摘要:

Solutions are presented for an infinite viscoelastic consolidating layer and an elastic and viscoelastic consolidating half‐space considering the quasi‐static response. The analogous coupled thermoelastic problems and applications in the field of secondary consolidation are discussed.

ISSN:0021-8979    

DOI:10.1063/1.1702529

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Negative resistance and large current densities have been observed in the direct‐current—voltage characteristics of five metal‐oxide‐metal sandwiches prepared from evaporated metal films. The systems studied and their voltages for maximum current are: Al‐SiO‐Au, 3.1 V; Al‐Al2O3‐Au, 2.9 V; Ta‐Ta2O5‐Au, 2.2 V; Zr‐ZrO2‐Au, 2.1 V; and Ti‐TiO2‐Au, 1.7 V. For aluminum oxide, which has been most extensively studied, the voltage for maximum current is independent of film thickness for films between 150 and 1000 Å thick; the phenomenon isnotfield dependent. Peak‐to‐valley ratios of 30:1 and current densities of 10 A/cm2are typical. Maximum current densities at peak voltage are 25 A/cm2; minimum current densities are 0.01 A/cm2. Switching time from peak current to valley current is <0.5 &mgr;sec but negative resistance is not found for 60‐cycle voltages. Establishment of the dc characteristics and dependence on temperature and atmosphere are described. Electron emission from aluminum oxide sandwiches can occur at 2.5 V. Space‐charge‐limited currents in the insulator provide a possible mechanism for the current‐voltage curves and large currents below the voltage for maximum current through the oxide films. The mechanism responsible for negative resistance is uncertain.

ISSN:0021-8979    

DOI:10.1063/1.1702530

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

An experimental investigation of the interdiffusion behavior of gases in a low permeability graphite was performed by sweeping the opposite faces of a graphite septum with helium and argon at uniform pressure and measuring the diffusive flux of both gases. The objectives were to ascertain the diffusion mechanism, to verify the applicable equations and associated theories, and to determine the parameters required to use these equations. At all experimental pressures, contributions of both normal and Knudsen diffusion effects were detectable via the pressure dependence of the diffusion fluxes. It was found that a previously proposed dusty‐gas model formed an excellent basis for correlating the results. The dusty‐gas model yields flux equations which predict the diffusion behavior over a wide range of pressures for particular gas concentrations at the boundaries. Only two experimentally determined parameters (characteristic of the gases and graphite) are required. These are: an effective normal‐diffusion coefficient obtained through interdiffusion experiments and a Knudsen coefficient obtained through single‐gas (permeability) experiments. The procedures used to evaluate these parameters in terms of the experimental data are described in detail.

ISSN:0021-8979    

DOI:10.1063/1.1702531

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Thermal dilation measurements through the temperature of transformation of some zirconium—rareearth alloys were utilized to compare the effect of the elements Nd, Y, Dy, Ho, and Er on the hcp‐bcc transformation temperature of Zr. Binary alloys were vacuum arc melted and concentrations of the individual rare earths were varied up to slightly beyond their solubility limits. All the elements investigated raised the transformation temperature similarly per atomic percent. Electrical resistivity measurements at room temperature and below also showed the same trend of equal change in property, irregardless of the alloying element at least up to the solubility limit.

ISSN:0021-8979    

DOI:10.1063/1.1702532

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The friction and wear of spherical single crystals of sapphire (&agr;‐Al2O3) sliding on a wet steel surface were observed. As a result of changing only the crystal orientation of the single‐crystal sphere, the rate of wear varied by more than three orders of magnitude, and the coefficient of friction varied by a factor of three. The rate of wear of the sapphire was greatest when the crystal structure offered least resistance to shear parallel to the sliding surface and in the direction of slide. It is concluded that wear of sapphire sliding on steel proceeds by shear through the sapphire, although interface adhesion may involve the formation of chemical bonds.

ISSN:0021-8979    

DOI:10.1063/1.1702533

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

A relation between the surface coverage and the surface potential of an adsorbed film is developed from a thermodynamic argument. It is found that the proper variables to be used in the theory of films are the temperature of the surface and the saturation temperature corresponding to the pressure of the vapor in equilibrium with the surface. The analysis is applied to the experimental data of Taylor and Langmuir for cesium on tungsten with good results. In the Appendix an estimate of the range over which the surface forces extend is obtained by means of a simple microscopic model.

ISSN:0021-8979    

DOI:10.1063/1.1702534

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Strain‐hardening caused by ``debris'' produced by multiple cross‐glide is discussed. This form of strain‐hardening is often linearly proportional to strain, because the debris concentration increases in proportion to strain. The rate of debris production should be sensitive to the applied stress, crystal structure, and crystal orientation as is observed.The debris mechanism is the only one that explains the self‐hardening of isolated half‐loops. It also explains the negative temperature dependence of strain‐hardening at low temperatures, unlike other theories.The cross‐gliding that leads to debris production is influenced by free surfaces which exert a cross‐glide force on obliquely incident dislocations, and which cause extended dislocations to become contracted so they can more easily cross‐glide.

ISSN:0021-8979    

DOI:10.1063/1.1702535

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

When a series of uniform acoustic pulses is transmitted through a medium whose refractive index varies in a random manner, the received pulses vary randomly about an average amplitude. A theory developed by Mintzer [J. Acoust. Soc. Am.25, 922 (1953)] predicts that the coefficient of variationV, defined as the fractional standard deviation of a series of pulses, is directly proportional tok(2&pgr;/acoustic wavelength), provided that the range from the source to receiver is greater thanka2, whereais the correlation distance of the refractive index variations. In a scaled model experiment the refractive index variations are caused by heating the medium (water) from below, thus causing turbulent convection. Observations show the linear dependence ofVupon frequency forr>ka2as predicted by the theory. At the higher frequencies, observations indicate possible oscillations inVas it tends toward a frequency independent value.

ISSN:0021-8979    

DOI:10.1063/1.1702536

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Hydromagnetic swirls develop in a rotating, gaseous plasma subjected to an electromagnetic braking action. Observations of these swirls and the effect of a conducting grid upon them are discussed.

ISSN:0021-8979    

DOI:10.1063/1.1702537

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Stress‐strain curves and transient creep curves for single crystals are obtained from calculations based on the observed behavior of dislocations in LiF, and the strain rate equation, &egr;˙=bnv. The pronounced yield drops and apparent ``delay times'' predicted by the calculations are observed experimentally. This agreement between calculation and experiment implies that further consideration of the calculations may give some insight into the yield point and transient creep behavior of single crystals. Several parameters are varied in the calculation in order to determine the effect of such things as testing machine speed, machine hardness, rate of dislocation multiplication, work‐hardening rate, number of mobile dislocations initially present, and the dependence of dislocation velocity on stress. The parameter that most strongly influences the yield points and transient creep behavior of a given material isn0, the number of mobile dislocations initially present. The wide range of observed yield point and transient creep behavior of various materials can be rationalized in terms of how dislocation velocity varies with stress; the less sensitive is the velocity to the applied stress, the more pronounced will be the yield drop or delay time. The calculation is applicable only whenn0≠0; and the yield points and yield drops develop continuously and relatively gradually as dislocation motion and multiplication begin before the upper yield point is reached. The upper yield stress is not closely related to the stress required to unpin dislocations. It is necessary to distinguish between this type of yield point, which is commonly observed, and the Cottrell type of yield point in which dislocation motion begins at the upper yield stress, and in which the upper yield stress is related to the unpinning stress.

ISSN:0021-8979    

DOI:10.1063/1.1702538

出版商:AIP    

年代:1962

数据来源: AIP