Inhomogeneity of density and mechanical properties of A357 aluminum alloy backward extruded in semi-solid state

The inhomogeneity of density and mechanical properties of A357 aluminum alloy in the semi-solid state were investigated.Numerical simulation and backward extrusion were adopted to study the preparation of cup shells.The results show that the relative density of the wall is the lowest in samples,and that of the base is the highest.With increasing the billet height,more time is needed for relative density of the corner to reach the maximum value,and the relative densities in every region improve evidently with increasing the pressure.The tensile stress was simulated to be the largest at the corner,and the hot tearings were forecasted to mainly appear at the corner too.By employing proper billet height and pressure,the extruded samples consisted of fine and uniform microstructures,and can obtain excellent mechanical properties and Brinell hardness.

A BEEM Study on Effects of Annealing Temperature on Barrier Height Inhomogeneity of CoSi_2/Si Contact Formed in Co-Ti-Si Systems

Ultra thin epitaxial CoSi 2 films are fabricated by solid state reaction of a deposited bilayer of Co(3nm)/Ti (1nm) on n Si(100) substrates at different temperatures.The local barrier heights of the CoSi 2/Si contacts are determined by using the ballistic electron emission microscopy (BEEM) and its spectroscopy (BEES) at low temperature.For CoSi 2/Si contact annealed at 800℃,the spatial distribution of barrier heights,which have mean barrier height of 599meV and a standard deviation of 21meV,obeys the Gaussian Function.However,for a sample that is annealed at 700℃,the barrier heights of it are more inhomogenous.Its local barrier heights range from 152meV to 870meV,which implies the large inhomogeneity of the CoSi 2 film.

非均匀强激光场下正负电子对的产生

随着强激光技术领域的不断突破,使得能量转化成物质的施温格过程的实验指日可待.在这样的背景下,在接近实际强激光的模型中理论研究施温格效应至关重要.本文采用量子场论模拟方法在非均匀电场中研究施温格效应的空间特性.首先,发现在能量保持不变的情况下电场的空间尺度显著影响正负电子对的产生率、动量和空间分布.正负电子对的动量和空间分布显示,当电场的空间尺度增大时,因为电场强度变小,所以产生的正负电子对无法及时被分开,抑制正负电子对的产生.最后,用连续性方程研究正负电子对的产生位置分布,发现正负电子对的产生位置分布与电场强度分布是对应的,电子和正电子的产生位置分离一个康普顿波长.此研究结果展示了施温格效应的空间特性,同时解释了弱电场下施温格效应的抑制机制.这些结论在人们常采用的均匀电场近似研究中无法得到.我们的研究对检测施温格实验中的正负电子对具有重要的指导意义.

Detecting Inhomogeneity in Daily Climate Series Using Wavelet Analysis

A wavelet method was applied to detect inhomogeneities in daily meteorological series, data which are being increasingly applied in studies of climate extremes. The wavelet method has been applied to a few well- established long-term daily temperature series back to the 18th century, which have been ＂homogenized＂ with conventional approaches. Various types of problems remaining in the series were revealed with the wavelet method. Their influences on analyses of change in climate extremes are discussed. The results have importance for understanding issues in conventional climate data processing and for development of improved methods of homogenization in order to improve analysis of climate extremes based on daily data.

Influence of Inhomogeneity on the Estimation of Mean and Extreme Temperature Trends in Beijing and Shanghai

Inhomogeneities in the temperature series from Beijing and Shanghai are analyzed, using the detailed histories of both sets of observations. The major corrections for different periods range from ?0.33 to 0.6°C for Beijing and ?0.33 to 0.3°C for Shanghai, Annual mean and extreme temperature series are deduced from the daily observations and trends in the adjusted and unadjusted series are compared. The adjusted yearly mean temperatures show a warming trend of 0.5°C/ century since the turn of this century and an enhanced one of 2.0°C/ century since the 1960s. In contrast, the unadjusted data show a twice this value trend for Shanghai but little trend for Beijing at the long-term scale and overestimate the recent warming by 50%–130%. Beijing experienced a decrease of frequency of the extremes together with a cooling during the 1940s–1970s and an increase of frequency of extremes together with a warming since then. The trends of frequency of extremes at Shanghai were more or less opposite. It is implied that the regional trends of strong weather variations may be different even when the regional mean temperatures coherently change. Key words Inhomogeneity - Daily temperature series - Climatic warming - Extreme temperature The study was supported by the China NKBRSF Project G 1999043400, IAP/ DF and CAS project (KZ951-A1-402).

Experimental verification of effect of horizontal inhomogeneity of evaporation duct on electromagnetic wave propagation

The evaporation duct which forms above the ocean surface has a significant influence on electromagnetic wave propagation above 2 GHz over the ocean. The effects of horizontal inhomogeneity of evaporation duct on electromagnetic wave propagation are investigated, both in numerical simulation and experimental observation methods, in this paper. Firstly, the features of the horizontal inhomogeneity of the evaporation duct are discussed. Then, two typical inhomogeneous cases are simulated and compared with the homogeneous case. The result shows that path loss is significantly higher than that in the homogeneous case when the evaporation duct height （EDH） at the receiver is lower than that at the transmitter. It is also concluded that the horizontal inhomogeneity of the evaporation duct has a significant influence when the EDH is low or when the electromagnetic wave frequency is lower than 13 GHz. Finally, experimental data collected on a 149-km long propagation path in the South China Sea in 2013 are used to verify the conclusion. The experimental results are consis- tent with the simulation results. The horizontal inhomogeneity of evaporation duct should be considered when modeling electromagnetic wave propagation over the ocean.

Local inhomogeneity of mechanical properties in stir zone of friction stir welded AA1050 aluminum alloy

The local inhomogeneity of the stir zone in friction stir welded face-centered cubic metal was investigated,which has multiple activated slip systems during plastic deformation,by selecting commercial AA1050 aluminum alloy as an ideal experimental material.The local inhomogeneity was evaluated by uniaxial tensile tests using small samples with a 1 mm gauge length.The corresponding microstructural parameters such as grain size,misorientation angle distribution,and micro-texture,were quantified by the backscattered electron diffraction technique.A comprehensive model was used to reveal the microstructure−mechanical property relationship.The experimental results showed that the uniaxial tensile property changes significantly across the weld.The maximum ultimate tensile strength(UTS)occurred in the center of the stir zone,which was 99.0 MPa.The weakest regions were located at the two sides of the stir zone.The largest difference value in UTS reached 14.9 MPa,accounting for 15%of the maximum UTS.The analysis on the structure−mechanical property relationship suggests that the micro-texture change with the location formed during the rotational material flow is the main reason for the local inhomogeneity.

ANTI-PLANE SHEAR WAVES SCATTERING FROM A PARTIALLY DEBONDED MAGNETO-ELECTRO-ELASTIC CIRCULAR CYLINDRICAL INHOMOGENEITY

This article presents an analysis of the scattering of anti-plane shear waves from a single cylindrical inhomogeneity partially bonded to an unbounded magneto-electro-elastic matrix. The magneto-electric permeable boundary conditions are adopted. The crack opening displacement is represented by Chebyshev polynomials and a system of equations is derived and solved for the unknown coefficients. Some examples are calculated and the results are illustrated. The results show that the COD increases when the piezomagnetic coefficient of the inhomogeneity bonded to the piezoelectric matrix becomes larger, and that the COD decreases when the piezomagnetic coefficient of the matrix with the piezoelectric inhomogeneity increases.

Interaction between a screw dislocation and an elastic elliptical inhomogeneity with interfacial cracks

The elastic interaction between a screw dislocation and an elliptical inhomogeneity with interfacial cracks is studied. The screw dislocation may be located outside or inside the inhomogeneity. An efficient complex variable method for the complex multiply connected region is developed, and the general solutions to the problem are derived. As illustrative examples, solutions in explicit series form for complex potentials are presented in the case of one or two interfacial cracks. Image forces on the dislocation are calculated by using the Peach-Koehler formula. The influence of crack geometries and material properties on the image forces is evaluated and discussed. It is shown that the interfacial crack has a significant effect on the equilibrium position of the dislocation near an elliptical-arc interface. The main results indicate, when the length of the crack goes up to a critical value, the presence of the interfacial crack can change the interaction mechanism between a screw dislocation and an elliptical inclusion. The present solutions can include a number of previously known results as special cases.

Zone inhomogeneity with the random asymmetric simple exclusion process in a one-lane system

In this paper we use theoretical analysis and extensive simulations to study zone inhomogeneity with the random asymmetric simple exclusion process （ASEP）. In the inhomogeneous zone, the hopping probability is less than 1. Two typical lattice geometries are investigated here. In case A, the lattice includes two equal segments. The hopping probability in the left segment is equal to 1, and in the right segment it is equal to p, which is less than 1. In case B, there are three equal segments in the system; the hopping probabilities in the left and right segments are equal to 1, and in the middle segment it is equal to p, which is less than 1. Through theoretical analysis, we can discover the effect on these systems when p is changed.

Equilibrium position of misfit dislocation dipole and critical parameters of buried strained nanoscale inhomogeneity in system of viscoelastic matrix

A theoretical model was suggested which describes the generation of the misfit dislocation dipole in the system of the viscoelastic matrix containing a circular stiff nanoscale inhomogeneity.The critical condition of misfit dislocation dipole and the solution of equilibrium position were given.The influence of the ratio of shear modulus,the misfit strain and viscosity on the equilibrium of the dislocation and critical parameter of inhomogeneity was investigated.The result shows that the equilibrium position de increases with the increase of the ratio of original shear modulus and the effect decreases with the increase of viscosity of matrix.Along with the increase of viscosity of matrix,de first increases and then decreases and possesses maximum value when t=0.3τ and tends to a stable value when t≥1.0τ.Along with the increase of viscosity of matrix,Rc first decreases and then increases and possesses minimum value when t=0.3τ and tends to a stable value when t≥1.0τ.

Effect of microstructure inhomogeneity on mechanical properties of different zones in TA15 electron beam welded joints

The effects of microstructure inhomogeneity on the mechanical properties of different zones in TA15 electron beam welded joints were investigated using a micromechanics-based finite element method.Considering the indentation size effect,the mechanical properties for constituent phases of the base metal(BM) and heat affected zone(HAZ) were determined by the instrumented nano-indentation test.The macroscopic mechanical properties of BM and HAZ obtained from the tensile test agree well with the numerical results.The incompatible deformation between the constituent phases tends to localize along the softer primary phase a where failure usually initiates in form of localized plastic strain.Compared with the BM,the mechanical properties of constituent phases in the HAZ differ substantially,leading to more serious strain localization behavior.

Influences of anisotropy and inhomogeneity on supporting pressure of tunnel face with kinematical approach

Based on the active failure mechanism generated by a spatial discretization technique, the stability of tunnel face was studied. With the help of the spatial discretization technique, not only the anisotropy and inhomogeneity of the cohesion but also the inhomogeneity of the internal friction angle was taken into account in the analysis of the supporting forces. From the perspective of upper bound theorem, the upper bound solutions of supporting pressure were derived. The influence of the anisotropy and heterogeneity on the supporting forces as well as the failure mechanisms was discussed. The results show that the spatial discretization characteristics of cohesion and internal frictional angle impose a significant effect on the supporting pressure, which indicates that above factors should be considered in the actual engineering.

Deformation inhomogeneity due to sample-anvil friction in cylindrical compression test

Finite element(FEM)analysis was used to systematically evaluate the inhomogeneity of deformation in cylindrical samples with various sample-anvil friction coefficients,m.It was found that the level of friction strongly influences the deformation homogeneity,which increases significantly with the friction coefficient although the overall geometry of the samples almost remains the same when m >0.4.The position,at which the effective strain along the maximum radial direction in a compressed sample is equal to the equivalent strain of the sample,does not vary greatly with respect to both equivalent strain of the sample and m.Hardness measurements of compressed cylindrical 5056B Al alloy samples revealed a change of effective strain distribution similar to that revealed by FEM analysis.There exists a quantitative relationship between the hardness and the effective strain if no recrystallization or recovery occurs during the compression process.

Influence of radial forging process on strain inhomogeneity of hollow gear shaft using finite element method and orthogonal design

Due to the current trend towards lightweight design in automotive industry,hollow stepped gear shafts for automobile and its radial forging process are widely investigated.Utilizing coupled finite element thermo-mechanical model,radial forging process of a hollow stepped gear shaft for automobile was simulated.The optimal combination of three process parameters including initial temperature,rotation rate and radial reduction was also selected using orthogonal design method.To examine the strain inhomogeneity of the forging workpiece,the strain inhomogeneity factor was introduced.The results reveal that the maximum effective strain and the minimum effective strain appeared in the outermost and innermost zones of different cross sections for the hollow stepped gear shaft,respectively.Optimal forging parameters are determined as a combination of initial temperature of 780°C,rotation rate of 21°/stroke and radial reduction of 3 mm.

Effects of Aerosol Vertical Inhomogeneity on the Upwelling Radiance and Satellite Remote Sensing of Surface Reflectance

There are two widely used radiative models without consideration of aerosol inhomogeneity for satellite remote sensing application, the Homogeneous Model and the Two-layer Model with aerosol in the lower layer. In this paper, effects of the aerosol vertical inhomogeneity on upwelling radiance and satellite remote sensing of surface reflectance are analyzed through numerical simulations by using two models. As shown in the simulations by using 24 representative aerosol models, there is often a considerably large error in upwel-ling radiance calculated by two models (Homogeneous and Two-layer) for the short wavelength channel with strong molecular scattering, owing to the difference between molecular and aerosol scattering proper-ties. For the long wavelength channel, the error is small if aerosol optical parameters are less variable with height, but it could also be significant if there are aerosol layers with different scattering phase functions and single scattering albedo. The radiance errors by the Homogeneous Model and the Two-layer Model can be up to 31.4% and 31.5% for the clean atmosphere, and in case of turbid atmosphere 67.8% and 59.2%, respectively. The radiance error could result in a large uncertainty of surface reflectance retrievals, especially for the short wavelength channel and the strongly absorbing aerosol. For the turbid atmosphere with strong-ly absorbing aerosol, the Homogeneous Model and the Two-layer Model are not suitable for atmospheric correction application. Key words Satellite remote sensing - Aerosol inhomogeneity - Surface reflectance - Radiance

Electrolyte inhomogeneity induced lithium plating in fast charging lithium-ion batteries

Fast charging capability of lithium-ion batteries is in urgent need for widespread economic success of electric vehicles. However, the application of the fast charging technology often leads to the inevitable lithium plating on the graphite anode, which is one of the main culprits that endanger battery safety and shorten battery lifespan. The in-depth understanding of the initiation of lithium metal nucleation and the following plating behavior is a key to the development of fast charging cells. Herein, we investigate the overlooked effect of the non-uniform distribution of electrolyte on lithium plating during fast charging. Prior lithium plating occurs on the saturated lithium-graphite compounds in the anode region with sufficient electrolyte since the lithium-ion transport is blocked in the anode region lacking electrolyte. The uniform distribution of electrolyte is crucial for the construction of safe lithium-ion batteries especially in fast charging scenarios.

Annealing temperature influence on the degree of inhomogeneity of the Schottky barrier in Ti/4H–SiC contacts

Tung＇s model was used to analyze anomalies observed in Ti/Si C Schottky contacts. The degree of the inhomogeneous Schottky barrier after annealing at different temperatures is characterized by the ‘T0anomaly＇ and the difference（△Φ）between the uniformly high barrier height（Φ0B） and the effective barrier height（Φeff B）. Those two parameters of Ti Schottky contacts on 4H–Si C were deduced from I–V measurements in the temperature range of 298 K–503 K. The increase in Schottky barrier（SB） height（ΦB） and decrease in the ideality factor（n） with an increase measurement temperature indicate the presence of an inhomogeneous SB. The degree of inhomogeneity of the Schottky barrier depends on the annealing temperature, and it is at its lowest for 500-°C thermal treatment. The degree of inhomogeneity of the SB could reveal effects of thermal treatments on Schottky contacts in other aspects.

Thermohaline structure inhomogeneity associated with polynia at the northern margin of Emery Ice-shelf

Based on the hydrographic data in austral summer during the 22nd Antarctic Expedition of China(2005/2006),some features can be found about the northern margin of Emery ice shelf as follows.The heat content in the surface layer(0-50 m) at the eastern end and the western end of the ice-shelf margin is much higher than that at the middle.The upper mixing-layer depth and the seasonal thermocline depth at the middle of the ice-shelf northern margin are much shallower than those at the both ends.However there is much less difference between the middle and the ends in the bottom layer.The remote sensing photos show that the inhomogeneity in the surface-layer water is closely related to the spatial distribution of the floes and polynia in the area.

Analytic solution for a circular nano-inhomogeneity in a finite matrix

The Gurtin-Murdoch model has found wide applications in analyzing the mechanical behaviors of nanocomposites with surface/interface effect. In the existing literature, the matrix is usually assumed to be infinite and the surface/interface effect is considered only at the inhomogeneity-matrix interface. This assumption is indeed valid as the matrix is usually at macroscale rather than nanoscale. However, if the size of the matrix decreases to the nanoscale too, the surface/interface effect will have to be considered at the outer boundary of the matrix. In this paper, the plane deformation of a circular nano-inhomogeneity embedded inside a finite circular matrix (which implies the matrix is also at nanoscale) is investigated. The stress boundary conditions are given at the inhomogeneity-matrix interface and the outer boundary of the matrix by the G-M model. The analytic solution for the stress field is finally obtained through the complex variable method. The results show that the stress field inside the inhomogeneity is still uniform (size-dependent) when the surface/interface effect is considered. In addition, the stress field inside the bulk (including the inhomogeneity and the matrix) can be influenced not only by the size and elastic constant of the inhomogeneity, but also by those of the matrix.