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Journal of Applied Physics

Issue 8 • Date Aug 1941

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Displaying Results 1 - 15 of 15
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • ``The Physics of Air Raids''

    Page(s): 583
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  • Influence of Certain Variables on the Stresses in Gear Teeth

    Page(s): 584 - 591
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    A photoelastic study was made to obtain a more accurate picture of the localized stresses in gear tooth fillets than can be obtained from the commonly used Lewis equation. A set of approximate stress concentration factors are presented for fillets in gear teeth based upon a set of variables such as the radius r of the fillets, thickness t of tooth, height h of load position on the tooth, etc. The problem was attacked by making a series of tests of ``conventionalized gear teeth'' in the form of short cantilever beams in which one factor at a time could be varied. The values of stress concentration factor were computed as the ratio of the maximum stress in the fillet to the calculated stress at the ``assumed weakest section,'' as defined by Lewis' equation. In general, it was noted that as the height of load position (h/t) was increased, the maximum stress increased, but the stress concentration factor decreased. An approximate equation for the tensile stress concentration factors, k, for the conventionalized models with sides of the tooth parallel is: k=1.25(t′/r)0.2(t/h)0.3. A definite decrease in the tensile stress concentration factor was observed as the tooth model was gradually tapered inward to approach Lewis' ideal shape of the parabola of uniform strength, whereas no change in the compressive stress concentration factor occurred as the angle was varied over a 25° range. Tests now in progress on generated gear teeth having a 14½‐degree pressure angle and a diametral pitch of 2 indicate that the stress concentration factor for the tensile fillet is given fairly accurately by the formula: K=0.22(t/r)0.2(t/h)0.4. View full abstract»

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  • On Similarities Between Stress and Flow Patterns

    Page(s): 592 - 595
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    The purpose of this paper is to review established relationships between stress and flow problems. Two‐dimensional plane stress systems were found to have features analogous to non‐viscous potential flow fields on one hand, and to viscous flow on the other hand. Accordingly, this discussion is divided into two parts. In each case the fluid is assumed to be continuous, homogeneous, and incompressible. View full abstract»

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  • Three‐Dimensional Photoelasticity Using Scattered Light

    Page(s): 610 - 616
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    It is possible to use the polarization caused by the scattering of light within a photoelastic model in place of the usual analyzer in a photoelastic polariscope. This enables one, in effect, to use an analyzer which lies within the interior of the model, and so make analyses of three‐dimensional stress systems very conveniently. This is accomplished in practice by projecting into the model a beam of polarized light which has been collimated and passed through a slit, thus confining the beam to a thin sheet of light. Such a sheet will illuminate any desired plane section of the model, and in this section will appear interference fringes from which the stresses in the section may be determined. By successive examination of plane sections one may completely investigate the model. In this method the spacing of the fringes is the significant feature, rather than their order, as in previous methods. It is possible, in many cases, to determine the directions of the principal stresses at interior points as well as the maximum shear at such points. Boundary stresses are evaluated both as to direction and magnitude. Equipment for this method differs in constructional details from that employed in plane stress studies in that a source of light of higher intensity must be provided and a slit is used to restrict the beam. View full abstract»

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  • A Photoelastic Study in Vibrations

    Page(s): 617 - 622
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  • Abstracts

    Page(s): 623 - 625
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  • Frictional Phenomena. II A. Gases

    Page(s): 626 - 633
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  • Velocity Measurement of Transient Mechanical Motions

    Page(s): 634 - 637
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    Measurements of velocity of rapid non‐recurrent mechanical motions by means of an oscillograph are described. Two methods of measurement are given: One by modifying the optical system of the oscillograph, and the other by employing a slotted disk mounted on mechanism under test. These methods offer practical means of time‐distance relation measurements of small devices, such as spring‐actuated levers, cam mechanisms, triggers, etc., whose performance would be affected due to the additional load required to operate auxiliary measuring instruments. View full abstract»

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  • A Simple and Rigorous Method for the Determination of the Heat Requirements of Simple Intermittently Heated Exterior Walls

    Page(s): 638 - 642
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    Buildings such as churches and auditoriums that are not continuously heated need larger heating plants than continuously heated buildings because of the large transient heat currents that must be supplied to the cold walls while the temperature of the building is being raised. The present unsatisfactory practice is to estimate the magnitude of these currents by various unreliable empirical methods. The purpose of this paper is twofold. First, for simple exterior walls, an equation is derived by means of which tables can be computed that will make rapid and reliable determinations possible. Second, the equation is put into such a form that the actual calculation of the tables can be carried out by N. Y. A. boys whose services can be obtained without cost. The unidirectional heat flow equation is solved for the boundary conditions that the outdoor temperature remains constant, the temperature of the wall is constant previous to time t=0, and after that time a constant heat current is applied to the wall. The solution is obtained in a form simple enough for the boys to handle by putting part of it in dimensionless form which makes it possible to plot a family of curves, which in turn make it possible to obtain numerical solutions without resorting to the very tedious ``cut and try'' process. View full abstract»

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  • The Heat Requirements of Simple Intermittently Heated Interior Walls and Furniture

    Page(s): 642 - 644
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    This paper does for simple interior walls and furniture what the previous paper did for simple exterior walls. Unidirectional heat flow is assumed and the boundary conditions are simpler than for the simple exterior wall so that the solution is easily expressed in the form of a formula. The treatment of the interior surface resistance as a constant quantity is justified. View full abstract»

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  • Effects of Heat Treatment on Field Emission from Metals

    Page(s): 645 - 652
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    The cylindrical electron projector tube affords a convenient means of investigating the effects of heat treatment on field emission from metals. It is found that large, unstable field currents, designated as ``anomalous'' field emission, are due to the presence of surface electro‐positive impurities. As evidenced by the ``blackout'' of the twinkling projector tube patterns, these impurities may be removed from tungsten, tantalum, or molybdenum by temperatures of 2200°K or greater, but it was found impossible to remove them from nickel. While the effect of gas adsorption on anomalous field emission is relatively minor, tube pressures even as low as 10-7 mm Hg increase the frequency of ``breakdown.'' This phenomenon is probably caused by rearrangement or disruption of impurity layers, or even of the metal itself, due to positive ion bombardment. Making surfaces microscopically smooth greatly decreases the magnitude of anomalous field emission currents, and therefore the likelihood of breakdown, but cannot take the place of sufficiently severe heat treatment in removing the anomalous type of emission completely. In the course of these experiments, calculations were made which make possible the prediction of the tension on the projection tube filament necessary to prevent violent vibration of the filament as high voltages are applied to the tube. Since such cylindrical tube geometry is of common use in experimental work, the results of these calculations are given. View full abstract»

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Aims & Scope

Journal of Applied Physics is the American Institute of Physics' (AIP) archival journal for significant new results in applied physics

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Editor
P. James Viccaro
Argonne National Laboratory