摘要:

A high speed stress‐strain machine has been developed which is capable of recording the stress‐strain curve of elastomers at elongation rates up to 270 percent/msec. Data are reported on two series of gum and tread stocks of hevea and of the synthetic elastomers, GR‐S, Hycar OR, butyl, Perbunan, and Neoprene GN. The second (elastomer) series was also run at 150°C. In general, stress‐strain curves fall into two classes. Stocks of elastomers which are known to crystallize on stretching tend to show tensiles which decrease with increasing speed up to about 10 percent/msec., pass through a minimum and rise more or less drastically to values 100 percent (or more) greater than the Scott tensile. Elastomers which do not crystallize on stretching tend to show a steady rise in tensile with increasing speed. Elongation at break curves show a maximum with crystallizing stocks and no maximum with non‐crystallizing stocks. The shape of the modulusversusspeed curves is accounted for on the hypothesis of different types of slipping bonds with different characteristic relaxation times. The shift of curves for tread stocks with temperature allows the estimation of a heat of activation of slippage. This comes out to be of the order of 3 kg cal.

ISSN:0021-8979    

DOI:10.1063/1.1699708

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

By means of a vector notation for surfaces, relations are derived among an incident wave front, reflector and reflected wave front. A method is introduced for evaluating the deviation of a wave front surface from a plane. Problems are included in order to indicate the simplicity and utility of the analysis.

ISSN:0021-8979    

DOI:10.1063/1.1699709

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

At radio wave‐lengths the use of mirrors and lenses in the measurement of radiators, by methods which are customary in physical optics, is possible only if errors, due to incidental diffraction from the relatively small apertures of such apparatus, can be corrected by calculation. Theory is developed in this paper from which these calculations can be derived for linear radiators. A new relation which expresses the Fresnel field in terms of the distant field is fundamental to the method. Satisfactory agreement has been obtained between the predicted and measured distant fields of several electromagnetic horns whose near fields were obstructed; the dispersion between measured and predicted values is given as under one‐half decibel but the details of the experiment are not reported.

ISSN:0021-8979    

DOI:10.1063/1.1699710

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

Dilatometric and viscometric data on fractionated polystyrenes containing diethylbenzene end groups are presented over wide temperature ranges. The second‐order transition temperature, viscosity‐temperature coefficient, and specific volume all change rapidly with increasing molecular weight toward asymptotic limits which are practically reached atM≅30,000. Empirical expressions are presented relating these properties to molecular weight and temperature. In each case the dependence on molecular weight is expressed as a simple function ofM¯n−1. These observations are interpreted and correlated on the basis of the hypothesis that the local configurational order in a liquid polymer is disturbed by the introduction of end groups to a degree that is proportional to their number. The second‐order transition does not represent an isoviscous state. The internal local configurational structure appears to be equivalent, and independent of temperature, in all polystyrenes below their second‐order transition temperatures.

ISSN:0021-8979    

DOI:10.1063/1.1699711

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

The breakdown potential of a new gas, CSF8, has been measured over the range fromp&dgr;=4 to 200 mm×cm under conditions approximating plane‐parallel geometry. A comparison of breakdown in air Freon‐12 and CSF8in the same apparatus indicates the ratio of the strengths of these gases to be approximately 1:2:3, respectively. CSF8decomposes rapidly during breakdown into CF4and SF4with a consequent doubling of pressure and appreciable increase in breakdown potential.

ISSN:0021-8979    

DOI:10.1063/1.1699712

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

With modern experimental technique, it is possible to measure a peak shape with sufficient accuracy to justify an interpretation based on the precise shape of the reflection. The corrected shape is represented by a cosine Fourier series and a set ofAncoefficients determined. A plot of theAncoefficientsvs. nwill distinguish between distortion and particle size broadening. From theAncoefficients, root mean square values of strain averaged over lengthsna3are obtained. The decrease in these values for increasing lengthna3is a direct indication of the non‐uniform nature of the strains in cold‐worked metal. By measuring several orders of a given plane, it is theoretically possible to obtain a distribution function of the strains directly from a Fourier transform of theAncoefficients.

ISSN:0021-8979    

DOI:10.1063/1.1699713

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

A theory of strain hardening is presented which utilizes the fact that metals deform blockwise rather than continuously. A metal is assumed to possess an orderly array of weak spots through which slip planes pass. The slip displacement which occurs upon a single plane is related to the spacing of weak points and the slip plane inclination. Use of a linear relation between shear plane displacement and resisting shear stress, enables the mean shear stress to be computed.In the two examples considered it is seen that the influence of normal stress on the shear plane is less important in cutting than has been generally believed. Strain hardening and the short range inhomogeneity of metals is seen to account for most of the dynamic increase in shear strength during cutting, including the increase in shear energy per unit volume with decreased depth of cut. This size effect is akin to the increase in tensile strength with decreased specimen diameter, both phenomena involving strain hardening as influenced by inhomogeneity. The quantityAa2which represents in a single number the strain hardening and short range inhomogeneity characteristics of a metal should prove particularly valuable in analyzing the cutting characteristics of metals which strain harden extensively.

ISSN:0021-8979    

DOI:10.1063/1.1699714

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

The temperature dependence of the dynamic mechanical and a.c. electrical properties of a given polyvinyl chloride plasticizer composition can be characterized by two quantities: (a) the transition temperature which is defined as the temperature of maximum dissipation factor and (b) the half‐widths of the loss factor‐temperature curve. A simple relationship exists between the transition temperature determined mechanically or electrically and the volume fraction of a compatible plasticizer. The modification of this relationship for non‐compatible plasticizer has been indicated. The half‐width is a function of the volume fraction of the plasticizer, although this relationship is not as simple as the one obtained for the transition temperature. A simple correlation exists between the electrical and mechanical half‐width. The compliance measured in tensile creep has been found to be a function of the applied load and the compliance‐load relationship varies depending on the region in which the material finds itself. The shape of the creep curve at different temperatures has been correlated with the dissipation factor‐temperature curve. The shape of the stress‐strain curve has been related to the modulus‐temperature curve and a correlation between the initial Young's modulus and the ultimate elongation and breaking strength has been established. It has been shown that the relaxation theory is not sufficient to explain certain features of the modulus (or dissipation factor) temperature relationship. The limited significance of the &mgr;‐value and of the viscosity of plasticizers with respect to plasticizer efficiency has been demonstrated.

ISSN:0021-8979    

DOI:10.1063/1.1699715

出版商:AIP    

年代:1950

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1699716

出版商:AIP    

年代:1950

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1699718

出版商:AIP    

年代:1950

数据来源: AIP