Showing papers on "Volume fraction published in 1992"
TL;DR: In this article, a constitutive equation for computing particle concentration and velocity fields in concentrated monomodal suspensions is proposed that consists of two parts: a Newtonian constitutive equations in which the viscosity depends on the local particle volume fraction and a diffusion equation that accounts for shear-induced particle migration.
Abstract: A constitutive equation for computing particle concentration and velocity fields in concentrated monomodal suspensions is proposed that consists of two parts: a Newtonian constitutive equation in which the viscosity depends on the local particle volume fraction and a diffusion equation that accounts for shear‐induced particle migration. Particle flux expressions used to obtain the diffusion equation are derived by simple scaling arguments. Predictions are made for the particle volume fraction and velocity fields for steady Couette and Poiseuille flow, and for transient start‐up of steady shear flow in a Couette apparatus. Particle concentrations for a monomodal suspension of polymethyl methacrylate spheres in a Newtonian solvent are measured by nuclear magnetic resonance (NMR) imaging in the Couette geometry for two particle sizes and volume fractions. The predictions agree remarkably well with the measurements for both transient and steady‐state experiments as well as for different particle sizes.
886 citations
TL;DR: In this article, the authors derived an analytical solution for transverse flow in an idealized unidirectional reinforcement consisting of regularly ordered, parallel fibres both for flow along and for flow perpendicular to the fibres, and showed excellent agreement between a numerical solution of the full flow equations and the approximate one at medium to high fibre volume fractions (V f > 0.35).
Abstract: The permeability of an idealized unidirectional reinforcement consisting of regularly ordered, parallel fibres is derived starting from first principles (Navier-Stokes equations) both for flow along and for flow perpendicular to the fibres. First, an approx imate analytical solution for transverse flow is derived which differs from the Kozeny- Carman equation for the permeability of a porous medium [9] in that the transverse flow stops when the maximum fibre volume fraction is reached. The solution for flow along the fibres has the same form as the Kozeny-Carman equation. A comparison shows excellent agreement between a numerical solution of the full flow equations and the approximate one at medium to high fibre volume fractions (V f > 0.35). The theoretical predictions of permeability were tested in a specially designed mould. The results from the experiments with an unsaturated polyester resin (Jotun PO-2454) and the unidirectional reinforcement did in all cases show excellent agreement with results pre...
862 citations
TL;DR: In this article, the effects of silicon and manganese contents on volume fraction and stability of retained Austenite particles in TRIP-aided dual-phase steels were investigated.
Abstract: The effects of silicon and manganese contents on volume fraction and stability of retained austenite particles in 0.2C-(1.0-2.5)Si-(1.0-2.5)Mn (mass%) TRIP-aided dual-phase steels were investigated. In addition, the relationships between above retained austenite parameters and ductility at room and moderate temperatures were discussed through studies on strain-induced transformation behavior of retained austenite.As increasing the silicon and manganese contents except for 2.5 mass% manganese steel, the initial volume fraction of retained austenite increased with accompanied by reducing carbon concentration in retained austenite. It was found that the ductilities of these steels became maximum at a given temperature between 23 and 175°C, i.e., a peak temperature. The peak temperature was concluded to agree well with the temperature at which the strain-induced transformation of retained austenite was suppressed moderately for each steel. Moreover, the peak temperature Tp (°C) was related to estimated martensite-start temperature Ms (°C) of the retained austenite as Tp=3.04Ms+187. Strength-ductility balance, i.e., the product of tensile strength and total elongation, at the peak temperature linearly increased with an increase in the initial volume fraction of retained austenite.
332 citations
TL;DR: In this paper, the role of volume fraction and size of reinfrecement on the steady state creep behavior of pure aluminium matrix-silicon carbide particulate composites have been studied in the temperature range 623-723 K.
Abstract: The roles of volume fraction and size of reinfrecement on the steady state creep behaviour of pure aluminium matrix-silicon carbide particulate composites have been studied in the temperature range 623–723 K. The observed apparent stress exponents are higher than 15 and apparent activation energy is 249 kJ mol−1. By considering the existence of a threshold stress, the data for 1.7 μm particulate reinforced composites with different volume fraction can be rationalized according to the substructure invariant model. The effective stress-strain rate behaviour of composites with 10 vol.% of coarser particulates (14.5 and 45.9 μm), however, agree with the stress dependent substructure model. The present analysis is validated by constructing a new type of “dislocation creep mechanism map”. The observed threshold stress varies with the volume fraction of reinforcement and is independent of particulate sizes and test temperatures. It is suggested that a model based on applied stress independent load transfer is required to explain the origin of such a threshold stress.
193 citations
TL;DR: In this article, a careful analysis of the available results on the basis of existing models suggests that there is a critical grain size below which the triple junction volume fraction increases considerably over the grain boundary volume fraction and this is suggested to be responsible for the observed softening at small grain sizes.
Abstract: Nanocrystalline materials have a grain size of only a few nanometers and are expected to possess very high hardness and strength values. Even though the hardness/strength is expected to increase with a decrease in grain size, recent observations have indicated that the hardness increases in some cases and decreases in other cases. A careful analysis of the available results on the basis of existing models suggests that there is a critical grain size below which the triple junction volume fraction increases considerably over the grain boundary volume fraction and this is suggested to be responsible for the observed softening at small grain sizes.
181 citations
TL;DR: In this article, a 3D finite element model was developed for prediction of temperatures of mixtures of liquids and multiple particles within a static heater, using cubic potato particles within sodium phosphate solutions, for various particle sizes, orientations, concentrations and liquid conductivities.
Abstract: Understanding of the ohmic heating of liquid-particle mixtures requires preliminary study and model development within a static heater. A mathematical (3D finite element) model was developed for prediction of temperatures of mixtures of liquids and multiple particles within a static heater. Experiments were conducted using cubic potato particles within sodium phosphate solutions, for various particle sizes, orientations, concentrations, and liquid conductivities. the mathematical model was found to yield satisfactory prediction of experimental trends. Critical parameters affecting the relative heating rates of particles and liquid were the conductivities of the two phases, and the volume fraction of each phase. Ohmic heating appears most promising with high-solids concentration mixtures.
143 citations
TL;DR: In this article, the Au volume fraction and effective medium theory screening parameter k were estimated from scanning electron microscopic analyses of cylinder dimensions and orientations in the composite membrane, and the spectra were consistent, however, with retarded polarization effects due to nonnegligible Au particle separation distances in the composites.
Abstract: Metal-insulator composites of varying metal volume fraction have been prepared by electrochemical deposition of gold into porous aluminum oxide membranes. The cylindrical pore array structure of the host oxide serves as a template for the formation of Au particles ca. 0.26 {mu}m in diameter with lengths ranging from 0.3 to 3 {mu}m depending on the deposition time. The composites display a significant transparency in the infrared spectrum between 2000 and 4000 cm{sup {minus}1}. The Au volume fraction and effective medium theory screening parameter k were estimated from scanning electron microscopic analyses of cylinder dimensions and orientations in the composite membrane. Comparison of experimental spectra with those calculated using Maxwell-Garnett or Bruggeman theories indicates that neither approach is entirely satisfactory. The spectra are consistent, however, with retarded polarization effects due to nonnegligible Au particle separation distances in the composites. 21 refs., 11 figs., 2 tabs.
138 citations
TL;DR: In this paper, finite element calculations were made in order to simulate coherency stresses in the commercial superalloy SRR 99 containing 70 vol.% of γ′ phase, and the influence of 2D/3D and isotropic/anisotropic modelling on the results was discussed in detail.
Abstract: Finite element calculations were made in order to simulate coherency stresses in the commercial superalloy SRR 99 containing 70 vol.% of γ′ phase. Stress and strain energy properties are calculated for the relevant morphologies observed in SRR 99. The influence of 2D/3D and isotropic/anisotropic modelling on the results is discussed in detail. Our results are applied to better understand the high temperature evolution of the microstructure. The sphere to cube transition with increasing precipitate size and the appearance of butterfly distorted cubes during cooling will be discussed.
132 citations
TL;DR: The tribological behavior of aluminium alloy 2014-graphite particle composites has been found to be a function of the volume fraction of graphite particles, and wear resistance can be improved by adding graphite, which causes a corresponding reduction in the coefficient of friction.
126 citations
TL;DR: The microstructural changes produced by large (38 to 53 μm), single-crystal ZrO2 inclusions within an Al2O3 powder matrix were detailed as a function of constrained densification as discussed by the authors.
Abstract: The microstructural changes produced by large (38 to 53 μm), single-crystal ZrO2 inclusions (0, 0.09, 0.30 volume fractions, based on solid volume) within an Al2O3 powder matrix were detailed as a function of constrained densification. Composite powder compacts were produced by pressure filtration for conditions where the Al2O3 slurry was either flocced or dispersed. For both conditions, the ZrO2 inclusions constrained densification. Microstructural observations for all composites revealed (1) the presence of cracks with large opening displacements between inclusions and (2) large density variations within the matrix. The cracks were most frequent at high volume fraction of inclusions in composites produced from flocced slurries and apparently originated during specimen preparation. Their large opening displacment was a result of matrix densification. Fewer cracks were observed in composites produced from dispersed slurries. Instead, these microstructures were dominated by large variations in matrix density, viz., dense regions surrounding low-density regions, not consitent with the initial packing density of the matrix powder. The denser regions were formed early in the densification schedule. The lower-density regions eventually developed into regions containing large, elongated voids as the Al2O3 matrix grains became larger with heat-treatment time. This pore enlargement process was shown to result from the disappearance of necks between originally sintered grains and appeared similar to the thermodynamic instability observed in thin films and constrained fibers.
118 citations
TL;DR: In this paper, the growth of porous aggregates during initial mixing is investigated in a series of numerical simulations, and the collision rate constants as a function of fractal dimension, D, and aggregation number, i.e. D is assumed to be independent of aggregate size.
TL;DR: In this article, the effects of calcium hydroxide dissolution on two material properties: the percolation properties or connectivity of the capillary pore space, and the relative ionic diffusivity were examined using computer simulation.
Abstract: As concrete is exposed to the elements, its underlying microstructure can be attacked by a variety of aggressive agents. For example, rainwater and groundwater can degrade the concrete by dissolving soluble constituents such as calcium hydroxide. Using computer simulation, this paper examines the effects of calcium hydroxide dissolution on two material properties: the percolation properties or connectivity of the capillary pore space, and the relative ionic diffusivity. A microstructural model for cement paste is used to produce a hydrated specimen which is subsequently subjected to the leaching process. Pore space percolation characteristics and relative ionic diffusivity are computed throughout the leaching process as a function of total capillary porosity. Material variables examined are water: solids ratio and silica fume content. Percolation theory is used to develop the concept of a critical volume fraction of calcium hydroxide plus capillary pore space. It is shown that this critical combined volume fraction determines the magnitude of the effect of leaching on relative ionic diffusivity.
TL;DR: In this paper, the fractional effect of porosity and clay on the velocities for dry clastic silicate rocks was described (above 120 MPa) by u = A - B# - CCluy, where v is the velocity of the P-wave or S-wave, # is the volume fraction of pores, and Clay is the volumetric fraction of clay.
Abstract: SUMMARY For clastic silicate rocks sampled from a Rotliegendes well core the velocities up and us were obtained at 10 pressures up to 300MPa using a pulse-transmission technique. The porosities of all rocks (57 sandstones, 26 siltstones, five claystones) ranged from 0.01 and 0.15 by volume fraction, and the clay content varied from less than 0.01 to 0.88 by volume fraction. Both velocities increase with pressure. In the low-pressure range the rate of increase is large, non-linear and is greater for up than for us. Above 120 MPa both velocities increase linearly. Velocities, porosity, and clay content were fitted by least-squares regression for pressures of 8, 24, 60, 120, 200, and 300 MPa. The fractional effect of porosity and clay on the velocities for dry clastic silicate rocks can be described (above 120 MPa) by u = A - B# - CCluy, where v is the velocity of the P-wave or S-wave, # is the volume fraction of pores, and Clay is the volume fraction of clay. From this it is possible to obtain pressure-dependent velocity functions u = a +pb - c exp (-dp), where u is the crack-free velocity, linear in porosity and clay, b is the velocity slope under high pressure, u - c is the zero-pressure velocity, and d is related to closure of cracks.
TL;DR: In this paper, the effects of the filler volume fraction and strength of adhesion on the mode of tensile failure of a particulate reinforced polypropylene (PP) are investigated using finite element simulation (FES).
Abstract: The effects of the filler volume fraction and strength of adhesion on the mode of tensile failure of a particulate reinforced polypropylene (PP) are investigated using finite element simulation (FES). When there is perfect adhesion between con- stituents, an upper bound for tensile yield strength is found to be 1.33 times the matrix yield strength above a critical volume of particulate concentration. Utilizing Sjoerdsma's model for interacting stress concentration fields, one can determine the concentration dependence of the yield strength below the critical filler volume fraction
TL;DR: In this paper, it was shown that microvoids a micrometre or so in diameter, with a volume fraction of ∼ 17%, would appear to give a significant increase in the toughness of a thermosetting epoxy polymer.
15 Mar 1992
TL;DR: In this paper, an appropriate mean force potential was utilized in Felderhof's theory to derive simple analytical expressions for the concentration dependence of the collective and short time self diffusion coefficients, as well as for sedimentation velocity of charged spherical particles.
Abstract: An appropriate mean force potential was utilized in Felderhof's Theory to derive simple analytical expressions for the concentration dependence of the collective and short time self diffusion coefficients, as well as for the sedimentation velocity of charged spherical particles. It is demonstrated theoretically that the osmotic viriat and the Oseen hydrodynamic terms play a dominant role. To check the theoretical model, the dependence of the collective diffusion coefficient on the volume fraction of latex particles was experimentally studied. Dynamic light scattering was used at several different concentrations of electrolyte. It turns out that our experimental results, as well as the results of other authors, are in very good agreement with the proposed theoretical model. The results show that the increase of the electrolyte concentration leads to increase of the particle charge, but almost does not change the particle surface potential. A minimum in the dependence of the diffusion coefficient of a single particle on the ionic strength was also obtained. © 1992 Academic Press, Inc.
TL;DR: In this article, the deformation behavior of carbon fiber bundles is compared to a recently developed 3D theory and it is shown that all available aligned carbon fiber bundle data, including bulk compression, axial extension, and coupling behavior, can be fit to the modified model by only adjusting the available fiber volume fraction.
Abstract: We review all available data for the deformation behavior of lubricated carbon fiber bundles and compare these data to a recently developed 3D theory (Cai and Gutowski, 1992). Most of the data, which is for transverse compression, exhibits very large scatter, but can be collapsed by shifting along the fiber volume fraction axis. It is hypothesized that the shifts represent different states for the fiber bundle, which can be represented in the model by a single variable, the available fiber volume fraction Va. It is then shown that all available aligned carbon fiber bundle data, including bulk compression, axial extension, and coupling behavior, can be fit to the modified model by only adjusting Va. In one case (the coupling behavior), the available fiber volume fraction was directly measured. Observations on how the state of the fiber bundle can be modified by the processing conditions are included. On the basis of this analysis, a simple, practical test to determine Va is proposed. 24 refs.
TL;DR: In this article, a micromechanical model for brittle particle reinforced metal matrix composites sustaining damage is developed for a three-phase damage cell consisting of a cracked particle in a cylindrical matrix cell embedded in an undamaged composite cylinder.
Abstract: A micromechanical model is developed for brittle particle reinforced metal matrix composites sustaining damage. A composite with uniformly distributed damage is modelled by a three-phase damage cell consisting of a cracked particle in a cylindrical matrix cell embedded in an undamaged composite cylinder. The fraction of broken particles to all particles is taken as the ratio of the broken-particle/matrix cell volume to the whole damage cell volume. Systematic analysis is carried out for aligned spherical and cylindrical particles in an elastic-perfectly plastic matrix subject to tensile loading normal to the plane of particle cracks. The influence of damage evolution paths on the composite stress-strain behavior is investigated. Results are given for the effects of damaged particle percentage, total particle volume fraction and particle shape on the overall composite limit flow behavior. Significant reduction in composite limit flow stress may occur if most of the particles are broken. For composite with spherical reinforcement, the reduction is found to be linearly dependent on the percentage of damaged particles.
TL;DR: In this article, a DGEBA/DDA network was used to study the toughening effect due to the introduction of glass beads with different volume fractions, and the influence of surface treatment was also studied by comparing untreated, silane-treated glass beads and beads coated with different thicknesses of an elastomeric adduct.
Abstract: A DGEBA/DDA network was used to study the toughening effect due to the introduction of glass beads with different volume fractions The influence of surface treatment was also studied by comparing untreated, silane-treated glass beads, and beads coated with different thicknesses of an elastomeric adduct The effect of the volume fraction of glass and the surface treatment were discussed in terms of elastic and plastic properties The results were compared with the usual theoretical models Linear elastic fracture mechanics and impact tests were performed to study the crack propagation process The various parameters influenced the deformation mechanism, especially for the coated glass bead composites, for which an optimum thickness was displayed A large improvement in GIc value was obtained with a slight decrease for the stiffness © 1992 John Wiley & Sons, Inc
TL;DR: In this paper, the rheological properties of aqueous concentrated polystyrene latex dispersions for three particles with core diameters of 155 nm, 612 nm, and 1004 nm were investigated using steady-state shear stress and oscillatory measurements.
TL;DR: In this paper, a γ-ray absorption technique was used to measure the evolution of volume fraction profiles during transient settling of flocculated alumina suspensions, and the experimental results showed that the permeability of aggregated particle networks at low volume fractions is larger than expected from simplistic permeability models.
Abstract: A γ-ray absorption technique has been used to measure the evolution of volume fraction profiles during transient settling of flocculated alumina suspensions. The experimental system consisted of a submicron, polydisperse alumina powder immersed in an organic solvent (decalin) with fatty acids of varying molecular weights adsorbed at the alumina/decalin interface. The interaction energy at particle contact was determined by the thickness of the adsorbed layer. The volume fraction profiles measured were compared with model predictions and it was found that the model only partly describes the settling process. Further, the experimental results showed that the permeability of aggregated particle networks at low volume fractions is larger than expected from simplistic permeability models.
TL;DR: In this article, the authors proposed new avenues for dispersion-strengthened copper alloys design based on thermal conductivity concept and recent Rosier-Artz theory of high-temperature strength.
Abstract: Processing methods for producing dispersion-strengthened (DS) copper alloys with high strength, high conductivity, and good long-term stability at elevated temperature are reviewed. Particle size and stability are related to material characteristics and processing route. Physical and mechanical properties of DS copper alloys are directly associated with microstructural features such as particle volume fraction, stability, size, solubility in the matrix, and interfacial properties. New avenues for DS copper alloys design are suggested based on thermal conductivity concept and recent Rosier- Artz theory of high-temperature strength.[1]
TL;DR: In this article, the steady-shear viscosity and dynamic viscoelasticity were measured under electric fields up to 3.0 kV/mm−1, showing that the electric polarization forces are much stronger than predicted by the bulk polarization theory.
Abstract: Monodisperse silica particles were formed by hydrolyzing tetraethylorthosilicate in an ethanol solution. For silica suspensions in a silicone oil, the steady‐shear viscosity and dynamic viscoelasticity were measured under electric fields up to 3.0 kV mm−1. At low shear rates and high field strength, the flow curve shows a plateau, showing development of a yield stress. The yield stress is proportional to the volume fraction of particles (Φ) and to the square of the electric field (E) for Φ<0.3. The number of chains linearly increases with volume fraction. At higher volume fractions it varies with (ΦE)2.4. The larger value of the exponent may be attributed to the crosslinking of chains. The scaling on Mason number is not applicable to the viscosity behavior in steady shear. This implies that the electric polarization forces are much stronger than predicted by the bulk polarization theory. The interparticle forces due to polarization are closely related to conditions at the surfaces of the particles, rather...
TL;DR: In this paper, a model soft-sphere suspension is compared with that of a model hard sphere suspension and the authors focus on the transition from liquid-like to solid-like behavior at the maximum packing volume fraction, γm.
TL;DR: In this article, a binary aqueous suspension of large (L) and small (S) nearly hard-sphere colloidal polystyrene spheres is shown to segregate spontaneously into L-rich and S-rich regions for suitable choices of volume fraction and size ratio.
Abstract: A binary aqueous suspension of large (L) and small (S) nearly-hard-sphere colloidal polystyrene spheres is shown to segregate spontaneously into L-rich and S-rich regions for suitable choices of volume fraction and size ratio. This is the first observation of such purely entropic phase separation of chemically identical species in which at least one component remains fluid. Simple theoretical arguments are presented to make this effect plausible.
TL;DR: In this paper, a quantitative general effective media (GEM) equation is used to describe a broad range of experimental resistivity-volume fraction results for graphite-polymer and carbon black polymer composites.
Abstract: A quantitative general effective media (GEM) equation is used to describe a broad range of experimental resistivity-volume fraction results for graphite-polymer and carbon black-polymer composites. The parameters used are the resistivities of each component and the two percolation morphology parameters, a critical volume fraction, O c , and an exponent, t. A preliminary model, also based on the GEM equation, is used to describe the temperature variation of the resistivity of the diphasic material near the critical volume fraction
TL;DR: The correction factor for the non-linear relationship between Δϵ′ and P is indeed independent of the cell radius, which has the important and useful consequence that a simple calibration curve of dielectric increment vs. dry weight or cell numbers permits one to determine the specific enclosed volume of the strain of interest.
01 Jun 1992
TL;DR: In this paper, the effective interaction between colloids in solutions containing dissolved polymer is investigated using integral equations, where the colloidal particles are modeled as hard spheres, the polymer molecules were modeled as freely jointed hard chains, and the solvent was treated as a continuum that didn't interact with either the colloid particles or the polymer molecule.
Abstract: The effective interaction between colloids in solutions containing dissolved polymer is investigated using integral equations. The colloidal particles are modeled as hard spheres, the polymer molecules are modeled as freely jointed hard chains, and the solvent is treated as a continuum that doesn't interact with either the colloidal particles or the polymer molecules. The model therefore concentrates on excluded volume effects in these systems. It is found that at low polymer volume fractions, the effective intermolecular potential (or potential of mean force) between the colloidal particles is attractive, thus facilitating a phase separation or precipitation of the colloids. As the polymer volume fraction is increased, the strength of this attraction increases; but a repulsive interaction appears at larger separations, which resembles the double-layer repulsion between charged colloidal particles in an aqueous solution. The effects of varying polymer chain length, colloid particle size, and polymer volume fraction on the effective potential are also studied.
TL;DR: In this paper, a detailed numerical study of the dissolution kinetics of particles in binary alloys during isothermal annealing was made by applying a finite difference technique to a spherical particle in a spherical cell of finite size.
Abstract: A detailed numerical study has been made of the dissolution kinetics of particles in binary alloys during isothermal annealing. In earlier models, the assumption was made that the dissolution reaction could be described by the dissolution of only one particle in an infinite matrix or the dissolution of a regular array of particles of equal size. This assumption has been relaxed and a log-normal size distribution of particles has been introduced instead. The calculations have been done numerically by applying a finite difference technique to a spherical particle in a spherical cell of finite size. The presence of a size distribution of particles was found to have a great effect on the dissolution kinetics and, therefore, must be included in a reliable model for the dissolution of particles. The results have been presented in diagrams, giving the volume fraction as a function of the dimensionless annealing time with the geometrical standard deviation as a parameter, and thus should be useful in making accurate predictions of the dissolution kinetics of binary alloys. The curves can be used for all volume fractions provided that all of the particles can be dissolved completely at the temperature considered. Also, equations have been derived that can easily be used to give an estimate of the annealing time to dissolve 90 pct of the initial volume fraction.
TL;DR: In this article, the repeating distances of dilute lyotropic lamellar phases have been measured as a function of the membrane volume fraction, for several ternary or quaternary systems.
Abstract: Using neutron and high-resolution X-ray scattering, the repeating distances of dilute lyotropic lamellar phases have been measured as a function of the membrane volume fraction, for several ternary or quaternary systems. In the case of systems dominated by undulation forces, a systematic logarithmic deviation is observed. It is attributed to the excess area coming from the undulations. A method for measuring the membrane bending elastic constant κ is proposed.