摘要:

A new method is given for measuring dynamic plastic strain in metals under impact loading. Strain‐time curves for initial and reflected wave fronts have been determined using a gauge length of132in. The measurements are made by observing the behavior during strain of the diffracted and central images of an 8300 line reflection grating ruled on the specimen surface.

ISSN:0021-8979    

DOI:10.1063/1.1722212

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

Change of voltage across a solid insulator produces a transient electric current. Measurements of such currents from the polymers of methyl methacrylate, monochlorotrifluoroethylene, ethylene, styrene, and tetrafluoroethylene were made for times from 10 to 104seconds after change in voltage at 25°C, 47°C, and several points below room temperature. The current produced by applying a constant voltage to an undisturbed specimen decays as the negativenth power of the time, wherenis a constant between 0.7 and 1.1. The currents from polyethylene and polytetrafluoroethylene do not conform to the superposition principle, in contradistinction to what is usually reported for solid insulators. The currents at 100 seconds exhibit maxima at −32°C for polymethyl methacrylate and at −50°C for polymonochlorotrifluoroethylene. It is suggested that permanent electric dipoles play an important role in the currents from polymethyl methacrylate and polymonochlorotrifluoroethylene.

ISSN:0021-8979    

DOI:10.1063/1.1722213

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

Theorems relating the plane wave modes (scalar or vector) transmitted and reflected by periodic structures of lossless elements bounded by two parallel planes are derived. One special case is continuity of energy flux normal to the boundary planes, and others relate the phases, or both phases and magnitudes, of the propagating modes. These relations are essentially discrete analogs (i.e., with integrals over all angles of observation replaced by sums over propagating mode directions) of the relations for a bounded scatterer given by Saxon. The essential difference in the two situations is that by restricting the parameters so that only a few modes propagate we obtain special cases which can be treated relatively explicitly. Thus the case of one propagating mode, and the cases corresponding to Bragg reflections are discussed in some detail; here there is both conservation of magnitude and phase.

ISSN:0021-8979    

DOI:10.1063/1.1722214

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

A study of high speed, metal‐to‐metal impact in the velocity range 1 to 5 mm/&mgr;sec using ⅛‐inch diameter spherical pellets is described. Pellet materials include aluminum, magnesium, steel, brass, lead, and zinc. Experiments relating to the mechanisms of cratering and the perforation of thin targets are presented. For the ⅛‐in. diameter spherical pellets, it is found that the volume of the crater per unit energy of the impacting pellet is essentially constant for each material and that the penetration is proportional to the velocity of the pellet so long as the pellet velocity is less than the velocity of sound in the target material. An attempt to model very high speed impact by using soft wax targets in which the sonic velocity is less than the impacting velocity is outlined.

ISSN:0021-8979    

DOI:10.1063/1.1722215

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

The breakup of large water drops during free fall is of importance to meteorologists. Theories of precipitation lean heavily on drop multiplication resulting from the shattering of large drops. An experiment is described in which the actual breakup of large drops is observed, and data obtained from which the mechanism of break may be inferred. Drops in the various stages of disintegration have been photographed and the size distribution of fragments noted. A large drop falling freely through the air deforms, inflates somewhat in the same manner as a parachute and bursts with considerable violence. The origin of various size groups of fragments and its significance in determining the observed size distribution has been noted. An experimental arrangement is described that permits a large number of photographs to be taken of all stages of disintegration.

ISSN:0021-8979    

DOI:10.1063/1.1722216

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

A stratified dielectric sheet with dielectric constant &egr;(x), permeability &mgr;(x) and thicknessdis uniformly contracted to yield a sheet with parameters &egr;(nx), &mgr;(nx),d/n. Nownof these contracted panels are stacked up to yield again a sheet of thicknessd. What can be said of the limiting medium obtained in this way, asn→∞ ? If the symbol [] denotes ``mean value of,'' the results of this paper may be summarized as follows: At perpendicular polarization, the limiting medium acts like a homogeneous medium with dielectric constant, permeability and thickness given respectively by[&egr;][&mgr;]−12[1/&mgr;]−12, [&mgr;]12[1/&mgr;]−12, d[&mgr;]12[1/&mgr;]12. At parallel polarization the parameters are, respectively,[&egr;]12[1/&egr;]−12, [&mgr;][&egr;]−12[1/&egr;]−12, d[&egr;]12[1/&egr;]12. The relevance of these results to topics of current interest is indicated. The analysis is not based on the equivalent‐circuit analogues which are sometimes used to study artificial dielectrics, but is developed without approximation from Maxwell's equations.

ISSN:0021-8979    

DOI:10.1063/1.1722217

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

The free‐flight motion of a satellite around a spherical earth is investigated neglecting atmospheric deceleration. This treatment is then extended by recognizing the earth's oblateness, which is represented by an additional quadrupole field. For nearly circular orbits, one finds that perturbations of the usual planar motion may be described analytically. These are characterized by a precession of the orbit plane around the equator, that is, a regression of the nodes, amounting to as much as forty miles per revolution. The large magnitude of these effects indicates that one may exploit a satellite's motion, as measured by conventional radio techniques, to determine the earth's oblateness to a new precision.

ISSN:0021-8979    

DOI:10.1063/1.1722218

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

When water flows over glass which has been treated with the vapor of dimethyldichlorosilane and thus made water repellent, slipping on the boundary between the solid surface and the water takes place. This is is shown in capillary tubes of various diameters. The amount of slipping is small, but measurable. It disappears or becomes extremely small in case of turbulent flow.

ISSN:0021-8979    

DOI:10.1063/1.1722220

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

When an explosive detonates underwater it creates a bubble of gas which performs damped radial oscillations of large amplitude. The usual theory of these oscillations treats the water as incompressible and yields undamped oscillations of constant period. We have modified this theory by taking account of the compressibility of the water. Our theory predicts damped oscillations of diminishing period. Comparison of the predicted and observed radius‐time curves for one particular case shows fairly good agreement. Radius‐time curves for four representative cases have been computed with a large number of periods in each case. These can be used to describe a variety of explosions.

ISSN:0021-8979    

DOI:10.1063/1.1722221

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

A theory for uniform field breakdown in air at microwave frequencies is developed and applied with success to predicting values of breakdown over a wide range of experimental conditions. Three distinct types of breakdown are treated; c.w. (continuous wave) breakdown, single pulse breakdown, and multipulse breakdown. The conditions for breakdown are determined from a solution of the electron continuity equation for an average electron, in which electron ionization, attachment, and diffusion are the dominant mechanisms. Modulation of the electron average energy at twice the frequency of the applied field becomes important at either high pressure or low frequency and modifies the values of the breakdown field. The breakdown field strengths are shown to be determined from a single curve for each type of breakdown power, either c.w. or pulsed. These theoretical curves are in accordance with the experimental results, thus verifying the assumption and the values of the coefficients used in the theory.

ISSN:0021-8979    

DOI:10.1063/1.1722222

出版商:AIP    

年代:1956

数据来源: AIP