Complicated Microstructure Research Articles

Strain analysis of trabecular bone using time-resolved X-ray microtomography

A micro-radiographic system composed of microfocus X-ray tube and a large flat panel detector has been adapted for imaging complicated internal microstructure of trabecular bone under applied deformation. To capture the deforming microstructure a load was applied in small increments while the sample was tomographically scanned. Reconstruction of the internal structure is provided using backprojection algorithm for equiangular cone-beam projection data. From the reconstructed cross-sections a finite element (FE) model of the microstructure was developed and loaded according to the experiment. Deformation behavior of the FE model was compared to the experimentally determined response of the sample.

Development of a Thermal Transport Database for Air Plasma Sprayed ZrO2-Y2O3 Thermal Barrier Coatings

Thermal diffusivities of air plasma sprayed (APS) thermal barrier coatings (TBCs) were measured by the laser flash method. The data were used to calculate thermal conductivity of TBCs when provided with density and specific heat data. Due to the complicated microstructure and other processing-related parameters, thermal diffusivity of TBCs can vary as much as three- to four-fold. Data collected from over 200 free-standing ZrO2-7-8wt.%Y2O3 TBCs are presented. The large database gives a clear picture of the expected “band” of thermal diffusivity values. When this band is used as a reference for thermal diffusivity of a specific TBC, the thermal transport property of the TBC can be more precisely described. This database is intended to serve researchers and manufacturers of TBCs as a valuable resource for the evaluation of TBCs.

鋼材の微視的不均質を考慮した応力解析のためのFEM-MD結合数値解析法の提案

FEM-MD combined method is proposed for the microscopic stress analysis of steels. In this numerical method, Finite Element Method (FEM) is applied to the stress analysis inside grains, and Molecular Dynamics (MD) is applied to the calculation of the atomic configuration near the grain boundary in order to consider the microscopic heterogeneity and the deformation near the grain boundary that influences the stress distribution. Slip length between two grains caused by the mismatch of the displacement near the grain boundary is calculated by FEM. Slip resistance, which is necessary to calculate slip length, is obtained by calculating the atomic configuration near the grain boundary by MD. The combination of FEM and MD is realized by using slip resistance in FEM and slip length in MD. The validity of modeling of the deformation near the grain boundary is investigated by comparing the deformation near the grain boundary calculated by FEM-MD combined method to that observed in the experiment in the case of a load applied to the specimen. Calculated slip length coincides with measured one. FEM-MD combined method is applied to the investigation of the influence of change in the grain shape caused by the thermal history such as the weld zone upon the strength characteristic. The high stress region tends to increase in the case of the grain diameter larger and it is indicated that grain coarsening due to the weld thermal history increases the possibility of the crack initiation. FEM-MD combined method is expected to be helpful in investigating the mechanism of fracture or the strength characteristic of the complicated microstructure such as the weld zone by evaluating the microscopic stress distribution.

Filament to filament bridging and its influence on developing high critical current density in multifilamentaryBi2Sr2CaCu2Ox round wires

Increasing the critical current density (Jc) of the multifilamentaryround wire Ag/Bi2Sr2CaCu2Ox(2212) requires understanding its complicated microstructure, in which extensive bridges betweenfilaments are prominent. In this first through-process quench study of 2212 round wire, wedetermined how its microstructure develops during a standard partial-melt process andhow filament bridging occurs. We found that filaments can bond together in the melt state.As 2212 starts to grow on subsequent cooling, we observed that two types of 2212 bridgesform. One type, which we call Type-A bridges, forms within filaments that bonded in themelt; Type-A bridges are single grains that span multiple bonded filaments. Theother type, called Type-B bridges, form between discrete filaments through 2212outgrowths that penetrate into the Ag matrix and intersect with other 2212 outgrowthsfrom adjacent filaments. We believe the ability of these two types of bridges tocarry inter-filament current is intrinsically different: Type-A bridges are high-Jc inter-filament paths whereas Type-B bridges contain high-angle grain boundaries and are typicallyweak linked. Slow cooling leads to more filament bonding, more Type-A bridges and a doubling ofJc without changing the flux pinning. We suggest that Type-Abridges create a 3D current flow that is vital to developing highJc in multifilamentary 2212 round wire.

Investigation of structural colors inMorphobutterflies using the nonstandard-finite-difference time-domain method: Effects of alternately stacked shelves and ridge density

We use the nonstandard-finite-difference time-domain (NS-FDTD) method to investigate the interaction of light with the complicated microstructures in the Morpho butterfly scales, which produce the well-known brilliant blue coloring. The NS-FDTD algorithm is particularly suitable to analyze such complex structures because the calculation can be performed in a short time with high accuracy on a relatively coarse numerical grid. We analyze (1) the microstructure obtained directly by binarizing an electron microgram of the cross section of a scale, (2) the reflection and diffraction properties of three model structures--flat, alternating, and tree-shaped alternating multilayers, and (3) an array of alternating multilayers with random noise superposed on the height of the structures. We found that the actual microstructure well reproduced the reflection spectrum in a blue region by integrating the reflection intensities over all the reflection angles. Under normal incidence, the flat multilayer mainly stresses on multilayer interference except for shorter wavelengths, while alternating multilayer rather enhances the effect of diffraction grating due to longitudinally repeating structure by strongly suppressing the reflection toward the normal direction. In the array of alternating multilayers, the reflection into larger angles is considerably suppressed and the spectral shape becomes different from that expected for a single alternating multilayer. This suppression mainly comes from the scattering of reflected light by adjacent structures, which is particularly prominent for the TM mode. Thus a clear difference between the TE and TM modes is observed with respect to the origin of spectral shape, though the obtained spectra are similar to each other. Finally, the polarization dependence of the reflection and the importance of the alternating multilayer are discussed.

Elastic properties of lamellar Ti–Al alloys

Abstract Ti–Al intermetallic alloys have a great potential for high-temperature lightweight applications. They also have rather complicated microstructure and sophisticated behaviour under thermal–mechanical loading. In many cases, Ti–Al component optimization is sufficient when using effective elastic properties of these alloys. Computation of such effective properties is difficult due to various orientations of the phases micro-constituents. Here a simple micromechanical model is applied to calculate effective stiffness and other elastic parameters of Ti–Al alloys as function of composition, orientation and temperature. The dependence of these properties is computed and possibility of simplified, quasi-isotropic or orthotropic properties application is discussed.

Drying of the Silica/PVA Suspension: Effect of Suspension Microstructure

The particle/polymer/solvent suspension system shows complicated microstructure. When the suspension system experiences an industrial process such as coating and drying, the system experiences microstructural change. In this study, we investigated the microstructural change during the drying of a silica/polyvinyl alcohol (PVA) suspension, with an emphasis on suspension stability. We controlled the amount of PVA adsorption on the silica surface by adjusting the pH (1.5, 3.6, and 9) of the silica/PVA suspension. The amount of adsorption was measured to increase with decreasing pH, and the degree of flocculation in the silica/PVA suspension became stronger with decreasing pH. However, through the measurement of stress development during drying and the observation of film microstructure after drying, we found that the more strongly flocculated suspension became a more disperse, close-packed film after drying. By evaluating the potential energy, we could suggest the role of adsorbed polymers in structural change during the drying of the silica/PVA suspension. As pH decreases, the adsorbed polymers could bridge the particles and lead to a flocculated suspension before drying. As the solvent evaporates during drying, the adsorbed polymers introduce steric repulsion between approaching particles, leading to a change from flocculated to dispersed microstructure. This implies that the required silica/PVA film performance and the microstructure of the silica/PVA suspension can be tailored through controlling the polymer adsorption in suspension.

Change in contribution of block boundary to macroscopic strength of 10Cr–1Mo–1W–VNbN steel due to creep

Outstanding strength performance of high Cr ferritic steels is attributable to the combined strengthening mechanisms of matrix and various grain boundaries. However, it is by no means easy to separate the contributions of such strengthening factors and quantitatively understand them because of extremely fine and complicated microstructures. In this study, the instrumented indentation test was carried out to clarify the change in contribution of “block” during creep. The materials used in this study were turbine rotor steel (Fe–10Cr–1Mo–1W–VNbN). The indentation test was applied to the as-tempered and creep damaged specimens under the maximum loads ranging from 1 to 1000 mN. The test results revealed that the decrease in contribution of block was the predominant factor controlling the material deterioration, namely, softening at the early stage of the creep life. This decrease in block's contribution was caused by the decrease in resistance of the block boundary to deformation.

Effect of homogenization on the hot-deformation ability and dynamic recrystallization of Mg–9Gd–3Y–0.5Zr alloy

Two states of Mg–9Gd–3Y–0.5Zr (wt.%) (GW93) alloy, as-cast (note as F state) and homogenized (note as T4 state), were hot compressed at strain rate of 0.1 s −1 and temperatures range from 623 K to 723 K. The stress-strain curves were established and volume fractions of dynamic recrystallized (DRX) grains were determined using point counting method. The results show that flow stresses are sensitive to the compression temperature and pretreatment state. Comparing with as-cast alloy, T4 state alloy has a higher flow stress and strain hardening rate θ, more complicated deformation microstructures, a smaller dynamic recrystallization rate and Avrami exponents. The phenomena are the results of the difference of initial nucleation sites and eutectic particles stimulated nucleation (EPSN) of two states. The initial nucleation sites of as-cast alloy include the original grain boundaries and eutectic particles, but as for T4 alloy, only original coarse grain boundaries can be act as nucleation sites.

Carbides in stainless steels: Results from ab initio investigations

The useful properties of steels are due to a complicated microstructure containing iron and chromium carbides. Only some basic physical properties of these carbides are known with high precision, although the carbides may have a vital impact on the performance and longevity of the steel. To improve on this situation, we have performed extensive density-functional theory calculations of several carbides. The quantitative results are in perfect agreement with the relative empirical stability of the carbides. Also, in contradiction with experimental data, we find that Cr23C6 responsible for the hardness of stainless steels is not the most stable chromium-dominated carbide.

A micro-mechanical approach to swelling behavior of unsaturated expansive clays under controlled drainage conditions

The focus of this work is to elucidate the effect of drainage conditions on the swelling behavior of unsaturated expansive clay soils using a new drainage controlled uniaxial swelling (DCUS) cell developed by the authors. The researc`h would aim at identification of the complicated micro-structures and distinguishing the mechanisms for the micro deferred alteration phenomena (the alteration of the swelling media by the end of the swelling process) of the porous swelling media, by swelling under K 0 constraint, constant volume condition using scanning electron microscopy (SEM) technique taking into account the influence of drainage condition as the remarkable environmental factor. It shall be noted that the micro deferred alteration concerns the phenomena in which the swelling media would be altered (in particle's arrangement and size) in micro-scale, by the end of the swelling process and not during the swelling process. Three types of clay have been evaluated of wide range of plasticities. Results demonstrate the promotion of swelling pressure for specimens compacted statically at optimum moisture level and below the optimum value, as the drainage condition converts to multilateral drainage. Furthermore, irrespective of the type of clay, the sensitivity of swelling pressure value to the drainage conditions increases as the initial dry unit weight increases.

이광자 흡수 광환원 공정을 이용한 마이크로 금속형상 제작의 정밀화에 관한 연구

A two-photon induced photoreduction process suggests a possibility for fabricating complicated metallic microstructures which can be applied to 3-D micro-circuits and optical devices, etc. The process employs the photoreduction of silver ions in a metallic solution which is composed of metallic salt (AgNO3) and watersoluble polymer ((poly(4-styrenesulfonique acid) 18wt. % in H2O, (C8H8O3S)n)). In this process, the improvement of the resolution and the uniformity of fabricated metallic structures are important issues. To address these problems, continuous forming window (CFW) is obtained from a parametric study on the conditions of laser power and scanning velocity and the direct seed generation (DSG) method is proposed. Silver nano particles are uniformly generated in a metallic solution through the DSG method, which enables the decrease of a laser power to trigger the photoreduction of silver ions as well as the increase of metal contents in a metallic solution. So the two-photon induced photoreduction property of a metallic solution is improved. Through this work, precise silver patterns are fabricated with a minimum line width of 400 nm.

Evaluation of Young's modulus of high stiffness aluminium die cast alloys using nanoindentation technique

A new correction method which is appropriate for the evaluation of Young's modulus of crystalline compounds has been examined and established to correct the size effect. Using a nanoindentation test and the established correction method, Young's moduli of primary Si phase, Al–(Fe,Mn)–Si and Al–Ni compound phases in the hypereutectic Al–Si die cast alloys were evaluated to be 182±9, 208±29 and 170±4 GPa respectively. The rule of mixtures for Young's modulus and the area fraction of each phase were applied to evaluate the Young's modulus of aluminium die cast alloys. The Young's modulus calculated by the rule of mixtures is in good agreement with the value obtained by a tensile test. The combination of the rule of mixtures and nanoindentation test is an effective approach to the precise evaluation of the Young's modulus of aluminium die cast alloys having complicated microstructures.

Mechanical and acid-etching properties of Bi2O3–ZnO–B2O3 glass-containing ceramic fillers

The properties of the composite, having a complicated microstructure, are decided by many factors such as those of glass matrix, crystal phases, fillers, and holes. We investigated how the addition of ceramic fillers to the glass matrix affects the mechanical and etching properties of the glass composite by forming new crystal phases. Different amounts of two fillers, ZnO and Al2O3, were added to a glass frit consisting of Bi2O3–ZnO–B2O3. It was sintered at 550 °C for 30 min. Based on the results of this study, the porosity and degree of crystallization of the composites could be controlled by adjusting the content of the ZnO and Al2O3 fillers. Therefore, porosity and degree of crystallization formed by the reaction between a glass matrix and fillers influence the mechanical and etching properties of the composite.

Transient flow patterns in a microfluidic chip with a complicated microstructure

AbstractThe transient flow patterns of the boiling flow in a microfluidic chip with a complicated microstructure were studied at low mass fluxes and high heat fluxes. The periodic flow pattern in the timescale of milliseconds and the stratified flow pattern were observed. For a specific separated zone, the liquid film thickness was increased along the flow direction and the dry‐out always occurred earlier at the microchannel upstream rather than downstream. However, for different microchannel zones, the dry‐out took place earlier in the downstream zone. It was determined that the low liquid Froude number was responsible for the formation of the stratified flow. The large boiling number resulted in a large shear stress at the vapor–liquid interface, leading to the accumulation of the liquid in the microchannel downstream, causing the increased liquid film thickness along the flow direction. © 2008 Wiley Periodicals, Inc. Heat Trans Asian Res, 37(4): 224–231, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20201

Mechanical analysis of functionally graded plates based on the input data of metallographic diagrams

A microelement method for scale-span analysis of material microstructure and member macro response has been proposed. Instead of material parameter input for traditional mechanical analysis, the method is based on the input of metallographic diagram information. In order to express the material microstructure, this method arranges concentrated microelements in ordinary finite element before calculation, and transfers the node degrees of freedom of each microelement into the ones of the same finite element via compatibility conditions. This method can realize direct transition analysis from material microstructure to macro responses of members, while computation elements and degrees of freedom are equal to those of ordinary FEM. Based on the complicated microstructure diagrams proposed by material metallographic diagram, the mechanics responses of functionally graded plates are calculated and 3-D distributions of macro-mechanical variables and identical stress lines tendency on microstructure are given.

Modeling of properties and motions of an inhomogeneous one-dimensional continuum of a complicated Cosserat-type microstructure

We consider an approach to modeling the properties of the one-dimensional Cosserat continuum [1] by using the mechanical modeling method proposed by Il’yushin in [2] and applied in [3]. In this method, elements (blocks, cells) of special form are used to develop a discrete model of the structure so that the average properties of the model reproduced the properties of the continuum under study. The rigged rod model, which is an elastic structure in the form of a thin rod with massive inclusions (pulleys) fixed by elastic hinges on its elastic line and connected by elastic belt transmissions, is taken to be the original discrete model of the Cosserat continuum. The complete system of equations describing the mechanical properties and the dynamical equilibrium of the rigged rod in arbitrary plane motions is derived. These equations are averaged in the case of a sufficiently smooth variation in the parameters of motion along the rod (the long-wave approximation). It was found that the average equations exactly coincide with the equations for the one-dimensional Cosserat medium [1] and, in some specific cases, with the classical equations of motion of an elastic rod [4–6]. We study the plane motions of the one-dimensional continuum model thus constructed. The equations characterizing the continuum properties and motions are linearized by using several assumptions that the kinematic parameters are small. We solve the problem of natural vibrations with homogeneous boundary conditions and establish that each value of the parameter distinguishing the natural vibration modes is associated with exactly two distinct vibration mode shapes (in the same mode), each of which has its own frequency value.

Finite Element Analysis on Microstructure Evolution of Hot Ring Rolling Process

Hot ring rolling (HRR) is a 3D unsteady-state and coupled thermo-mechanical process, the metal undergoes complicated unequal deformation and microstructure evolution. In this paper a 3D rigid-plastic and coupled thermo-mechanical FEM model for hot ring rolling was developed based on DEFORM3D platform, taking dynamic recrystallization (DRX) volume fraction, DRX grain size, recystallization volume fraction and average grain size as objects, the mechanism of material microstructure evolution and distributions in HRR process are thoroughly studied. The results show that: with the HRR progressing, the DRX volume fraction, volume fraction, DRX grain size and average grain size have the similar distributing characteristic, and the distribution zones expand from a small local area into the whole ring strip, then diffuse to the mid-layer of ring with small deformation, their distributions become more uniform. Meanwhile with increase of deformation, the values of the DRX volume fraction and recrystallization volume fraction augment, i.e. the degree of recystallization increases. The DRX grain size also augments due to local high temperature, while the average grain size decreases. In general during HRR process the distributions of DRX volume fraction, recrystallization volume fraction, DRX grain size, and average grain size are ununiform due to unequal deforming in HRR process.

Positivity and time behavior of a linear reaction–diffusion system, non‐local in space and time

AbstractWe consider a general linear reaction–diffusion system in three dimensions and time, containing diffusion (local interaction), jumps (nonlocal interaction) and memory effects. We prove a maximum principle and positivity of the solution and investigate its asymptotic behavior. Moreover, we give an explicit expression of the limit of the solution for large times. In order to obtain these results, we use the following method: We construct a Riemannian manifold with complicated microstructure depending on a small parameter. We study the asymptotic behavior of the solution to a simple diffusion equation on this manifold as the small parameter tends to zero. It turns out that the homogenized system coincides with the original reaction–diffusion system. Using this and the facts that the diffusion equation on manifolds satisfies the maximum principle and its solution converges to a easily calculated constant, we can obtain analogous properties for the original system. Copyright © 2008 John Wiley & Sons, Ltd.

Modeling of properties and motions of an inhomogeneous one-dimensional continuum of a complicated Cosserat-type microstructure

Modeling of properties and motions of an inhomogeneous one-dimensional continuum of a complicated Cosserat-type microstructure