Influence Of Particle Volume Fraction Research Articles

Optimal design of laminated-MRE bearings with multi-scale model

In the design of a laminated magneto-rheological elastomeric bearing (MREB), the passive rubbers are replaced with composite layers of rubber and MREs. The applied magnetic field, produced by the built-in electromagnet through the input current, changes the stiffness and damping of MREs, and thus that of the device. Typically, a good MREB should possess higher adjustable properties with less activating power in avoiding overheating problem. Thus an optimized design of MREB should integrate the MRE material design into mechanical and electromagnetic components to achieve a trade-off between power consumption and adjustability of stiffness. In this study, we propose a method to analyze and design a laminated MRE bearing, in which the optimal parameters of materials and mechanical structure of the MRE bearing are determined. Based on the multi-scale and magneto-mechanical coupling theories, we establish a multi-scale model for the MRE bearing considering the influence of particle volume fraction, particle distribution, and thickness of MRE laminated layers on its mechanical performance. Within the micro-scale analysis, the representative volume unit is used to address the effect of particle volume fraction and distribution on mechanical and magnetic properties of MRE itself. Within the macro-scale analysis, we build both mechanical and magnetic models for the laminated MRE bearing. Based on the theoretical analysis, a laminated MRE bearing with four-layer MRE is designed and fabricated. The performance of the MRE bearing has been tested by using MTS test bench. The results are compared with that of model analysis. Both experimental and theoretical results indicate that optimal design of MREB depends on the MRE’s particle volume fraction which is related with MREB’s input power limitation.

English

This paper reports on the application of a special purpose finite element analysis tool that combines augmented finite element methodologies (AFEM) and cohesive zone model (CZM) methods to simulate initiation and propagation of both cohesive and adhesive cracks. The constitutive behaviour of an aluminium/silicon carbide metal matrix composite was predicted and compared with experimental data as an example of a material system controlled by cohesive cracks. The simulation allowed to determine the strain level, at which particle fracture was initiated and illustrates how the overall material response is dominated by particle fracture beyond that strain level. The effects of silica filler particles on the lifetime of polyurethane matrix aircraft coating systems were investigated in a second example in which adhesive cracks at the filler/matrix interface are a dominant failure mechanism. The influence of particle volume fraction and particle/matrix interface adhesion strength on coating lifetime predictions were investigated and the results show that low filler particle volume fraction and high interface adhesion strength improve coating durability. In general, the paper demonstrates the potential of combined AFEM and CZM micromechanical damage simulation to gain improved understanding of damage mechanisms in heterogeneous materials and to support analysis and design of advanced material systems. Key words: Augmented finite element method, phantom node method, cohesive zone modelling, metal matrix composite, aircraft coatings.

CFD–DEM simulations of current-induced dune formation and morphological evolution

Understanding the fundamental mechanisms of sediment transport, particularly those during the formation and evolution of bedforms, is of critical scientific importance and has engineering relevance. Traditional approaches of sediment transport simulations heavily rely on empirical models, which are not able to capture the physics-rich, regime-dependent behaviors of the process. With the increase of available computational resources in the past decade, CFD–DEM (computational fluid dynamics–discrete element method) has emerged as a viable high-fidelity method for the study of sediment transport. However, a comprehensive, quantitative study of the generation and migration of different sediment bed patterns using CFD–DEM is still lacking. In this work, current-induced sediment transport problems in a wide range of regimes are simulated, including ‘flat bed in motion’, ‘small dune’, ‘vortex dune’ and suspended transport. Simulations are performed by using SediFoam, an open-source, massively parallel CFD–DEM solver developed by the authors. This is a general-purpose solver for particle-laden flows tailed for particle transport problems. Validation tests are performed to demonstrate the capability of CFD–DEM in the full range of sediment transport regimes. Comparison of simulation results with experimental and numerical benchmark data demonstrates the merits of CFD–DEM approach. In addition, the improvements of the present simulations over existing studies using CFD–DEM are presented. The present solver gives more accurate prediction of sediment transport rate by properly accounting for the influence of particle volume fraction on the fluid flow. In summary, this work demonstrates that CFD–DEM is a promising particle-resolving approach for probing the physics of current-induced sediment transport.

A Fatigue Model for Discontinuous Particulate-Reinforced Aluminum Alloy Composite: Influence of Microstructure

In this paper, the use of a microstructure-sensitive fatigue model is put forth for the analysis of discontinuously reinforced aluminum alloy metal matrix composite. The fatigue model was used for a ceramic particle-reinforced aluminum alloy deformed under conditions of fully reversed strain control. Experimental results revealed the aluminum alloy to be strongly influenced by volume fraction of the particulate reinforcement phase under conditions of strain-controlled fatigue. The model safely characterizes the evolution of fatigue damage in this aluminum alloy composite into the distinct stages of crack initiation and crack growth culminating in failure. The model is able to capture the specific influence of particle volume fraction, particle size, and nearest neighbor distance in quantifying fatigue life. The model yields good results for correlation of the predicted results with the experimental test results on the fatigue behavior of the chosen aluminum alloy for two different percentages of the ceramic particle reinforcement. Further, the model illustrates that both particle size and volume fraction are key factors that govern fatigue lifetime. This conclusion is well supported by fractographic observations of the cyclically deformed and failed specimens.

Viscosity of carbon nanotubes water-based nanofluids: Influence of concentration and temperature

Experimental results on the steady-state viscosity of carbon nanotubes water-based nanofluids are presented considering the influence of particle volume fraction and temperature ranging from 0 to 40 °C. The suspensions consist of multi-walled carbon nanotubes dispersed in de-ionized water and they are stabilized by a surfactant. The aspect ratio of nanotubes is close to 160 and the particle volume fraction varies between 0.0055% and 0.55%. It is shown that the nanofluids behave as shear-thinning materials for high particle content. For lower particle content, the nanofluids are quite Newtonian. It is also observed that the relative viscosity of nanofluids at high shear rate does not vary with temperature. Moreover, the evolution of relative viscosity at high shear rate is well predicted by the Maron–Pierce model considering the effect of nanoparticles agglomerates.

On the Volume Fraction Effects of Inertial Colliding Particles in Homogeneous Isotropic Turbulence

Abstract The main objective of the present study is the investigation of volume fraction effects on the collision statistics of nonsettling inertial particles in a granular medium as well as suspended in an unsteady homogeneous isotropic turbulent flow. For this purpose, different studies with mono-disperse Lagrangian point-particles having different Stokes numbers are considered in which the volume fraction of the dispersed phase is varied between 0.001 and 0.01. The fluid behavior is computed using a three-dimensional Lattice-Boltzmann method. The carrier-fluid turbulence is maintained at Taylor microscale Reynolds number 65.26 by applying a spectral forcing scheme. The Lagrangian particle tracking is based on considering the drag force only and a deterministic model is applied for collision detection. The influence of the particle phase on the fluid flow is neglected at this stage. The particle size is maintained at a constant value for all Stokes numbers so that the ratio of particle diameter to Kolmogorov length scale is fixed at 0.58. The variation of the particle Stokes number was realized by modifying the solids density. The observed particle Reynolds and Stokes numbers are in between [1.07, 2.61] and [0.34, 9.79], respectively. In the present simulations, the fluid flow and the particle motion including particle-particle collisions are based on different temporal discretization. Hence, an adaptive time stepping scheme is introduced. The particle motion as well as the occurrence of inter-particle collisions is characterized among others by Lagrangian correlation functions, the velocity angles between colliding particles and the collision frequencies. Initially, a fluid-free particle system is simulated and compared with the principles of the kinetic theory to validate the implemented deterministic collision model. Moreover, a selection of results obtained for homogeneous isotropic turbulence is compared with in literature available DNS and LES results as well. According to the performed simulations, the collision rate of particles with large Stokes numbers strongly depends on the adopted volume fraction, whereas for particles with small Stokes numbers the influence of particle volume fraction is less pronounced.

CFD Analysis of Two-Phase Flow in a Solid-Liquid Hydrocyclone

This paper presents a performance analysis of a solid-liquid hydrocyclone using Ansys-CFX software. Based on the simulation, the influence of particle volume fraction of feed flow, mean diameter of particles and viscosity of liquid phase on the two-phase flow and separating performance has been investigated for optimizing design.

Electrokinetic and rheological properties of highly concentrated kaolin dispersions: Influence of particle volume fraction and dispersant concentration

An industrial kaolin was selected and characterised. Different dispersions were prepared with solids volume fractions between ϕ = 0.20 and ϕ = 0.47 in the presence of sodium silicate (between X s = 0.075 mg dispersant/m 2 and X s = 0.225 mg dispersant/m 2), to determine the electrokinetic and rheological properties. The Fe, Ca, Mg, Na, and Si concentrations, pH, and electrical conductivity of the solutions increased after dispersant addition, X s, and/or the solids volume fraction, ϕ, was raised. Electrophoretic mobility, negative for all studied dispersions, became more negative after dispersant addition and less negative with increasing solids fraction. The dispersions with X s ≤ 0.075 mg dispersant/m 2 displayed plastic behaviour (in the shear flow test) and exhibited the characteristics of a gel (in the oscillatory test), owing to the extensive aggregation of the kaolinite particles. The dispersions with X s ≥ 0.105 mg dispersant/m 2 displayed shear-thinning behaviour (in the shear flow test) and viscoelastic fluid characteristics (in the oscillatory test). This behaviour is typical of dense dispersions of plate-shaped colloidal particles, which are well stabilised by electrostatic repulsion. The rheological properties of well-stabilised dispersions were analysed and readily interpreted by redefining the kaolin platelets as new effective hard particles, the thickness of the plate-like particle with its ionic double layer being considered as effective thickness. This enabled an effective volume fraction to be calculated that describes the combined effect of the solids volume fraction and the dispersant addition on dispersion rheological properties. The study showed that excluded volume interactions are essential to understanding the effect of ionic strength on the rheological properties of well-stabilised highly concentrated dispersions.

Second-order moment model for dense two-phase turbulent flow of Bingham fluid with particles

The USM-ϑ model of Bingham fluid for dense two-phase turbulent flow was developed, which combines the second-order moment model for two-phase turbulence with the particle kinetic theory for the inter-particle collision. In this model, phases interaction and the extra term of Bingham fluid yield stress are taken into account. An algorithm for USM-ϑ model in dense two-phase flow was proposed, in which the influence of particle volume fraction is accounted for. This model was used to simulate turbulent flow of Bingham fluid single-phase and dense liquid-particle two-phase in pipe. It is shown USM-ϑ model has better prediction result than the five-equation model, in which the particle-particle collision is modeled by the particle kinetic theory, while the turbulence of both phase is simulated by the two-equation turbulence model. The USM-ϑ model was then used to simulate the dense two-phase turbulent up flow of Bingham fluid with particles. With the increasing of the yield stress, the velocities of Bingham and particle decrease near the pipe centre. Comparing the two-phase flow of Bingham-particle with that of liquid-particle, it is found the source term of yield stress has significant effect on flow.

Optical characterization of concentrated dispersions: applications to laboratory analyses and on‐line process monitoring and control

AbstractLight scattering methods are often used to study the stability of suspensions or emulsions and to estimate the dispersed phase properties such as particle size and volume fraction. However, such optical methods often require a previous dilution of the dispersion because of a limited measurement range, and are then unable to give information about the real physical state of dense heterogeneous media. A new technology based on multiple light scattering analysis and called Turbiscan has been recently developed by a French company, Formulaction, to fill this gap and to characterize both diluted and concentrated dispersions. In the first part, we review the physical concepts of multiple light scattering by dispersions. In relation to the optical analyser Turbiscan, we present physical and statistical models for the radiative transfer in dense suspensions. In the second part, we investigate the influence of particle volume fraction and particle size (polystyrene latex bead suspensions) on the backscattered and transmitted light fluxes measured by Turbiscan. The experimental data are compared with results from the physical models. In the last section, we use the optical analyser Turbiscan Lab to detect and characterize various concentrated dispersions destabilization (coalescence, flocculation, creaming and sedimentation), and then the Turbiscan On Line to monitor and characterize an emulsification process under ultrasonic agitation. Copyright © 2004 Society of Chemical Industry

Influence of Particle Volume Fraction on Packing in Responsive Hydrogel Colloidal Crystals

We describe the influence of particle concentration on the formation of crystals from soft colloidal particles. Specifically, laser scanning confocal and differential interference contrast microscopies are used to directly observe the packing in entropic crystals formed from submicron-sized particles composed of the thermoresponsive polymer poly-N-isopropylacrylamide (pNIPAm) and the thermoresponsive/pH-responsive copolymer poly-N-isopropylacrylamide-co-acrylic acid (pNIPAm-AAc). Close-packed crystals are observed when either the pNIPAm and pNIPAm-AAc particles are concentrated by centrifugation. At that point the particle−particle spacing is smaller than the hydrodynamic diameter as determined by photon correlation spectroscopy, reflecting compression of the soft particles. Upon dilution of the pNIPAm crystals, the melting point of the assembly is reached when the repulsive particle interactions are no longer sufficient to dictate long-range order in the assembly. However, excellent crystallization is ob...

Influence of particle volume fraction, shape, and aspect ratio on the behavior of particle-reinforced metal–matrix composites at high rates of strain

Compressive plastic deformation of particle-reinforced metal–matrix composites is investigated through numerical modeling at high rates of strain. The numerical modeling is performed using axisymmetric unit cell models, with the particles treated as elastic ellipsoids or cylinders embedded within a viscoplastic matrix. The constitutive behavior of the matrix material uses a power law strain-rate hardening formulation and is obtained from independent experimental results on the matrix. The flow stress of the composites is predicted over a range of strain rates for different particle volume fractions and for varying particle shapes and particle aspect ratios. The results show that both the flow stress and the strain-rate hardening increase with increasing volume fraction of the reinforcement. It is also shown that the rate-dependent flow stress is influenced not only by particle aspect ratio but also by particle shape (spheroidal or cylindrical). A simple analytical model has been constructed that is able to capture the quantitative features of the computational predictions. Both computational and analytical models have been compared with experimental data on two different composites from two different sources in the literature, with excellent quantitative agreement on the rate-dependent stress–strain behavior.

Incremental damage theory and its application to glass-particle-reinforced nylon 66 composites

This paper deals with influence of particle volume fraction and debonding damage between particles and matrix on the stress-strain response in particle-reinforced ductile matrix composites. Tensile tests are carried out on seven kinds of glass-particle-reinforced nylon 66 composites, which are different in a particle volume fraction and treatment of interface between the particles and matrix. The stress-strain response of the composites depends on both the particle volume fraction and the interface treatment. Young's modulus and Poisson's ratio are characterized by only the particle volume fraction, while tensile strength depends on both the particle volume fraction and interface treatment. With increasing particle volume fraction, the tensile strength increases first and then becomes constant in the interface-treated composites, and decreases in the interface-untreated composites. Numerical analyses of the stress-strain response and damage behavior of the composites are carried out based on an incremental damage theory which describes the plasticity of the matrix and the debonding damage. The stress-strain relations of the interface treated composites are characterized only by influence of particle volume fraction while those of the interface-untreated composites are explained by considering the particle volume fraction and interfacial debonding.

Elastic and plastic properties of metal-matrix composites: geometrical effects of particles

Three-dimensional finite element simulations on the base of cell models and micromechanics have been made in this investigation to predict effective elastic moduli and elastoplastic stress-strain behavior of particulate-reinforced metal-matrix composites. Numerical results are given for the influence of particle volume fraction, shape and orientation to the overall behavior of the composite.

Influence of SiC particle volume fraction on the compressive behaviour of partially remelted Al [sbnd]Si-based composites

Al-7%Si-0.3%Mg (A356) matrix composites containing 10, 20 and 30 vol.% of SiC particles were fabricated by the compocasting technique followed by rapid reheating up to the liquid state, casting and solidification under pressure. The obtained composite ingots were then extruded at 480 °C with an extrusion ratio of 9:1. Specimens obtained from the extruded bars were subjected, after a globularization treatment, to semisolid state filtration to produce samples with various volume fractions of the liquid phase. These samples were thereafter deformed in uniaxial compression in the semisolid state at different constant strain rates ranging from 2.4 × 10 −3 to 3.0 × 10 −1 s −1. The influence of the parameters characterizing the volume fractions of the liquid phase and the particles for different strain rates was investigated. A rheological analysis shows that the partially remelted composites behave as non-newtonian fluids, following a power-law model of the typeσ = Kέ m with m in the range 0.25–0.4. Increasing the liquid volume fraction decreases strongly the compressive stress, whereas the influence of the particle volume fraction is more complex and depends on the liquid volume fraction.

Particle reinforcement of ductile matrices against plastic flow and creep

A theoretical investigation is made of the role of non-deforming particles in reinforcing ductile matrix materials against plastic flow and creep. The study is carried out within the framework of continuum plasticity theory using cell models to implement most of the calculations. Systematic results are given for the influence of particle volume fraction and shape on the overall behavior of composites with uniformly distributed, aligned reinforcement. The stress-strain behavior of the matrix material is characterized by elastic-perfectly plastic behavior or by power-law hardening behavior of the Ramberg-Osgood type. A relatively simple connection is noted between the asymptotic reference stress for the composite with the power-law hardening matrix and the limit flow stress of the corresponding composite with the elastic-perfectly plastic matrix. The asymptotic reference stress for the composite with the power-law matrix is applicable to steady-state creep. A limited study is reported on the overall limit flow stress for composites with randomly orientated disc-like or needle-like particles when the particles are arranged in a packet-like morphology.

Application Of Incremental Damage Theory ToGlass Particle Reinforced Nylon 66 Composites

In this paper, tensile tests are carried out on seven kinds of glass particle reinforced nylon 66 composites in which a particle volume fraction is varied in 0%, 10%, 20% and 30%, and glass particles treated or untreated with silan-coupling are used. The stress-strain response of the composites depends on both the particle volume fraction and the treatment of interface between the particles and matrix. Young's modulus and Poisson's ratio are characterized by only the particle volume fraction, while tensile strength is described as a function of the particle volume fraction and interface treatment. With increasing particle volume fraction, the tensile strength increases first and then becomes constant in the interface-treated composites, and decreases in the interface-untreated conventional composites. Numerical analysis is also carried out on stress-strain response and damage behavior of the seven kinds of composites. The stress-strain relations of the interface treated composites are explained only by influence of particle volume fraction while those of the conventional composites are characterized by considering the particle volume fraction and interfacial debonding between the particles and matrix.