ISSN:0021-8979    

DOI:10.1063/1.1710355

出版商:AIP    

年代:1938

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1710362

出版商:AIP    

年代:1938

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1710354

出版商:AIP    

年代:1938

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1710356

出版商:AIP    

年代:1938

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1710357

出版商:AIP    

年代:1938

数据来源: AIP

摘要:

It is shown here that the shearing stress distribution in the combined shear and bending is represented with practical accuracy by the distribution of velocity in the flow of a perfect fluid over the area of the cross section. This flow is produced by a linear distribution of sources above the neutral axis and of sinks below the neutral axis, the intensity of these sources and sinks being proportional to the distance to the neutral axis. For hollow beams the additional condition must be added that the circulation of the velocities is zero around each hole of the cross section. The analogy which is rigorous for a material of zero Poisson ratio holds within a small correction for the general case.

ISSN:0021-8979    

DOI:10.1063/1.1710358

出版商:AIP    

年代:1938

数据来源: AIP

摘要:

Curves are presented from which it is possible to obtain the adiabatic compressibility of a petroleum oil in the range of 40°–200°F and up to 5000 pounds per square inch when only the specific gravity at 60°F and the kinematic viscosity at 100°F are known. A chart is given for obtaining the velocity of a pressure wave in an oil in which both the viscous drag and expansion of the containing tube are neglected. A table showing compressibilities and wave velocities for a number of Diesel fuel oils at 120°F and 1750 pounds per square inch pressure is given. The effects of viscosity and tube wall expansion on wave velocity are discussed and a chart is presented to aid in determining the wave velocity in steel tubes. The paper is concluded with a discussion of the effect of wave velocity on the point of injection of the fuel in the Diesel cycle.

ISSN:0021-8979    

DOI:10.1063/1.1710359

出版商:AIP    

年代:1938

数据来源: AIP

摘要:

This paper presents a new theory of failure for materials subjected to a combined state of stress. The theory is developed for brittle materials, such as concrete, in which the compressive and tensile strengths are of different magnitudes. It is a semi‐empirical theory which has some experimental support. Based on it working stresses are defined for various loading conditions. The use of these proposed working stresses in some cases makes considerable difference in design as compared to the present specifications requirements. These working stress values are conveniently represented by a diagram to facilitate the computations in design. The application of this information can be made simply in most cases where there are stresses acting in two right‐angled directions—such as slabs in buildings, roads and bridges, retaining walls, dams and other hydraulic structures of concrete and reinforced concrete.

ISSN:0021-8979    

DOI:10.1063/1.1710360

出版商:AIP    

年代:1938

数据来源: AIP

摘要:

Convection speeds in commercial high pressure Hg vapor lamps are measured by photographing on a moving film, the tracks of incandescent particles of CaO and MgO. A deep red filter and panchromatic film are used. The convection system is found to consist of a laminar flow of hot gas upward in the center and of cold gas downward near the walls. For the 400 watt lamp (p≅1 atmosphere,m= mass of Hg per cm of tube length = 11.5 mg cm−1) an upward speed of about 40 cm sec.−1is found at the axis in the mid‐section of the lamp. The speed is somewhat greater near the bottom, this effect increasing withm. Speeds are found to increase somewhat less rapidly than in proportion tomas predicted. An approximate theory of these currents is presented, based largely on the work of Elenbaas, which accounts sufficiently well for the order of magnitude of the observed speeds. Forsimilardischarges, speeds do not depend on the tube diameter but simply onm; for such discharges the watts lost by convection are proportional tom2and independent of diameter and length. Convection losses for the 400‐w, 250‐w and 85‐watt lamps are calculated to be 12‐w and roughly 0.9‐w and 0.8‐w, respectively. When a lamp is operated on half‐wave a dark space develops at the bottom of the arc in the off half‐cycle, due to uprush of cold gas from below. Convection speeds estimated from the length of this dark space and the period of zero current are about twice too high; probable reasons for this are given. When the lamp is operated in the horizontal position, the arc bows up against the wall of the tube and softens it. The magnetic force necessary to keep the arc in the axial position is measured and found to be proportional tom(F=0.126mdyne cm−1). This force will be independent of tube diameter forsimilardischarges. An approximate theory is developed which accounts sufficiently well for the order of magnitude of this force. Rotation is also used to center the arc in the horizontal position; for the 400‐watt lamp a speed of at least 7 r.p.s. is necessary for this purpose. No appreciable changes in arc voltage or efficiency are found for horizontal operation with magnetic or rotational control as compared with vertical operation. Photographs of particle tracks show in a striking manner the migration of ions in the electric field; Ca and Mg vapors from the evaporating particles are strongly ionized and excited at the high temperatures and progress rapidly in the field.

ISSN:0021-8979    

DOI:10.1063/1.1710361

出版商:AIP    

年代:1938

数据来源: AIP