Volume 14, Issue 6, 01 June 1943
Index of content:
14(1943); http://dx.doi.org/10.1063/1.1714983View Description Hide Description
14(1943); http://dx.doi.org/10.1063/1.1714984View Description Hide Description
IN this chapter technical applications of the solid friction concept in four different fields are discussed. These are: (1) mechanical engineering, (a) damping of unwanted vibrations in machinery—for instance, crank‐shaft vibrations, (b) vibrations excited by internal friction—for instance, whirl of rotating shafts; (2) metallurgy in which damping measurement promises to be a useful new tool; (3) rubber technology, as applied to automobile tires with regard to the heat generated therein; and (4) electrical engineering, specifically dielectric losses in electrical insulating materials.
14(1943); http://dx.doi.org/10.1063/1.1714987View Description Hide Description
If a rod is twisted while subjected to longitudinal compression it will support without fracture angles of twist many‐fold greater and maximum torques somewhat greater than is possible in the absence of load. Under compressional load the curve of shearing stress against shearing strain rises to a maximum and then sinks with a long drawn out tail to an approximate asymptote. Fracture is never complete, but some coherence always remains, probably due to cold welding. The maximum torque is not marked by any visible beginning of fracturing or other discontinuity. The strain hardening curve in torsion, therefore, under proper circumstances passes through a maximum. The whole mechanism of strain hardening appears to be different in torsion and in tension, and reasons are given for anticipating such a difference because of the difference of the atomic kinetics in torsion and tension. It is shown in particular that the method of correlating tension and torsion through the ``octahedral'' coordinates which is applicable for small strains is not applicable to the large strains which are the subject of the present discussion. It is shown that the equations of conventional plasticity theory correctly reproduce certain qualitative aspects of the secondary longitudinal and radial flow which accompany twisting, but it is possible to establish large failures of isotropy not covered by the elementary theory. With regard to fracture, it is necessary to distinguish sharply between fracture in tension and in shear. The latter is not clean cut and it is probably possible to realize a continuous gradation of atomic disorganizations, culminating under proper conditions in complete shearing fracture.
A Tension‐Compression Device for Quantitative X‐Ray Diffraction Evaluation of Strain in Metals and a Calibrated Series of Aluminum Alloys14(1943); http://dx.doi.org/10.1063/1.1714988View Description Hide Description
An easily constructed apparatus is described for applying tension and compression stresses to metal and alloy samples while being subjected to x‐ray diffraction analysis. The back reflection technique is employed in which diffraction patterns can be photographed in five minutes or less. The apparatus and technique have been developed because of the increasing interest in the measurement of strain in a variety of metallurgical materials of primary war interest. A series of patterns on a familiar aluminum alloy under calibrated tension stresses is reproduced as an example by means of which evaluation of residual strains in large castings can be non‐destructively evaluated.
14(1943); http://dx.doi.org/10.1063/1.1714989View Description Hide Description
A study was made of thin films of aluminum,cadmium,copper,gold, magnesium, and zinc using an RCA electron microscope capable of 30A resolving power. The films were formed by evaporation and condensation on collodion substrates in vacuum. An evaporating chamber was devised that permitted control of the temperature of the condensing surface. Photographs of the surfaces show that all the films are made of agglomerates of the metals separated by interstices of various widths. All evidence leads to the conclusion that the surface structure is explainable by assuming migration of the atoms over the surface. The observed structure can be used to explain the electrical conductivity, the optical reflectivity, and adsorptivity of thin films. Electron microscopic studies also provide a ready means of classifying surfaces according to the mobility of the atoms comprising them, and thus enable a rough estimate of the potential distribution over the surface to be made.
14(1943); http://dx.doi.org/10.1063/1.1714990View Description Hide Description
An expression is derived for the mutual impedance of a symmetrical center‐driven antenna in proximity to an untuned parasitic element, when the wires are parallel, and are not displaced in length. An integral, frequently occurring in antenna problems, is evaluated graphically over the range required in the present analysis.