Minimal dissipation theory and shear bands in biaxial tests

True biaxial tests of granular materials are investigated by applying the principle of minimal dissipation and comparing to two dimensional contact dynamics simulations. It is shown that the macroscopic steady state manifested by constant stress ratio and constant volume is the result of the ever changing microscopic structure which minimizes the dissipation rate. The shear band angle in the varying shear band structures is found to be constant. We also show that introducing friction on the walls reduces the degeneracy of the optimal shear band structures to one for a wide range of parameters which gives a non-constant stress ratio curve with varying aspect ratio that can be calculated.     

Breakage behaviour of spherical granulates by compression

This paper describes the deformation and breakage behaviour of granulates in single particle compression test. Three industrial spherical granulates—γ-Al₂O₃, the synthetic zeolite Köstrolith^® and sodium benzoate (C₆H₅COONa) were used as model materials to study the mechanical behaviour from elastic to plastic range. The elastic compression behaviour of granulates is described by means of force-displacement curves, by application of Hertz-Huber contact theory and continuum mechanics. An elastic-plastic contact model was proposed to describe the deformation behaviour of elastic-plastic granules. The effects of granulate size and stressing velocity on the breakage force and contact stiffness during elastic and elastic-plastic displacement are examined. It is shown that the zeolite granulates with elastic-plastic behaviour have viscous properties as well. Breakage mechanisms of granulates during elastic, elastic-plastic and plastic deformation are also explained. The breakage probability is approximated by Weibull distribution function. The behaviour of the granulate during compression under the repeated loading-unloading conditions was investigated.     

Interfacial Energy in Phase-Separated Glasses from Emulsion Rheology

Classical theories of emulsion rheology yield information on the deformation of a liquid drop dispersed into another liquid matrix phase. By connecting the deformation and relaxation, respectively, and the capillary number of the dispersed phase, interfacial energy can be estimated. This was applied to demixing borosilicate and lead borate glasses, which are known to exhibit significant form anisotropy after elongation. Interfacial energies in these two systems were calculated based on graphical data of prior isothermal elongation experiments. The method is discussed in terms of experimental difficulties. It might provide an alternative way to overcome the obvious lack of information on interfacial energies in glasses.     

Gaschromatographische Bestimmung der h?heren Ester in Weindestillat, Weinbrand, Branntwein und Wein. II

Zusammenfassung Auf Grund der Beobachtung, daß freie Fettsäuren die Bestimmung höherer Äthylester \ bei gaschromatographischer Trennung an Carbowax 20 M stören können, wurden Reihenversuche zur Eliminierung dieser Störpartner durchgeführt. Dabei erwies sich Natriumhydrogencarbonat günstiger als Natriumcarbonat. Eine geeignete Methode zur Bestimmung der gradkettigen Äthylester der Capron- bis Stearinsäure, die auch für die Äthylester von ungesättigten C₁₆- und C₁₈-Säuren verwendet werden kann, wird angegeben.

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Determination of the ethyl esters of long chain fatty acids in wine distillate, brandy, and wine. II

Summary Free fatty acids are able to interfere the determination of the ethyl esters by gas chromatography on Carbowax 20 M. Therefore series of tests were made to remove the fatty acids. Sodium hydrogen carbonate was found to be more suitable than sodium carbonate. A method is described to determine the ethyl esters of fatty acids of caproic to stearic acid and of the unsaturated fatty acids with 16 and 18 carbon atoms.

     

Dynamic Min-Max Problems

In this paper a method to check the solvability of a set of linear equations in the (max, min, +) algebra is described. Then, extensions to dynamic (or periodic) systems in the (max, min, +) algebra are provided. Further, some results regarding the uniqueness of solutions in both cases are given. Finally, we address a more general quasi periodic problem and provide an algorithm for its solution.     

Influence of Grain Refinement on Slurry Formation and Surface Segregation in Semi-solid Al-7Si-0.3Mg Castings

This study aims to evaluate the effect of grain refinement on slurry formation and surface segregation in semi-solid castings produced by the Rheometal™ process. The effect of two grain refiners, Al-8B and Al-5Ti-1B, on the slurry α-Al grain size, shape factor and solid fraction was evaluated. The results suggest that the addition of a grain refiner can affect the solid fraction obtained in the Rheometal^TM process and, consequently, reduce the solute content near the casting surface. Grain refiner addition resulted in a larger fraction of α-Al grains ≤ 60 µm for the refined alloys compared with the unrefined alloy. Additionally, the growth of α-Al slurry globules was greater for the unrefined alloy compared with the refined alloy during solidification in the die-cavity. A more homogeneous and finer microstructure was observed near the surface in the grain-refined castings compared with the unrefined castings. Evidence of significant liquid penetration was identified in some α-Al globules, indicating that disintegration of α-Al globules may occur during the Rheometal™ casting process.