In Silico Study of the Electrically Conductive and Electrochemical Properties of Hybrid Films Formed by Bilayer Graphene and Single-Wall Nanotubes under Axial Stretching

Using the self-consistent-charge density-functional tight-binding (SCC-DFTB) method, we studied the effect of axial stretching on the electrical conductivity and quantum capacitance of hybrid films formed by AB-stacked bilayer graphene and horizontally oriented single-walled carbon nanotubes (SWCNTs) with indices chirality (12,6). The paper discusses several topological models of hybrid graphene/SWCNT(12, 6) films, which differ in the width of the graphene layer in the supercell and in the value of the shift between the graphene layers. It is shown that axial stretching has a different effect on the electrical conductivity and quantum capacity of the hybrid graphene/SWCNT (12, 6) film depending on the width of the graphene layer. For a topological model with a minimum width of the graphene layer (2 hexagons) under a 10% stretching strain, the transformation of bilayer graphene from planar to wave-like structures is characteristic. This transformation is accompanied by the appearance of the effect of anisotropy of electrical conductivity and a sharp decrease in the maximum of quantum capacitance. For a topological model with a graphene layer width of 4 hexagons, axial stretching, on the contrary, leads to a decrease in the effect of anisotropy of electrical conductivity and insignificant changes in the quantum capacitance. Based on the obtained results, the prospects for using hybrid graphene/SWCNT(12, 6) films as a material for creating flexible electrodes of supercapacitors are predicted.

Detecting vortical structures in time-resolved volumetric flow fields

The detection of three-dimensional coherent vortical structures that get advected as well as deformed with time is a challenge. However, it is critical for the statistical analysis of these vortices, for example, the quasi-streamwise vortices (QSVs) in the near field of a turbulent shear layer, where cavitation inception typically occurs. These structures exhibit underlying correlations among different properties that can be derived from the velocity gradients. Exploiting these correlations, a pseudo-Lagrangian vortex detection method is proposed that uses k-means clustering based on vorticity magnitude and direction, values of λ2, strain rate structure, axial stretching, and location. The method facilitates the finding that QSVs have pressure minima that are lower than those in the surrounding flow, including the primary spanwise vortices. These minima typically appear after a period of axial stretching and before contraction events.

Elasto-capillary circumferential buckling of soft tubes under axial loading: existence and competition with localised beading and periodic axial modes

We provide an extension to previous analysis of the localised beading instability of soft slender tubes under surface tension and axial stretching. The primary questions pondered here are as follows: under what loading conditions, if any, can bifurcation into circumferential buckling modes occur, and do such solutions dominate localisation and periodic axial modes? Three distinct boundary conditions are considered: in case 1 the tube’s curved surfaces are traction-free and under surface tension, whilst in cases 2 and 3 the inner and outer surfaces (respectively) are fixed to prevent radial displacement and surface tension. A linear bifurcation analysis is conducted to determine numerically the existence of circumferential mode solutions. In case 1 we focus on the tensile stress regime given the preference of slender compressed tubes towards Euler buckling over axisymmetric periodic wrinkling. We show that tubes under several loading paths are highly sensitive to circumferential modes; in contrast, localised and periodic axial modes are absent, suggesting that the circumferential buckling is dominant by default. In case 2, circumferential mode solutions are associated with negative surface tension values and thus are physically implausible. Circumferential buckling solutions are shown to exist in case 3 for tensile and compressive axial loads, and we demonstrate for multiple loading scenarios their dominance over localisation and periodic axial modes within specific parameter regimes.

Increasing the Monolithic Nature of Masonry Made of Cellular Concrete Blocks by Using Polyurethane Foam Glue as a Masonry Mortar

This study is a continuation of previously published work [1]. The results of experimental determination of the strength of normal adhesion (under axial tension) in masonry made of autoclave–hardened cellular concrete blocks of compressive strength classes B1,5-B3,5 on cement mortars and polyurethane foam adhesives are presented. The tests were carried out in the laboratory of the Department “Reinforced Concrete and Stone Structures” of the Moscow State University of Civil Engineering (National Research University). The experiment was carried out on samples-cubes with a size of 150x150x150 mm, which were cut out of cellular concrete blocks, fastened (glued) together using masonry (binding) compositions. In the course of the study, it was found that when using various polyurethane foam glue compositions in masonry made of cellular concrete blocks of compressive strength classes B1,5–B3,5, the resistance to axial stretching over an unbound section (normal adhesion) of the masonry increases by approximately 9–25%. It was also found that the nature of the destruction of samples made on polyurethane foam adhesives (destruction occurs along the body of concrete), indicates the monolithic nature of the masonry. The analysis of the results obtained makes it possible to conclude that the resistance to axial tension along the unbound section of the masonry depends on the strength of the material from which the block is made, and not on the compressive strength of the masonry (binder) mortar used, as indicated in table 11 of SP 15.13330.2012 “Stone and reinforced masonry structures”. This factor must be taken into account when calculating masonry from autoclave-hardened cellular concrete blocks on polyurethane foam compositions.

Deformation Assessment of Stainless Steel Sheet Using a Shock Tube

In the present study, a high-velocity sheet metal forming experiment has been performed using a hemispherical end nylon striker inside the shock tube. The striker moves at a high velocity and impacts the sheet mounted at the end of the shock tube. Three different velocity conditions are attained during the experiment, and it helps to investigate the forming behavior of the material at different ranges of velocity conditions. Various forming parameters such as dome height, effective strain distribution, limiting strain, hardness, and grain structure distribution are analysed. The dome height of the material increases monotonically with the high velocity. The effective-strain also follows the similar variation and a bi-axial stretching phenomenon is observed. The comparative analysis with the quasi-static punch stretching process illustrates that the strain limit is increased by 40%-50% after the high-velocity forming. It is because of the inertial effect generated on the material during the high-velocity experiment, which stretches the sheet further without strain localization.

Coupled fluid and energy flow in fabrication of microstructured optical fibres

We consider the role of heating and cooling in the steady drawing of a long and thin viscous thread with an arbitrary number of internal holes of arbitrary shape. The internal holes and the external boundary evolve as a result of the axial drawing and surface-tension effects. The heating and cooling affects the evolution of the thread because both the viscosity and surface tension of the thread are assumed to be functions of the temperature. We use asymptotic techniques to show that, under a suitable transformation, this complicated three-dimensional free boundary problem can be formulated in such a way that the transverse aspect of the flow can be reduced to the solution of a standard Stokes flow problem in the absence of axial stretching. The solution of this standard problem can then be substituted into a system of three ordinary differential equations that completely determine the flow. We use this approach to develop a very simple numerical method that can determine the way that thermal effects impact on the drawing of threads by devices that either specify the fibre tension or the draw ratio. We also develop a numerical method to solve the inverse problem of determining the initial cross-sectional geometry, draw tension and, importantly, heater temperature to obtain a desired cross-sectional shape and change in cross-sectional area at the device exit. This precisely allows one to determine the pattern of air holes in the preform that will achieve the desired hole pattern in the stretched fibre.