ISSN:0021-8979    

DOI:10.1063/1.1721356

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

The general nature of radiation effects in solids is reviewed briefly. Current theoretical understanding of the mechanical properties of solids is critically evaluated. The effect of nuclear radiation on the mechanical properties is discussed in detail. It is shown that the changes in the mechanical properties of crystalline substances (mostly metals) can be quite satisfactorily interpreted on the basis of the production of interstitial atoms and vacant lattice sites by fast particle irradiation. Isolated vacancies and interstitials may not be able to account for all the observations, and attention is called to the possible need of postulating the existence of aggregates of these lattice defects. In molecular solids (mostly high polymers) nuclear radiations bring about changes in the substance which are best described as chemical ones. Ions and free radicals are formed leading to subsequent chemical reactions thereby altering the properties of the substance. Drastic changes in the mechanical properties of high polymers are observed. Correlation with structural changes has hardly been started. Experiments are suggested which, in the writer's opinion, should give further insight into the fundamental processes involved.

ISSN:0021-8979    

DOI:10.1063/1.1721357

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

Experimental data published by Garner, Nissan, and Wood on secondary stresses in a viscoelastic liquid have been analyzed in terms of the superelasticity theory of secondary stresses as developed by Mooney. The theory was slightly modified to be consistent with the reported viscosity rate of shear behavior of the test liquid. With this modification the theory agreed within experimental error with observed normal stresses at various radii on a stationary circular plate mounted parallel to a rotating plate.One reported qualitative experimental result is in disagreement with the theory, but this particular result is questioned. Other theories of secondary stress are briefly discussed.

ISSN:0021-8979    

DOI:10.1063/1.1721358

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

The dynamic rigidities and viscosities of solutions of polystyrene (number‐average molecular weight 197 000) in decalin have been measured by three experimental methods over ranges of concentration from 10 to 62 percent, of temperature from −5° to 50°C, and of frequency from 30 to 2000 cps. Similar measurements were made on the undiluted polystyrene from 115° to 133°C and 30 to 2800 cps. The data for the solutions, when reduced to a reference state of unit density and viscosity at a standard temperature, provide single composite curves for dynamic rigidity and viscosity. The distribution function of relaxation times calculated from these curves overlaps that previously derived from stress relaxation measurements on this system, and the combined function covers a range of time scale of ten powers of ten. It shows the three characteristic regions previously identified in the relaxation distribution function of polyisobutylene; there are no obvious anomalies associated with the fact that decalin is a very poor solvent for polystyrene. The data for the undiluted polymer, when reduced to a standard temperature, provide single composite curves for dynamic rigidity and viscosity. The temperature reduction factors provide apparent energies of activation for relaxation which agree with those for viscous flow obtained by Fox and Flory. The relaxation distribution function of the undiluted polymer is similar in shape to, but somewhat sharper than, those for other polymers in the transition from soft to glassy consistency. When reduced to a reference state of unit density and viscosity, the distribution function of the undiluted polymer lies near that reduced from data on solutions, but is considerably sharper than the latter.

ISSN:0021-8979    

DOI:10.1063/1.1721359

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

A method has been found for measuring the shear moduli and losses of elastomers in a range of frequencies of about 1 to 106, from 10 cps down. This method provides for large cyclic shear stresses and deformations without employing resonance methods. Only one sample is needed for a complete study, the frequency of stress being the only variable. The method gives results that fit the ``box‐distribution function'' developed by Kuhn and Kuenzle. Results for a series of elastomers show that such investigations are important in ascertaining the mechanical properties of elastomers in practice.

ISSN:0021-8979    

DOI:10.1063/1.1721360

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

The viscoelastic properties of dilute solutions of chain polymers have been measured at frequencies in the range from 200 cps to 60 kc. The data are compared with theoretical curves calculated from the steady‐flow viscosities of the solution and solvent, the molecular weight and concentration of the polymer, and the absolute temperature; this calculation made use of equations obtained from a recently developed theory. The equations contain no adjustable constants. The theory is shown to be at least a good first approximation to the viscoelastic properties of the solutions studied.The agreement of the data and the theory implies that, up to 60 kc at least, the viscoelastic properties of dilute solutions of polystyrene and polyisobutylene are the result of the thermal motions of the segments of the polymer molecules. These segmental motions coordinate with one another to produce changes in the configurations of the molecules. The configurational changes have associated with them a series of relaxation times. These relaxation times are shown to depend upon molecular weight of the polymer, concentration, type of solvent, and viscosity of solvent.

ISSN:0021-8979    

DOI:10.1063/1.1721361

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

Viscosity decreases with increasing shearing stress or rate of shear in the non‐Newtonian flow of high polymeric systems. It is shown that it follows from this fact that the variation of viscosity with temperature is greater at fixed shearing stress than at fixed rate of shear.For such systems, it is shown experimentally that the variation of viscosity with temperature at fixed shearing stress is independent of shearing stress. However, the variation at fixed rate of shear is always less than that at very low shearing stress, and decreases with increasing rate of shear.This behavior is reproduced by Eyring's hyperbolic sine flow equation, which is the antecedent for most other, more adequate, non‐Newtonian flow equations. However, this equation is shown to be inadequate in that it predicts incorrect values of shearing stress for the occurrence of non‐Newtonian behavior.

ISSN:0021-8979    

DOI:10.1063/1.1721362

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

Fractions of polystyrene, varying in molecular weight from 0.3×106to 10×106approximately, were prepared by careful tertiary fractionation. Inherent viscosities were determined at various rates of shear in the approximate range 100–20 000 sec−1, viscosity measurements being made at several different temperatures in benzene and toluene (good solvents for polystyrene), in butanone (an intermediate solvent), and in cyclohexane (a poor solvent). From these values intrinsic viscosities at various rates of shear were determined. These viscosity functions are sensitive to shear rate at high molecular weights; at a given temperature the shear effects are greater the higher the molecular weight and the better the solvent, and with increasing temperature they decrease in a good solvent and increase in a poor one This behavior is shown to be consistent with current ideas regarding the size and shape of polymer molecules in solution as affected by weight, temperature, and solvent power. It is concluded, among other things, that with flexible polymers (or polymer fractions) of very high molecular weight, measurements of intrinsic viscosity should be made in a poor solvent at a low temperature.

ISSN:0021-8979    

DOI:10.1063/1.1721363

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

Fluid suspensions of a solid phase in a liquid, for example, paints and printing inks, have been presumed to exhibit anomaly of flow at very low rate of shear. The consistency characteristics of such materials require an experimental shear rate and shear stress much lower than has heretofore been reported.This paper describes a translated cylinder, or translational, viscometer of a modified Pochettino type, which possesses a shear stress sensitivity of 5×10−3dyne/cm2, and a shear rate sensitivity of 1×10−4sec−1. A rubber Latex of high solids content exhibited no anomaly of flow within this range of sensitivity. A rubber dissolved in organic solvent was observed to approximate a Bingham material of 0.05‐dyne/cm2yield value, while a gum tragacanth suspension in water exhibited a yield value of 0.4 dyne/cm2with marked post‐yield anomalous flow. Household paints exhibited yield value ranging from zero to 6 dyne/cm2. These yield values were related to leveling‐out of brushmarks, and to sagging or ``curtain,'' except for examples exhibiting marked thixotropic behavior. Industrial organosol coatings likewise possessed yield values ranging up to 5 dyne/cm2which were related to leveling characteristics. These yield values agree with those postulated by Waring from consideration of the forces of leveling of brushmarks. They are considerably smaller than those reported in the literature from extrapolation of flow curves from much higher rate of shear.

ISSN:0021-8979    

DOI:10.1063/1.1721364

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

A general analysis is made of the relations between output signal and noise powers and input signal and noise powers for band‐pass limiters having odd symmetry in their limiting characteristics. Specific results are given for the case where the limiter has annth root characteristic, and they include the ideal symmetrical limiter (or clipper) as a limiting case. This analysis shows that, for the band‐pass limiter, the output signal‐to‐noise power ratio is essentially directly proportional to the input signal‐to‐noise power ratio for all values of the latter. This result is due to the band‐pass characteristics rather than to the symmetrical limiting action.

ISSN:0021-8979    

DOI:10.1063/1.1721365

出版商:AIP    

年代:1953

数据来源: AIP