Showing papers on "Volume fraction published in 2003"
TL;DR: In this article, the theory of Brownian motion and diffusion-limited aggregation model are applied to simulate random motion and the aggregation process of the nanoparticles, and a theoretical model is developed to predict the thermal conductivity of nanofluids.
Abstract: Nanofluids are obtained by suspending metallic nanoparticles in conventional base liquids. Such a new class of heat-transfer fluid is superior to the base liquids in energy-transport performance, which depends on the distribution, volume fraction and thermal properties of the suspended nanoparticles. The theory of Brownian motion and the diffusion-limited aggregation model are applied to simulate random motion and the aggregation process of the nanoparticles. A theoretical model is developed to predict the thermal conductivity of nanofluids. Comparison between the theoretical and experimental results shows the validity and accuracy of the theoretical model.
746 citations
TL;DR: In this article, the morphology, crystallinity and mechanical properties of electrospun poly(e-caprolactone) nonwoven mats were characterized by scanning electron microscopy (SEM), wide angle X-ray diffraction (WAXD) and universal testing method (UTM), respectively.
577 citations
TL;DR: In this paper, the QTM-D3 conductivity tester developed in Japan was used to investigate factors influencing thermal conductivity of concrete, mortar, and cement paste, and seven testing variables such as age, water-cement (W/C) ratio, types of admixtures, aggregate volume fraction, fine aggregate fraction, W/C ratio, temperature, and humidity condition of specimen were adopted in this test.
495 citations
TL;DR: In this article, the specific surface area of activated carbon nanofibers (ACNFs) activated at 700°C was the highest but mesopore volume fraction of that was lowest.
Abstract: Poly(acrylonitrile) solutions in dimethylformamide were electrospun to be webs consisting of 300 nm ultrafine fibers. The webs were oxidatively stabilized and activated by steam resulting in activated carbon nanofibers (ACNFs). The specific surface area of the ACNF activated at 700 °C was the highest but mesopore volume fraction of that was lowest. On the other hand, the ACNFs activated at 800 °C showed opposite trends to those activated at 700 °C. The high specific surface area, mainly due to the micropores, introduced maximum specific capacitance at low current density (173 F/g at 10 mA/g). The elevated volume fraction of mesopores gave maximum specific capacitance at high current density (120 F/g at 1000 mA/g). The behavior is explained on the basis of ion mobility in the pores.
474 citations
TL;DR: In this paper, three types of hybrid composites were constructed using fiber combinations of polypropylene (PP) and carbon, carbon and steel, and steel and PP fibers at the same volume fraction (0.5%) in terms of compressive, splitting tensile, and flexural properties.
460 citations
TL;DR: In this article, the authors measured the gas permeability of adhesives of organically modified montmorillonite (OM) and polyurethane (PU) composites to oxygen and water vapor.
Abstract: Adhesive nanocomposites of organically modified montmorillonite (OM) and polyurethane have been synthesized and their permeability to oxygen and water vapor has been measured. The gas permeation through the composites was correlated to the volume fraction of the impermeable inorganic part of the OM. The incorporation of small volume fractions of the platelike nanoparticles in the polymer matrix decreased the gas transmission rate, when the interface between the two heterogeneous phases was properly designed. The oxygen transmission rate decayed asymptotically with increasing aluminosilicate volume fraction and a 30% reduction was achieved at 3 vol %, when the clay was coated with bis(2-hydroxyethyl) hydrogenated tallow ammonium or alkylbenzyldimethylammonium ions. In contrast, coating the clay surface with dimethyl dihydrogenated tallow ammonium ions leads to an increase in the gas transmission rate with augmenting inorganic fraction. This was attributed to a probable change in morphology resulting from phase separation at the interface between the apolar pure hydrocarbon clay coating and the relatively polar PU. The water vapor permeation through the PU nanocomposites was more strongly reduced than oxygen and a 50% reduction was observed at 3 vol % silicate fraction. This was attributed to stronger interactions and hydrogen bonding of the water molecules with the PU matrix as well as to their clustering. Differences in the hydrophobicity of the clay coating influenced the water transmission rate. No spectroscopic evidence could be obtained for a reaction between the hydroxyl groups of the clay organic coating and the isocyanate groups of the prepolymer. A mixed morphology, that is, exfoliated layers and intercalated particles was observed in all composites. WAXRD and TEM gave a qualitative picture of the microstructure of the nanocomposites but no conclusive information. Some of the problems to be solved before a correlation between the nanocomposite properties and their microstructure can be established have been outlined.
293 citations
TL;DR: In this paper, the microstructure and mechanical properties of two-phase α+β titanium alloys after different heat treatment were investigated and the influence of the morphology of lamellar microstructures and phase composition on the tensile properties and fracture toughness of the alloys was studied.
284 citations
TL;DR: In this article, it was shown that the molar refraction deviation function must be calculated on a mole fraction basis and the refractive index deviation function on a volume fraction basis, which can be interpreted as a sign-reversed measure of the deviation of reduced free volume from ideality.
Abstract: Prompted by the observation that recent literature displays marked disagreement as to the proper treatment of data on the refractive indices of binary liquid mixtures, this paper clarifies the relationships among refractive index, molar volume and molar refraction and the corresponding mixing properties. It is shown that the molar refraction deviation function must be calculated on a mole fraction basis and the refractive index deviation function on a volume fraction basis, which makes it directly interpretable as a sign-reversed measure of the deviation of reduced free volume from ideality.
275 citations
TL;DR: In this article, a framework for the prediction and control of microstructure evolution during heat treatment of wrought alpha/beta titanium alloys in the two-phase field was established via carefully controlled induction heating trials on Ti-6Al-4V and accompanying mathematical modeling based on diffusion-controlled growth.
Abstract: A framework for the prediction and control of microstructure evolution during heat treatment of wrought alpha/beta titanium alloys in the two-phase field was established via carefully controlled induction heating trials on Ti-6Al-4V and accompanying mathematical modeling based on diffusion-controlled growth. Induction heat treatment consisted of heating to and soaking at a peak temperature T
p=955 °C, controlled cooling at a fixed rate of 11 °C/min, 42 °C/min, or 194 °C/min to a variety of temperatures, and final water quenching. Post-heat-treatment metallography and quantitative image analysis were used to determine the volume fraction of primary (globular) alpha and the nucleation sites/growth behavior of the secondary (platelet) alpha formed during cooling. The growth of the primary alpha during cooling was modeled using an exact solution of the diffusion equation which incorporated diffusion coefficients with a thermodynamic correction for the specific composition of the program material and which took into account the large supersaturations that developed during the heat-treatment process. Agreement between measurements and model predictions was excellent. The model was also used to establish a criterion for describing the initiation and growth of secondary alpha as a function of supersaturation, diffusivity, and cooling rate. The efficacy of the modeling approach was validated by additional heat treatment trials using a peak temperature of 982 °C.
274 citations
TL;DR: The specific magnetization of the particles was determined from the magnetic moment, the particle size observed by transmission electron microscopy, and the total iron concentration found from calibrated X-ray fluorescence as discussed by the authors.
Abstract: Fe nanoparticles prepared by iron carbonyl decomposition using different methods are compared structurally, chemically, and magnetically. The specific magnetization of the particles was determined from the magnetic moment, the particle size observed by transmission electron microscopy, and the total iron concentration found from calibrated X-ray fluorescence. The volume fraction of oxide is reported for particles of different sizes and for particles made by slightly different techniques.
250 citations
TL;DR: In this article, a microscopic kinetic description of single-particle transient localization and activated transport in glassy fluids is developed which combines elements of idealized mode-coupling theory, density functional theory, and activated rate theory.
Abstract: A microscopic kinetic description of single-particle transient localization and activated transport in glassy fluids is developed which combines elements of idealized mode-coupling theory, density functional theory, and activated rate theory. Thermal fluctuations are included via a random force which destroys the idealized glass transition and restores ergodicity through activated barrier hopping. The approach is predictive, containing no adjustable parameters or postulated underlying dynamic or thermodynamic divergences. Detailed application to hard-sphere colloidal suspensions reveals good agreement with experiment for the location of the kinetic glass transition volume fraction, the dynamic incoherent scattering relaxation time, apparent localization length, and length scale of maximum nongaussian behavior. Multiple connections are predicted between thermodynamics, short-time dynamics in the nearly localized state, and long-time relaxation by entropic barrier crossing. A critical comparison of the fluid volume fraction dependence of the hopping time with fit formulas which contain ideal divergences has been performed. Application of the derivative Stickel analysis suggests that the fit functions do not provide an accurate description over a wide range of volume fractions. Generalization to treat the kinetic vitrification of more complex colloidal and nanoparticle suspensions, and thermal glass-forming liquids, is possible.
TL;DR: In this paper, the volume fraction of dispersoids precipitated during heating measured from TEM images is in good agreement with that calculated from electrical conductivity data, and the evolution of dispersoid during heat treatment is controlled by nucleation, growth, dissolution and coarsening.
TL;DR: In this article, the R-curve and fracture toughness behavior of single-edge notch beams of Ti-Al3Ti metallic-intermetallic laminate composites has been investigated.
25 Apr 2003-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, a load transfer model was proposed to estimate the strength and fracture toughness of the Al 2024-SiC metal matrix composite (MMC) powders produced by centrifugal atomization to investigate the effect of clustering on their mechanical properties.
Abstract: Al 2024–SiC metal matrix composite (MMC) powders produced by centrifugal atomization were hot extruded to investigate the effect of clustering on their mechanical properties. Fracture toughness and tension tests were conducted on specimens reinforced with different volume fractions of SiC. A model was proposed to suggest that the strength of the MMCs could be estimated from the load transfer model approach that takes into consideration the extent of clustering. This model has been successful in predicting the experimentally observed strength and fracture toughness values of the Al 2024–SiC MMCs. On the basis of experimental observations, it is suggested that the strength of particulate-reinforced MMCs may be calculated from the relation: σ y = σ m V m + σ r ( V r − V c )− σ r V c , where σ and V represent the yield strength and volume fraction, respectively, and the subscripts m, r, and c represent the matrix, reinforcement, and clusters, respectively.
TL;DR: The results of this study provide a new insight into deformation-dependent permeability behavior of agarose gel and cartilage, and are important for understanding biological responses of cells to interstitial fluid flow in gel or in cartilage under dynamic mechanical loading.
01 Mar 2003
TL;DR: In this paper, a microscopic kinetic description of single-particle transient localization and activated transport in glassy fluids is developed which combines elements of idealized mode-coupling theory, density functional theory, and activated rate theory.
Abstract: A microscopic kinetic description of single-particle transient localization and activated transport in glassy fluids is developed which combines elements of idealized mode-coupling theory, density functional theory, and activated rate theory. Thermal fluctuations are included via a random force which destroys the idealized glass transition and restores ergodicity through activated barrier hopping. The approach is predictive, containing no adjustable parameters or postulated underlying dynamic or thermodynamic divergences. Detailed application to hard-sphere colloidal suspensions reveals good agreement with experiment for the location of the kinetic glass transition volume fraction, the dynamic incoherent scattering relaxation time, apparent localization length, and length scale of maximum nongaussian behavior. Multiple connections are predicted between thermodynamics, short-time dynamics in the nearly localized state, and long-time relaxation by entropic barrier crossing. A critical comparison of the fluid volume fraction dependence of the hopping time with fit formulas which contain ideal divergences has been performed. Application of the derivative Stickel analysis suggests that the fit functions do not provide an accurate description over a wide range of volume fractions. Generalization to treat the kinetic vitrification of more complex colloidal and nanoparticle suspensions, and thermal glass-forming liquids, is possible.
25 Nov 2003-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the effects of nanosized particles on nanocomposite bulk mechanical properties were investigated using a direct ultrasonification method, and the presence of the particles had the greatest effect on fracture toughness; negligible influence was observed in the remaining quasi-static properties.
Abstract: Unsaturated polyester resin specimens embedded with small loadings of 36 nm average diameter TiO 2 particles were fabricated using a direct ultrasonification method to study the effects of nanosized particles on nanocomposite bulk mechanical properties. The ultrasonification method employed produced nanocomposites with excellent particle dispersion as verified by transmission electron microscopy (TEM). Quasi-static fracture toughness, tension, and compression testing was carried out. The presence of the particles had the greatest effect on fracture toughness; negligible influence was observed in the remaining quasi-static properties. Scanning electron microscopy (SEM) of fracture surfaces was carried out to identify toughening mechanisms. The inadequacy of the bond between the filler and the matrix and the presence of minor particle agglomerations in specimens containing higher volume fractions of particles were believed to be responsible for a consistent decrease in property values beyond a volume fraction of 1 vol.%. Dynamic fracture toughness testing was carried out, and an increase in dynamic fracture toughness relative to quasi-static fracture toughness was observed. High strain rate testing conducted using a split Hopkinson pressure bar (SHPB) apparatus revealed a moderate stiffening effect with increasing particle volume fraction, although no marked effect was observed on the ultimate strength.
TL;DR: In this article, the strain dependence of particle cracking in aluminum alloys A356/357 in the T6 temper has been studied in a range of microstructures produced by varying solidification rate and Mg content, and by chemical modification of the eutectic silicon.
Abstract: The strain dependence of particle cracking in aluminum alloys A356/357 in the T6 temper has been studied in a range of microstructures produced by varying solidification rate and Mg content, and by chemical (Sr) modification of the eutectic silicon. The damage accumulates linearly with the applied strain for all microstructures, but the rate depends on the secondary dendrite arm spacing and modification state. Large and elongated eutectic silicon particles in the unmodified alloys and large π-phase (Al9FeMg3Si5) particles in alloy A357 show the greatest tendency to cracking. In alloy A356, cracking of eutectic silicon particles dominates the accumulation of damage while cracking of Fe-rich particles is relatively unimportant. However, in alloy A357, especially with Sr modification, cracking of the large π-phase intermetallics accounts for the majority of damage at low and intermediate strains but becomes comparable with silicon particle cracking at large strains. Fracture occurs when the volume fraction of cracked particles (eutectic silicon and Fe-rich intermetallics combined) approximates 45 pct of the total particle volume fraction or when the number fraction of cracked particles is about 20 pct. The results are discussed in terms of Weibull statistics and existing models for dispersion hardening.
TL;DR: In this paper, Ni-based carbon nanotube (CNT) composite coatings with different volume fraction (from 5 to 12 vol%) of CNTs were deposited on medium carbon steel substrates by electroless plating.
TL;DR: In this paper, a micromechanical model is developed to capture the mechanical behavior of dual phase steels, adopting the constitutive behavior of the constituents from the literature, and several idealizations are investigated out of which the axisymmetric model is shown to display intrinsic ability to capture expected material behavior in terms of the trend of the stress-strain curves with increasing volume fraction of the second phase and the deformation fields of the constituent.
TL;DR: There is a crossover Mason number (ratio of viscous to magnetic forces) above which the rotation of the field prevents the particle aggregation to form chains, and at these high Mason numbers, more isotropic clusters and isolated particles appear.
Abstract: The spatiotemporal evolution of field-induced structures in very dilute polarizable colloidal suspensions subject to rotating magnetic fields has been experimentally studied using video microscopy. We found that there is a crossover Mason number (ratio of viscous to magnetic forces) above which the rotation of the field prevents the particle aggregation to form chains. Therefore, at these high Mason numbers, more isotropic clusters and isolated particles appear. The same behavior was also found in recent scattering dichroism experiments developed in more concentrated suspensions, which seems to indicate that the dynamics does not depend on the volume fraction. Scattering dichroism experiments have been used to study the role played by the volume fraction in suspensions with low concentration. As expected, we found that the crossover Mason number does not depend on the volume fraction. Brownian particle dynamics simulations are also reported, showing good agreement with the experiments.
TL;DR: In this article, a vacuum infiltration process was developed to produce aluminium alloy composites containing various volume fractions of ceramic particles, which were successfully infiltrated and the effect of infiltration temperature and volume fraction of particle on infiltration behavior was investigated.
Abstract: A vacuum infiltration process was developed to produce aluminium alloy composites containing various volume fractions of ceramic particles. The matrix composites of aluminium with 9.42 wt%Si and 0.36 wt%Mg containing up to 55 vol% SiCp were successfully infiltrated and the effect of infiltration temperature and volume fraction of particle on infiltration behaviour was investigated. In addition to aluminium powder, magnesium was used to improve the wetting of SiC particles by the molten aluminium alloy. The infiltration rate increased with increasing infiltration time, temperature and volume fraction of particle, but full infiltration appeared at the optimum process parameters for the various volumes of fraction composite compacts. In addition, the microstructure, hardness, density, porosity and wear resistance of the composites were also examined. It is observed that the distribution of SiC particles was uniform. The hardness and density of the composite increased with increasing reinforcement volume fraction and porosity decreased with increasing particle content. Moreover, the wear rate of the composite increased with increasing load and decreased with increasing particle content.
TL;DR: In this article, the influence of porosity parameters on mechanical and biological properties was investigated for β-tricalcium phosphate ceramic scaffolds with pore sizes in the range of 300-500 μm and pore volumes of 25-45% using the indirect fused deposition process.
TL;DR: In this article, the effect of thermal treatment and the resulting microstructure on the wear properties of coupons using a micro-abrasion test was investigated using a series of cobalt-chromium-molybdenum (CoCrMo) alloy sample coupons with different combinations of thermal treatments.
TL;DR: The thermal response and the coefficient of thermal expansion (CTE) of aluminum matrix composites with high volume fractions of SiC particulate have been investigated in this article, showing that the hysteresis in the thermal strain response curves is proportional to the square root of the particle surface area per unit volume of metal matrix.
TL;DR: In this article, the bulk glass forming alloy Pd43Ni10Cu27P20 is processed into a low-density amorphous metallic foam and the bubble diameter ranges between 2×10^-4 and 1×10−3 m.
Abstract: The bulk glass forming alloy Pd43Ni10Cu27P20 is processed into a low-density amorphous metallic foam. Pd43Ni10Cu27P20 is mixed with hydrated B2O3, which releases gas at elevated temperature and/or low pressure. Very homogeneous foams are achieved due to the high viscosity of the alloy even at its liquidus temperature. By processing at the liquidus temperature and decreasing the pressure to 10^–2 mbar, well-distributed bubbles expand to foam the material. Foam densities as low as 1.4×10^3 kg/m^3 were obtained, corresponding to a bubble volume fraction of 84%. The bubble diameter ranges between 2×10^–4 and 1×10^–3 m. Thermal analysis by differential scanning calorimetry confirms the amorphous nature of the foam. Furthermore, it reveals that the foam's thermal stability is comparable to the bulk material.
TL;DR: The Langevin molecular dynamics simulations systematically the influence of polydispersity in the particle size, and subsequently in the dipole moment, on the physical properties of ferrofluids show a significant effect of the small particles on the structural properties of the system.
Abstract: We study by Langevin molecular dynamics simulations systematically the influence of polydispersity in the particle size, and subsequently in the dipole moment, on the physical properties of ferrofluids. The polydispersity is in a first approximation modeled by a bidisperse system that consists of small and large particles at different ratios of their volume fractions. In the first part of our investigations the total volume fraction of the system is fixed, and the volume fraction phiL of the large particles is varied. The initial susceptibility chi and magnetization curve of the systems show a strong dependence on the value of phiL. With the increase of phiL, the magnetization M of the system has a much faster increment at weak fields, and thus leads to a larger chi. We performed a cluster analysis that indicates that this is due to the aggregation of the large particles in the systems. The average size of these clusters increases with increasing phiL. In the second part of our investigations, we fixed the volume fraction of the large particles, and increased the volume fraction phiS of the small particles in order to study their influence on the chain formation of the large ones. We found that the average aggregate size formed by large particles decreases when phiS is increased, demonstrating a significant effect of the small particles on the structural properties of the system. A topological analysis of the structure reveals that the majority of the small particles remain nonaggregated. Only a small number of them are attracted to the ends of the chains formed by large particles.
TL;DR: Carbon-carbon composites rank first among ceramic composite materials with a spectrum of properties and applications in various sectors as discussed by the authors, and are used in a variety of sectors requiring high mechanical properties at elevated temperatures, good frictional properties for brake pads in high speed vehicles or high thermal conductivity for thermal management applications.
Abstract: Carbon-carbon composites rank first among ceramic composite materials with a spectrum of properties and applications in various sectors. These composites are made of fibres in various directions and carbonaceous polymers and hydrocarbons as matrix precursors. Their density and properties depend on the type and volume fraction of reinforcement, matrix precursor used and end heat treatment temperature. Composites made with thermosetting resins as matrix precursors possess low densities (1.55–1.75g/cm3) and well-distributed microporosity whereas those made with pitch as the matrix precursor, after densification exhibit densities of 1.8–2.0g/cm3 with some mesopores, and those made by the CVD technique with hydrocarbon gases, possess intermediate densities and matrices with close porosities. The former (resin-based) composites exhibit high flexural strength, low toughness and low thermal conductivity, whereas the latter (pitch- and CVD-based) can be made with very high thermal conductivity (400–700 W/MK) in the fibre direction. Carbon-carbon composites are used in a variety of sectors requiring high mechanical properties at elevated temperatures, good frictional properties for brake pads in high speed vehicles or high thermal conductivity for thermal management applications. However, for extended life applications, these composites need to be protected against oxidation either through matrix modification with Si, Zr, Hf etc. or by multilayer oxidation protection coatings consisting of SiC, silica, zircon etc.
TL;DR: In this article, a detailed quantitative study on precipitation strengthening in AA6111, which is the alloy of choice in North America for exposed body panels, was performed using transmission electron microscopy to characterize the average size, the size distribution, the volume fraction, and the crystal structure of the hardening precipitates for aging at 180 °C.
Abstract: There is an increasing use of aluminum alloy sheet in automotive applications due to the desire to decrease vehicle weight. The current study provides a detailed quantitative study on precipitation strengthening in AA6111, which is the alloy of choice in North America for exposed body panels. Transmission electron microscopy was used to characterize the average size, the size distribution, the volume fraction, and the crystal structure of the hardening precipitates for aging at 180 °C (a) directly after solution treatment and (b) following 2 weeks of natural aging. The results indicate that both β″ and Q′ phases co-exist throughout the aging cycle with the relative amount of Q′ being increased both with increased aging time at 180 °C and when natural aging precedes aging at 180 °C. A strengthening model was developed which uses the size distribution and the volume fraction of precipitates as the primary inputs to predict the yield stress. An important feature of this model was that only one fitting parameter was necessary to give very good agreement with the experimental results.
TL;DR: In this paper, new equations for the relative viscosity of concentrated bubble-bearing suspensions are developed using a differential scheme along with the solution of an infinitely dilute suspension of bubbles, which is useful in modeling the volcanic processes.