Showing papers on "Volume fraction published in 2011"
TL;DR: In this article, two empirical correlations for predicting the effective thermal conductivity and dynamic viscosity of nanofluids, based on a high number of experimental data available in the literature, are proposed and discussed.
971 citations
TL;DR: The impact of CNT density on thermal conduction considering boundary resistances, increased defect concentrations, and the possibility of suppressed phonon modes in the CNTs is discussed.
Abstract: Nanostructured composites containing aligned carbon nanotubes (CNTs) are very promising as interface materials for electronic systems and thermoelectric power generators. We report the first data for the thermal conductivity of densified, aligned multiwall CNT nanocomposite films for a range of CNT volume fractions. A 1 vol % CNT composite more than doubles the thermal conductivity of the base polymer. Denser arrays (17 vol % CNTs) enhance the thermal conductivity by as much as a factor of 18 and there is a nonlinear trend with CNT volume fraction. This article discusses the impact of CNT density on thermal conduction considering boundary resistances, increased defect concentrations, and the possibility of suppressed phonon modes in the CNTs.
459 citations
TL;DR: Investigation of the yielding behaviour of frustrated colloid–polymer systems with equal attraction strength and range indicated distinct shear rate regimes: At steady state, low and intermediate shear rates create denser or smaller flowing clusters, whereas high rates may lead to complete break-up into independent particles.
Abstract: Steady and oscillatory rheology was utilized to study the mechanical response of colloidal glasses and gels with particular emphasis in their yielding behaviour. We used a suspension of hard sphere colloidal particles with short-range depletion attractions induced by the addition of non-adsorbing linear polymer. While high volume fraction hard sphere glasses exhibit a single yield point due to cage breaking, attraction dominated glasses show a two-step yielding reflecting bond and cage breaking, respectively. Here we investigated the yielding behaviour of frustrated colloid–polymer systems with equal attraction strength and range, varying the particle volume fraction, φ, spanning the region from an attractive glass (φ = 0.6) to a low volume fraction (φ = 0.1) attractive gel. Yielding throughout this range, probed both by oscillatory and steady shear, is found to remain a two step process until very low φ's. The first yield strain related with in-cage or inter-cluster bond braking remains constant for φ > 0.3 while the second yield strain, attributed to braking of cages or clusters into smaller constituents, increases as volume fraction is decreased due to enhancement of structural inhomogeneities in the gel. Steady shear tests indicated distinct shear rate regimes: At steady state, low and intermediate shear rates create denser or smaller flowing clusters, whereas high rates may lead to complete break-up into independent particles. When the range of attraction was increased, both yield strains increased scaling with the range of attraction and accompanied structural changes. Finally, ageing leads to an overall strengthening of both the gel and the attractive glass accompanied by an enhancement of the second stress overshoot in steady shear, while the attractive glass also becomes more brittle.
281 citations
TL;DR: In this paper, the viscosity of the stable nanofluids, prepared by dispersing 40-nm diameter spherical CuO nanoparticles in gear oil, was investigated.
262 citations
TL;DR: In this article, the authors investigated the effect of the dislocation density and dislocation character on the work hardening of Type 304 stainless steel and showed that the strengthening mechanism in cold-rolled Type 304 steel changes with differences in the dislocations density between the γ and the α′ phase.
258 citations
25 Jan 2011-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the authors investigated the structural, mechanical properties and wear resistance of FSP-processed materials as a function of volume fraction of SiC particles and found that adding micro-and nano-sized particles decreases the tensile strength and percent elongation.
Abstract: In this experiment, copper-base composites reinforced with 30 nm and 5 μm SiC particles are fabricated on the surface of a purecopper sheetvia friction stir processing (FSP). Microstructure, mechanical properties and wear resistance of friction stir processed (FSPed) materials are investigated as a function of volume fraction of SiC particles. Results show that, applying FSP, without SiC particles, increases the percent elongation significantly (more than 2.5 times) and decreases copper's strength. Adding micro- and nano-sized SiC particles decreases the tensile strength and percent elongation. Increasing the volume fraction or decreasing the reinforcing particle size enhances the tensile strength and wear resistance and lowers the percent elongation.
248 citations
TL;DR: Carbon black nanofluids had good absorption ability of solar energy and can effectively enhance the solar absorption efficiency.
Abstract: In this article, carbon black nanofluids were prepared by dispersing the pretreated carbon black powder into distilled water The size and morphology of the nanoparticles were explored The photothermal properties, optical properties, rheological behaviors, and thermal conductivities of the nanofluids were also investigated The results showed that the nanofluids of high-volume fraction had better photothermal properties Both carbon black powder and nanofluids had good absorption in the whole wavelength ranging from 200 to 2,500 nm The nanofluids exhibited a shear thinning behavior The shear viscosity increased with the increasing volume fraction and decreased with the increasing temperature at the same shear rate The thermal conductivity of carbon black nanofluids increased with the increase of volume fraction and temperature Carbon black nanofluids had good absorption ability of solar energy and can effectively enhance the solar absorption efficiency
226 citations
TL;DR: Inherently hydrophilic Fe(3)O(4) nanoparticles can be used to prepare stable dodecane- water and silicone-water emulsions, but they cannot stabilize butyl butyrate-water and decanol-water mixtures with macroscopic phase separation occurring, which is in good agreement with the contact angle data.
Abstract: Superparamagnetic Fe(3)O(4) nanoparticles prepared by a classical coprecipitation method were used as the stabilizer to prepare magnetic Pickering emulsions, and the effects of particle concentration, oil/water volume ratio, and oil polarity on the type, stability, composition, and morphology of these functional emulsions were investigated. The three-phase contact angle (θ(ow)) of the Fe(3)O(4) nanoparticles at the oil-water interface was evaluated using the Washburn method, and the results showed that for nonpolar and weakly polar oils of dodecane and silicone, θ(ow) is close to 90°, whereas for strongly polar oils of butyl butyrate and 1-decanol, θ(ow) is far below 90°. Inherently hydrophilic Fe(3)O(4) nanoparticles can be used to prepare stable dodecane-water and silicone-water emulsions, but they cannot stabilize butyl butyrate-water and decanol-water mixtures with macroscopic phase separation occurring, which is in good agreement with the contact angle data. Emulsions are of the oil-in-water type for both dodecane and silicone oil, and the average droplet size increases with an increase in the oil volume fraction. For stable emulsions, not all of the particles are adsorbed to drop interfaces; the fraction adsorbed decreases with an increase in the initial oil volume fraction. Changes in the particle concentration have no obvious influence on the stability of these emulsions, even though the droplet size decreases with concentration.
226 citations
TL;DR: In this article, a novel chemical reduction followed by calcination at considerably low temperature is used to synthesize copper oxide decorated graphene (CuO/HEG), and the thermal transport properties of those nanofluids are studied.
Abstract: In the present work, a novel chemical reduction followed by calcination at considerably low temperature is used to synthesize copper oxide decorated graphene (CuO/HEG). Graphene has been synthesized via hydrogen induced exfoliation/reduction of graphite oxide. As-synthesized graphene is functionalized in acid medium to decorate copper oxide nanoparticles as well as to disperse it in polar medium. CuO/HEG is dispersed in deionized (DI) water and ethylene glycol without any surfactant, and the thermal transport properties of those nanofluids are studied. Thermal conductivity of CuO/HEG dispersed in DI water based nanofluid shows an enhancement of ∼28% at 25 °C for a volume fraction of 0.05%. In addition to thermal conductivity, the electrical conductivity of the nanofluids is also measured for different volume fractions at different temperatures. Heat transfer coefficient is measured in an indigenously fabricated setup for different volume fractions for different flow rates.
189 citations
TL;DR: The results indicate that higher aspect ratio fillers show promising potential to improve the energy density of nanocomposites, leading to the development of advanced capacitors with high energy density.
Abstract: High energy storage plays an important role in the modern electric industry. Herein, we investigated the role of filler aspect ratio in nanocomposites for energy storage. Nanocomposites were synthesized using lead zirconate titanate (PZT) with two different aspect ratio (nanowires, nanorods) fillers at various volume fractions dispersed in a polyvinylidene fluoride (PVDF) matrix. The permittivity constants of composites containing nanowires (NWs) were higher than those with nanorods (NRs) at the same inclusion volume fraction. It was also indicated that the high frequency loss tangent of samples with PZT nanowires was smaller than for those with nanorods, demonstrating the high electrical energy storage efficiency of the PZT NW nanocomposite. The high aspect ratio PZT NWs showed a 77.8% increase in energy density over the lower aspect ratio PZT NRs, under an electric field of 15 kV mm − 1 and 50% volume fraction. The breakdown strength was found to decrease with the increasing volume fraction of PZT NWs, but to only change slightly from a volume fraction of around 20%–50%. The maximum calculated energy density of nanocomposites is as high as 1.158 J cm − 3 at 50% PZT NWs in PVDF. Since the breakdown strength is lower compared to a PVDF copolymer such as poly(vinylidene fluoride-tertrifluoroethylene-terchlorotrifluoroethylene) P(VDF-TreEE-CTFE) and poly(vinylidene fluoride-co-hexafluoropropylene) P(VDF-HFP), the energy density of the nanocomposite could be significantly increased through the use of PZT NWs and a polymer with greater breakdown strength. These results indicate that higher aspect ratio fillers show promising potential to improve the energy density of nanocomposites, leading to the development of advanced capacitors with high energy density.
185 citations
TL;DR: In this article, a slurry-based process was developed to achieve the uniform dispersion of a high volume fraction of carbon nanotubes (CNTs) in aluminum powder.
TL;DR: In this article, a new homogenization framework for magnetoelastic composites accounting for the effect of magnetic dipole interactions, as well as finite strains, was proposed, which is capable of handling strongly nonlinear effects associated with finite strains and magnetic saturation of the particles at sufficiently high deformations and magnetic fields, respectively.
Abstract: This paper proposes a new homogenization framework for magnetoelastic composites accounting for the effect of magnetic dipole interactions, as well as finite strains. In addition, it provides an application for magnetorheological elastomers via a “partial decoupling” approximation splitting the magnetoelastic energy into a purely mechanical component, together with a magnetostatic component evaluated in the deformed configuration of the composite, as estimated by means of the purely mechanical solution of the problem. It is argued that the resulting constitutive model for the material, which can account for the initial volume fraction, average shape, orientation and distribution of the magnetically anisotropic, non-spherical particles, should be quite accurate at least for perfectly aligned magnetic and mechanical loadings. The theory predicts the existence of certain “extra” stresses—arising in the composite beyond the purely mechanical and magnetic (Maxwell) stresses—which can be directly linked to deformation-induced changes in the microstructure. For the special case of isotropic distributions of magnetically isotropic, spherical particles, the extra stresses are due to changes in the particle two-point distribution function with the deformation, and are of order volume fraction squared, while the corresponding extra stresses for the case of aligned, ellipsoidal particles can be of order volume fraction, when changes are induced by the deformation in the orientation of the particles. The theory is capable of handling the strongly nonlinear effects associated with finite strains and magnetic saturation of the particles at sufficiently high deformations and magnetic fields, respectively.
TL;DR: In this paper, aluminum nitride nanoparticles (AlNs) have been found to be a good additive for enhancing the thermal conductivity of traditional heat exchange fluids, at a volume fraction of 0.1.
TL;DR: In this article, the authors investigated the nonlinear rheological response of colloidal gels with an intermediate volume fraction and variable interparticle attraction and observed two distinct yielding processes.
Abstract: The depletion attraction, induced upon addition of a nonadsorbing polymer to a colloidal solution, can lead to gel formation at sufficiently high polymer concentrations, which corresponds to strong attractive interactions. We have investigated the nonlinear rheological response, in particular the yielding, of colloidal gels with an intermediate volume fraction and variable interparticle attraction. Two distinct yielding processes are observed in both oscillatory experiments, namely, dynamic strain sweeps and transient experiments, here step rate, creep, and recovery tests. The first yielding process occurs at strains similar to the range of the interparticle potential and is interpreted as the breaking of bonds, which destroys the particle network and leads to individual clusters. The process of bond breaking is successfully modeled as the escape of a particle from the potential well of its nearest neighbor. The second yield point occurs at larger strains and is related to the deformation and fragmentatio...
25 Jan 2011-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the α-phase nucleated after 10min isothermal holding time at 673 K, and the volume fraction increased to more than 80% after 8h of holding time.
Abstract: Development of different morphologies of the α-phase and their influence on the mechanical properties during low temperature isothermal aging of the near-β titanium alloy Ti–5Al–5Mo–5V–3Cr (Ti-5553) have been studied. A wide variety of different morphologies of the α-phase resulted from variations of the isothermal temperature and/or time. While after aging at 673 K or higher, a Widmanstatten star-shape was the dominant morphology of the α-phase, aging at lower temperatures resulted in the formation of triangular-shaped precipitate morphology. The first α-phase nucleated after 10 min isothermal holding time at 673 K, and the volume fraction increased to more than 80% after 8 h of holding time. This increase in the volume fraction of the α-phase caused an increase in the micro-hardness of the bulk material. X-ray diffraction and microstructural analyses provided evidence of ω-assisted nucleation of the α-phase. It is proposed that this mechanism by which the α-phase nucleates on pre-existing ω-phase particles account for the formation of the very large number of small α-particles that precipitated in the β-matrix.
TL;DR: In this paper, the stiffness of cellulose nanocrystals or whiskers has been investigated and a correlation exists between stiffness of the films and aspect ratio of the constituent rod-like nanoparticles.
TL;DR: In this article, the authors studied the mechanical behaviour of concrete reinforced with steel fibres of different geometry and volume fraction and found improvement in the mechanical properties, in particular the toughness, was observed with the increase of the volume fraction of steel-fibres in the concrete.
Abstract: This work aims in studying the mechanical behaviour of concrete, reinforced with steel fibres of different geometry and volume fraction. Experiments include compression tests and fourpoint bending tests. Slump and air content tests were performed on fresh concrete. The flexural toughness, flexural strength and residual strength factors of the beam specimens were evaluated in accordance with ASTM C1609/C1609M-05 standard. Improvement in the mechanical properties, in particular the toughness, was observed with the increase of the volume fraction of steel-fibres in the concrete. The fibre geometry was found to be a key factor affecting the mechanical performance of the material.
TL;DR: In this paper, the effect of temperature cycle on the void volume fraction, shape and spatial distribution was determined by means of X-ray microtomography in 10 AS4/8552 composite laminates manufactured by compression molding.
TL;DR: In this article, the effect of the solution treatment on the tensile property and fracture toughness of aluminum alloy 7050 were investigated by means of optical microscopy, scanning electron microscopy (SEM), transmission electron microscope (TEM), tensile test and the plane-strain fracture toughness test.
25 Mar 2011-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the effect of residual Al at the intermetallic centerline on composite strength and fracture toughness, as well as fracture and failure modes were investigated with an emphasis on the effect on the residual Al.
Abstract: Metal-intermetallic laminate (MIL) composites consisting of alternating layers of Ti, Al, and the intermetallic Al3Ti have been fabricated by reactive foil sintering in open air. Six initially identical stacks of alternating Ti–3Al–2.5 V and 1100-Al foils were processed for different lengths of time, yielding specimens with different metal and intermetallic volume fractions. Their mechanical properties have been investigated with an emphasis on the effect of residual Al at the intermetallic centerline on composite strength and fracture toughness, as well as fracture and failure modes. Samples were cut from each composite plate (in layer orientations parallel and perpendicular to the intended load direction) for mechanical testing in compression and four-point bending under quasi-static and high-rate loading conditions. Examination of the damaged specimens and their fracture surfaces by optical and scanning electron microscopy was performed to establish a correlation between the failure mechanisms present, composite strength, and microstructure. Results indicated that regardless of loading direction, cracks always initiated in the intermetallic region, rarely at the centerline, and crack propagation and failure were heavily influenced by the thickness of the residual aluminum layers. There is an ideal residual aluminum volume fraction that represents the amount of ductile reinforcement that maximizes the combined properties of strength, toughness and stiffness.
TL;DR: In this paper, temperature induced degradation in Solid Oxide Fuel Cell (SOFC) Ni-YSZ anodes was studied using both impedance spectroscopy and three-dimensional tomography via Focused Ion Beam-Scanning Electron Microscopy.
TL;DR: In this article, the N-layered spherical inclusion theory is applied to develop a multi-scale model to predict the effective diffusion coefficient of chloride ion in concrete, which treats concrete as four-phase composite materials consisting of matrix phase, aggregate phase, ITZ (interfacial transition zone) and their homogenization phase.
TL;DR: In this paper, the effects of coherent and incoherent interfaces in large-scale simulations were analyzed for a bi-material and a tri-material system composed of both coherent and non-coherent interfaces.
TL;DR: In this paper, a homogeneous and stable magnetic nanofluids containing iron oxide nanoparticles, α-Fe2O3 (hematite) and Fe3O4 (magnetite) in ethylene glycol, were prepared at concentrations up to 25% in mass fraction.
Abstract: Homogeneous and stable magnetic nanofluids containing iron oxide nanoparticles, α-Fe2O3 (hematite) and Fe3O4 (magnetite) in ethylene glycol, were prepared at concentrations up to 25% in mass fraction. Commercial Hexagonal Scalenohedral-shaped α-Fe2O3 nanoparticles were selected while Fe3O4 nanoparticles were synthesized using a coprecipitation method. The products were characterized by transmission and scanning electron microscopy and x-ray diffraction. The thermal conductivity of both nanofluids was measured as a function of volume fraction and temperature. The results illustrate that the enhanced thermal conductivity of the nanofluids increases with volume fraction but is temperature independent. The experimental results show that both types of nanoparticles in this base fluid present no significant aggregation. These experimental values were also compared with theoretical models. Moreover, the density of these nanofluids was measured as a function of volume fraction, temperature, and pressure. The volu...
TL;DR: In this article, a physically-based model for large deformation stress-strain response and anisotropic damage in rubber-toughened glassy polymers is developed.
TL;DR: In this paper, the electrostrictive properties of polyether-based polyurethane elastomer and its corresponding composites filled with conductive carbon black (CB) were studied by measuring the thickness strain SZ induced by external electric fields E.
TL;DR: In this paper, the glass transition and thermoelastic properties of cross-linked epoxy-based nanocomposites and their filler-size dependency are investigated through molecular dynamics simulations.
TL;DR: In this paper, a diamond-particle-dispersed-aluminum (Al) matrix composites were fabricated in a unique fabrication method where continuous solid-liquid co-existent state of the powder mixture of diamond, pure Al and Al 5mass%Si alloy was designed during spark plasma sintering (SPS) process.
Abstract: Diamond-particle-dispersed-aluminum (Al) matrix composites were fabricated in a unique fabrication method where continuous solid–liquid co-existent state of the powder mixture of diamond, pure Al and Al–5mass%Si alloy was designed during spark plasma sintering (SPS) process. Microstructures and thermal properties of the composites fabricated in such a way were investigated. The composites can be well consolidated in the temperature range between 773 K and 878 K and scanning electron microscopy detects no reaction at the interface between the diamond particle and the Al matrix. The relative packing density of the diamond–Al composite fabricated was 99% or higher in a volume fraction range of diamond between 35 and 50%. The thermal conductivity of the diamond–Al composite containing 50 vol.% diamond reached 552 W/mK, higher than 95% the theoretical thermal conductivity calculated by Maxwell–Eucken’s equation. The coefficient of thermal expansion of the composites falls in the upper line of Kerner’s model, indicating strong bonding between the diamond particle and the Al matrix in the composite.
TL;DR: In this article, the collective effect of a high volume fraction of ∑3 twin boundaries on the response of nanotwinned Cu to high dose He implantation near room temperature was investigated.
Abstract: We investigate the collective effect of a high volume fraction of ∑3 twin boundaries on the response of nanotwinned Cu to high dose He implantation near room temperature and find that they do not curtail the formation of vacancy and interstitial clusters. This result is rationalized through atomistic modeling, which shows that point defects at these boundaries have nearly identical properties to those in pure fcc Cu.
TL;DR: In this paper, the effects of rare earth element addition on the microstructure evolution, thermal stability and shear strength of AZ91 alloy were investigated in the as-cast and annealed conditions.