摘要:

Based upon the thermodynamic formulation for linearly viscoelastic fracture developed earlier, an extension has been made to fatigue fracture resulting from repeated (oscillatory) load applications. The theoretical analysis of internal spherical‐flaw growth, due to a uniformly distributed radial oscillatory input of displacement, predicts a growth‐rest cycle whose characteristics depend upon the mechanical properties of the medium. The results for this idealized problem are compared to experimental data for crack growth in a precracked sheet specimen subjected to oscillatory displacement input, and a qualitative similarity is observed. It is therefore believed that the analytical model is representative, and its study can reveal the main features of macroscopic flaw growth.

ISSN:0021-8979    

DOI:10.1063/1.1709152

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Optical measurements on silicon and germanium together with Hall measurements on germanium were performed on crystals containing predominantly edge or screw dislocation arrays. An apparent extended absorption tail in deformed germanium and silicon was found to depend markedly upon the direction of light propagation relative to the active slip planes. Photographs of the transmitted radiation through deformed silicon showed that the apparent extended absorption tail was due to strong anisotropic scattering from active slip planes. Hall measurements on sections from plastically deformed germainium are interpreted to give evidence of dislocation acceptors located in the lower half of the band gap.

ISSN:0021-8979    

DOI:10.1063/1.1709153

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

When a plane wave is obliquely incident from vacuum on a semi‐infinite moving medium, the energy flow carried by the incident wave, is in general, not carried away by the reflected and transmitted waves. This is only the case when the medium velocity is parallel to its vacuum interface. Otherwise there is a net inflow or outflow of electromagnetic energy, which can be accounted for by the change of stored energy in the system, and the work done by the mechanical forces acting on the medium. A detailed energy balance is drawn up for two different media moving normal to their vacuum interfaces: (a) a moving conductor and (b) a moving dielectric.

ISSN:0021-8979    

DOI:10.1063/1.1709154

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Theoretical equations for the strain coefficient of resistance in metallic thin films are derived. The films considered range from ultrathin, discontinuous films of theoreticalaveragethickness of less than an angstrom to relatively thick films of about 6000 Å which exhibit bulk material properties. The films are classified into five thickness ranges according to the predominating conduction mechanisms. It is found that ultrathin films exhibit strain sensitivity of two orders of magnitude higher than the bulk metal. The sensitivity reduces with increasing average film thickness to a minimum value which occurs in the transition region in which the film conduction properties change from those of a semiconductor to those of a metal. With further increase in thickness the bulk value of sensitivity is approached. The theory is compared with experimental studies and possible misinterpretations in previous studies are discussed.

ISSN:0021-8979    

DOI:10.1063/1.1709155

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Three new laser lines are reported: Two lines, at 1.0448 and 1.0661 &mgr;, occur for a CaF2crystal which is heavily doped with NdF3; a line at 1.0336 &mgr; occurs for a CaF2crystal containing NdF3and YbF3. Details of the absorption and fluorescence spectra indicate that the laser oscillations arise from Nd3+ions at noncubic sites in the first crystal and from Yb3+ions in the second crystal. The growth techniques are summarized; the special growth procedures minimize the oxygen content, thereby reducing the number of impurities in sites for Nd3+and Yb3+.

ISSN:0021-8979    

DOI:10.1063/1.1709156

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The field intensification factor, &bgr;, was found theoretically to be a function of gap length, projection height, and projection tip radius. The electrode projection was approximated by a grounded plane and separate grounded sphere, the opposing electrode by a charged plane. The results may be used to find the height and tip radius of a projection in a small gap by measuring &bgr; as a function of gap length.

ISSN:0021-8979    

DOI:10.1063/1.1709157

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The velocities of ultrasonic shear and compressional waves in tungsten crystals have been measured in several directions and as functions of temperature to 1800°C. Adiabatic crystal elastic stiffnesses have been calculated from these velocities as follows:C11=5.2349×1012−4.5967×108T−5.467×104T2±0.25% dyn·cm−2C44=1.6028×1012−1.0320×108T−2.054×104T2±0.25% dyn·cm−2CN=5.2480×1012−3.5005×108T−3.163×104T2±0.25% dyn·cm−2C12=2.0445×1012−0.3403×108T+3.249×104T2±2.3% dyn·cm−2C′=1.5952×102 −2.1282×108T−4.358×104T2±1.8% dyn·cm−2.Values for the elastic constants of random, polycrystalline tungsten were calculated from these crystal stiffnesses. They agree well with values determined on polycrystalline tungsten as functions of temperature.

ISSN:0021-8979    

DOI:10.1063/1.1709158

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

A technique for solving the three‐level Q‐switched laser rate equations for both pulse reflection mode and pulse transmission mode switches is presented. Results are compared for both energy and peak power.

ISSN:0021-8979    

DOI:10.1063/1.1709159

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The effects of thermionic sputtering parameters on crystalline orientation and coercive force of magnetic films are discussed in this paper. By controlling the crystalline orientation within the film it is possible to produce films with a coercive‐force range from 0.9 Oe to 35.8 Oe. The crystalline orientation is controlled by the magnetic field, the electric field, and the substrate position within the apparatus. All of the films were prepared on substrates which were not exposed to the sputtered material until the target had the adsorbed gases removed.The texture of the films is described by means of several x‐ray photographs taken on a specially designed Laue camera, capable of giving a pattern from films as thin as 100 Å.

ISSN:0021-8979    

DOI:10.1063/1.1709160

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

A study is made of the rate of transport of Hg in a uniform positive column in a mixture of a rare gas and Hg vapor. In one case, the phenomenon of retrograde cataphoresis is encountered, that of Xe+Hg at currents above 1 A, in which the Hg is carried to the anode end of the tube. In all other cases, the Hg is transported to the cathode end.A pulsating discharge is described in which the color changes from the red of Ne to the blue‐white of Hg and back again within a period of 1–2 sec. The boundary between the two colors travels along as a wave motion. This phenomenon is related to the properties of the tube walls and the nature of the ions striking them.When an ac discharge is passed through a cataphoretic mixture, the trace gas of lower ionizing potential is urged from the ends toward the center of the tube, e.g., Hg in Ar, Ne and Kr, but from the center to the ends in He+Hg. With a trace of Ar in He, the Ar is urged toward the center of the lamp. With Xe+Hg, the Hg may go either to the center or to the ends, depending upon conditions. The phenomenon is believed to be due to traveling striations which start out from the anode and progress only part way toward the cathode. Such a striated discharge pumps Hg faster than a steady discharge in the case of Ar, Kr, and Ne, but apparently slower in the case of He.Attempts to demonstrate electrophoretic effects in a straight sealed‐off tube failed. However, the positive pressure effects are quite striking in a tube with an external return path.

ISSN:0021-8979    

DOI:10.1063/1.1709161

出版商:AIP    

年代:1967

数据来源: AIP