Semisolid Casting and Die Casting of Al-4.8%Mg-2%Si Alloy

An aluminum alloy, Al–4.8%Mg–2%Si, was cast by die casting and thixocasting, and the properties of the cast specimens were investigated. When the poured molten metal temperature was lower than 640 °C during die casting, it was lower than the liquidus temperature, and the metal became a semisolid slurry in the sleeve of the die casting machine; this fulfills the conditions for rheocasting. A tension test was conducted to investigate the effects of semisolid casting on the mechanical properties of Al–4.8%Mg–2%Si. The ultimate tensile strength and elongation of the ingots cast by die casting and rheocasting were affected by the size of ingot. When the ingot had a circular base of 4.5 mm diameter, the ultimate tensile strength and elongation were excellent; however, when the cross section of the ingot was a square with a side length of 20 mm, the tensile strength and elongation were inferior. The thixocasting was conducted using square ingots with a side length of 20 mm, and the tensile strength and elongation were poor in this case as well. The results of this study demonstrate that semisolid casting cannot improve the mechanical properties of Al–4.8%Mg–2%Si ingots with a high thickness. Semisolid casting cannot produce fine-grained Mg2Si, and the mechanical properties of the material could not be improved by this casting method.

Avita. Nuevo anillo visigodo de oro

Un nuevo anillo visigodo de oro, seguramente procedente de Soria y datado en el siglo VI d.C., es editado. Sobre su chatón circular, hay un epígrafe inciso que corresponde con un nombre personal femenino: Auita. Además, el anillo constituye un buen testimonio de la onomástica latina en época visigoda. A new Visigothic gold ring is published. It was probably found in Soria and its chronology is from the 6th century A.D. The bezel, in the form of a shallow lens with roughly circular base, is engraved an incised epigraph, which corresponds to a personal female name: Auita. Furthermore, the gold ring is a good Latin onomastic testimony during the Visigothic period.

ANALYSIS OF COMBINED PLATES WITH ALLOWANCE FOR CONTACT WITH ELASTIC FOUNDATION

The paper covers the problems of combined plates with circular base and consisting of a few sections with different laws of thickness variation. Analytical methods of analysis of similar structures are not yet devel­oped. The present work suggests the analytical method for solving of the stated problems, the contact with the elas­tic subgrade is also considered. The above-mentioned approach is shown on the example of the analysis of the bot­tom of the cylindrical reservoir, resting on the elastic subgrade. The inner part of this construction is represented by the ring plate of variable thickness which increases along the direction from the internal boundary. The outer part is represented by the ring plate of the constant thickness. The influence of the elastic basis and the upper part of the reservoir is taken into consideration. The solutions for stresses and deflections of the combined plate are given in closed form in terms of Bessel functions. The conditions of the plate’s sections conjugation are fulfilled.

Nematic twist–bend phase in an external field

The response of the nematic twist–bend (NTB) phase to an applied field can provide important insight into the structure of this liquid and may bring us closer to understanding mechanisms generating mirror symmetry breaking in a fluid of achiral molecules. Here we investigate theoretically how an external uniform field can affect structural properties and the stability of NTB. Assuming that the driving force responsible for the formation of this phase is packing entropy, we show, within Landau–de Gennes theory, that NTB can undergo a rich sequence of structural changes with the field. For the systems with positive anisotropy of permittivity, we first observe a decrease of the tilt angle of NTB until it transforms through a field-induced phase transition to the ordinary prolate uniaxial nematic phase (N). Then, at very high fields, this nematic phase develops polarization perpendicular to the field (Np+). For systems with negative anisotropy of permittivity, the results reveal new modulated structures. Even an infinitesimally small field transforms NTB to its elliptical counterpart (NTBe), where the circular base of the cone of the main director becomes elliptic. With stronger fields, the ellipse degenerates to a line, giving rise to a nonchiral periodic structure, the nematic splay–bend (NSB), where the two nematic directors are restricted to a plane. The three structures—NTB, NTBe, and NSB—with a modulated polar order are globally nonpolar. But further increase of the field induces phase transitions into globally polar structures with nonvanishing polarization along the field’s direction. We found two such structures, one of which is a polar and chiral modification of NSB, where splay and bend deformations are accompanied by weak twist deformations (NSB*p). Further increase of the field unwinds this structure into a polar nematic (Np−) of polarization parallel to the field.

Steady-State Resonant Sloshing in an Upright Cylindrical Container Performing a Circular Orbital Motion

The nonlinear Narimanov-Moiseev multimodal equations are used to study the swirling-type resonant sloshing in a circular base container occurring due to an orbital (rotary) tank motion in the horizontal plane with the forcing frequency close to the lowest natural sloshing frequency. An asymptotic steady-state solution is constructed and the response amplitude curves are analyzed to prove their hard-spring type behavior for the finite liquid depth (the mean liquid depth-to-the-radius ratio h>1). This behavior type is supported by the existing experimental data. The wave elevations at the vertical wall are satisfactorily predicted except for a frequency range where the model test observations reported wave breaking and/or mean rotational flows.