Electrodynamic fluidization of microparticles with a finite electrical conductivity

We report the results from statistical simulation of the electrodynamic fluidization of microparticles in an electric field with allowance for their finite electrical conductivity. The maximum attainable microparticle concentration is estimated and the form of the charge distribution function of the particles is discussed.Translated from Inzhenerno-fizicheskii Zhurnal, Vol. 60, No. 5, pp. 758–764, May, 1991.     

Weak discontinuities in a dissociating gas

Summary The effects of non-equilibrium dissociation and that of the wave front curvature on the propagation of weak discontinuities headed by wave fronts of arbitrary shape and their consequent formation into shock waves are examined. It is found that all compressive waves, except in one special case of converging waves, grow without bound only if the magnitude of the initial discontinuity associated with the wave exceeds a critical value. It is shown that, in this special case, the stabilizing influence of curvature for converging waves is not strong enough to overcome the instabilities associated with the gasdynamic phenomenon involved.

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Schwache Unstetigkeiten in einem dissoziierenden Gas

Zusammenfassung Es werden die Einflüsse der Nichtgleichgewichts-Dissoziation und die der Wellenfrontkrümmung auf die Ausbreitung schwacher, von allgemein geformten Wellenfronten vorangetriebener, Unstetigkeiten und ihre darauf folgende Aufsteilung zu Stoßwellen untersucht. Es wird gefunden, daß alle Verdichtungswellen mit Ausnahme eines Spezialfalles zusammenlaufender Wellen nur ohne Grenze anwachsen, wenn der Betrag der Anfangsunstetigkeit der Welle einen kritischen Wert überschreitet. Es wird gezeigt, daß in diesem speziellen Fall der stabilisierende Einfluß der Krümmung für zusammenlaufende Wellen nicht stark genug ist, um die dem gasdynamischen Phänomen zugeordneten Instabilitäten zu überwinden.

     

Arbitrary discontinuities in finite elements

A technique for modelling arbitrary discontinuities in finite elements is presented. Both discontinuities in the function and its derivatives are considered. Methods for intersecting and branching discontinuities are given. In all cases, the discontinuous approximation is constructed in terms of a signed distance functions, so level sets can be used to update the position of the discontinuities. A standard displacement Galerkin method is used for developing the discrete equations. Examples of the following applications are given: crack growth, a journal bearing, a non‐bonded circular inclusion and a jointed rock mass. Copyright © 2001 John Wiley & Sons, Ltd.     

Treatment of material discontinuities in finite element computations

We consider finite element analysis of problems with discontinuous material coefficients. For applications in which the material interface crosses an element, we develop special elements with an embedded flux constraint at the interface. This new procedure is compared with the standard finite element method with interface coincident with the element boundary and with an existing method proposed by Steven.¹ Supporting numerical studies are conducted and rates of convergence for the solution and interface flux are examined. Some local superconvergence behaviour is observed.     

Weak discontinuities in a non-equilibrium flow of a dusty gas

Summary The behavior of a discontinuity in flow gradients at the head of a disturbance propagating through a homogeneous mixture of gas and small dust particles has been studied. It is shown that the presence of dust particles results in increasing the shock formation time as compared with a similar pure-gas case. When the disturbance is arbitrarily small in amplitude, the solution to the first order in the whole disturbed domain is constructed and analysed. It is found that the concentration of solid particles has a decaying, effect on the shock strength as one, might expect.     

Weak discontinuities in relativistic magnetohydrodynamics in the presence of dissipative mechanisms

In this work the study of propagation of weak discontinuities in relativistic magnetohydrodynamics in the presence of dissipative mechanisms of finite electrical and heat conductivities, is carried out. It is shown that a weak discontinuity exists only in the fluids in which the pressure is proportional to the total energy density, if the first order partial derivatives of heat flux vector are continuous across the discontinuity surface. If the latter are discontinuous then singular surfaces exist in low temperature case but not in the ultrarelativistic case. In all these cases the role of dissipation is to cause damping of the wave while shocks can occur in the case of initially compressive waves.     

Numerical simulation of dynamic fracture using finite elements with embedded discontinuities

This paper presents the extension of some finite elements with embedded strong discontinuities to the fully transient range with the focus on dynamic fracture. Cracks and shear bands are modeled in this setting as discontinuities of the displacement field, the so-called strong discontinuities, propagating through the continuum. These discontinuities are embedded into the finite elements through the proper enhancement of the discrete strain field of the element. General elements, like displacement or assumed strain based elements, can be considered in this framework, capturing sharply the kinematics of the discontinuity for all these cases. The local character of the enhancement (local in the sense of defined at the element level, independently for each element) allows the static condensation of the different local parameters considered in the definition of the displacement jumps. All these features lead to an efficient formulation for the modeling of fracture in solids, very easily incorporated in an existing general finite element code due to its modularity. We investigate in this paper the use of this finite element formulation for the special challenges that the dynamic range leads to. Specifically, we consider the modeling of failure mode transitions in ductile materials and crack branching in brittle solids. To illustrate the performance of the proposed formulation, we present a series of numerical simulations of these cases with detailed comparisons with experimental and other numerical results reported in the literature. We conclude that these finite element methods handle well these dynamic problems, still maintaining the aforementioned features of computational efficiency and modularity.     

Strong and weak arbitrary discontinuities in spectral finite elements

Methods for constructing arbitrary discontinuities within spectral finite elements are described and studied. We use the concept of the eXtended Finite Element Method (XFEM), which introduces the discontinuity through a local partition of unity, so there is no requirement for the mesh to be aligned with the discontinuities. A key aspect of the implementation of this method is the treatment of the blending elements adjacent to the local partition of unity. We found that a partition constructed from spectral functions one order lower than the continuous approximation is optimal and no special treatment is needed for higher order elements. For the quadrature of the Galerkin weak form, since the integrand is discontinuous, we use a strategy of subdividing the discontinuous elements into 6‐ and 10‐node triangles; the order of the element depends on the order of the spectral method for curved discontinuities. Several numerical examples are solved to examine the accuracy of the methods. For straight discontinuities, we achieved the optimal convergence rate of the spectral element. For the curved discontinuity, the convergence rate in the energy norm error is suboptimal. We attribute the suboptimality to the approximations in the quadrature scheme. We also found that modification of the adjacent elements is only needed for lower order spectral elements. Copyright © 2005 John Wiley & Sons, Ltd.     

Ternary polyurethane nanocomposites with remarkable electrical conductivity

ABSTRACT

A series of polyurethane composites with constant 5 wt-% loading of 2D graphene nanosheets and varying levels of 1D silver nanowire (AgNW) were prepared by a solution mixing method. The electrical conductivity of composite films was measured using a 4-point probe method. An extremely high conductivity of 3,657?S?cm^–1 was achieved with a polyurethane composite containing 25?wt-% AgNW and 5?wt-% graphene, confirming that a combination of AgNW and graphene is very effective in producing conducting pathways to achieve high conductivity. The incorporation of AgNW and graphene was confirmed by scanning electron microscopy and energy dispersive spectrometry. Additionally, the results of tensile strengths and thermogravimetric analysis showed that the as-prepared polyurethane composite films possessed good mechanical properties and stable thermal properties.     

Boundary layer flow with variable tensor electrical conductivity

Summary Studies are made on laminar compressible magnetohydrodynamic (MHD) boundary layer flow over an insulated wall with variable tensor electrical conductivity. The effects of the electromagnetic loading parameter, the magnetic interaction parameter and the ratio of the wall temperature to the free stream temperature on the boundary layer physical parameters have been discussed.With 3 Figures     

溶剂萃取法制备高电导率聚苯胺

分别以丙酮、四氢呋喃(THF)以及THF与二甲基甲酰胺(DMF)混合溶剂对聚苯胺(PANI)进行萃取.萃取使PANI的平均分子量增大,增大程度与溶剂对PANI的溶解度成正比.电导率测定结果表明,萃取使PANI的电导率有效提高,其中THF与DMF混合溶剂萃取产物的电导率较未萃取前提高了近3倍.光谱测定结果表明,3种溶剂萃取都不会改变PANI的分子结构,但萃取后PANI的π电子共轭程度降低.结晶度测定结果表明,萃取使PANI的结晶度大幅下降.     

V带静电特性检测

根据国际标准ISO1813环形V带———静电特性及检测方法 ,设计出V带静电特性检测装置 ,并对几种不同材料配方的V带进行了检测和分析 ,为胶带在特殊工况下的应用提供了依据     

The effect of finite electrical conductivity of small-scale beam resonators on their vibrational response under electrostatic fields

International Journal of Mechanics and Materials in Design - Electrostatic actuation is one of the most commonly used methods for excitation and measurement in micro and nanoscale resonators. In...     

An augmented finite element method for modeling arbitrary discontinuities in composite materials

An augmented finite element method (“A-FEM”) is presented that is a variant of the method of Hansbo and Hansbo (Comput Methods Appl Mech Eng, 193: 3523–3540, 2004), which can fully account for arbitrary discontinuities that traverse the interior of elements. Like the method of Hansbo and Hansbo, the A-FEM preserves elemental locality, because element augmentation is implemented within single elements and involves nodal information from the modified element only. The A-FEM offers the additional convenience that the augmentation is implemented via separable mathematical elements that employ standard finite element nodal interpolation only. Thus, the formulation is fully compatible with standard commercial finite element packages and can be incorporated as a user element without access to the source code. Because possible discontinuities include both elastic heterogeneity and cracks, the A-FEM is ideally suited to modeling damage evolution in structural or biological materials with complex morphology. Elements of a multi-scale approach to analyzing damage mechanisms in laminated or woven textile composites are used to validate the A-FEM and illustrate its possible uses. Key capabilities of the formulation include the use of meshes that need not conform to the surfaces of heterogeneities; the ability to apply the augmented element recursively, enabling modeling of multiple discontinuities arising on different, possibly intersecting surfaces within an element; and the ease with which cohesive zone models of nonlinear fracture can be incorporated.     

Graphene-wrapped hybrid spheres of electrical conductivity

We present a simple approach for the fabrication of monodisperse electroconductive hybrid spheres using graphene sheet-wrapping via ionic interaction-based self-assembly. The graphene sheets partially charged with anion, which were prepared by controlled chemical reduction of graphite oxide, were mixed with monodisperse polymer nanospheres containing cationic surface charge to form ionic self-assembled hybrid spheres of core-shell structure. The resulting graphene-wrapped hybrid spheres were found to have graphene layer thickness of ca. 10 nm and to exhibit electrical conductivity of 1.33-4.21 S/m as well as monodisperse distributions in shape and diameter.     

A method for modelling microstructural material discontinuities in a finite element analysis

A new method is proposed for studying the effects of various microstructural material discontinuities, within a body, in a finite element analysis. The material discontinuities are accounted for by introducing a transformation strain in those regions. This formulation leads to two matrix equations; the first corresponds to the finite element analysis of the body without material discontinuities, and the second accounts for the microstructure. An important feature of the new method is that the first equation is solved only once, then the second equation can be solved repetitively for different microstructures. Thus, it is possible to study the effect of different microstructures within the body without reanalysing the entire body. It is expected that this method will be particularly useful in materials research to study the mechanisms that occur in materials at the microstructural level. The transformation strain formulation is reviewed, and the matrix equations for the new method are derived. Several numerical examples are presented to illustrate the versatility of the new method.     

High-temperature electrical conductivity of aluminium nitride

The electrical conductivity of hot-pressed polycrystalline aluminium nitride doped with oxygen and beryllium was measured as a function of temperature from 800 to 1200° C and over a range of nitrogen partial pressure from 10² to 10⁵ Pa. The effect of beryllium dopant, the independence of conductivity from nitrogen partial pressure, and the observed activation energy suggested extrinsic electronic species or aluminium vacancies as charge carriers. Polarization measurements made with one electrode blocking to ionic species indicated that the aluminium nitride with oxygen impurity was an extrinsic electronic conductor.