Heterogeneous Distribution Of Particles Research Articles

Computational Evaluation of Elasto-Viscoplastic Deformation and Strength of Rubber Blended Semi-crystalline Polymer

In order to clarify the elasto-viscoplastic deformation behavior and strength of rubber blended semi-crystalline polymer, micro- to mesoscopic mechanical behavior was modeled by using large deformation finite element homogenization method. In this model, dimension of mesostructure is identified by the volume fraction of interface region around the rubber particles. The effects of strain rate and the size of rubber particles on the mesoscopic true stress—strain relation, strain rate distribution in mesoscopic area, and change in mesoscopic morphology with deformation are investigated by numerical simulation of uniaxial tensile deformation of semi-crystalline polymer with nonuniformly distributed rubber particles. A series of computational simulations clarified that mechanical behavior of blend polymer is strongly affected by the size of rubber particles. Mesoscopic true stress—strain relationship shows softening for blend polymer with large rubber particles, which is closely related to the distribution of strain rate on mesoscopic scale. When the rubber particles are large, local strain rate is highly concentrated in the ligament area between adjacent rubber particles, while it distributes in larger area of semi-crystalline polymer matrix in case of small rubber particles. The difference in these localized deformation leads to characteristic change in the size and shape of rubber particles with straining. Nonuniform deformation in mesoscopic area caused by heterogeneous rubber particle distribution is emphasized by high strain rate and large rubber particles. Furthermore, maximum mean stress generated in semi-crystalline polymer matrix is very high when the size of rubber particles is smaller than or ligament thickness is larger than a specific value. The specific thickness corresponds to the critical value for brittle-ductile transition of rubber blended semi-crystalline polymer obtained by impact test.

Nonlinear viscoelasticity, percolation and particles dispersibility of PVA/aluminum hydroxide composite gels

We investigated the rheological properties of a composite gel consisting of poly(vinyl alcohol) and aluminum hydroxide particles, and discussed the relation among nonlinear viscoelasticity, percolation and particles dispersibility. The dynamic viscoelastic measurements revealed that the storage modulus at volume fractions ϕ < 0.04 satisfied with the Krieger–Dougherty equation representing random dispersion of particles. The storage modulus did not show any nonlinear viscoelastic response at ϕ < 0.04. However, the storage modulus at ϕ > 0.06 took a value which is far larger than that expected by the equation, indicating heterogeneous distribution of particles. Additionally, the nonlinear viscoelastic response was recognized clearly at ϕ > 0.06, suggesting a partial contact between particles. The storage modulus at ϕ > 0.18 showed a further increase satisfied with the percolation theory, therefore, the volume fraction is considered to be the percolation threshold of 3-dimension. Microscopic observations of the gel showed a clear network with a mesh size of few μm that is considered to be a partial network of particles.

Grain Growth Behaviors in a Friction-Stir-Welded ZK60 Magnesium Alloy

Grain growth during annealing of a friction-stir-welded (FSWed) ZK60 magnesium alloy has been investigated. We have found that (1) thermal stability exhibited in different parts of stirred zone (SZ) was very different, (2) grain growth was fairly abnormal, and (3) grain growth was directional and shapes of developed grains resembled flow patterns inherent to FSWed structure. We have shown that all peculiarities of the grain growth behaviors can be explained in terms of heterogeneous distribution of second phase particles resulted from FSW.

Functional and Structural Characterization of Rhodopsin Oligomers

A major question in G protein-coupled receptor signaling concerns the quaternary structure required for signal transduction. Do these transmembrane receptors function as monomers, dimers, or larger oligomers? We have investigated the oligomeric state of the model G protein-coupled receptor rhodopsin (Rho), which absorbs light and initiates a phototransduction-signaling cascade that forms the basis of vision. In this study, different forms of Rho were isolated using gel filtration techniques in mild detergents, including n-dodecyl-beta-D-maltoside, n-tetradecyl-beta-D-maltoside, and n-hexadecyl-beta-D-maltoside. The quaternary structure of isolated Rho was determined by transmission electron microscopy, demonstrating that in micelles containing n-dodecyl-beta-D-maltoside, Rho exists as a mixture of monomers and dimers whereas in n-tetradecyl-beta-D-maltoside and n-hexadecyl-beta-D-maltoside Rho forms higher ordered structures. Especially in n-hexadecyl-beta-D-maltoside, most of the particles are present in tightly packed rows of dimers. The oligomerization of Rho seems to be important for interaction with its cognate G protein, transducin. Although the activated Rho (Meta II) monomer or dimers are capable of activating the G protein, transducin, the activation process is much faster when Rho exists as organized dimers. Our studies provide direct comparisons between signaling properties of Meta II in different quaternary complexes.

Simulation of the mechanical properties of an aluminum matrix composite using X-ray microtomography

Aluminum-based particulate-reinforced metal matrix composites (PMMCs) frequently have a heterogeneous distribution of reinforcement particles whether produced by a powder or liquid processing route. The applicability of X-ray microtomography (XMT) for the characterization of this heterogeneity, and its influence on final properties, was investigated for the case of a powder blended and extruded AA2124 matrix with Ni particulate. Three-dimensional image analysis techniques were used to quantify the embedded Ni particle size distribution and the extent and texture of clusters formed. The XMT data were exploited as a rapid method to generate a microstructurally accurate and robust three-dimensional mesh for input for finite-element modeling. Simulation of the elastoplastic response of the material showed excellent correlation with experimental results.

Effect of a heterogeneous distribution of particles on the formation of banded grain structure in wrought Alloy 718

Alloy 718 is known to be sensitive to interdendritic segregation formed during ingot solidification. The occurrence of banded grain structures under heat treating conditions close to 1000 ° C related to interdendritic segregation is often reported. In order to have a better understanding of this microstructural evolution, an extensive experimental program has been carried out. Consequently, a model taking into account the selective dissolution of δ -phase (Ni 3Nb) is proposed. A grain growth simulation by Monte-Carlo method is then used to illustrate the grain structure evolution in a banded particle distribution. By comparing experimental data and computer simulation, the relationship between the Monte-Carlo step and the real time is assessed and the range of parameters when heterogeneous microstructures appear is specified.

An estimation of three-dimensional finite element crystal geometry model for the strength prediction of particle-reinforced metal matrix composites

Particles reinforced metal matrix composites have higher specific modulus, higher specific strength, and better properties at elevated temperatures and better wear resistance than monolithic alloys. However, the discrepancy of the material properties between the reinforced particle, SiC p, and the matrix material, Al6061, makes some residual stresses inside of metal matrix composites. For example, the coefficient of thermal expansion (CTE) of Al6061 is five times higher than that of SiC p. This work investigated SiC p/Al6061 composites at high temperatures in the microscopic viewpoint by three-dimensional elasto-plastic finite element analysis and compares the analytical results with the experimental ones. The shape of particle is various and particles distribution is not homogeneous in experimental specimen. However, the theoretical model is not able to consider the non-uniform shape and heterogeneous distribution of particles. Therefore, it was assumed that the particle distribution is homogeneous and shape of particles is global and hexahedral. The types of particle distribution were three—simple-cubic array (SC array), face-centered cubic array (FCC array) and hexahedral array (HEX array).

Microstructure refinement and mechanical properties of severely deformed Al–Mg–Li alloys

Experiments have been conducted to investigate the possibility of producing aluminium aerospace-alloys, with properties similar to those of the powder metallurgical alloy AA5091, by the potentially cheaper route of spray-casting and severe deformation. Two alloys with compositions based on the commercial alloy AA5091 were spray-cast to obtain a large density of Al 3(Zr,Ti) dispersoids as a substitute for the oxide and carbide particles present in AA5091. The materials were subsequently severely deformed using equal channel angular extrusion (ECAE) to effective strains as high as ten. After deformation the grain sizes in both materials were as fine as 0.3–0.6 μm, while the fraction of high angle grain boundary area was >70%. The severely deformed alloys were stable up to 400 °C, but at higher temperatures abnormal grain growth was observed initiated by the heterogeneous distribution of dispersoid particles inherited from the spray-castings. Encouragingly, for similar heat-treatment conditions, the yield strengths of the experimental materials were found to be comparable to the values specified for the commercial alloy AA5091 while the ductilities were up to three times higher.

Some Results from X-Ray Computed Tomography Applied to Metal Matrix Composites

This study presents computed tomography (CT) results from a medical scanner carried out on metal matrix composite materials obtained by a casting process. In order to test the capabilities of the CT technique to study the flaws in the sample, few precautions have been taken during the manufacturing process, resulting in composite ingots with many flaws (porosity, segregation, etc.). The mold was modified to obtain a concentration of particles at the bottom of the ingot. CT images and scanning electronic microscopy images were taken at the same slice surface and show good agreement in the distribution of particles and porosity. The spatial resolution of the medical scanner (12 pairs of lines/cm) lets us distinguish between, at the mesoscopic scale, heterogeneous distribution of particles and porosity, but not individual flaws.

A model for damage in a clustered particulate composite

Abstract Previous models for the deformation of two-phase materials containing hard, brittle particles have been extended to allow the simultaneous treatment of damage and particle clustering. The model is based on a self-consistent analysis and uses an incremental, tangent modulus approach. Two problems are tackled. In the first we treat the effect of a distribution of particle sizes on damage development. We show that once the effect of the size distribution on the overall level of damage has been calculated a single damage parameter can be used to determine the stress–strain behavior with good precision. This validates the approach taken in our previous work. In the second problem we incorporate damage (in the form of particle cracking) into an elastic–plastic deformation model for a material containing a heterogeneous distribution of particles. The level of damage, as well as the local stress and strain, is allowed to vary between regions with different particle densities. The results indicate that clustering has a small but significant weakening effect on two-phase materials. This is in contrast with the effect of clustering in the absence of damage when a strong strengthening effect results. The results can be rationalized in terms of load redistribution between regions during the course of deformation.

La distribution des émetteurs α peu solubles déposés après inhalation dans les tissus pulmonaires : nouveaux abords méthodologiques

We have developed an autoradiograp hic method to provide representative images of dose rate and dose distribution in the lungs after actinide oxide inhalation. This was based on the study of 30 um thick dry sections obtained from 200 um thick cryostat sections. In this case, solid track detector had a recording yield similar to that obtain for 5 um thin sections and the resolution was less than 90 um. Using this method, we visualized a heterogeneous particle distribution as soon as 3 months after exposure of rats to (U, Pu)0 2 aerosols. Key-words - autoradiography, lungs, inhalation, actini.de oxides, dosimetry.

Freeze-fracture analysis of the effects of intermediates of the phosphatidylinositol cycle on fusion of rough endoplasmic reticulum membranes

While searching for the identity of the effector of the putative GTP-binding protein involved in fusion of rough endoplasmic reticulum (RER) cell-free incubation conditions were found permitting fusion in a GTP-independent manner. Membrane fusion was obtained using medium required to study synthesis of phosphatidylinositol (PI). We now report on the effects of various co-factors and intermediates of the PI cycle on the interaction of rough microsomes. By freeze-fracture, fusion of rough microsomes was defined as the appearance of fracture-planes of membrane larger than those of unincubated membrane. Cytosine triphosphate (CTP, 3 mM) in the presence of 2 mM MnCl 2 was most effective in stimulating fusion. Guanosine triphosphate (GTP) at the same concentration, could substitute for CTP to stimulate fusion, ATP, ITP, UTP and guanosine 5′-[γ-thio]triphosphate (GTPγS) could not. When combined together in the same medium CTP potentiated the effect of GTP. Arachidonic acid (20 μg/ml) also stimulated fusion in the presence of MnCl 2. This led to the appearance of large fracture-planes of membrane with a heterogeneous distribution of intramembranous particles. Other saturated fatty acids at the same concentration did not stimulate fusion. Phosphatidylinositol (PI, 50 μg) and 2 mM MnCl 2 had a similar effect as arachidonic acid and MnCl 2 in stimulating fusion. The PI effect was largely augmented in the presence of CTP. Our results are consistent with the concept that metabolism of phospholipids may modulate GTP-dependent fusion of RER membranes.

A study of the relationship among pulpal response, microbial microleakage, and particle heterogeneity in a glass-ionomer-base material

This investigation was designed to study the pulpal responses to glass-ionomer base materials that differ in particle size distribution. The study was carried out according to the BSI (1980) recommendations for testing restorative materials in vivo. The base materials caused more pulpal inflammation than the control material, Kalzinol, although by an indirect mechanism. A significant association was demonstrated in the statistical model between bacterial presence within the experimental cavity and pulpal inflammation. The type of restorative material has no direct association with the degree of inflammation, although the model suggests that it exerts an indirect influence via its antibacterial properties, and hence its influence on microbial microleakage. The base material, with a heterogeneous particle distribution, was associated with greater bacterial microleakage. Particle size distribution, therefore, has some effect upon bacterial microleakage, but, because of its complex effect upon several physical properties of materials, further studies are indicated.

Heterogeneous distribution of conductive particles in polymer blends studied by electron microscopy.

The distribution state of carbon black (CB) was observed in polymer blends by scanning (SEM) and transmission (TEM) electron microscopies. CB distributed unevenly in the polymer blend. There were two types of distribution. In the first type, CB particles were predominantly distributed in one phase of the blend matrix. In the second type, the fillers concentrate at the interface of two polymers. This heterogeneous distribution of fillers in a polymer blend matrix was mainly due to the difference in affinity of CB particles to each component of the polymer blend. In high density polyethylene/polypropylene blend, CB particles were mainly located in the polyethylene phase. When oxidated CB particles were used, however, they were concentrated at the interface of the two polymer phases.

High-strain deformation processing of NiW alloys

This paper discusses the potential of NiW alloys of differing initial microstructures, for high-strain cold deformation processing, and thus their suitability for development as heavily deformed, high strength in situ composites. Varying initial phase morphologies and tungsten volume fractions were produced by variations in initial processing. Liquid-phase sintered structures, containing 48 vol.% W, can be cold rolled to true strains of 2.4. They presumably could be cold worked further, but size limitations imposed by our processing capability prevented that being done in this study. Likewise, low volume fraction (of less than 15 vol.%) tungsten alloys, produced by casting of a hypoeutectic nickel-rich alloy and by transient liquid-phase sintering, can be cold rolled to the same strain as the liquid-phase sintered NiW structure. In contrast, as-cast arc melted alloys cannot be cold drawn to any extent at room temperature. They can be made capable of limited drawability by subjecting them to a coarsening heat treatment, which also spheroidizes eutectic tungsten to some extent, prior to cold working. The limited malleability of this alloy appears to be related to the heterogeneous distribution of nondeforming tungsten particles. Fracture surfaces of material that failed during drawing are populated heavily by such particles. The strengths of cold worked NW alloys of the present study exceed those of comparably deformed directionally solidified NiW eutectic alloys, at least up to deformation strains of 2.4. Since the latter type of alloy manifests extensive work hardening for deformation strains greater than 3.0, we expect this would also hold for the alloys described in this paper. Thus the NiW system, composed of a strong, tough nickel phase and a linear work hardening tungsten phase, is a likely candidate for development as a strong, tough, heavily deformed in situ composite.

Temporal variation of trace element concentrations in selected rainfall events at Tsukuba, Japan

Using ICP emission spectrometry, the temporal variation of the concentration of dissolved Al, Fe. Si, Mn, Zn. Cu and B in rain-water during an event was observed at Tsukuba, Japan. The relationships between trace element variations and rainfall characteristics were compared with those for major elements such as Na, K, Ca and Mg. In many cases, the concentration of minor elements was highest in the initial stage. The exception was in rain with very short duration or very strong intensity at the initial stage of rainfall. No significant relationship was observed between rainfall intensity and soluble elemental concentration, although in a few cases AI, Zn, Na and Fe showed an inverse correlation with rainfall intensity. It was found that the concentration of minor elements such as Fe, Al and Zn fluctuated, whereas those of Na and other major elements changed smoothly. This difference is considered to be caused by differences in the scavenging process of the elements as well as the heterogeneous and varying distribution of atmospheric particles which supply minor elements in rain-water.

Computational method for coal slurry pipelines with heterogeneous size distribution

Design of industrial slurry pipelines is usually performed by applying semi-empirical procedures, requiring a significant experimental study for each project. This paper presents a new computational technique for coal slurry pipelines based on a two-phase flow analysis. The calculation model gives numerical solutions for the concentration, velocity and particle size distributions in the pipeline cross-section, which can be integrated to provide mean velocities and flowrates, delivered concentration, etc. Design calculations for headlosses can be performed using this approach for any set of given conditions: the properties of the transported material, carrier liquid and pipeline. The computational technique was developed using data for uniform sand—water mixtures flowing in pipelines of 51.5 mm, 263 mm and 495 mm diameter. The approach is extended to coal—water mixtures with heterogeneous size distribution of particles, and tested with experimental measurements in pipelines of 158 mm and 495 mm diameter. The model is shown to be a useful vehicle for generalizing experimental measurements and scale-up to headloss predictions.

Effects of cholesterol on lipid organization in human erythrocyte membrane.

The molar ratio of cholesterol to phospholipid (C/P) in human erythrocyte membrane is modified by incubating the cells with liposomes of various C/P ratios. The observed increase in cell surface area may be accounted for by the addition of cholesterol molecules. Fusion between liposomes and cells or attachment of liposomes to cells is not a significant factor in the alteration of C/P ratio. Onset temperatures for lipid phase separation in modified membranes are measured by electron diffraction. The onset temperature increases with decreasing C/P ration from 2 degrees C at C/P = 0.95 to 20 degrees C at C/P = 0.5. Redistribution of intramembrane particles is observed in membranes freeze-quenched from temperatures below the onset temperature. The heterogeneous distribution of intramembrane particles below the onset temperature suggests phase separation of lipid, with concomitant segregation of intramembrane protein into domains, even in the presence of an intact spectrin network.

Cortical changes in Spisula eggs upon insemination

Freeze—fracture replicas of fertilized and unfertilized Spisula eggs demonstrate a heterogeneous distribution of intramembranous particles within the plasmalemma. There is a structural reorganization of microvilli and an approximate twofold increase in particles on the protoplasmic face of the plasma membrane following insemination. These transformations in microvillar structure and intramembranous particle number may be involved in establishing a block to polyspermy.