Analysis of Dislocation-Induced Strain Field in an Idealized Wafer-Bonded Microstructure

The localized dislocation at the interface induces uneven strain distribution in two wafer-bonded layers. Because of the different elastic properties of two bonding layers and this uneven strain distribution, the bilayered microstructure deflects and deflection relaxes the strains. Depending on the microstructure dimensions, elastic properties and lattice parameters, the contribution of deflection to strain field can be very significant. The interface condition also plays an important role in relaxing strain. Two models capable of describing different interface conditions are used for the analysis and offer a more comprehensive study on the dislocation-induced strain field in a wafer-bonded bilayered microstructure. The combined effect of microstructure dimensions and interface condition on the strain is presented and compared.

Numerical Analysis of LEC Growth of GaAs with an Axial Magnetic Field

A set of numerical analyses for momentum and heat transfer For a 3 in. (0.075 m) diameter Liquid Encapsulant Czochralski (LEC) growth of single-crystal GaAs with or without all axial magnetic field was carried Out using the finite-element method. The analyses assume a pseudosteady axisymmetric state with laminar floats. Convective and conductive heat transfers. radiative heat transfer between diffuse surfaces and the Navier-Stokes equations for both melt and encapsulant and electric current stream function equations Cor melt and crystal Lire considered together and solved simultaneously. The effect of the thickness of encapsulant. the imposed magnetic field strength as well as the rotation rate of crystal and crucible on the flow and heat transfer were investigated. (C) 2002 Published by Elsevier Science Ltd.

Interface Layer Effect On The Stress Distribution Of A Wafer-Bonded Bilayer Structure

The interface layer plays an important role in stress transfer in composite structures. However, many interface layer properties such as the modulus, thickness, and uniformity are difficult to determine. The model developed in this article links the influence of the interface layer on the normal stress distribution along the layer thickness with the layer surface morphology before bonding. By doing so, a new method of determining the interfacial parameter(s) is suggested. The effects of the layer thickness and the surface roughness before bonding on the normal stress distribution and its depth profile are also discussed. For ideal interface case with no interfacial shear stress, the normal stress distribution pattern can only be monotonically decreased from the interface. Due to the presence of interfacial shear stress, the normal stress distribution is much more complex, and varies dramatically with changes in the properties of the interface layer, or the dimensions of the bonding layers. The consequence of this dramatic stress field change, such as the shift of the maximum stress from the interface is also addressed. The size-dependent stress distribution in the thickness direction due to the interface layer effect is presented. When the interfacial shear stress is reduced to zero, the model presented in this article is also demonstrated to have the same normal stress distribution as obtained by the previous model, which does not consider the interface layer effect.

A field model interpretation of crack initiation and growth behavior in ferroelectric ceramics: change of poling direction and boundary condition

Strain energy density expressions are obtained from a field model that can qualitatively exhibit how the electrical and mechanical disturbances would affect the crack growth behavior in ferroelectric ceramics. Simplification is achieved by considering only three material constants to account for elastic, piezoelectric and dielectric effects. Cross interaction of electric field (or displacement) with mechanical stress (or strain) is identified with the piezoelectric effect; it occurs only when the pole is aligned normal to the crack. Switching of the pole axis by 90degrees and 180degrees is examined for possible connection with domain switching. Opposing crack growth behavior can be obtained when the specification of mechanical stress sigma(infinity) and electric field E-infinity or (sigma(infinity), E-infinity) is replaced by strain e and electric displacement D-infinity or (epsilon(infinity), D-infinity). Mixed conditions (sigma(infinity),D-infinity) and (epsilon(infinity),E-infinity) are also considered. In general, crack growth is found to be larger when compared to that without the application of electric disturbances. This includes both the electric field and displacement. For the eight possible boundary conditions, crack growth retardation is identified only with (E-y(infinity),sigma(y)(infinity)) for negative E-y(infinity) and (D-y(infinity), epsilon(y)(infinity)) for positive D-y(infinity) while the mechanical conditions sigma(y)(infinity) or epsilon(y)infinity are not changed. Suitable combinations of the elastic, piezoelectric and dielectric material constants could also be made to suppress crack growth. (C) 2002 Published by Elsevier Science Ltd.

Effect of Fe content on the thermal stability and dynamic mechanical behavior of NdAlNiCu bulk metallic glasses

The dependence of microstructure and thermal stability on Fe content of bulk Nd60Al10Ni10Cu20-xFex (0 less than or equal to x less than or equal to 20) metallic glasses is investigated by means of differential scanning calorimetry (DSC), X-ray diffraction (XRD) and high-resolution transmission electron micrograph (HRTEM). All samples exhibit typical amorphous feature under the detect limit of XRD, however, HRTEM results show that the microstructure of Nd60Al10Ni10Cu20-xFex alloys changes from a homogeneous amorphous phase to a composite structure consisting of clusters dispersed in amorphous matrix by increasing Fe content. Dynamic mechanical properties of these alloys with controllable microstructure are studied, expressed via storage modulus, the loss modulus and the mechanical damping. The results reveal that the storage modulus of the alloy without Fe added shows a distinct decrease due to the main a relaxation. This decrease weakens and begins at a higher temperature with increasing Fe content. The mechanism of the effect of Fe addition on the microstructure and thermal stability in this system is discussed in terms of thermodynamics viewpoints. (C) 2004 Elsevier B.V. All rights reserved.

Finite element analysis on stresses field of normalized layer thickness within ceramic coating on aluminized steel

Multilayer ceramic coatings were fabricated on steel substrate using a combined technique of hot dipping aluminum(HDA) and plasma electrolytic oxidation(PEO). A triangle of normalized layer thickness was created for describing thickness ratios of HDA/PEO coatings. Then, the effect of thickness ratio on stresses field of HDA/PEO coatings subjected to uniform normal contact load was investigated by finite element method. Results show that the surface tensile stress is mainly affected by the thickness ratio of Al layer when the total thickness of coating is unchanged. With the increase of A] layer thickness, the surface tensile stress rises quickly. When Al2O3 layer thickness increases, surface tensile stress is diminished. 'Meanwhile, the maximum shear stress moves rapidly towards internal part of HDA/PEO coatings. Shear stress at the Al2O3/Al interface is minimal when Al2O3 layer and Al layer have the same thickness.

Effect of nonlinear wave-current interaction on flow fields and hydrodynamic forces

A fifth-order theory for solving the problem of interaction between Stokes waves and exponential profile currents is proposed. The calculated flow fields are compared with measurements. Then the errors caused by the linear superposition method and approximate theory are discussed. It is found that the total wave-current field consists of pure wave, pure current and interaction components. The shear current not only directly changes the flow field, but also indirectly does sx, by changing the wave parameters due to wave-current interaction. The present theory can predict the wave kinematics on shear currents satisfactorily. The linear superposition method may give rise to more than 40% loading error in extreme conditions. When the apparent wave period is used and the Wheeler stretching method is adopted to extrapolate the current, application of the approximate theory is the best.

Transient effect on ideally plastic stationary crack-tip fields

This paper analyses the transient effect on ideally plastic stationary crack-tip fields under mode I plane strain conditions, when the inertial forces are not negligible. It is shown that the governing equation for such a problem can be expressed in formal simplicity when referred to a system of moving curvilinear coordinates, which is a generalization of the system defined by the slip-line field in quasi-static plasticity. A perturbation method of solving the equations is described and illustrated by application to problems of ideally plastic stationary crack-tip fields when the inertia forces are not negligible.

Transient effect on ideally plastic stationary crack-tip fields

This paper analyses the transient effect on ideally plastic stationary crack tip fields under mode I plane strain conditions, when the inertial forces are not negligible. It is shown that the governing equation for such a problem can be expressed in formal simplicity when referred to a system of moving curvilinear coordinates, which is a generalization of the system defined by the slip-line field in quasi-static plasticity. A perturbation method of solving the equations is described and illustrated by application to problems of ideally plastic stationary crack tip fields when the inertial forces are not negligible.

A hall dynamo model for the reversed field pinch

A mechanism for the reversed field pinch (RFP) dynamo is proposed, based on the nonlinear Hall effect of a saturated helical MHD instability. The sign and magnitude of the effect are shown to be those required for the RFP dynamo. Predictions of the model are in accord with RFP fluctuation measurements.

Effect of current on the evolution of a solitary wave

In this paper, the effect of current on the evolution of a solitary wave is studied. The governing equation in the far field, KdV equation with variable coefficients, is derived. A solitary wave solution is obtained. The fission of a solitary wave is discussed, and the fissible region on the Q～h2-plane and the criterion of the number of the solitary waves after fission are found.

Chemical Nonequilibrium Effects on Flow Field for Reusable Launch Vehicles

High temperature chemical non-equilibrium phenomena have a great effect on the flow field around a reentry vehicle. A set of three dimensional Navier-Stokes equations have been solved by implicit finite volume NND scheme. Both ideal gas viscous flow and chemical non-equilibrium flow are calculated for a spherical-cone at a small angle of attack. The results of the two flows have been compared and the effect of chemical non-equilibrium has been analyzed. The effect of wall material's properties, such as catalysis and radiation were studied. The results are in good agreement with the referenced paper.

Effect of humidity on microstructure and properties of YBCO film prepared by TFA-MOD method

Epitaxial YBCO superconducting films were deposited on the single crystal LaAlO3 (001) substrate by metal organic deposition method. All YBCO films were fired at 820 degrees C in humidity range of 2.6%-19.7% atmosphere. Microstructure of YBCO thin films was analyzed by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). Superconducting properties of YBCO films were measured by four-probe method. XRD results showed that the second phase (such as BaF2)and a-axis-oriented grains existed in the films prepared at 2.6% humidity condition; a-axis-oriented grains increased in the film prepared at higher than 4.2% humidity condition; almost pure c-axias-oriented grains existed in the films fired at 4.2% humidity condition. Morphologies of the YBCO films showed that all films had a smooth and crack-free surface. YBCO film prepared at 4.2% humidity condition showed J(c) value of 3.3 MA/cm(2) at 77 K in self-field.

Two-Phase Flow In Anode Flow Field Of A Small Direct Methanol Fuel Cell In Different Gravities

An in-situ visualization of two-phase flow inside anode flow bed of a small liquid fed direct methanol fuel cells in normal and reduced gravity has been conducted in a drop tower. The anode flow bed consists of 11 parallel straight channels. The length, width and depth of single channel, which had rectangular cross section, are 48.0, 2.5 and 2.0 mm, respectively. The rib width was 2.0 mm. The experimental results indicated that when the fuel cell orientation is vertical, two-phase flow pattern in anode channels can evolve from bubbly flow in normal gravity into slug flow in microgravity. The size of bubbles in the reduced gravity is also bigger. In microgravity, the bubbles rising speed in vertical channels is obviously slower than that in normal gravity. When the fuel cell orientation is horizontal, the slug flow in the reduced gravity has almost the same characteristic with that in normal gravity. It implies that the effect of gravity on two-phase flow is small and the bubbles removal is governed by viscous drag. When the gas slugs or gas columns occupy channels, the performance of liquid fed direct methanol fuel cells is failing rapidly. It infers that in long-term microgravity, flow bed and operating condition should be optimized to avoid concentration polarization of fuel cells.

Ballistic Electron Transport In Hybrid Ferromagnet/Two-Dimensional Electron Gas Sandwich Nanostructure: Spin Polarization And Magnetoresistance Effect

We have theoretically investigated ballistic electron transport through a combination of magnetic-electric barrier based on a vertical ferromagnet/two-dimensional electron gas/ferromagnet sandwich structure, which can be experimentally realized by depositing asymmetric metallic magnetic stripes both on top and bottom of modulation-doped semiconductor heterostructures. Our numerical results have confirmed the existence of finite spin polarization even though only antisymmetric stray field B-z is considered. By switching the relative magnetization of ferromagnetic layers, the device in discussion shows evident magnetoconductance. In particular, both spin polarization and magnetoconductance can be efficiently enhanced by proper electrostatic barrier up to the optimal value relying on the specific magnetic-electric modulation. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3041477]