Showing papers on "Volume fraction published in 2013"

Effect of polypropylene fiber on durability of concrete composite containing fly ash and silica fume

Abstract: A parametric experimental study has been conducted to investigate the effect of polypropylene fiber on the workability and durability of the concrete composite containing fly ash and silica fume. Four different fiber volume fractions (0.06%, 0.08%, 0.1% and 0.12%) were used. The results indicate that the addition of polypropylene fiber has a little adverse effect on the workability of concrete composite containing fly ash and silica fume. With the increase of fiber volume fraction, both of the slump and slump flow are decreasing gradually. However, the addition of polypropylene fiber has greatly improved the durability of the concrete composite containing fly ash and silica fume. The length of water permeability, the dry shrinkage strain and the carbonation depth of concrete containing fly ash and silica fume are decreasing gradually with the increase of fiber volume fraction as the fiber volume fraction is below 0.12%. Besides, freeze–thaw resistance of polypropylene fiber reinforced concrete containing fly ash and silica fume was found to slightly increase when compared to the concrete composite without fibers. Moreover, there is a tendency of increase in the freeze–thaw resistance with the increase of fiber volume fraction as the fiber volume fraction is below 0.08%. However, the freeze–thaw resistance begins to decrease slightly after the fiber volume fraction beyond 0.08%.

Thermal conductivity of porous materials

Abstract: Incorporation of porosity into a monolithic material decreases the effective thermal conductivity. Porous ceramics were prepared by different methods to achieve pore volume fractions from 4 to 95%. A toolbox of analytical relations is proposed to describe the effective thermal conductivity as a function of solid phase thermal conductivity, pore thermal conductivity, and pore volume fraction (νp). For νp 0.65, the thermal conductivity of kaolin-based foams and calcium aluminate foams was well described by the Hashin Shtrikman upper bound and Russell’s relation. Finally, numerical simulation on artificially generated microstructures yields accurate predictions of thermal conductivity when fine detail of the spatial distribution of the phases needs to be accounted for, as demonstrated with a bio-aggregate material.

Polymer reinforcement using liquid-exfoliated boron nitride nanosheets

Abstract: We have exfoliated hexagonal boron nitride by ultrasonication in solutions of polyvinylalcohol in water. The resultant nanosheets are sterically stabilised by adsorbed polymer chains. Centrifugation-based size-selection was used to give dispersions of nanosheets with aspect ratio (length/thickness) of ∼1400. Such dispersions can be used to produce polyvinylalcohol–BN composite films. Helium ion microscopy of fracture surfaces shows the nanosheets to be well dispersed and the composites to fail by pull-out. We find both modulus, Y, and strength, σB, of these composites to increase linearly with volume fraction, Vf, up to Vf ∼ 0.1 vol% BN before falling off. The rates of increase are extremely high; dY/dVf = 670 GPa and dσB/dVf = 47 GPa. The former value matches theory based on continuum mechanics while the latter value is consistent with remarkably high polymer–filler interfacial strength. However, because the mechanical properties increase over such a narrow volume fraction range, the maximum values of both modulus and strength are only ∼40% higher than the pure polymer. This phenomenon has also been observed for graphene-filled composites and represents a serious hurdle to the production of high performance polymer–nanosheet composites.

On the Selection of the Optimal Intercritical Annealing Temperature for Medium Mn TRIP Steel

Abstract: A model is proposed to predict the room temperature austenite volume fraction as a function of the intercritical annealing temperature for medium Mn transformation-induced plasticity steel. The model takes into account the influence of the austenite composition on the martensite transformation kinetics and the influence of the intercritical annealing temperature dependence of the austenite grain size on the martensite start temperature. A maximum room temperature austenite volume fraction was obtained at a specific intercritical annealing temperature T M. Ultrafine-grained ferrite and austenite were observed in samples intercritically annealed below the T M temperature. The microstructure contained a large volume fraction of athermal martensite in samples annealed at an intercritical temperature higher than the T M temperature.

Nanofluid flow and heat transfer due to a stretching cylinder in the presence of magnetic field

Abstract: In this paper, flow and heat transfer of a nanofluid over a stretching cylinder in the presence of magnetic field has been investigated. The governing partial differential equations with the corresponding boundary conditions are reduced to a set of ordinary differential equations with the appropriate boundary conditions using similarity transformation, which is then solved numerically by the fourth order Runge–Kutta integration scheme featuring a shooting technique. Different types of nanoparticles as copper (Cu), silver (Ag), alumina (Al2O3) and titanium oxide (TiO2) with water as their base fluid has been considered. The influence of significant parameters such as nanoparticle volume fraction, nanofluids type, magnetic parameter and Reynolds number on the flow and heat transfer characteristics is discussed. It was found that the Nusselt number increases as each of Reynolds number or nanoparticles volume fraction increase, but it decreases as magnetic parameter increase. Also it can be found that choosing copper (for small of magnetic parameter) and alumina (for large values of magnetic parameter) leads to the highest cooling performance for this problem.

Rheology of Disperse Systems

Abstract: The rheology of disperse systems is an important processing parameter. Being able to characterize and manipulate the flow behavior of dispersions one can ensure their optimal performance. Waterborne automotive coatings, for example, should exhibit a distinct low-shear viscosity necessary to provide good leveling but to avoid sagging at the same time. Then, a strong degree of shear thinning is needed to guarantee good pumpand sprayability. The rheological properties of dispersions, especially at high solids content, are complex and strongly dependent on the applied forces and flow kinematics. Adding particles does not simply increase the viscosity of the liquid as a result of the hydrodynamic disturbance of the flow; it also can be a reason for deviation from Newtonian behavior, including shear rate dependent viscosity, elasticity, and time-dependent rheological behavior or even the occurrence of an apparent yield stress. In colloidal systems particle interactions play a crucial role. Depending on whether attractive or repulsive interactions dominate, the particles can form different structures that determine the rheological behavior of the material. In the case of attractive particle interactions loose flocs with fractal structure can be formed, immobilizing part of the continuous phase. This leads to a larger effective particle volume fraction and, correspondingly, to an increase in viscosity. Above a critical volume fraction a sample-spanning network forms, which results in a highly elastic, gel-like behavior, and an apparent yield stress. Shear-induced breakup and recovery of floc structure leads to thixotropic behavior. Electrostatic or steric repulsion between particles defines an excluded volume that is not accessible by other particles. This corresponds to an increase in effective volume fraction and accordingly to an increase in viscosity. Crystalline or gel-like states occur at particle concentrations lower than the maximum packing fraction. Characterization of the microstructure and flow properties of dispersions is essential for understanding and controlling their rheological behavior. In this chapter we first introduce methods and techniques for standard rheological tests and then characterize the rheology of hard sphere, repulsive, and attractive particles. The effect of particle size distribution on the rheology of highly concentrated

Temperature Effect on the Nanostructure of SDS Micelles in Water.

Abstract: Sodium dodecyl sulfate (SDS) surfactants form micelles when dissolved in water. These are formed of a hydrocarbon core and hydrophilic ionic surface. The small-angle neutron scattering (SANS) technique was used with deuterated water (D2O) in order to characterize the micelle structure. Micelles were found to be slightly compressed (oblate ellipsoids) and their sizes shrink with increasing temperature. Fits of SANS data to the Mean Spherical Approximation (MSA) model yielded a calculated micelle volume fraction which was lower than the SDS surfactant (sample mixing) volume fraction; this suggests that part of the SDS molecules do not participate in micelle formation and remain homogeneously mixed in the solvent. A set of material balance equations allowed the estimation of the SDS fraction in the micelles. This fraction was found to be high (close to one) except for samples around 1 % SDS fraction. The micelle aggregation number was found to decrease with increasing temperature and/or decreasing SDS fraction.

Buckling analysis of quadrilateral laminated plates with carbon nanotubes reinforced composite layers

Abstract: The buckling behavior of quadrilateral laminated thin-to-moderately thick plates composed of perfectly bonded carbon nanotube reinforced composite (CNTRC) layers is studied. The stability equations are derived using the adjacent equilibrium (Trefftz) buckling criterion and based on the first-order shear deformation theory (FSDT) of plates. Four different profiles of the single walled carbon nanotubes (SWCNTs) distribution through the thickness of layers are considered, which include their uniform distribution (UD), functionally graded (FG) symmetric and asymmetric distributions. The stability equations subjected to arbitrary boundary conditions are discretized by employing a mapping-differential quadrature technique. The formulation and method of solution are validated by showing their fast rate of convergence and performing comparison studies with the available results in the open literature wherever possible. In addition, analytical solution for the simply supported symmetric laminated rectangular plate with CNTRC layers is derived and excellent agreement of the numerical results with the analytical solution is exhibited. Then, the effects of volume fraction of carbon nanotubes (CNTs), geometrical shape parameters, thickness-to-length ratio, different kinds of CNTs distribution along the layers thickness and boundary conditions on the critical buckling load of the quadrilateral laminated plates are investigated.

Shear Thickening in Non-Brownian Suspensions : An Excluded Volume Effect

Abstract: Shear thickening appears as an increase of the viscosity of a dense suspension with the shear rate, sometimes sudden and violent at high volume fraction. Its origin for noncolloidal suspension with non-negligible inertial effects is still debated. Here we consider a simple shear flow and demonstrate that fluid inertia causes a strong microstructure anisotropy that results in the formation of a shadow region with no relative flux of particles. We show that shear thickening at finite inertia can be explained as an increase of the effective volume fraction when considering the dynamically excluded volume due to these shadow regions.

Numerical study of the melting of nano-enhanced phase change material in a square cavity

Abstract: A comprehensive numerical study was conducted to investigate heat transfer enhancement during the melting process in a 2D square cavity through dispersion of nanoparticles. A paraffin-based nanofluid containing various volume fractions of Cu was applied. The governing equations were solved on a non-uniform mesh using a pressure-based finite volume method with an enthalpy porosity technique to trace the solid-liquid interface. The effects of nanoparticle dispersion in a pure fluid and of some significant parameters, namely nanoparticle volume fraction, cavity size and hot wall temperature, on the fluid flow, heat transfer features and melting time were studied. The results are presented in terms of temperature and velocity profiles, streamlines, isotherms, moving interface position, solid fraction and dimensionless heat flux. The suspended nanoparticles caused an increase in thermal conductivity of nano-enhanced phase change material (NEPCM) compared to conventional PCM, resulting in heat transfer enhancement and a higher melting rate. In addition, the nanofluid heat transfer rate increased and the melting time decreased as the volume fraction of nanoparticles increased. The higher temperature difference between the melting temperature and the hot wall temperature expedited the melting process of NEPCM.

Phase Diagram of Diblock Copolymers Confined in Thin Films

Abstract: The phase behaviors of diblock copolymers confined in thin films with two identical preferential surfaces are investigated using the self-consistent field theory. Around 20 morphologies, including centrosymmetric and non-centrosymmetric ones, are considered to construct the two-dimensional phase diagram with respect to the volume fraction and the film thickness, while the interaction parameter χN and the surface preferences are fixed. When these morphologies are classified into four categories of ordered phases—sphere, cylinder, perforated lamella (corresponding to gyroid phase in bulk), and lamella—the phase diagram directly reveals the impact of the film confinement on the order–order transitions as a function of volume fraction via the comparisons to those in bulk. Our results also provide a comprehensive understanding over the dependence of the structure formations on the film thickness for each volume fraction.

Role of hybrid ratio in microstructural, mechanical and sliding wear properties of the Al5083/Graphitep/Al2O3p a surface hybrid nanocomposite fabricated via friction stir processing method

Abstract: Hybrid ratio of each reinforcement phase in hybrid composite can be defined as proportion of its volume to total reinforcement volume of the composite. The hybrid ratio is an important factor which controls the participation extent of each reinforcement phase in overall properties of hybrid composites. Hence, in the present work, surface hybrid nanocomposites of Al5083/Graphite p /Al 2 O 3p with different hybrid ratios were fabricated by friction stir processing method. Subsequently, effect of hybrid ratio on microstructural, mechanical and tribological properties of the nanocomposite was investigated. Optical microscopy and scanning electron microscopy were utilized to perform microstructural observation on the samples. Hardness value measurements, tensile and pin on disk dry sliding wear tests were carried out to investigate effect of hybrid ratio on mechanical and tribological properties of the nanocomposites. Microstructural investigations displayed better distribution with less agglomeration of reinforcement for lower volume fraction of reinforcement for both alumina and graphite particles. Hardness value, yield strength, ultimate tensile strength and wear rate of the nanocomposites revealed a two stage form along with hybrid ratio variation. The results are discussed based on microstructural observations of the nanocomposites and worn surface analyses.

Main and interaction effects of matrix particle size, reinforcement particle size and volume fraction on wear characteristics of Al–SiCp composites using central composite design

Abstract: The aim of this study was to investigate the effects of matrix particle size, reinforcement particle size, volume fraction, and their interactions on the wear characteristics of Al–SiC p composites. Central composite design method was used to perform a series of experiments. The statistical analysis of experimental results showed that both main effect and interaction effect of factors investigated were effective on the wear behavior of Al–SiC p composites. Wear loss decreased as volume fraction increased; however, beyond volume fraction of 17.5%, it increased due to reinforcement particle clustering depending on volume fraction and matrix particle size to reinforcement particle size ratio. With decreasing of matrix particle size and increasing of reinforcement particle size, wear loss also decreased. However, after a certain volume fraction, large sized reinforcement particles had a negative effect on the wear resistance.

Crossover from tumbling to tank-treading-like motion in dense simulated suspensions of red blood cells

Abstract: Via computer simulations, we provide evidence that the shear rate induced red blood cell tumbling-to-tank-treading transition also occurs at quite high volume fractions, where collective effects are important. The transition takes place as the ratio of effective suspension stress to the characteristic cell membrane stress exceeds a certain value and does not explicitly depend on volume fraction or cell deformability. This value coincides with that for a transition from an orientationally less ordered to a highly ordered phase. The average cell deformation does not show any signature of transition, but rather follows a simple scaling law independent of volume fraction.

Theoretical analysis of natural fiber volume fraction of reinforced composites

Abstract: In the latest years industry is attempting to decrease the dependence on petroleum based fuels and products due to the increased environmental consciousness. This is leading to the need to investigate environmentally friendly, sustainable materials to replace existing ones, and to solve the problems of recycling of agriculture waste. We are trying to understand composites due to their high potential as a material with suitable strength, low weight and low deformation. Fiber and epoxy as lamina are used to form composite laminates with desired directional properties. Mechanical properties for composites are derived starting from properties of fiber and matrix, using the rule of mixtures, and the fiber volume fraction plays a significant role in the determination of the mechanical properties. In this work the value of the fiber volume fraction is determined considering fibrous structure constituent, random fiber, yarns or fabric.

Spontaneous Transition of Micelle–Vesicle–Micelle in a Mixture of Cationic Surfactant and Anionic Surfactant-like Ionic Liquid: A Pure Nonlipid Small Unilamellar Vesicular Template Used for Solvent and Rotational Relaxation Study

Abstract: The micelle–vesicle–micelle transition in aqueous mixtures of the cationic surfactant cetyl trimethyl ammonium bromide (CTAB) and the anionic surfactant-like ionic liquid 1-butyl-3-methylimidazolium octyl sulfate, [C4mim][C8SO4] has been investigated by using dynamic light scattering (DLS), transmission electron microscopy (TEM), surface tension, conductivity, and fluorescence anisotropy at different volume fractions of surfactant. The surface tension value decreases sharply with increasing CTAB concentration up to ∼0.38 volume fraction and again increases up to ∼0.75 volume fraction of CTAB. Depending upon their relative amount, these surfactants either mixed together to form vesicles and/or micelles, or both of these structures were in equilibrium. Fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene (DPH), incorporated in this system at different composition of surfactant indicates the formation of micelle and vesicle structures. The apparent hydrodynamic diameter of these large multilamellar vesic...