摘要:

An apparatus for measuring stress relaxation of plastics at constant strain in the time range of 0.01 to 2.5 sec after load application is described. Experimental results obtained indicate that rigid plastics at room temperature may be classified as either brittle or ductile. Brittle plastics sustain only low strains without fracture at the testing speed of the apparatus and undergo little relaxation of stress in this time range; ductile plastics sustain higher strains and undergo considerable relaxation of stress. The factors affecting relaxation behavior are briefly discussed. Increasing the strain, temperature, or plasticizer content generally increases the relaxation rate.Many of the results yield a linear plot of stressvslogarithmic time, as has been reported in the literature for various materials tested at longer times. By application of one form of the Eyring absolute rate theory, an average free energy of activation for the relaxation process can be calculated. The value thus calculated for polymethyl methacrylate is in the range reported in the literature for other polymers.An empirical measure of ``toughness'' can be based on these results. For many plastics this measurement is in accord with service performance.

ISSN:0021-8979    

DOI:10.1063/1.1722074

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

Experimental results of the near zone diffraction field of circular and elliptical apertures and of the infinite slit are presented. The investigations were made on apertures which were illuminated by a plane polarized electromagnetic wave and whose characteristic dimensions were varied over a considerable range with respect to the wavelength of the incident radiation.Most of the measurements are compared with predictions from recently published approximate theories and in a few cases with exact solutions. In general the agreement between theory and experiment is found to be satisfactory. Some of the discrepancies are discussed.

ISSN:0021-8979    

DOI:10.1063/1.1722075

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

The low‐frequency noise spectra of germanium and silicon rectifiers have been determined. Two methods were employed: a numerical analysis according to the Wiener‐Khintchine relationship, and a frequency translation photo playback method. No evidence of a deviation from a 1/fa(a>1) noise power law was found down to frequencies as low as 6×10−5cps.

ISSN:0021-8979    

DOI:10.1063/1.1722076

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

In the study of the surface properties of semiconductors, it is valuable to know the relation between carrier density at the surface and the shift in electrostatic potential from the bulk to the surface. By a solution of Poisson's equation utilizing Boltzmann statistics, the space charge, electric field, and change in free carrier concentration have been calculated for a semiconductor surface. The results are expressed as a function of the deviations of the Fermi energy from its intrinsic value in the bulk and at the surface. The calculated curves may be used for any nondegenerate semiconductor at any temperature, provided that the donor and acceptor levels are completely ionized. Numerical values are given for germanium and silicon at room temperature.

ISSN:0021-8979    

DOI:10.1063/1.1722077

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

Currents preceding breakdown have been measured between closely spaced tungsten electrodes in high vacuum. It is found that field emission currents sufficient to evaporate anode metal flow before breakdown. These currents follow the Fowler‐Nordheim equation when field magnification due to surface irregularities on the cathode is taken into account. The field magnification is a function of distance at electrode separations less than 4×10−4cm.Explanation of the observed breakdown at low voltage and small spacing requires an unusually high yield of electrons at the cathode per ion formed in the gap. Furthermore there is no measurable direct enhancement of the current by ionization even at higher voltages. The high electron yield must therefore exist over the entire observed range of breakdown voltages. This high yield is satisfactorily accounted for by the increase in field emission due to the positive ion space charge, which in turn increases the positive ion current density until there is breakdown. It is shown that breakdown occurs when the field emission current is increased by only 65 percent. This condition is reached with the ion current density much smaller than the electron current density.

ISSN:0021-8979    

DOI:10.1063/1.1722078

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

X‐ray diffraction profiles from filed solid silver specimens were measured with a Geiger counter spectrometer using crystal‐reflected Cu K&agr; radiation. It is shown that for values ofn>7, the assumption of a Gauss strain distribution fits the observed Fourier coefficients far better than a Cauchy distribution. The results obtained from solid specimens are consistent with those previously measured for silver filings. The influence of background errors is discussed.

ISSN:0021-8979    

DOI:10.1063/1.1722079

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

The energy relations associated with the plastic deformation by cold working of a 75 percent gold—25 percent silver alloy at two temperatures were investigated. The samples were produced by drilling under controlled conditions, which is a suitable method of deformation. The energy stored in the chips was measured by tin solution calorimetry and the total energy expended in the deformation was determined from dynamometer measurements.The results for cutting with a drill having the most suitable geometry were as follows. The energy stored at room temperature was 0.50 cal/g and the corresponding value for 78°K was 1.48 cal/g. The values of the total energy of deformation were 53.5 cal/g at room temperature and 109 cal/g at 78°K. The true stress‐true strain curve at room temperature was normal for a nonferrous metal and the curve for 78°K showed the behavior expected at low temperature from a face‐centered cubic metal.

ISSN:0021-8979    

DOI:10.1063/1.1722080

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

The work functions of the low emitting crystallographic planes of tungsten, (011) and (112), are not well known. In previous experiments scattered secondaries and some other disturbing effects covered the small emission particularly of the (011) plane. A method combining the field emission microscope with a probe collector has been applied. The current density in the (011) plane turned out to be 4 to 5 orders of magnitude smaller than in strongly emitting planes. Applying the Fowler‐Nordheim theory, &phgr;011was found between 5.70 and 5.99 ev and &phgr;112between 4.65 and 4.88 ev depending on the temperature at which the tungsten crystal has been annealed previously. This is not a temperature effect of the work function, but the result of freezing in thermal imperfections of the planes. The work function of the ideal (011) plane appears to be as high as 5.99 ev. The existence of such a high value is further suggested by the ionization of aluminum on a hot polycrystalline tungsten wire, indicating that a part of the surface has a work function as high as the 5.96 ev ionization energy of aluminum.

ISSN:0021-8979    

DOI:10.1063/1.1722081

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

This paper presents an intensive study of the viscous and elastic properties of the poly methacrylates. Variation of these properties is studied as a function of temperature in the range 60<T<160°C, as a function of molecular weight in the range 5×103<M<5×106, and as a function of plasticizer concentration over the range 0–100 percent. Capillary viscometers were used in the low‐viscosity systems and tensile creep and recovery measurements under very small loads were used to study the less fluid systems. Principal effort was confined to polymethyl methacrylate but enough work was done using the butyl and decyl esters to show that the whole series of these polymers fits into a relatively simple picture. Consequently, given a certain minimum amount of data, it is now possible to predict the viscoelastic behavior of these polymers in the range of variables given above.The theory of viscoelasticity previously given has been extended so as to take account of the effects of chain entanglements and distributions in molecular weight. Moderately good agreement is found between theory and experiment.

ISSN:0021-8979    

DOI:10.1063/1.1722082

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

An experimental study was made of the behavior of two rubbers, Butyl (GR‐I‐18) and Paracril‐35, in the low extension region (0 to 15 percent), at temperatures ranging from −40°C to +60°C. The results have been compared with the Guth‐James theory of rubber elasticity. In general, good agreement with theory was observed. Two effects predicted by the theory have been confirmed, namely, the nonlinear dependence of stress upon temperature at constant extended length, and the shift of the thermoelastic inversion extension to higher values with increasing temperature. Small deviations, which increased with increasing extension and with decreasing temperature, were observed.

ISSN:0021-8979    

DOI:10.1063/1.1722083

出版商:AIP    

年代:1955

数据来源: AIP