Plastic Strain Localization in Polycrystalline Titanium. Numerical Simulation

Russian Physics Journal - The paper presents numerical simulation of polycrystalline titanium deformation in terms of the crystal plasticity theory. Based on the experimental data, a...     

Dynamic Strength of a Titanium Alloy with an Electron-Beam-Modified Surface

Data are presented of plane-wave experiments aimed at determining the dynamic strength of 3M titanium alloy with a surface processed by a microsecond electron beam. It has been found that the dynamic strength of processed specimens is higher than that of unprocessed specimens. Metallographic examination of test specimens has revealed spallation macrofracture inside the unprocessed specimens and spallation microfracture at the interface between the hardened layer and the substrate in the beam-processed specimens.     

Localization of Surface Spectra

We study spectral properties of the discrete Laplacian H on the half-space with random boundary condition ; the V(n) are independent random variables on a probability space and λ is the coupling constant. It is known that if the V(n) have densities, then on the interval [-2(d+1), 2(d+1)] (=σ(H ₀), the spectrum of the Dirichlet Laplacian) the spectrum of H is P-a.s. absolutely continuous for all λ [JL1]. Here we show that if the random potential P satisfies the assumption of Aizenman–Molchanov [AM], then there are constants λ _d and Λ _d such that for |λ|<lambda; _d and |λ|> Λ _d the spectrum of H outside σ(H ₀) is P-a.s. pure point with exponentially decaying eigenfunctions. Received: 3 December 1998 / Accepted: 27 May 1999     

Model of a Surface Liquid-Like Layer of Ice

The previously developed model of an intermediate phase of ice with a liquid system of hydrogen bonds has been applied to describe a quasiliquid surface layer. This approach leads to a two-component model of a quasiliquid ice surface layer. In the outer part of the layer, both the proton and oxygen sublattices are melted, constituting water or the Thomson sublayer. In the inner part of the layer, only the proton sublattice is melted, whereas the oxygen sublattice holds its structure (the liquid state of the system of hydrogen bonds or the Faraday sublayer). The proposed model gives correct-in-magnitude estimates of various physical characteristics of the layer, explains the contradiction between the Faraday and Thomson hypotheses, and is consistent with recent experimental results and numerical studies.     

Specificities of Ultrasonic Vibrations upon Strain Localization

Doklady Physics - Powerful ultrasonic vibrations of a rigid body that arise during shock-wave loading are the result of the interaction of compression and unloading waves with the faces of the...     

Plastic Strain Localization and Its Stages in Al-Mg Alloys

The paper describes an experimental technique based on the use of a Vic-3D contactless digital optical system and digital image correlation for research in the mechanical behavior of a solid and its plastic deformation with space-time inhomogeneities. Using this technique, we analyze the evolution of inhomogeneous strain and local strain rate fields in AMg2m alloy at constant uniaxial tension rates. The analysis reveals quasi-periodic strain field homogenization in jerky flow: alternating phases of active local plastic flow (shear banding) and macroscale strain levelling. Also analyzed are the parameters of localized microscale plastic flow such as the height and width of shear bands, their velocity, and coefficient of plastic strain inhomogeneity. From a series of mechanical tests, the influence of the specimen geometry and loading rate on these parameters is estimated.     

MHD Boundary Layer Flow of a Non-Newtonian Fluid on a Moving Surface with a Power-Law Velocity

A theoretical analysis for MHD boundary layer flow on a moving surface with the power-law velocity is presented. An accurate expression of the skin friction coefficient is derived. The analytical approximate solution is obtained by means of Adomian decomposition methods. The reliability and efficiency of the approximate solutions are verified by numerical ones in the literature.     

Boundary Layer Flow over a Curved Surface Imbedded in Porous Medium

This research is made to visualize the boundary layer flow by a curved stretching sheet embedded in porous medium. The geometry is bended(curved), therefore the curvilinear coordinates are used to model the present problem.Fluid is electrically conducting with the presence of uniform magnetic field. The governing non-linear partial differential equation reduces to non-linear ordinary differential equations by using the dimensionless suitable transformations. The numerical solutions are obtained by using the method bvp4c from MATLAB. The effects of curvature parameter, nondimensional magnetic parameter, and porosity parameter on the velocity field and skin friction coefficient are examined.The skin friction profile enhances with enhancing the values of porosity and magnetic parameter. Comparison of the present results with the existing results in the literature for the flat surface is also given.     

RTV Silicone Rubber Filled with Surface Modified Montmorillonite

The surface modification of pristine montmorillonite (MMT) with four kinds of coupling agents for reinforcement of the room temperature vulcanized vinyl-terminated polydimethylsiloxane (RTV PDMS) networks was investigated. The four coupling agents containing γ-glycidoxypropyltrimethoxysilane (KH-560), γ-methacryloxypropyltri methoxysilane (KH-570), isopropyl trioleic titanate (NDZ-105), and stearic acid (SA) without N, P, or S compounds were used because the coupling agents harmless to the platinum catalyst used normally in the curing of RTV vinyl-terminated PDMS. The interaction between MMT particles and coupling agents was confirmed by diffused reflectance infrared spectroscopy (DR-FTIR) tests. By scanning electron microscopy (SEM) characterization, surface modified MMT was dispersed heterogeneously in the PDMS matrix for all four coupling agents. By X-ray diffraction (XRD) characterization, the interlayer distances of the four surface modified MMT were not changed. Dielectric tests showed that the dielectric constant and dielectric loss of PDMS filled with KH-560, KH-570, and SA treated MMT were decreased comparing with those of PDMS filled with pristine MMT. With the increasing content of MMT treated with KH-570, the dielectric constant and dielectric loss value of PDMS composites increased.     

Studying Strain Localization in Brittle Materials during the Brazilian Test

Russian Physics Journal - Sintered yttrium-stabilized zirconia is numerically and experimentally investigated during the Brazilian test. The strain and fracture of homogeneous and inhomogeneous...     

Localization of Excitations near a Thin Defect Layer with Nonlinear Properties,Separating Linear and Nonlinear Crystals

Technical Physics - It is shown that localized and quasi-local states exist near a thin defect layer with nonlinear properties, separating a linear medium from a Kerr-type nonlinear medium....     

Localization of Surface Plasmon Waves in Hybrid Photodetectors with Subwavelength Metallic Arrays

The spectral characteristics of the hole photocurrent in plasmon photodetectors based on Ge/Si heterostructures with Ge quantum dots combined with regular arrays of subwavelength apertures of various shapes in a gold film on the semiconductor surface are investigated. Dispersion relations characterizing the propagation of surface plasmon waves along the metal–semiconductor interface are determined from the dependences of the photocurrent on the angle of incidence of light. It is established that the plasmonic enhancement of the photocurrent in rectangular aperture array is suppressed as compared to that in circular and square aperture arrays. It is found that, in hybrid structures with rectangular apertures, there exists a range of wave vectors where the energy of surface plasmons is independent of the wave vector of incident radiation. The results are explained by the excitation of dipole modes localized at rectangular apertures with a large aspect ratio by light waves.     

Simulation of the Interaction of Graphene with a Copper Surface Using a Modified Morse Potential

JETP Letters - A new carbon–copper interaction potential is proposed to simulate the moiré structure of graphene on the copper surface. It is shown that the resulting moiré...     

Characteristics of Photonic Bandgap Fibres with Hollow Core＇s Inner Surface Coated by a Layer Material

Hollow core＇s inner surface coating in a photonic bandgap fibre （PBCF） is investigated by means of finite element method. The coat material and thickness-dependence dispersion curve and group velocity dispersion are numerically studied. The coating with materials of low index or small thickness will rise up the dispersion curve but will not induce surface modes. However, coating with materials of high index or big coat thickness will induce surface modes and avoided-crossings. By varying coat material＇s refractive index and thickness, the appearances of surface modes and avoided-crossings can be changed. It is found that the avoided-crossing can enormously enlarge the negative dispersion which can find applications in dispersion compensation. We numerically achieve a negative dispersion as large as -21416.15ps/nm/km. The results give a physical insight into the propagation properties of PBGFs with the hollow core coated by a layer of material and are of crucial significance in the applications of PBGF coating.     

Physicochemical Processes Accompanying Plastic Strain Localization under Pulsed Loading

Technical Physics - Analysis of the development of deformations under pulsed loading has shown the decisive role of powerful ultrasonic vibrations of a sample in the standing wave mode. The effect...     

Variations in the Strain Parameters of Titanium Nickelide during Martensitic Transformation Cycling

Doklady Physics - The results of analyzing the long-term variations in the strain rate of a TiNi element during martensitic transformation cycling have been reported. It is shown that the factors...