Showing papers on "Volume fraction published in 1995"
TL;DR: In this paper, the viscosity of partially crystallized Mg3Al2Si3O12 melts has been measured under uniaxial compression in the interval 1010 - 1013 poise as a function of the volume fraction of crystals.
Abstract: The viscosity of partially crystallized Mg3Al2Si3O12 melts has been measured under uniaxial compression in the interval 1010 - 1013 poise as a function of the volume fraction of crystals. These inclusions are well-rounded spherulites of aluminous enstatite, having the same composition as the melt, and whose growth rate is negligible at the temperature of the measurements. The viscosity increases by less than 1 order of magnitude for crystal fractions ϕ of 40 vol % and remains Newtonian up to the maximum stress exerted, namely 1 kbar. The Einstein-Roscoe equation, η = η0 (1 - ϕ/ϕm)−n, provides very good fits to the measurements only if either the ϕm or n parameter is allowed to depend on temperature. For modeling of magmatic processes, however, the widely recommended constant values ϕm = 0.6 and n = 2.5 should be adequate. The rheology changes abruptly when the clustered spherulites begin to oppose shear deformation, at a crystal fraction of about 40 vol %. The viscosity becomes non-Newtonian, with yield strengths of a few tens of bars at temperatures at which the viscosity of the melt is higher than 1010 poise. As long as the crystal fraction remains lower than 70 vol %, the deformation proceeds in an irregular manner with a nonuniform distribution of crystals and melt. The deformation becomes again regular at low stresses with lower melt fractions, but samples undergo extensive fracturation along the direction of uniaxial stress. Similar rheology changes have been observed during the isothermal crystallization of Li2Si2O5 melts, which produces small ellipsoidal inclusions. These results suggest that the influence of solid suspensions on the rheology of magmas is primarily determined by the crystal fraction, even though additional measurements would be useful to determine the possible influence of other factors such as the size distribution or the shape of the inclusions.
497 citations
TL;DR: In this article, a simple method to prepare various porous and nonporous hollow microspheres composed of poly( d,l -lactic-co-glycolic acid) using a water/oil/water (W/O/W) multiple emulsion solvent evaporation technique is described.
268 citations
TL;DR: In this article, simultaneous optical and gravimetric measurements were performed in the postflame region of an acetylene/ air premixed flame where the temperature of the soot/gas mixture was reduced to 500 K through nitrogen dilution.
229 citations
TL;DR: A recently developed laser-induced incandescence technique is used to make novel planar measurements of soot volume fraction within turbulent diffusion flames and droplet flames, finding that approximately an 80% reduction was found when the Reynolds number of the fuel jet increased from 4000 to 8000.
Abstract: A recently developed laser-induced incandescence technique is used to make novel planar measurements of soot volume fraction within turbulent diffusion flames and droplet flames. The two-dimensional imaging technique is developed and assessed by systematic experiments in a coannular laminar diffusion flame, in which the soot characteristics have been well established. With a single point calibration procedure, agreement to within 10% was found between the values of soot volume fraction measured by this technique and those determined by conventional laser scattering-extinction methods in the flame. As a demonstration of the wide range of applicability of the technique, soot volume fraction images are also obtained from both turbulent ethene diffusion flames and from a freely falling droplet flame that burns the mixture of 75% benzene and 25% methanol. For the turbulent diffusion flames, approximately an 80% reduction in soot volume fraction was found when the Reynolds number of the fuel jet increased from 4000 to 8000. In the droplet flame case, the distribution of soot field was found to be similar to that observed in coannular laminar diffusion flames.
185 citations
TL;DR: In this article, the authors investigated magnetic field-induced chain formation of superparamagnetic latex particles via optical microscopy and digital image analysis and found that the mean chain size has a power-law dependence on time, as predicted by the Smoluchowski equation and threedimensional simulations of diffusion-limited aggregation of oriented particles.
Abstract: Magnetic‐field‐induced chain formation of superparamagnetic latex particles is investigated via optical microscopy and digital image analysis. Our experiment is unique in that the aggregation process takes place in the bulk, where particles are free to diffuse in three dimensions, rather than on a surface. We find that the mean chain size 〈s(t)〉 has a power‐law dependence on time, 〈s(t)〉∼tz, as predicted by the Smoluchowski equation and three‐dimensional simulations of diffusion‐limited aggregation of oriented particles. The value of the exponent z is found to have a weak inverse dependence on particle volume fraction φ and dimensionless dipole strength λ. We propose a new model for a characteristic time scale proportional to 1/λ and 1/φ. Comparison with experimental observations shows this scaling to be very effective but to break down suddenly above a critical volume fraction.
180 citations
TL;DR: The flow behavior of Portland cement paste was studied as a function of its concentration in this article, and the relationship between viscosity and concentration was found to be well described by the Krieger-Dougherty equation.
177 citations
TL;DR: In this paper, two-phase (air-water) flow experiments were conducted in artificial horizontal fractures (narrow channels) and two experimental set-ups were utilized, one set of experiments was performed by using two glass plates (1 × 0.5 m) with a gap width of 1 mm.
175 citations
TL;DR: In this paper, the effects of varying triaxiality and strain rate on the critical void volume fraction were investigated under different constitutive models for the matrix material, i.e., rate independent plastic material with isotropic hardening, visco-plastic material under both isothermal and adiabatic conditions, and porous plastic materials with a second population of voids nucleating strain controlled.
167 citations
TL;DR: In this paper, a phase diagram of an adhesive hard-sphere dispersion is constructed using various experimental techniques, and a gel phase is found in which the Brownian particles form an interconnected static structure.
166 citations
TL;DR: In this paper, a study of the tribological properties of two locally developed polymeric composite materials for bearing applications is presented, based on a scanning electron microscope examination, which revealed that the reinforcement volume fraction as well as orientation have considerable effect on the friction and wear of polyester composites.
154 citations
TL;DR: In this paper, it was found that the presence of micelles had only a small but systematic effect upon the rate of Ostwald ripening, contrary to expectation, where micells might be expected to aid the process of ripening through solubilization of oil.
TL;DR: In this article, the role of the ceramic particles in the wear behavior of particulate composites was investigated by minimizing the influence of the often intricate metallic matrix (high speed steel, Al alloys, Mg alloys).
TL;DR: In this paper, a theoretical analysis of bubble growth in porous media by solute diffusion is presented based on visualization experiments, and the effect of (heterogeneous) nucleation on the growth of multiple clusters is analyzed.
TL;DR: In this paper, an empirical equation is derived which describes the packing density as a function of the initial packing efficiencies of particles, the particle size ratio, and the volume fraction variations of the system.
Abstract: The maximum particle packing density in a binary powder system can be predicted by the Furnas model. The packing density is lower when the size ratio of coarse particles to fine particles decreases, and is also governed by the volume fraction of coarse or fine particles. Here an empirical equation is derived which describes the packing density as a function of the initial packing efficiencies of particles, the particle size ratio, and the volume fraction variations of the system.
TL;DR: In this article, the authors formed millimeter-sized two-dimensional particle arrays on inclined microslides using water suspensions of the particles and found that the array porosity depended on the particle diameter, the particle volume fraction, and the rate of array growth.
TL;DR: In this paper, a transparent mixture of two types of particles in dispersion, one composed of a high-T g polymer [poly(methyl methacrylate), PMMA] ; the other a copolymer of butyl methacyl and butyl acrylate [P(BMA-co-BA] with T g ≤ 10 °C, were obtained under air-drying conditions.
Abstract: Latex blend films were prepared from mixtures of two types of particles in dispersion, one composed of a high-T g polymer [poly(methyl methacrylate), PMMA] ; the other a copolymer of butyl methacrylate and butyl acrylate [P(BMA-co-BA)] with T g ≤ 10 °C. Transparent films were obtained under air-drying conditions if the PMMA particles had diameters less than ∼250 nm and if the volume fraction of low-T g latex polymer exceeded a certain critical fraction Φ c . Values of Φ c varied over a narrow range (0.40-0.50) with P(BMA-co-BA) particle size, and were independent of the T g of the soft latex, ranging from ca. -35 to +10 °C. Film morphologies were examined by scanning electron microscopy and by freeze-fracture transmission electron microscopy. In all films, the hard particles retain their original size and spherical shape. In the transparent films, they are uniformly distributed in a polymer matrix generated from deformed soft particles, whereas clustering of PMMA microspheres is observed in turbid films. Various factors, such as increasing the size ratio between the two types of particles, removing of surfactant in the systems, and annealing of the films after drying, disrupt the uniform particle packing required for transparent films.
TL;DR: In this article, the authors present the load displacement curves for monotonic loading, and for relaxation after repeated reloading cycles to a maximum load, and the loading cycle responses for the fabric have been fitted to power-law relationships.
TL;DR: The authors' results demonstrate the feasibility of a simple method for measuring tissue cell fraction that is robust across a broad range of vascular volume, flow, and exchange conditions and may prove to be an important means for evaluating the response of tumors to therapy.
Abstract: A new technique for measuring tissue cellular volume fraction, based on an improved modeling of the dynamic distribution of Gd-DTPA and the effect of proton exchange, is described. This technique uses peak T1 enhancement and blood Gd-DTPA concentration to compute tissue cellular volume fraction. The feasibility of this technique is demonstrated with computer simulations that explore the limits of the simplifying assumptions (small vascular space, slow vascular-extravascular proton exchange), and by direct comparison of MR and radionuclide cell fraction measurements made in muscle, liver, and tumor tissue in a rat model. The computer simulations demonstrate that with slow to intermediate vascular proton exchange and vascular fractions less than 10% the error in our cell fraction measurements typically remains less than 10%. Consistent with this prediction, a direct comparison between MR and radionuclide measurements of cell fraction demonstrates mean percent differences of less than 10%:1.9% in muscle (n = 4); 9% in liver (n = 1) and 9.5% in tumor (n = 4). Similarly, for all rats studied, the MR-measured cell fractions (muscle (0.92 +/- 0.04, n = 20); liver (0.76 +/- 0.11, n = 9); whole tumor (0.69 +/- 0.15, n = 22)) agree with the cell fraction values reported in the literature. In general, the authors' results demonstrate the feasibility of a simple method for measuring tissue cell fraction that is robust across a broad range of vascular volume, flow, and exchange conditions. Consequently, this method may prove to be an important means for evaluating the response of tumors to therapy.
TL;DR: In this article, the effect of fiber volume fraction on the off-crack-plane fracture energy in a strain-hardening engineered cementitious composite (ECC) is presented.
Abstract: In this paper, the results of an experimental study on the effect of fiber volume fraction on the off-crack-plane fracture energy in a strain-hardening engineered cementitious composite (ECC) are presented. Unlike the well-known quasi-brittle behavior of fiber-reinforced concrete, ECC exhibits quasi-ductile response by developing a large damage zone prior to fracture localization. In the damage zone, the material is microcracked but continues to strain-harden locally. The areal dimension of the damage zone has been observed to be on the order of 1,000 cm{sup 2} in double cantilever beam specimens. The energy absorption of the off-crack-plane inelastic deformation process has been measured to be more than 50% of the total fracture energy of up to 34 kJ/m{sup 2}. This magnitude of fracture energy is the highest ever reported for a fiber cementitious composite.
01 Oct 1995-Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science
TL;DR: In this article, the authors measured the Darcy permeability of columnar-dendritic microstructures with a volume fraction of liquid as high as 0.98 and calculated the velocity and pressure at the nodes at the microstructural level.
Abstract: Experiments for measuring permeability in columnar-dendritic microstructures have provided data only up to a volume fraction of liquid of 0.66. Hence, the permeability for flow perpendicular to the primary dendrite arms in columnar-dendritic microstructures was calculated, extending our data base for permeability to volume fractions of liquid as high as 0.98. Analyses of the dendritic microstructures were undertaken first by detecting the solid-liquid interfaces with a special computer program and then by generating a mesh for a finite-element fluid flow simulation. Using a Navier-Stokes solver, the velocity and pressure at the nodes were calculated at the microstructural level. In turn, the average pressure gradient was used to calculate the Darcy permeability. Permeabilities calculated by this versatile technique provided data at high volume fractions of liquid that merged with the empirical data at the lower volume fractions.
TL;DR: In this paper, the rheological and microstructural properties of dense suspensions of uniform, charge stabilized colloidal spheres with diameters greater than 200 nm are investigated at volume fractions just below the ordering transition up to 0.6.
Abstract: The rheological and microstructural properties of dense suspensions of uniform, charge stabilized colloidal spheres with diameters greater than 200 nm are investigated at volume fractions just below the ordering transition up to 0.6. Shear stresses marking static and dynamic yielding, discontinuous shear thinning, and shear thickening are weakly dependent on volume fraction and particle size when scaled on the crystal’s elastic modulus G0. As shear stress is increased microstructures evolve through similar states independent of volume fraction. As rest, presheared suspensions exhibit long‐range orientational order. Above the dynamic yield stress, the suspensions deform with a polycrystalline microstructure which, at intermediate shear rates, evolves to hexagonally close‐packed planes lying parallel to the rheometer walls. At higher shear rates the suspensions melt. Thickening is only observed above a volume fraction of 0.4–0.5, depending on particle size and at shear rates above that where the hexagonal c...
01 Jun 1995-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: Grain growth in TiO 2 -doped alumina was studied in a high density, ultrafine matrix (0.4 μm) as mentioned in this paper, and the volume fraction of anisotropic grains ranged from 20 to 100 vol% suggesting that physical properties dependent on grain shape and volume fraction can be tailored.
Abstract: Grain growth in TiO 2 -doped alumina was studied in a high density, ultrafine matrix (0.4 μm. Normal grain growth, anisotropic grain growth and abnormal grain growth were observed. With 0.15-0.4 wt.% TiO 2 , samples initially undergo normal grain growth until a crystal microstructure is attained and anisotropic grain growth in nucleated. Large anisotropic, platelet-shaped grains grow rapidly by a step growth process until impingement of the large grains essentially stops further growth. The volume fraction of anisotropic grains ranged from 20 to 100 vol.% suggesting that physical properties dependent on grain shape and volume fraction can be tailored. Critical requirements are proposed for the in situ growth of anisotropic grains.
01 Oct 1995-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, a model for dilute dispersion-strengthened aluminum was extended to the case of a large volume fraction of large particles, whereby the interaction of primary glide dislocations with secondary loops punched by dispersoids was considered.
Abstract: Oxide-dispersion-strengthened aluminum containing 25 vol.%, 0.28 μm, alumina dispersoids was fabricated by pressure infiltration. The mechanical properties at room and elevated temperature are presented for both as-cast, coarse-grained materials and extruded, fine-grained materials. Although the room temperature yield strength is low (about 60 MPa), the 0.2% proof stress and ultimate tensile stress are much higher (about 200 MPa and 330 MPa respectively) as a result of the very high strain hardening rate. However, the initially high strain hardening rate decreases with strain. This behavior is explained by extending a model by Ashby for dilute dispersion-strengthened metals to the case of a matrix containing a large volume fraction of large particles, whereby the interaction of primary glide dislocations with secondary loops punched by dispersoids is considered.
TL;DR: In this article, the authors derived an approximate relationship between the limiting volume fraction V f and the slenderness λ of the fibres defined as length divided by diameter of the fiber.
Abstract: An investigation has been carried out of the limiting packing density of an array of long straight rigid fibres distributed randomly in space as a function of the length of the fibre. We derive an approximate relationship between the limiting volume fraction V f and the slenderness λ of the fibres defined as length divided by diameter. The formula agrees well with our experimental results and those found in the literature.
TL;DR: In this article, it was demonstrated that accurate values of the interfacial free energy, λ, and solute diffusivities, D, can be obtained from experimental data when the kinetics of particle growth are measured in conjunction with independent measurements of either the decrease of the matrix supersaturation or the increase in volume fraction with aging time.
Abstract: Using recent theoretical modifications of the kinetic constants characterizing Ostwald ripening, it is demonstrated that accurate values of the interfacial free energy, λ, and solute diffusivities, D, can be obtained from experimental data when the kinetics of particle growth are measured in conjunction with independent measurements of either the decrease of the matrix supersaturation or the increase in volume fraction with aging time. The accuracy of λ is limited only by the assumption that the matrix phase is an ideal solid solution, and is effectively independent of the influence of equilibrium volume fraction, Φe, on the kinetics of coarsening. Analyses of the available data on the coarsening of γ′-type (Ni3X) precipitates in binary Ni−Al, Ni−Si and Ni−Ti alloys yield values of λ=6.9±0.3, 10.2±3.0 and 13.0 mJ/m2, respectively, assuming ideal solution thermodynamics; a more realistic thermodynamic model for the Ni−Al solid solution raises the value of λ in Ni−Al alloys to 8.1±0.2 mJ/m2. Proportional increases probably obtain in the other two alloys. The accuracy with which D can be evaluated from comparable data depends theoretically on Φe. However, analyses of the same data yield values of D in very good agreement with the results of conventional diffusion experiments. This is consistent with the absence of an effect of Φe on the kinetics of Ostwald ripening in these alloys over the ranges of Φe investigated.
TL;DR: In this article, the authors examined binary mixtures of large and small symmetric AB diblock copolymers using self-consistent field theory and found that when the ratio of their polymerization indexes exceeds about 1:5, they become immiscible producing a coexistence between long and short-period lamellar phases.
Abstract: We examine binary mixtures of large and small symmetric AB diblock copolymers using self‐consistent field theory. In accord with experiment, we find that when the ratio of their polymerization indexes exceeds about 1:5, they become immiscible producing a coexistence between long‐ and short‐period lamellar phases. As in experiment, the short‐period phase contains few large diblocks, but the long‐period one contains a substantial volume fraction of small diblocks.
TL;DR: In this article, the Orowan bowing hardening mechanism is explained in terms of the volume fraction of the reinforcing phase of a Ni/Al2O3 composite material.
Abstract: Nanocomposite Ni/Al2O3 films have been produced by electrochemical deposition where 50 and 300 nm Al2O3 particles are dispersed in a nickel matrix. These films exhibit considerable enhancements in their hardness in comparison to pure nickel. The strengthening mechanism is explained in terms of an Orowan bowing hardening mechanism and, hence, related to the volume fraction of the reinforcing phase. These films may have application as strong coatings that retain many of the physical properties (e.g., optical, thermal, electrical) of the metal.
TL;DR: In this article, the scaling exponent relating droplet diameter and time was determined, and it was found that this scaling exponent was a strong function of the droplet phase volume fraction and this strong dependence on volume fraction was relatively insensitive to temperature.
TL;DR: Qualitative two-dimensional nonintrusive optical measurements of the soot evolution versus time from single fiber-supported burning fuel droplets of heptane and decane are demonstrated.
Abstract: Laser-induced incandescence (LII) is ideally suited for obtaining high temporally and spatially resolved measurements of soot volume fraction in transient combustion phenomena. We demonstrate qualitative two-dimensional nonintrusive optical measurements of the soot evolution versus time from single fiber-supported burning fuel droplets of heptane and decane. Quantitative measurement of the soot volume fraction is also demonstrated through calibration of the LII signal against a small coflow ethylene diffusion flame.
TL;DR: In this article, the effects of phase morphology, interfacial adhesion, rigid filler particle shape and elastomer volume fraction on the tensile yield strength of polypropylene (PP) filled with inorganic filler (CaCO3 or Mg(OH)2) and EPR was investigated.
Abstract: The effects of phase morphology, interfacial adhesion, rigid filler particle shape and elastomer volume fraction on the tensile yield strength of polypropylene (PP) filled with inorganic filler (CaCO3 or Mg(OH)2) and ethylene-propylene elastomer (EPR) were investigated. Separation of the filler and elastomer particles was achieved using maleic-anhydride-grafted PP (MPP) to enhance the filler-matrix adhesion. Encapsulation of the rigid filler by the elastomer was achieved using maleic-anhydride-grafted EPR (MEPR) to increase the filler-elastomer adhesion. The two limiting morphologies differ significantly in mechanical properties under tensile loading at the same material composition. Elastomer particles separately dispersed in the matrix enhance the shear banding in the bulk matrix which prevents the crazes growing from the filler surface from becoming unstable and, thus, increases the ductility of the material. Encapsulation by an elastomer layer on the filler surface relieves triaxial stresses at the filler surface, changing the major local failure mechanism from crazing to shear yielding and, hence, increasing the ductility of the material. Increase of the elastomer volume fraction also causes, in both cases, an increase in matrix ductility. Composite models are used to predict upper and lower limits of yield strength (σy) for the two limiting morphologies over an interval of elastomer volume fractions (V
e) from 0 to 0.2 at a constant filler loading of 30 vol.% and over a filler volume fraction from 0 to 0.4 at a constant EPR content in the matrix. Satisfactory agreement was found between the experimental data and theoretical predictions.