摘要:

Numerical methods, such as those of Southwell, have made amenable to approximate analysis a large class of problems in the theory of elasticity. However, certain loadings must occasionally be considered which may give rise to theoretical stress singularities. In such cases an analytical study, at least in the immediate neighborhood of the singularities, would appear to be mandatory.One such problem is that of determining the thermal stresses in a partially clamped elastic half‐plane. The solution given in this paper assumes self‐equilibrating tractions over the clamped portion of boundary so that the results apply approximately also to large finite areas.

ISSN:0021-8979    

DOI:10.1063/1.1702039

出版商:AIP    

年代:1952

数据来源: AIP

摘要:

A metallographic study was made of the diffusion zones present in copper‐&agr;‐brass, copper‐nickel, and gold‐silver diffusion couples. Usual sandwich type couples and also vapor‐solid type couples in which the higher vapor pressure component was diffused either into or out of the couple through the vapor phase were investigated. Significant porosity was always generated by diffusion in the sandwich couples and also in the vapor‐solid couples when the higher vapor pressure component was diffused out of solid solution. Upon inward diffusion from the vapor porosity formed in the gold‐silver couples but not in the copper‐&agr;‐brass or copper‐nickel couples.It is concluded that porosity may form in any alloy system when the components diffuse at different rates and that it may cause appreciable error in the measurement of diffusion coefficients if ignored.

ISSN:0021-8979    

DOI:10.1063/1.1702040

出版商:AIP    

年代:1952

数据来源: AIP

摘要:

Radioactive tracer techniques have been employed to measure the rate of self‐diffusion in silver in polycrystalline and single crystal solvents over a wide range of temperatures, and to investigate the effect of bombardment with 10‐Mev protons on this diffusion process. A least squares fit of the data from laboratory control experiments with both single crystal and polycrystalline solvents in the temperature range 903°C to 640°C has yielded the diffusion constantsQ=40,800±700 cal/mole andD0=0.11±0.05 cm2/sec for the volume diffusion process. No effect of intense proton bombardment ranging from 0.5 to 5&mgr;a/cm2has been detected on the volume self‐diffusion process in silver specimens which were simultaneously irradiated in the cyclotron target box and annealed at temperatures ranging from 852°C to 555°C. These results are, at least semiquantitatively, in accord with both the elastic collision model and the thermal spike model of radiation damage. Cyclotron techniques and apparatus are described in some detail.

ISSN:0021-8979    

DOI:10.1063/1.1702041

出版商:AIP    

年代:1952

数据来源: AIP

摘要:

The effect of the potential drop across the filament of a diode with directly heated emitter on the plate current of the diode is considered. Calculations are made for both space‐charge‐limited and retarding‐field conditions. Filament heating by direct current and by alternating current is considered. The results are given in convenient graphical form.

ISSN:0021-8979    

DOI:10.1063/1.1702042

出版商:AIP    

年代:1952

数据来源: AIP

摘要:

The hafnium‐hydrogen system at room temperature consists of three phases. The lattice parameters of the hafnium metal used in this investigation and of the three phases are as follows: hafnium,a0=3.200A,c0=5.061A, andc=1.58; deformed cubic phase,a0=4.702±0.012A,c0=4.678±0.012A, andc=0.995; face‐centered cubic phase,a0=4.708±0.002A; and face‐centered tetragonal phase,a0=4.882±0.002A,c0=4.384±0.002A, andc=0.898. The deformed cubic phase extends up to HfH1.53and converts into the face‐centered cubic phase between HfH1.53and HfH1.70. The face‐centered cubic phase transforms into the tetragonal phase between HfH1.80and HfH1.87. The tetragonal phase extends up to HfH1.98.

ISSN:0021-8979    

DOI:10.1063/1.1702043

出版商:AIP    

年代:1952

数据来源: AIP

摘要:

Thermionic emitters consisting of barium oxide dispersed throughout a body of porous tungsten can be successfully made if suitable compounds of barium are employed as the source of the oxide. Compounds such as the carbonate, which can oxidize tungsten and react to form Ba3WO6:3BaCO3+W→Ba3WO6+3CO,are unsuitable. However, if by various means, BaO is dispersed in tungsten, reaction occurs at operating temperature of the cathode to slowly generate free barium: 6BaO+W→Ba3WO6+3Ba, which diffuses to the surface and lowers the work function.Cathodes consisting of approximately 5 percent of BaO in W are capable of supplying continuous emission in excess of 100 amp/cm2, give equivalent dc and pulsed emission, and are highly resistant to damage by arcing, temporary poor vacuum, ion bombardment, and high temperatures.Emission current of approximately 8 amp/cm2was obtained at an operating temperature of 1000°C from a typical cathode of this type. The life of this cathode, at 1100°C, was in excess of 650 hours. Constants of the Richardson equation for a relatively inactive cathode were &fgr;=1.56 ev,A=0.6 amp/cm2/deg2.

ISSN:0021-8979    

DOI:10.1063/1.1702044

出版商:AIP    

年代:1952

数据来源: AIP

摘要:

The creep rate of copper under deuteron bombardment has been investigated using the 16‐Mev external beam of the University of Pittsburgh cyclotron. Measurements were made of the second stage creep rate of a copper wire under deuteron bombardment at a temperature of 260°C and a loading of 10,000 psi. Within the precision of the experiment ±20 percent, the creep rate during and after bombardments of 10 to 20 hours duration was unchanged from the creep rate preceding bombardment. Theoretical considerations of the type discussed by Slater, predict that with the available deuteron flux of 1012particles per cm2per sec there should be no appreciable change in creep rate. The available deuteron flux cannot displace enough atoms from their normal lattice sites to produce a dislocation involving a hundred atoms or more; further, the steady‐state density of displaced atoms is not enough to impede the motion of those dislocations present in the crystals. While regions of increased local temperature are produced during bombardment, these also should not affect the creep rate. Thus, apparently the considerations of solid‐state theory are confirmed and creep rates should not be expected to increase for all metals under bombardment.

ISSN:0021-8979    

DOI:10.1063/1.1702045

出版商:AIP    

年代:1952

数据来源: AIP

摘要:

Graphs of the theoretical pressure distribution resulting from diffraction of a weak shock by a rigid right‐angled corner are presented and compared with graphs of measured pressure distributions. The agreement is found to be satisfactory. A graph of the electric field resulting from diffraction of an electromagnetic pulse by a perfectly conducting right‐angled corner is also presented.

ISSN:0021-8979    

DOI:10.1063/1.1702046

出版商:AIP    

年代:1952

数据来源: AIP

摘要:

At timet=0 a unit sphere containing a perfect gas at uniformly high pressure is allowed to expand suddenly into a homogeneous atmosphere. Solutions for short times later are sought by analytic (i.e., not numerical) methods. Viscosity and heat conduction are neglected. The particle velocity, sound speed, and entropy are developed in powers ofy, which is proportional to the time (more precisely, the distance moved by the head of the rarefaction wave in timet), with coefficients depending on a slope coordinateq=(1/2N)[(2N−1) +(1−x)/y], wherexis the radial coordinate,N=(½)(&ggr;+1)/(&ggr;−1), and &ggr; is the ratio of specific heats. The zero‐order coefficients are the plane shock‐tube solution. First‐order corrections are derived for the various regions. Boundary conditions are approximated for smallyat the surfaces of discontinuity, and the method for matching the solutions in the different regions is outlined. This matching process is carried out for the expansion of a diatomic gas into diatomic air.

ISSN:0021-8979    

DOI:10.1063/1.1702047

出版商:AIP    

年代:1952

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1702048

出版商:AIP    

年代:1952

数据来源: AIP