摘要:

In order to supplement dynamic measurements in shear and bending, the vibration tester of the Franklin Institute Laboratories was used to measure the bulk compressibility of plastics using harmonic vibrations. Polyethylene and plasticized polyvinyl chloride were investigated. The values of the compressibility were comparable to the static values as far as they are known. A noticeable phase shift between pressure changes and volume changes could not be detected with certainty so that the bulk modulusBin dynes/cm2is not a complex quantity. Especially for the polyethylene, a temperature range from −25 to +95°C and a frequency range from 0.0003 to 5 cps was used. The isothermals obtained could be shifted together using the method of reduced variables of Ferry. From the frequency shiftsaT, an activation energy of 60 kcal/mole was obtained.

ISSN:0021-8979    

DOI:10.1063/1.1722106

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

The yield strength of many materials is much higher for minute specimens than for bulk samples. The region around the point of highest shear stress in a solid undergoing deformation by a small spherical indenter can be regarded as such a minute specimen which may be ``protected'' by the size effect against plastic yielding if it is small enough. Formulating the effective yield strength and the elastic stress under the indenter in terms of a common parameter provides a basis for assessing the influence of size scale on the plastic yield threshold. Four size categories are identified, including a critical case for which a small change of loading may cause a discontinuous transition from the elastic to the plastic regime throughout the region of contact, and another, more frequently encountered, in which the supportable pre‐yield elastic stress is materially enhanced. The latter effect may exert an important influence on the rate of rubbing wear since it can make available a wider range of loading for which a low wear rate prevails. Reported wear tests on steel riders and on sapphire phonograph styli confirm these predictions qualitatively.

ISSN:0021-8979    

DOI:10.1063/1.1722107

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

Studies were made of the change in the resistivity and magnetoresistivity of samples of AuCu, which had been thermally disordered, while annealed at 150°C, of samples, completely disordered by cold work, while annealed at 150°C and 265°C, and of initially ordered samples when subjected to varying amounts of cold work. The curves of magnetoresistivity against resistivity for the last three cases agree with one another, but differ from that for the thermally disordered sample annealed at 150°C and from a previously obtained curve for the annealing of a thermally disordered sample at 265°C. These last two curves are also markedly different from each other. All five curves appear distinct from the previously obtained curve for AuCu in equilibrium. An interpretation of the results in terms of the production of a more or less pronounced admixture of AuCu II during certain stages of the cold working or annealing process is presented.

ISSN:0021-8979    

DOI:10.1063/1.1722108

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

The elastic constants of germanium (c11,c12, andc44) increase on cooling and approach constant values for very low temperatures.

ISSN:0021-8979    

DOI:10.1063/1.1722110

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

A series of monodisperse polystyrene latexes has been prepared by carefully controlled emulsion polymerizations. The particle diameters of three of these latexes were determined by electron microscopy. The latex particles were dispersed on collodion membranes supported by copper grids. The microscopes had previously been calibrated with collodion replicas of a 30 000 line/inch diffraction grating. In general, the reproducibility of measurements from many photographic exposures was good; however, a few exposures yielded particle diameters considerably higher than the averages.An investigation of this technique indicated that: (1) polystyrene latex particle diameters (collodion membranes—copper grid supports) increased considerably on electron irradiation, (2) collodion diffraction grating replicas (copper grid supports) shrank slightly on electron irradiation, and (3) the magnification of the electron microscope varied slightly from exposure to exposure. It was found that variations of particle diameter resulting from the foregoing sources of error were negligible when the particles were dispersed directly on a silicon monoxide diffraction grating replica supported by a stainless steel grid.The particle diameters of the latexes determined in this manner ranged from 880 to 11 720 A. Many photographic exposures of each latex were used for these measurements. The monodispersity of the latex particles is evident from the small values of the standard deviations of the over‐all particle‐size distributions. The reproducibility of particle diameters determined from different exposures is evident from the small values of the standard deviations of the means of the exposure averages.

ISSN:0021-8979    

DOI:10.1063/1.1722111

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

Ordering in the alloy AuCu was studied by measurements of the electrical resistivity as a function of time and temperature of ordering for samples disordered at various temperatures above the critical point. It has been established experimentally that the disordering temperature has a profound affect upon the rate of ordering. The higher the disordering temperature the faster is the rate of subsequent ordering. The dependence of the rate of ordering on the ordering temperature seems to indicate that the transformation is nucleated even at very low temperatures. The appearance of a twin‐like structure during the disorder‐to‐order transformation has also been studied as a function of the previously mentioned variables.

ISSN:0021-8979    

DOI:10.1063/1.1722112

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

The direct observation of transformations in plain carbon steels at temperatures above about 625°C is demonstrated for both theA3andA1transformations.It is concluded from emission studies of the decomposition of austenite below theA3line that the transformation is of a diffusionless type rather than carbon diffusion controlled. It is shown that carbon is associated with ``memory'' in the austenite grain structure, the memory improving with increasing carbon content. The emission images also indicate that the growth of a ferrite grain in austenite induces a recrystallization of the surrounding austenite. A model to account for the memory is advanced based on thin sheets of retained austenite in newly transformed ferrite.Studies of a 0.77 percent carbon steel below theA1line illustrate the formation of pearlite. The images suggest that these decompositions take place in two distinct steps. The first is the formation of a metastable crystal which subsequently decomposes by carbon diffusion to the final ferrite‐carbide products. Austenite recrystallization about a growing pearlite nodule is demonstrated. A model for the transformation based on a diffusionless type reaction followed by a diffusion decomposition is suggested to explain the emission images.

ISSN:0021-8979    

DOI:10.1063/1.1722113

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

An equation of state is formulated from the classical Maxwell assumptions of superposition of the effects due to strain and rate of deformation in a strained fluid. Except for the form of the time derivative, these assumptions result in the usual expression for a Maxwell element. The time derivative of the stress, however, is computed with respect to a set of axes in the fluid which are rotating (with respect to fixed axes) at a rate measured by the vorticity of the assumed velocity distribution. The usual transformation between rotating and fixed reference axes introduces cross terms between the stress and vorticity components.The resulting equation of state predicts non‐Newtonian behavior and the simultaneous appearance of normal stresses. It reduces to the Newtonian case for low rates of shear (or for small relaxation times) and, if the cross terms are sufficiently small (but not otherwise), to the usual Maxwell element expression in the dynamic case. A common origin is thus assigned to these several phenomena. Reduced variable and distribution function procedures, at least in principle, should be as applicable to the viscosity and pressure phenomena as to dynamic data.

ISSN:0021-8979    

DOI:10.1063/1.1722114

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

An analysis is made of the phenomena at the electrodes of a high‐current short‐time arc. It is shown that the input power density to the anode spot is in the range 5×104to 1×106watts/cm2. To a first‐order approximation, all this power can be carried off by evaporation. Power conducted into the metal and lost by radiation is negligible in the probable operating range. For most materials, the anode spot is probably considerably above the boiling temperature. The process of evaporation holds the spot temperature constant at a value such that the input power and evaporation power are equal. Experimental data indicate that for any given metal the anode spot temperature is that for which the evaporation power density is at least 3×105watts/cm2. As an example, for copper the theoretical limits of temperature are 2490 to 3040°K, while experimental data indicate a temperature of 2920°K. Other metals considered are: Ag, Al, C, Fe, Mo, Sn, Ti, W, Zn, Zr. It is also shown that for the maximum power input that can be expected at the cathode, the thermionic emission current density is very small compared to the observed values of current density.

ISSN:0021-8979    

DOI:10.1063/1.1722115

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

The Griffith energy criterion,dW= −dU(dW= crack propagation work, −dU= released elastic energy), cannot be applied to essentially ductile fractures. In particular, it does not represent the condition of rapid ductile fracture propelled by the elastic energy of the specimen. The condition of such fractures isd2W/dx2=−d2U/dx2wherexis the plastic extension accompanying the propagation of the crack.

ISSN:0021-8979    

DOI:10.1063/1.1722116

出版商:AIP    

年代:1955

数据来源: AIP