Recommended codes of engineering and industrial practice (including safety codes) developed in cooperation with interested industries, professional organizations, and regulatory bodies. In many cases recommended requirements are given official status through their incorporation in local ordinances by State and municipal regulatory bodies.

H44. Specifications, tolerances, and other technical requirements for commercial weighing and measuring devices, H. F. Wollin, Compiler and Editor, Nat. Bur. Stand. (U.S.), Handb. 44, Fourth Edition, 222 pages (Dec. 1971).

Key words: Commercial weighing and measuring devices; specifications; technical requirements; tolerances.

NBS Handbook 44, Fourth Edition, "Specifications, Tolerances, and Other Technical Requirements for Commercial Weighing and Measuring Devices," is a revision of the Third Edition of Handbook 44. This Fourth Edition adopted by the National Conference on Weights and Measures is given legal status in practically every state in the United States. (Supersedes NBS Handbook 44 - 3rd Edition.)

H105-2. Specifications and tolerances for reference standards and field standard weights and measures. 2. Specifications and tolerances for field standard measuring flasks, B. C. Keysar, Nat. Bur. Stand. (U.S.), Handb. 105-2, 6 pages (Jan. 1971). Key words: Accurate measurements of volume of liquids; field standard measuring flasks; specification; tolerances; weights and measures inspection.

These specifications and tolerances are recommended as minimum requirements for standards used in the field by State

and local weights and measures officials in quantity determinations of liquid commodities.

H105-3. Specifications and tolerances for reference standards and field standard weights and measures. 3. Specifications and tolerances for metal volumetric field standards, B. C. Keysar, Nat. Bur. Stand. (U.S.), Handb. 105-3, 8 pages (May 1971). Key words: Accurate measurements of volumes; field standard; metal volumetric field standards; provers; specifications; test measures; tolerances; weights and measures inspection.

These specifications and tolerances are recommended as minimum requirements for standards used in the field by State and local weights and measures officials in quantity determinations of liquid commodities.

H108. Weights and measures labeling handbook, D. E. Edgerly, Nat. Bur. Stand. (U.S.), Handb. 108, 406 pages (May 1971)

Key words: Consumer package; exemption; fluid measure; labeling; net quantity; principal display panel; regulations; weights and measures.

The Weights and Measures Labeling Handbook has been prepared for use by State weights and measures officials in the enforcement of State laws and regulations pertaining to the packaging and labeling of commodities. The Handbook provides a cross indexed compilation of the requirements of the Model State Packaging and Labeling Regulation, U. S. Department of Agriculture regulations, and regulations of the Food and Drug Administration and Federal Trade Commission issued pursuant to the Fair Packaging and Labeling Act.

This series includes proceedings of high-level national and international conferences sponsored by NBS, precision measurement and calibration volumes, NBS Research Highlights, and other special publications appropriate to this grouping, such as administrative pamphlets, wall charts and bibliographies.

SP236, 1971 Edition. NBS frequency and time broadcast services. Radio stations WWV, WWVH, WWVB, and WWVL, P. P. Viezbicke, Editor, Nat. Bur. Stand. (U.S.), Spec. Publ. 236, 1971 Edition, 15 pages (July 1971).

Key words: Broadcast of standard frequencies; high frequency; low frequency; standard frequencies; time signals; very low frequency.

Detailed descriptions are given of the technical services provided by the National Bureau of Standards radio stations WWV, WWVH, WWVB, and WWVL. These services are: 1. Standard radio frequencies; 2. Standard audio frequencies; 3. Standard musical pitch; 4. Standard time intervals; 5. Time signals; 6. UT corrections; and 7. Official announcements. In order to provide users with the best possible services, occasional changes in broadcasting schedules are required. This publication shows the schedules in effect on July 1, 1971. Annual revisions will be made. Current data relating to standard frequencies and time signals are available monthly in the Time and Frequency Services Bulletin. Advance notices of changes occurring between revisions will be sent to users of NBS broadcast services who request such notice on the basis of need. Supersedes NBS Special Publication 236, 1970 and previous issues.

SP250, 1970 Edition. Calibration and test services of the National Bureau of Standards, Nat. Bur. Stand. (U.S.), Spec. Publ. 250, 1970 Edition, 353 pages (Dec. 1971).

Key words: Calibration services; fees for testing; test fee schedule; test procedures.

This publication contains a descriptive listing, item by item, of most of the test and calibration work done at the National Bureau of Standards with the respective fees. The content is fully indexed providing easy access to data on specific measurement services. Included also is information about the Bureau's organization and statutory functions, the procedures for requesting tests, and the reports issued thereon. Throughout the text are mentioned various other publications which form a bibliography in measurement techniques. This publication supersedes Special Publication 250, 1968 Edition and the supplementary material in Measurement Users Bulletins Numbers 1 through 11. Supersedes Miscellaneous Publication 250, 1968 Edition.

SP260-21. Analysis of interlaboratory measurements on the vapor pressures of cadmium and silver. (Certification of Standard Reference Materials 746 and 748), R. C. Paule and J. Mandel, Nat. Bur. Stand. (U.S.), Spec. Publ. 260-21, 30 pages (Jan. 1971).

Key words: Cadmium; components of error (within- and between-laboratory); heats of sublimation (second and third law); interlaboratory measurements; silver; standard errors; standard reference materials; vapor pressure.

Detailed statistical analyses have been made of results obtained from a series of interlaboratory measurements on the vapor pressures of cadmium and silver. Standard Reference Materials 746 (cadmium) and 748 (silver) which were used for the measurements have been certified over the respective pressure ranges 10-11-10-4 atm and 10-12-10-3 atm. The temperature ranges corresponding to these pressures are 350-594 K for

cadmium and 800-1600 K for silver. The heats of sublimation at 298 K and the associated two standard error limits for cadmium and silver are 26660±150 cal/mol and 68010± 300 cal/mol, respectively. Estimates of uncertainty have been calculated for the certified temperature-pressure values as well as for the uncertainties expected from a typical single laboratory's measurements. The statistical analysis has also been made for both the second and third law methods, and for the within- and betweenlaboratory components of error. The uncertainty limits are observed as functions of both the heat of sublimation and the temperature.

SP260-22. Homogeneity characterization of Fe-3Si Alloy, H. Yakowitz, C. E. Fiori, and R. E. Michaelis, Nat. Bur. Stand. (U.S.), Spec. Publ. 260-22, 30 pages (Feb. 1971).

Key words: Fe-3 Si alloy; homogeneity testing; metallography; microprobe analysis; spectrometric analysis; Standard Reference Materials.

An alloy of iron-3.22 wt. pct. silicon (Fe-3Si) was characterized with regard to chemical homogeneity of iron and silicon at the micrometer level of spatial resolution. This alloy is satisfactory for use as a homogeneous standard for electron probe microanalysis. The samples were cut from coarse-grained sheet stock to a final size of about 3 mm × 3 mm × 0.28 mm thick. Homogeneity was checked by means of quantitative raster scanning in which a square matrix (1.1 mm × 1.1 mm) of individual points is analyzed by the microprobe. Each matrix represents 400 separate analyses. Usually, the same matrix was rerun so that each point was sampled twice. The coefficient of variation for both the iron and silicon is less than one percent. Quantitative microprobe analysis was also carried out on this alloy giving a silicon content of 3.14% and an iron content of 96.9%.

SP260-25. A standard reference material containing nominally four percent austenite, G. E. Hicho, H. Yakowitz, S. D. Rasberry, and R. E. Michaelis, Nat. Bur. Stand. (U.S.), Spec. Publ. 260-25, 22 pages (Feb. 1971).

Key words: Austenite in ferrite; electron microprobe; powder metallurgy; quantitative microscopy; SRM; x-ray fluorescence analysis.

This standard was produced by powder metallurgical techniques using known amounts of austenite. Using these techniques, 134 specimens were prepared. Because these standards are expected to be used primarily for the calibration of xray diffraction equipment, only one surface of each standard is certified, and these surfaces range from 3.1 percent to 5.2 percent in austenite content. To make the specimens, 310 stainless steel powder (austenitic) was blended with 430 stainless steel powder (ferritic) to make a mixture of 5 percent austenite in ferrite. The material was compacted, sintered, polished and etched so the austenite appears white and the ferrite, a deep brown. Then quantitative microscopy methods were used to determine the percentage of austenite near the surface. Furthermore, the 310 powder contains 20 percent of nickel while the 430 powder contains virtually no nickel. Therefore, after establishing a meaningful calibration curve, x-ray fluorescence analysis for the nickel content was also used as a direct measurement of the amount of austenite on the surface of the compact. Both procedures were carried out on fifteen specimens statistically selected from the total number of compacts produced. Agreement, within experimental error limits, was obtained between the x-ray fluorescence results and quantitative microscopy results.

The x-ray fluorescence method was used to characterize all additional compacts. X-ray diffraction determinations of austenite content are in good agreement with the x-ray fluorescence and quantitative microscopy results. The compacts may be used as x-ray diffraction standards for austenite or in special cases as xray fluorescence standards for nickel content.

SP260-26. Standard reference materials: National Bureau of Standards-U.S. Steel Corporation joint program for determining oxygen and nitrogen in steel, J. F. Martin, Nat. Bur. Stand. (U.S.), Spec. Publ. 260-26, 40 pages (Feb. 1971).

Key words: Inert gas fusion; one ppm of oxygen and nitrogen in steel; Research Associate Program; simultaneous determination of oxygen and nitrogen; Standard Reference Material for oxygen.

Because of a need for a method for the rapid, simultaneous determination of small concentrations of oxygen and nitrogen in steel, a joint project under the Industrial Fellowship Program of U.S. Steel and the Research Associate Program of the National Bureau of Standards (NBS) was established. After investigation of various techniques, an analytical apparatus was constructed with excellent sensitivity for both elements. This apparatus consists of an inert gas fusion system coupled to a gas chromatograph. Recommended modifications have been completed on this equipment, and simultaneous determinations of oxygen and nitrogen in steel are presently being made. The detection limit is < 1 ppm for both oxygen and nitrogen, and the analysis time is about 5 minutes.

A direct result of this program has been the issuance by NBS of a new Standard Reference Material (SRM), a maraging steel, for oxygen. This SRM has the lowest oxygen concentration (4.5 ppm) of any steel standard yet issued by NBS.

SP260-27. Uranium isotopic standard reference materials, E. L. Garner, L. A. Machlan, and W. R. Shields, Nat. Bur. Stand. (U.S.), Spec. Publ. 260-27, 162 pages (Apr. 1971).

Key words: Absolute isotopic abundance; ignition procedure; isotopic standards, mass spectrometry; stoichiometry; uranium.

An ignition procedure has been developed that will yield reproducible stoichiometry for U3O8. The effects of temperature, length of ignition, rate of cooling, pressure and type of atmosphere were investigated. This ignition procedure has been used for the blending of high purity 235U and 238U separated isotopes to prepare calibration standards for the determination of bias effects in the thermal emission mass spectrometry of uranium. Weight aliquoting was used to prepare calibration mixes with 235 U/238U ratios of more than 10 and less than 0.1 and to add a 233U spike for the determination of minor isotope abundances in the uranium isotopic standards by the isotope dilution technique.

A description of the unique features of the mass spectrometer instrumentation including the source, NBS collector and expanded scale recorder are given. Two specific analytical procedures were used for the isotopic analysis of uranium and are adaptable, within a general framework, to fit the particular ion current intensity requirements of a wide range of isotopic distributions. Mass discrimination due to evaporation and ionization on the filaments, and other parameters such as temperature, time, sample size, sample mounting, total sample composition, acidity, filament material, pressure, non-ohmic response, R-C response and source memory were studied as part of the development effort to establish sound analytical procedures.

The absolute isotopic abundances of 18 uranium SRMS were determined by thermal emission mass spectrometry. The general approach was to determine absolute 235U/238U ratios by using calibration mixes to correct for filament bias. Then the absolute

234U and 236U were determined by 233U isotope dilution. For SRM U-0002, isotope dilution was the only practical means of determining the low abundance of 235U as well as the 234U. The limits given for the isotopic composition of the uranium SRMS are at least as large as the 95 percent confidence limits for a single determination and include terms for inhomogeneities of the material as well as analytical error.

SP260-28. Standard reference materials: Preparation and evaluation of SRM's 481 and 482 gold-silver and gold-copper alloys for microanalysis, K. F. J. Heinrich, R. L. Myklebust, S. D. Rasberry, and R. E. Michaelis, Nat. Bur. Stand. (U.S.), Spec. Publ. 260-28, 100 pages (Aug. 1971).

Key words: Alloys; corrections; electron probe; homogeneity; matrix scanner; microanalysis; quantitative analysis; standard reference materials; x-ray emission.

The reasoning behind the choice of the systems Au-Ag and Au-Cu for SRM's, and their suggested uses are described. We also report on the preparations of the materials, their chemical analysis, the tests performed to ascertain macroscopic and microscopic homogeneity, and on relative x-ray intensity measurements at various x-ray lines and voltages. A description of the instrumentation (matrix scanner), techniques, and programs employed in the homogeneity studies, as well as tables and graphs of the x-ray intensity measurements, are appended. SP260-29. Calibration of NBS secondary standard magnetic tape (computer amplitude reference) SRM 3200 using the reference tape amplitude measurement "Process A" Model II, S. B. Geller, Nat. Bur. Stand. (U.S.), Spec. Publ. 260-29, 57 pages (June 1971).

Key words: Average signal peak level; computer amplitude reference; magnetic tape; master standard; saturation curves; secondary standard; signal level calibration; standard reference materials; unrecorded reference.

This publication describes the design, operation and calibration of the NBS signal amplitude measuring system (Process A-Model II) that is used for calibrating unrecorded Secondary Standard Magnetic Tapes (Computer Amplitude Reference) SRM 3200. This system supersedes the measurement system that was described in the NBS Special Publication 260-18 (November 1969). The signal level calibration is made with respect to a reference signal level derived from the NBS Master Standard Magnetic Tape (Computer Amplitude Reference) that is kept in repository at NBS. The techniques for measuring and recording the data that accompany each Secondary Standard Magnetic Tape in the form of strip chart recordings and saturation curves are described.

SP260-30. Standard reference materials: standard samples issued in the USSR, R. S. Gorozhanina, A. Y. Freedman, and A. B. Shaievitch, All-Union Scientific Research Institute of Metrology Sverdlovsk Branch, All-Union Scientific Research Center of the State Service for Standard Samples, translated from the Russian by M. C. Selby, Nat. Bur. Stand. (U.S.), Spec. Publ. 260-30, 86 pages (June 1971).

Key words: Standard reference materials; standard samples; standards in Russia; USSR standards.

This reference handbook contains information on standard samples of properties and composition of substances and materials including areas of their application, nomenclature, certified characteristics, and values of the certified quantities.

The handbook was prepared for personnel of metrological establishments, for laboratories of ferrous and non-ferrous metallurgy, for all branches of industry employing metals and alloys, for the mining industry, geological research service, oil refining industry, scientific research organizations, and institutes of higher education.

SP260-31. Thermal conductivity of electrolytic iron, SRM 734, from 4 to 300 K, J. G. Hust and L. L. Sparks, Nat. Bur. Stand. (U.S.), Spec. Publ. 260-31, 19 pages (Nov. 1971).

Key words: Cryogenics; electrical resistivity; electrolytic iron; Lorenz ratio; Seebeck effect; thermal conductivity; transport properties.

Thermal conductivity data are reported for a specimen of electrolytic iron, SRM 734, for temperatures from 4 to 300 K. Variability of this iron was studied by means of electrical residual resistivity ratio measurements on 63 specimens. This study showed that with a two-hour anneal at 1000 °C one can obtain a thermal conductivity Standard Reference Material that has variability of less than 1 percent in thermal conductivity.

SP300. Volume 7. Precision measurement and calibration. Radiometry and photometry, H. K. Hammond, III, and H. L. Mason, Editors, Nat. Bur. Stand. (U.S.), Spec. Publ. 300, Vol. 7,685 pages (Nov. 1971).

Key words: Emissivity; flashing light; flux measurement; irradiance; material properties; photometry; projectors; radiance; radiometry; reflectometry.

This volume is one of an extended series which brings together some of the previously published papers, monographs, abstracts and bibliographies by NBS authors dealing with the precision measurement of specific physical quantities and the calibration of the related metrology equipment. The contents have been selected as being useful to the standards laboratories of the United States in tracing to NBS standards the accuracies of measurement needed for research work, factory production, or field evaluation.

Volume 7 contains reprints of more than 60 items on radiometry and photometry published between 1957 and 1970. The material has been placed in groups according to the following subjects: general radiometry, emissivity standards, emissivity measurements and techniques, material properties, irradiance standards, radiometric measurement techniques, radiance standards, flux measurement, reflectometry, general photometry, projectors, flashing lights, and chronological bibliography of publications by NBS staff.

SP305. Supplement 1. Publications of the National Bureau of Standards 1968-1969. A compilation of abstracts and key word and author indexes, B. L. Oberholtzer, Nat. Bur. Stand. (U.S.), Spec. Publ. 305 Suppl. 1, 497 pages (Dec. 1970).

Key words: Articles; publications.

This Supplement lists the publications of the NBS from January 1968 to December 1969. A brief abstract for each publication is given. It also includes abstracts of those papers by Bureau authors that have appeared in non-NBS media. Subject and author indexes are included and general publication information is furnished. This catalog and previous lists give reference to the publications printed by the Bureau during the period 1901 to December 1969. To accompany NBS Circular 460, its Supplement, Miscellaneous Publication 240, its Supplement, and Special Publication 305.

SP305. Supplement 2. Publications of the National Bureau of Standards 1970. A compilation of abstracts and key word and author indexes, B. L. Oberholtzer, Nat. Bur. Stand. (U.S.), Spec. Publ. 305 Suppl. 2, 378 pages (July 1971).

Key words: Abstracts, NBS publications; key words; publications.

This Supplement to Special Publication 305 Supplement 1 of the National Bureau of Standards lists the publications of the Bureau issued between January 1, 1970 and December 31, 1970. It includes an abstract of each publication (plus some earlier papers

omitted from Special Publication 305 Supplement 1), key word and author indexes, and general information and instructions about NBS publications. Previous catalogs of NBS publications referenced in Special Publication 305, Supplement 1 remain in effect. To accompany National Bureau of Standards Circular 460, its Supplement, Miscellaneous Publication 240, its Supplement, Special Publication 305 and its Supplement 1. SP317. Volumes I and II. Fundamental aspects of dislocation theory. Proceedings of a conference held at the National Bureau of Standards, Gaithersburg, Md., April 21-25, 1969. J. A. Simmons, R. de Wit, and R. Bullough, Editors, Nat. Bur. Stand. (U.S.), Spec. Publ. 317, Vol. 1, 752 pages, Vol. II, 624 pages (Dec. 1970).

Key words: Conference; continuum mechanics; crystal physics, disclinations; dislocations; elasticity; electrondislocation interactions; lattice defects; phonon-dislocation interactions; solid-state; theoretical physics; thermally activated processes; twinning.

These Proceedings contain research papers, discussions thereon, and panel discussions for the conference on "Fundamental Aspects of Dislocation Theory," held under the auspices of the Institute for Materials Research, April 21-25, 1969, at the laboratories of the National Bureau of Standards, Gaithersburg, Maryland. Approximately 75 contributed papers and two panel discussions are included. Topics covered are Discrete Dislocations in Continuum Elasticity, Lattice Theories, DislocationPhonon Interactions, Applications of the Geometry of Dislocations, Intrinsic Properties of Dislocations, Dislocation Field Theories, Thermally Activated Processes and Statistical Theories, Dislocation-Electron Interactions, and Future Directions for Dislocation Theory. These proceedings include the following papers (indented):

Discrete dislocations in continuum elasticity, A. K. Head, SP317, pp. 5-9 (Dec. 1970).

Key words: Dislocation observations; dislocation theory; status and problems.

As a framework in which to survey some of the current questions in this long-established part of dislocation theory, the problem of the experimental determination of stacking fault energy is considered. Attention is restricted to those methods which observe and measure in the electron microscope a simple dislocation-stacking fault configuration. It is assumed that the configuration is in equilibrium with the forces between the dislocation balancing the surface tension of the stacking fault. The stacking fault energy then follows if these dislocation forces are known from theory for the observed dimensions of the configuration.

Experimental techniques have improved to the point where a reproducibility of 1 to 5 percent standard deviation is claimed. This calls for theory which has at least a similar standard of accuracy. It is doubtful if the theory which is in current use has this accuracy and this is surveyed under the following headings: (a) The treatment of the core; (b) Elastic anisotropy; (c) Zig-zag instabilities; (d) The effect of the stacking fault; (e) The observation of dislocations by electron microscopy.

The image force on dislocations at free surfaces-comments on the concept of line tension, J. Lothe, SP317, pp. 11-22 (Dec. 1970).

Key words: Dislocation nodes; dislocations-image series; dislocation-surface interactions; line tension of dislocations.

It is shown that a straight dislocation emerging at a planar free surface is acted upon by a force distributed according to the law dF=x-(-E cotan 0+E/00)dx. Here is angle of inclination to surface. E is dislocation energy factor, and X is distance from surface along the dislocation. The proof in

volves use of a slightly generalized version of the energy flow theorem for straight dislocations (Lothe, Phil. Mag. 15, 9 (1967)). The above formula is the exact linear elasticity law corresponding to the usual approximate line tension result. According to this law there are certain angles of incidence for which the forces vanish so that the dislocation can be straight. Similarly, when only elastic terms are considered, there are certain node orientations for which the forces on the branches vanish so that the branches can be truly straight (Indenbom and Dubnova, Sovj. Phys. (Solid State) 9, 915 (1967)). In this paper a discussion is given of how core energy terms may modify the results. It is concluded that also for nodes in the characteristic orientation for no elastic forces on the branches, some branch curvature will be present near the node.

Stability and some characteristics of uniformly moving dislocations, K. Malén, SP317, pp. 23-33 (Dec. 1970).

Key words: Anisotropic elasticity; Cerenkov waves; dislocation dynamics; dislocation stability.

The stability of uniformly moving dislocations has been studied in the case of elastic anisotropy using computer. The velocity for instability to occur for a screw dislocation in an isotropic medium is so high, 0.98 C, with C, the transverse sound velocity, that it may well be unattainable. Inclusion of anisotropy gives the possibility of more reasonable instability velocities. Some data showing this for Fe, Li and Cr are given.

The stress field around a uniformly moving dislocation has been studied. Increasing the velocity of a dislocation corresponds to some extent to a change in the anisotropy of the crystal.

In uniform motion above the lowest velocity of sound in the direction of motion one can have associated with the moving dislocation 2, 4 or 6 Çerenkov waves, above the next sound velocity 4 or 6 and above the highest sound velocity 6 waves.

The formula developed earlier for the stress field around a uniformly moving planar dislocation loop can be generalized directly to three dimensions using the theorems of Indenbom and Orlov for the fields from three-dimensional sources using data for two-dimensional sources.

The generalization can also be made using the fact that the choice of cut surface is arbitrary.

The dislocation in a semi-infinite isotropic medium, D. J. Bacon and P. P. Groves, SP317, pp. 35-45 (Dec. 1970). Key words: Dislocation loops; elasticity; finite bodies.

The displacement associated with an infinitesimal dislocation loop (displacement dipole) of arbitrary orientation in an isotropic, semi-infinite elastic medium has been obtained, and on integration this yields the displacement associated with a finite dislocation loop. The solution for the infinitesimal loop has been obtained by finding the relationship between point forces and displacement dipoles in an infinite medium, and using the same relations with Mindlin's solution for the point force in an elastic half-space. This approach leads to a rather simpler analysis than that of Steketee, and the expressions for the displacements of all the infinitesimal loops near a free surface are presented here for the first time. The solution is being used to study the stability of a prismatic dislocation loop on a glide prism of square cross-section near a free surface. Preliminary results are presented for the forces on the loop sides and changes in loop energy on rotation for the situation in which the Burgers vector is normal to the surface.

Theoretical considerations on the extension of 1/2(110), {111} dislocations in isotropic fcc metals into Shockley partials, Doris Kuhlmann-Wilsdorf and T. R. Duncan, SP317, pp. 47-55 (Dec. 1970).

Key words: Dislocation geometry; Shockley partials; stacking faults.

The energy changes and equilibrium separations associated with the extension of 1/2 (110), {111} dislocations in fcc metals into Shockley partials have been calculated and were found considerably smaller than the previous corresponding values due to Seeger and Schöck. The new results may be shown to be credible on the basis of the following simple estimates:

The theoretical shear fracture strength of a crystal may be written as Terit = G/q, with G the appropriate shear modulus, and the numerical parameter q near 30 for {111} planes in fcc metals. The resolved shear stress required to force the Shockley partials into coincidence at vanishing stacking fault energy, (Teq)Max, must approach but cannot exceed Terit so that (Teq)Mar ≤ G/30, i.e. much smaller than the value of √6G/8π = G/9 previously assumed. Similarly, the stacking fault energy cannot exceed the value of Yerit = Ga/V6q with a the lattice constant, and the dislocation core energy must be in the order of Ec=2ro Yerit 1/4ED where ED is the total dislocation energy, and the core radius, ro, is taken to be that distance from the dislocation axis at which the resolved shear stress on the slip plane would become equal to Terit in linear elastic behavior. Lastly, Do, the actual equilibrium separation between the partials must be considerably smaller than Do*, the separation calculated from linear elastic theory, as long as Do* < 2ro. One finds easily that Do* <2ro for yYcrit/6 and yYerit/10 for edge and screw dislocations, respectively, depending somewhat on Poisson's ratio, so that only in silver will edge dislocations have an equilibrium separation a little larger than 2ro, but much less than 2ro in the other common pure fcc metals. For Do= 2ro, when the core energy is reduced by about 1/3 according to the rule of the square of the Burgers vectors but the elastic energy is virtually unaffected, and remembering that work 2roy with y≈ Yerit/6 must be done to spread out the stacking fault, the relative energy gain due to the extension of edge dislocations is simply estimated as (AE/Ep) = [1/3Ec/4E-1/6Ycrit/4Yerit] = 4% which may be compared to the calculated value of 4.6% in silver.

Screw dislocations in inhomogeneous solids, G. P. Sendeckyj, SP317, pp. 57-69 (Dec. 1970).

Key words: Dislocations-elasticity; dislocation surface interactions; finite elasticity; inhomogeneities.

The problem of screw dislocations interacting with free surfaces and inhomogeneities is reconsidered and a general method is presented for solving a large class of screw dislocation problems. The method is based on knowledge of certain general solutions in the theory of antiplane deformation of elastic solids. It can be shown that all the known screw dislocation solutions for solids undergoing antiplane deformation can be found by using this approach.

As an illustration of the method, three new solutions for screw dislocations near inhomogeneities are given. These are the screw dislocation near (1) an elastic elliptic cylindrical inclusion, (2) two circular cylindrical inclusions, and (3) a curvilinear cavity or rigid inclusion. The interaction energy between the dislocation and the inhomogeneities is also computed.

Subsonic, supersonic, and transonic dislocations moving on an interface separating two media of differing elastic properties, H. M. Berg, J. E. Bloom, H. Ishii, R. H. Marion, D. E. Pease, D.