A note on stress

Summary Consider an arbitrary stress system at a pointP in a continuum. AtP there exists at least one circle of directions of the unit vectorn for which the corresponding traction vectorst(_n) lie on a circle.     

A note on measuring normal science

Scientometrics - Petrovich provides an insightful study on analytic philosophy (AP) with the intention of determining whether this sub-field of philosophy has been operating within what Kuhn calls...     

Porosity dependence of material elastic moduli

A new equationE =E ₀(1+aP+bP ²)/(1+cP), whereE andE ₀ are Young's moduli at porosityP and zero, respectively, anda, b, c are constants, has been derived. Our theoretical derivation is based on the dependence of sound velocity on the Young's modulus of the material.     

A note on the solar elevation dependence of clear-sky snow albedo

Recent attempts to match the short-wave albedo of snow for clear skies using approximate spectral solar fluxes and solutions of the radiative transfer equation for snow were unsuccessful until a separate surface reflection term was introduced. A separate consideration of specular reflection from surface snow grains has been objected to as being ad hoc. Results based on a new parametrization of short-wave radiation are discussed. Compared with previous radiation models, the new model gives higher diffuse insolation and predicts higher albedos. The difference between observed and predicted albedos is substantially reduced without invoking surface reflection.     

Features of the temperature dependence of failure stress for zirconium dioxide

Institute of Material Science Problems, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Problemy Prochnosti, No. 3, pp. 77–79, March, 1988.     

A note on the composition dependence of elastic properties of Se-P glasses

Longitudinal and shear wave ultrasonic velocities are reported in Se-P glasses over the composition range 0–50 at % P. The glass transition temperaturesT _g show maxima at 30 and 50 at % of P, in consonance with earlier data. The bulk modulus shows minima at these compositions, contrary to the expectation of maxima. These are discussed in relation to the formation of compounds at specific compositions and the nature of the covalent bonding in the glasses.     

The temperature and strain rate dependence of the flow stress of tantalum

The temperature and strain rate dependence of the flow stress of tantalum was studied between 78 to 800 K at strain rates from 10^–5 to 2×10⁴ sec^–1. The effect of temperature and strain rate on the lower yield stress can be explained by a model incorporating the combined operation of the Peierls mechanism and dislocation drag processes. The general behaviour of the stress—strain curve at various strain rates and temperatures is analysed in terms of a rate—temperature parameter.     

On the temperature dependence of the flow stress of metals and solid solutions

The linear correlation between the logarithm of the CRSS, or of the yield stress in the case of polycrystals, and temperature, frequently encountered in representations of experimental data on metals and solid solutions, is shown to be consistent with the requirements of models in which kink-pair formation processes control the migration of dislocations.     

The temperature and pressure dependence of the normal fraction of superfluid3He-B

Measurements have been made of the normal fluid fraction of superfluid³He-B at eight different pressures between 0 and 29.2 bar. The minimum temperatures were such that _n / was reduced to less than 0.5%. The experiments, carried out independently at Cornell and Texas A&M Universities, used similar Andronikashvilli-type torsional oscillators. The results are qualitatively similar, but show significant differences due to the use of different temperature standards. Both sets of results are presented in tabular form. The inconsistencies in the temperature scales preclude the examination of the results for possible strong coupling effects.     

Influence of stress concentrators on the temperature dependence of the liquid metal embrittlement of Armco iron

We study temperature dependences of the effects of liquid indium and lead-bismuth eutectics on the ultimate strength and tensile elongation of Armco iron. Tests were performed on Armco iron cylindrical specimens with stress concentrators and with square cross section under active strain with a rate of 8.3 · 10^–4 s^–1. It was found that, under identical test conditions, the decrease in the ultimate strength of the specimens with concentrators caused by the effect of melts occurs in a broader temperature range than the embrittlement of specimens without concentrators. The effect of liquid metal also depends on the size of the grains in iron (26 – 110 µm) but its character is different for specimens with and without concentrators.Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 29, No. 5, pp. 65–72, September–October, 1993.     

The influence of the temperature dependence of the yield stress on the stress distribution in a thermally assembled elastic-plastic shrink fit

Summary The subject of the investigation is the thermal assembly of an elastic-plastic shrink fit with hollow inner component. Based on Tresca's yield condition and the flow rule associated with it, the transient stress distribution is studied. Special attention is paid to the influence of the reduction of the yield stress at elevated temperatures on the interface pressure. However, it turns out that this influence is not significant.Dedicated to Prof. Dr. Kurt Desoyer on the occasion of the 70^th anniversary of his birthday     

Temperature dependence of elastic moduli of lanthanum gallogermanate glasses

Temperature dependence of sound velocities of a series of Lanthanum Gallogermanate glasses have been determined from ultrasonic pulse-echo and Brillouin scattering measurements ranging from room temperature up to and through the glass transition temperature. Both longitudinal and transverse velocities of these glasses are composition dependent. The density and index of refraction of the samples were also studied. The experimental results are used to obtain elastic moduli. The correlation of elastic stiffness, the crosslink density, and the fractal bond connectivity of the glass are discussed. The normal behavior of negative temperature dependence of elastic properties is observed in these glasses. A possible explanation of the observed discrepancy of high temperature sound velocity of these glasses from two different measurements is given.     

A note on concrete creep analysis under static temperature fields

The analysis of concrete structures in the presence of sustained temperature fields is discussed, and, in particular, the variation of strain compliance with position in the structure as a result of the temperature variation. A form of the constitutive relationship for linear creep is proposed. By means of the use of a fictitious time, it is invariable in form; that is, the equations depend on duration since loading and not on the age at loading. Thus, it is possible to perform analyses using viscoelastic methods; in iterative schemes, considerable saving of computation effort is achieved. Direct solutions are also possible in some cases. The method reduces to the familiar rate of creep method if the reversible creep is ignored.

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Résumé Lorsque les ouvrages en béton sont soumis à des gradients thermiques, il peut en résulter de grandes déformations et une importante redistribution des contraintes. La principale raison en est l'effet de la température sur la vitesse de fluage, quoiqu'on ait aussi constaté une variation du module élastique avec la température. Cet article analyse deux formes de l'adaptation du fluage pour les déformations du béton; la première repose sur l'application de fonctions de variation de température, tandis que la seconde est essentiellement une formulation de la vitesse de fluage. Il faut souligner que l'utilisation des fonctions de variation de température (pour des matériaux thermo-rhéologiquement simples) en analyse structurelle est quelque peu restreinte, car on doit tenir compte de l'effet de l'age du chargement tant sur ses fonctions que sur la courbe de fluage de référence. D'autre part, on montre que la méthode de la vitesse de fluage, qui est d'application beaucoup plus simple, peut être étendue jusqu'à inclure le fluage réversible. Le fluage irréversible est pris en compte exactement et l'analyse du fluage réversible se fait avec une certaine approximation; étant donné que le fluage réversible n'atteint pas 30% du fluage total, les approximations introduites sont peu importantes. On montre que les solutions disponibles en régime permanent de contrainte sont indépendantes du fluage réversible. La solution proposée peut s'exprimer sous une forme visco-élastique et peut par conséquent servir à obtenir des solutions directes; en outre, la tache est simplifiée lorsqu'on a à effectuer des calculs itératifs.