-11 sq cm per sec.2 The same method of subtracting grain-boundary diffusion effects to obtain lattice diffusion coefficients has been successfully used to determine self-diffusion coefficients of Th230 in polycrystal- line thoria.

Jan 1, 1962

By Charles M. Cooley

THE continual improvements in. the two extremes of the drilling, unit, the drill and bit, have prompted critical examination of the drill steel, the weak link of this drilling unit. Obviously, little is to be gained from the betterment of the drill and bit if the drill steel which transmits the force needed for drilling from the machine to the bit cannot stand long hard service. The technology of the bit has advanced from the integral type to steel detachables, thence to the tungsten carbide insert. The carbide insert is the most significant advance in the bit, bringing it to the level of a machine tool with its performance records under constant surveillance. Long steel changes have become advantageous because the carbide bit will drill greater footages without replacement than did the steel bit: The development of the tungsten carbide insert opened new fields of endeavor in drilling with percussion drills here- to fore known, but limited by the steel bit. After the introduction of the tungsten carbide bit, drill manufacturers began promotion of long feed shells, lighter drifters and stopers, and easily handled auxiliary equipment. Ultimately this promotion of better equipment was intended to increase the bit-against-rock time of the drill shift. Advantages of the uninterrupted drilling period of a long steel change and faster setup time of lighter drill machines are lost when the shank fails in the machine, rod failure requires continual changing, or the bit breaks off in the hole. The quest for reduced

Jan 1, 1952

By John J. Reed

This paper was prepared as a supplement to the general review by Dr. N. G. W. Cook. His analysis of the problem in terms of the strain energy involved in making the excavation is excellent. It will contribute much towards a clearer understanding of rock behavior and control. Several of the practical applications described herein can be directly related to Dr. Cook's theories and conclusions, and are based on the very same principles. CONTROLLED BLASTING IN ROCK EXCAVATION Generally speaking, the natural rock is a relatively strong and competent structural material, if we conserve its inherent good properties and perhaps reinforce its weak spots. The difficulty often lies in blasting out the tunnel or chamber without damaging the walls and roof we wish to have remain afterwards. Much progress has been made in the last five years in better understanding the controlled excavation of rock. The specialized techniques known as smooth wall blasting and presplit blasting have now developed from the status of curiosities of rock excavation to the point where these techniques are specified in contracts drawn up for such rock excavation projects as tunnels, underground pourer houses, etc. These techniques have been well described and discussed in previous publications; there is no need to reiterate here. It might be well to point out that recent research has demonstrated the effect that inherent rock stress may have on presplitting in certain directions. Material can be presplit most readily parallel to the direction of maximum compressive stress, and this may not always be in the direction desired. Inherent rock stress measurements by stress relief over coring, etc., may have important value in deciding how to best presplit proposed excavations. In addition, recent work at the Colorado School of Mines has demonstrated the feasibility of con-

Jan 1, 1967

By H. F. Yancey

THE jig may be termed the standard coal-washing machine. Although exact figures on the relative tonnages of coal treated by the various coal-cleaning processes are not available, it is known that a large part of all the coal given special cleaning treatment is handled by jigs. This wide use of the jig warrants a special study of its performance. In this paper are presented the results of an analysis of work done by a three-compartment jig in treating bituminous coal from the Thick Freeport bed in Allegheny County, Pa. Certain systems of washing coal require sizing before washing, while others treat unsized coal. The prevailing practice, however, for the preparation of coking coal from the more easily washed coal is to treat an unsized or natural feed at about -1 in. size and smaller. Under such conditions, the minimum size of particle that is beneficiated has long been and is still a matter of discussion and conjecture. In a careful laboratory investigation Jüngst1 concluded that the practical limit of settling of fine coal is reached at from 0.02 to 0.008 in. On the other hand, Hancock2 has found that single-compartment jigs, used in preparing coal for the domestic market, usually allow most of the heavy (refuse) particles smaller than 1/4 in. to go into the washed coal. He also states that it is impossible with the ordinary coal jig to make any noticeable improvement in the quality of the coal finer than 20 mesh (about 1/30 in.). Because of its importance in coal cleaning, the work described in this paper was undertaken for the purpose of obtaining information on this subject, as a part of the general coal beneficiation program being carried out by the Bureau of Mines.

Jan 4, 1925

By Meng-Cherng Sun, Fun-Den Wang, David M. Ropchan

A proposed technique for improving coal-mine roof stability by softening parts of coal pillars along the sides of entries developed from structural analysis is presented. This technique is based on the transference of the high stress concentration in the roof near the upper corners of a rectangular opening to the roof rock and coal over the solid away from the opening. This transferral is accomplished by softening parts of the coal pillars by drilling a series of parallel holes into the coal in the ribs and face of the entry prior to advance. The effectiveness of the pillar softening in terms of reducing the opening width (so that the stress in the roof near the corner is equivalent to that of a narrower opening) ranges from 3 to 5 ft for a 16-ft entry using a series of 4 to 5-ft-deep parallel drill holes of 3 to 6-in.-diam on a 1 to 2-ft spacing for a particular geology. Pillar softening should be highly effective in controlling roof where cutter-roof cave conditions exist, because this technique reduces the high stress concentration in the roof at the upper corners of the opening. It may also be effective for reducing tensile roof failure and coal rib sloughing for certain specific geological conditions. This technique appears to be a simple, effective, and practical method that can be used to supplement conventional roof support methods of roof bolting, timbering, roof truss, and other existing methods in underground coal mines. The authors consider the technique feasible and believe that it merits underground trials.

Jan 1, 1975

By Chase Palmer

INTRODUCTION. WHILE the reducing action of organic matter, of ferrous sulphate, and of hydrogen sulphide has frequently been invoked to account for the deposition of native gold and silver from ore-forming solutions, the high efficiency in this respect of certain of the metallic minerals which form the ore itself has not been sufficiently recognized. If a little finely powdered chalcocite is placed. in a test-tube and 2 or 3 cc. of a dilute solution of gold chloride are poured over it, two or three shakes of the tube suffice to remove all the gold from the solution. The color of the solution changes from yellow to pale green, showing that copper is dissolved simultaneously with the precipitation of metallic gold. If a piece of chalcocite is hung in a dilute aqueous solution of silver sulphate (1 normal), a coating of silver begins immediately to form on the mineral, and within a few moments a beautiful silver tree has developed, similar to that formed when metallic zinc is immersed in a similar solution.

Jan 5, 1913

By Tell Ertl

THE term oil shale is defined. Foreign oil-shale developments are outlined briefly, The richest and most extensive oil-shale deposits in the United States lie in Western Colorado. The Bureau of Mines is opening two adjacent areas for underground mining in Western Colorado. From the first area the oil shale is mined selectively as required by the retorting plant. The second area is being developed as a unit of a full scale oil-shale mine to ascertain the most practical methods of mining oil shale and to determine costs. In both of these mining areas, research will be carried on to develop new and improved practices for mining oil shale.

Jan 1, 1947

By William M. Brewer

Until quite recently, in fact within the past two gears, but little attention has been given to the outcrops on the west coast of Vancouver Island, and their copper-contents. During the past few months the writer has been engaged in examining and developing some of these prospects. In many respects he has found characteristics associated with these prospects which, in his experience, are unique. In the first place, nearly all the outcroppings which overlie chalcopyrite-ore along the west coast of the island are composed of a high-grade magnetite. The magnetic qualities of some of these outcrops arc so pronounced that the magnetite possesses polarity. Although the writer hinlsclf had no analyses of this magnetite made, yet from its appearance he can readily believe that analyses made for other parties, which show a yield' of 62 or 63 per cent. of metallic iron, with only traces of phosphorus and silica, are correct. At a very shallow depth, masses of chalcopyrite, yielding in some instances as high as 32.6 per cent. of copper, occur associated with the magnetite; and in one instance, which recently came under the writer's observation, a solid body of high-grade chalcopyrite, fully 4 feet in thickness, occurs Within 6 feet of ; the surface. Usually this solid sulphide-ore carries low values in gold. Probably ail average of' $2 per toil would be fairly representative. But in some instances development has determined the occurrence of narrow stringers of pyritous quartz, associated with the sulphide-ores, which yield by assay more than $20 per ton in gold. In the districts examined by the writer, the country-rock is usually crystalline limestone, with dikes of igneous rock as intrusions. Sometimes the outcrops of magnetic iron-ore are

Jan 1, 1900

By J. L. McK. Yardley

There are two general classes of problems in connection with electric furnaces. First, those relating to the best utilization of the electrical power inside the furnace; second, those connected with the bringing of the electrical power to the point where it is to be utilized. Referring particularly to the latter class of problems, many calculations have been made, covering a wide variety of furnaces, to check the electrical capacity and power factor found from test. The following analysis, made for the purpose of determining the maximum capacity and approximate performance of a new furnace, to operate at 160 volts on a 60-cycle circuit, may be of interest. The first characteristic necessary to determine is the inductance, since this is the factor that limits the amount of power which can be put into the furnace. Inductance is calculated from the dimensions of the furnace, according to formulas of the U. S. Bureau of Standardsll as follows. Formula 99, for mutual inductance, is: M = 2l [log 2l/d-1 +d/l] Formula 103, for self-inductance, is: Both of these formulas are approximations which are nearly correct when 1 is great compared to d or R. 1 = length of circuit, in centimeters, d = separation between the conductors, in centimeters, R = geometric mean radius of conductors. For a circular tube, R = the radius of the circle. For a solid circular conductor, R = 0.7788 X the radius of the conductor. For a rectangular conductor, R = 0.2235 X (a + b), a being the length, and b being the width of the rectangle. To calculate the inductance of a three-phase circuit, it is customary to figure the inductance of one leg. In circuits where the three conductors

Jan 1, 1920

By Sukeyuki Mori, Kinjiro Aso, Tsuyoshi Hara, Hisao Okamoto

A theoretical calculation of the electro-osmotic circulation of liquid in a rectangular micro-electro-phoresis cell was presented by Smoluchowski (1921) and Komagata (1933). According to their theories, the velocity of liquid changes with depth such that the velocity distribution may be represented by a symmetrical parabola in the cell. Their theories appear contrary to the results of our experiments which show that the velocity distribution curve is represented by a symmetrical parabola whose symmetrical axis is displaced from the center line of the cell. A similar phenomenon had been suggested by Lane and White in 1937 based on the latter's theory which seemingly was incomplete. By using methods of measuring electrophoretic velocities based on the above three theories, serious errors are obvious. We are thus proposing a unified theory for determining the electrophoretic velocity of mineral particles in a rectangular cell. The equations of Smoluchowski, Komagata and White can be derived from our theory as special cases. On the basis of our theory, we are proposing an improved method of determining the precise electrophoretic velocity of mineral particles based solely on the coefficients of the velocity distribution curve. In our experiments, this method gives satisfactory results. We determined the relation between the zeta-potential and pH value of suspension for several minerals.

Jan 1, 1980

By H. K. Livingston

THE first person to investigate intensively the vast field of surface phenomena and capillary effects was the eminent English scientist, Lord Rayleigh (1842-1919), who laid down most of the fundamentals of this subject. This work was greatly amplified by Irving Langmuir,1 who, in connection with research for the General Electric Co., spent 25 years on the study of the surface chemistry of films, finally receiving the Nobel Prize in Chemistry for 1932 in recognition of his work. At present, William Harkins,2 of the University of Chicago, is the world's foremost authority on surface-tension measurement and his independent work, when combined with that of Langmuir, resulted in the orientation con-cept of solubility and surface activity, which is now an important funda-mental in chemistry. The theory laid down by these men was first applied to practical considerations regarding petroleum reservoirs by F. E. Bartell,3 of the University of Michigan, in connection with an American Petroleum Institute research grant. The latest and most advanced application of Bartell's work is contained in an article published in 1935 by Allen Garrison,4 of Rice Institute, in which he relates Bartell's measurements to the ratio of oil to water produced by wells and shows the types of petroleum reservoirs where the effects studied by Bartell are significant. This article is intended as a minor extension of such work.

Jan 1, 1938

By J. E. Powers, T. D. Taylor, N. E. Wood

A computer program has been developed to simulate a gas transmission 1ine operating under transient conditions. The program was developed by application of the basic mass and momentum balance equations. The nonlinear equations thus obtained were transformed by the method of characteristics and finite-difference techniques to make them suitable for machine computation. Three tests of the computer program were made. In each of these, the initial condition was assumed to be steady-state flow, the inlet density was held constant at the initial condition, and the outlet mass flow rate was varied with time. One test was theoretical in nature, but the others were made for direct comparison with actual field data. Results of the tests are presented in graphical form. INTRODUCTION Theoretical investigations of the transient flow of gas in long pipelines have been limited in number. In 1951, Olds and Sage4 developed a gaphical method of solving the nonlinear flow equations describing transient gas flow in a long pipeline. Research in this field at the U. of Oklahoma was initiated by Nelson1 in 1956. Nelson utilized a computer to solve numerical equations involving a lengthy trial-and-error procedure, and his results have been reported in the literature? It does not seem likely that Nelson's method can be extended to the analysis of transient behavior of pipeline networks; therefore, the investigation to be discussed in this paper was undertaken to improve and extend the previous work. The following discussion presents, briefly: (1) the basic differential equations governing transient flow, (2) transformation of these equations into a form suitable for machine computation. (3) role of boundary conditions in the calculations, (4) a very brief description of the computer program which was developed to simulate the pipeline and (5) results of tests of the computer program.

By Robert Yerkes

THE following is a brief account of the methods of measuring intelligence especially prepared for use in the U. S. Army, of typical results, and of some of their immediately practical applications. It has been prepared for the assistance of army examiners and for the information of all who are interested in the relations of scientific placement to military efficiency. PURPOSE OF THE INTELLIGENCE TESTS Under the direction of the Division of Psychology, Medical Department, and in accordance with provisions of War Department General Order No. 74, mental tests are given recruits during the 2-wk. detention period. These tests provide an immediate and reasonably dependable classification of the men according to general intelligence. Their specific purposes are to aid: 1. In the discovery of men whose superior intelligence suggests their consideration for advancement; 2. In the prompt selection and assignment to development battalions of men who are so inferior mentally that they are suited only for selected assignments; 3. In forming organizations of uniform mental strength where such uniformity is desired; 4. In forming organizations of superior mental strength where such superiority is demanded by the nature of the work to be performed; 5. In selecting suitable men for various army duties or for special training in colleges or technical schools; 6. In the early formation of training groups within regiment or battery in order that each man may receive instruction and drill according to his ability to profit thereby;

Jan 2, 1919

By Walter Larsh

The Ruth orebody, so far developed, is roughly oval in plan, major and minor axes about 1600 ft. (487 m.) and 1200 ft. (365 m.) respectively, average thickness about 120 ft. (36 m.), and with a general dip of about 15° to the northwest. According to the generally accepted theory, the ore is a secondary enrichment of the porphyry due to leaching in situ by meteoric waters. Copper occurs as chalcocite, chalcocite coating pyrite, and a little chalcopyrite. The leached zone, or capping, covering the ore varies in thickness from 110 to 540 ft. (33 to 164 m.), average about 410 ft. (124 m.). The ore is blue gray in color, and the capping, light yellow to brown. Ore was first discovered in quantity in the workings from the Ruth shaft, now caved. Further development work was done by churn drills, and the outline of the orebody, as stated above, determined in this manner. Drilling is still being carried on. The porphyry area is entirely surrounded by sedimentaries, lime-stones and shales; and, in so far as the underground workings have shown, the porphyry' itself, the sedimentaries near the contact, and the country underlying the ore (igneous or sedimentary) is very soft, heavy, and in places swelling ground. All openings have to be carefully and stoutly timbered, and, after once driven, they have to be constantly eased off and repaired. The mine is at present served by two shafts, the Star Pointer, the main working shaft; a vertical, and the Ingersoll, an incline used for waste and material. The two shafts are about 2600 ft. (792 m.) apart, connected on the 500 level; a connection is now being driven on the 600 level. (Dec., 1917. This connection is now completed.) The 300 level, which is finished, and the 400 level which is nearly completed, are accessible only from the Ingersoll and connections with the 500 level.

Jan 1, 1918

By C. Wert, P. Bunn

Determination of the solid solubility of gases in metals is usually done by one of two methods. The first is an additive method, in which measurement is made at temperature of the maximum amount of gas absorbed by an initially degassed piece of the metal. Gas additions are made until the dissolved gas first comes into equilibrium with a compound. This method is most useful at relatively high temperatures where the amount of gas absorbed is relatively large and where equilibration of the dissolved gas with the gas atmosphere can be achieved in a relatively short time. The second is a precipitation method. A supersaturated solution of the gas in the metal is held at temperature until equilibrium is established between the gas atoms in solution and a compound. The quantity of dissolved gas is then determined by some physical measurement which is sensitive only to the gas in solution. This method is generally useful in low temperatures. This paper describes measurement of solubility of nitrogen in tantalum whereby measurements at low temperatures using internal-friction methods are plotted together with existing measurements at high temperatures. The solubility is thereby known from less than 0.5 at. pet at 350°C to near 13 pet at 2300°C. Several measurements have been reported of the solubility of nitrogen in tantalum. These are collected in Fig. 1. Three single determinations by Ke,1 Andrews,2 and Brauer and zapp3 are plotted along with a series of measurements by Vaughn, Stewart and schwartz4 and Gebhardt, Seghezzi, and Fromm.5 Although not much doubt exists about the solubility being in excess of 10 at. pet above 2000°C, the solubility indicated at low temperatures depends on whose data are selected as being most reliable. The variation is enormous, being at least an order of magnitude at 500°C. Accordingly, a measurement was begun to examine this discrepancy. The method of measurement finally selected was that of internal friction. A solid solution of nitrogen in tantalum was prepared by heating a tantalum wire in a dilute at-

Jan 1, 1964

By R. F. Pilgrim

A digital computer program to mathematically simulate the effect of limited changes in feed rate in the range of 80 to 95 tph on a plant-scale wet grinding circuit has been developed and tested. The circuit studied included an 8-ft-diam X 12-ft rod mill operating in open circuit and feeding two parallel 12-ft-diam x 10-ft pebble mills, each one operating in closed circuit with an 8 X 32-ft rake classifier. The simulation is an empirical one based on two sets of data collected manually from the operating circuit under what was said to be steady-state feed rates of 80 and 95 tph with all other operating variables also at steady state. The procedure is a combination of several published approaches to the modeling of grinding mills and classifiers and it is applicable to a wide range of circuits. The program permits the computing of the size distributions of all feeds and discharges of all grinding units and classifiers in the circuit for a specified feed rate. The data used in this report for demonstrating the program are unsatisfactory since the circuit was not operating under steady-state conditions when it was sampled. Consequently the circuit model parameters could not be accurately estimated. The predictive power would be greatly improved if new data were obtained under true steady-state conditions.

Jan 1, 1973

By R. O. Scattergood, P. Beardmore, M. B. Bever

THE stored energy and microhardness of a Au-Ag alloy deformed by explosive loading were measured previously as functions of shock pressure' and compared with corresponding data for drawn wires.' The difference of the two processes has been explored further by investigating the annealing behavior of explosively loaded specimens and drawn wires. Sheet specimens, 0.042 in. thick, of a Au-Ag alloy containing 82.6 wt pct Au were explosively loaded in stacks of four.3 Wires prepared from the same melt of alloy were drawn through dies.' The annealing kinetics were determined by microhardness measurements on separate specimens for each annealing temperature and time. Several values of the stored energy were measured by tin-solution calorimetry Experimental details are given elsewhere. Wires were drawn until the microhardness or stored energy equalled the corresponding values of the explosively loaded specimens as nearly as possible. Wire drawn to a true strain 7 of 0.09 had approximately the same hardness and stored energy as specimens explosively loaded to a shock pressure of 70 kbar. The microhardness of specimens

Jan 1, 1963