High Volume Fraction Particle Research Articles

Particle-resolved direct numerical simulation of particle-laden turbulence modulation with high Stokes number monodisperse spheres

Graphic processing units (GPU)-accelerated direct numerical simulations of particle–fluid systems based on lattice Boltzmann method combined with discrete element method are successfully performed. This method is validated to be accurate and efficient in the four-way coupling simulation of particle–fluid systems. Particle-laden homogeneous isotropic turbulence under particle size dp=30.1η (the Kolmogorov length scale), a wide range of solid volume fraction ϕV=2%−20% and particle Stokes number St=503.87−50 387 are systematically studied. The additional energy dissipation rate εaddi induced by particles is quantitatively calculated. One criterion for turbulence enhancement or attenuation based on energy balance is proposed and successfully used in different particle-laden turbulence. The relative magnitude of two-way coupling rate ψ and particle-induced dissipation εaddi is the direct factor determining the modulation effect on turbulence. Turbulence laden with high Stokes number particles is enhanced. Turbulence laden with high volume fraction particles transited rapidly from enhancement to attenuation, which is attributed to the more rapid decay of ψ relative to εaddi in the freely decaying turbulence.

Microscopic theory of the influence of strong attractive forces on the activated dynamics of dense glass and gel forming fluids.

We theoretically study the nonmonotonic (re-entrant) activated dynamics associated with a finite time scale kinetically defined repulsive glass to fluid to attractive glass transition in high volume fraction particle suspensions interacting via strong short range attractive forces. The classic theoretical "projection" approximation that replaces all microscopic forces by a single effective force determined solely by equilibrium pair correlations is revisited based on the "projectionless dynamic theory" (PDT). A hybrid-PDT approximation is formulated that explicitly quantifies how attractive forces induce dynamical constraints, while singular hard core interactions are treated based on the projection approach. Both the effects of interference between repulsive and attractive forces, and structural changes due to attraction-induced bond formation that competes with caging, are included. Combined with the microscopic Elastically Collective Nonlinear Langevin Equation (ECNLE) theory of activated relaxation, the resultant approach appears to properly capture both the re-entrant dynamic crossover behavior and the strong nonmonotonic variation of the activated structural relaxation time with attraction strength and range at very high volume fractions as observed experimentally and in simulations. Testable predictions are made. Major differences compared to both ideal mode coupling theory and ECNLE theory based on the full force projection approximation are identified. Calculations are also performed for smaller time and length scale intracage dynamics relevant to the non-Gaussian parameter based on analyzing the dynamic free energy that controls particle trajectories. Implications of the new theory for thermal glass forming liquids with relatively long range attractive forces are briefly analyzed.

Stable second phase: The key to high-temperature creep performance of particle reinforced aluminum matrix composite

High-temperature creep behavior of 45vol%-SiCp/2024Al was studied at 250–350 °C under 40–140 MPa. True stress exponent and activation energy were measured 8 and 227.7 kJ/mol, respectively. The feature substructure of SiCp/2024Al was the second phase Al2Cu dispersed at the interface. The evolution of microstructure and the reason for its high creep activation energy were both analyzed and discussed. θ′ phase and S′ phase underwent different evolution processes during creep. θ′ phase gradually transformed to θ phase and remain stable from the steady-state creep until creep rupture. High content of the interface facilitated the dispersion of Al2Cu. The relationship between true stress exponent and interface content as well as the key to high true stress exponent of high volume fraction particle reinforced aluminum matrix composite were also discussed. This research provided new perspectives and guidance for designing and fabricating composites with superior high-temperature creep properties.

3D microstructure model and thermal shock failure mechanism of a Si3N4-bonded SiC ceramic refractory with SiC high volume ratio particles

In this study, an efficient method was proposed to establish 3D microstructure model of a Si3N4-bonded SiC ceramic refractory with SiC high volume ratio particles and its failure mechanism under thermal shock was studied based on the established microstructure model. The proposed modeling method based on modified 3D Voronoi tessellation method and “precise shrinkage ratio method” was able to establish 3D geometric model of a SiC ceramic refractory with SiC high volume fraction particles more quickly than usual methods. The modified 3D Voronoi tessellation method generated Voronoi polyhedrons (VPs) limited in finite space perfectly. The proposed “precise shrinkage ratio method” achieved a precise volume fraction of SiC particles in the established microstructure model. The crack initiation and propagation under thermal shock were calculated by employing the extended finite element method (XFEM) on the established microstructure model. The results showed the failure mode on micro-scale clearly and efforts of interface strength on the failure mode were also explored. The proposed modeling method was especially suitable for establishing 3D microstructure models of ceramic composites or isotropic metal-ceramic particle composites with high volume fraction particles and extended the use of VPs.

Study on the Reinforcement of Aluminum Alloy A356 Using SiC Particles by Mechanical Stirring

This paper is to research the manufacturing process of A356 alloy matrix composites reinforced by SiC particles by mechanical stirring and how the size of particles ,volume fraction affect mechanical property has been studied , too. The text results revealed that larger particles especially particle size larger than 30um were suitable using this technique, meanwhile, it will hard to adding particles into the alloy when particle lower than 20um size. The effects of SiC particle addition on the hardness properties of A356 alloy and with higher volume fraction particles lead to greater hardness.

Plasticity improvement of ZrCu-based bulk metallic glass by ex situ dispersed Ta particles

Abstract The (Zr 48 Cu 36 Al 8 Ag 8 ) 99.25 Si 0.75 -based bulk metallic glass composite (BMGC) rods ex situ dispersed with Ta particles (with a diameter of 2–4 mm) have been successfully fabricated by suction casting and characterized. These Ta-added BMGCs exhibit similar thermal properties in comparison with its base alloy counterpart, with relatively high glass forming ability (GFA). The results of compression test show that a superior mechanical performance with up to 22% compressive plastic strain, 1800 MPa yield strength and 1850 MPa fracture strength at room temperature can be obtained for the 2 mm diameter rod of the ZrCu-based BMGC with 10 vol.% Ta particles. These ex situ dispersed Ta particles (20 ± 8 μm) would arrange as semi-uniform confinement zones to restrict the shear band propagation. In addition, for a given Ta particle size, higher volume fraction particles would lead to more interfacial areas, shorter inter-particle spacings, smaller confinement zone sizes than the smaller volume fraction particles, and results in presenting larger compression plasticity.

Experimental Research on Ultrasonic Vibration Milling Metal Matrix Composites SiCp/Al

Although particle reinforced metal matrix composites possess excellent physical properties, its machining performance is rather bad because of its specific structure. It is difficult to obtain good cutting effect by traditional machining method. So machining has become the bottleneck which strictly restricts its industry application. This paper mainly focuses on both wear characteristics of different tool materials and material removal mechanism in ultrasonic milling high volume fraction particle reinforced metal matrix composites SiCp/Al. An acoustic device for ultrasonic vibration milling was developed to introduce the ultrasonic vibration into the traditional machining process. Through the contrast experiment of traditional milling and ultrasonic vibration milling SiCp/Al, the mechanism of tool wear and characteristics of surface topography were analyzed. The experimental results showed that the surface integrity and tool life in the ultrasonic vibration milling SiCp/Al were improved. This template explains and demonstrates how to prepare your camera-ready paper for Trans Tech Publications. The best is to read these instructions and follow the outline of this text.

Colloidal glass transition in unentangled polymer nanocomposite melts

The linear and non-linear rheology of a high volume fraction particle filled unentangledpolymer melt is measured. The particles in the polymer melt behave like hard spheres asthe particle volume fraction is raised. At high volume fractions, the suspension develops aplateau elastic modulus. Over the frequency range of the elastic modulus plateau, theviscous modulus develops a minimum and a maximum. The frequencies of the two localextrema initially have critical power law scaling, suggesting the approach of a singular glasstransition. At higher volume fractions in excess of the glass transition, the viscous moduluscontinues to show a well defined minimum and a well defined maximum. The non-linearmoduli show a single perturbative yield point beyond which the suspension softens. Theyielding behavior of the nanocomposite is shown to be sensitive to the strainfrequency and the proximity of the strain frequency to the maximum frequencyfor the linear viscous modulus from linear rheology which characterizes thermalrelaxation of glassy particle clusters in the zero strain limit. The linear and non-linearmeasurements are compared against a recently developed mechanical theory for colloidalglasses.

Nano-Underfills for High-Reliability Applications in Extreme Environments

Silica particles are used as a filler material in electronic underfills to reduce coefficient of thermal expansion of the underfill-epoxy matrix. In traditional underfills, the size of silica particles is in the micrometer range. Reduction in particle sizes into the nanometer range has the potential of attaining higher volume fraction particle loading in the underfills and greater control over underfill properties for higher reliability applications. Presently, no-flow underfills have very low or no filler content because micron-size filler particles hinder solder joint formation. Nano-silica underfills have the potential of attaining higher filler loading in no-flow underfills without hindering solder interconnect formation. In this paper, property prediction models based on representative volume element (RVE) and modified random spatial adsortion have been developed. The models can be used for development of nano-silica underfills with desirable thermo-mechanical properties. Temperature dependent thermo-mechanical properties of nano-underfills have been evaluated and correlated with models in a temperature range of -175degC to 150degC. Properties investigated include, temperature dependent stress-strain, creep and stress relaxation behavior. Nano-underfills on 63Sn37Pb eutectic and 95.5Sn3.5Ag1.0Cu leadfree flip-chip devices have been subjected to thermal shock tests in the range of -55degC to 125degC and -55degC to 150degC, respectively. The trade-offs between using nano-fillers instead of micron-fillers on thermo-mechanical properties and reliability has been benchmarked.

A Generalized Dipole-Enhanced Approximation for a Dielectric Mixture

This paper presents a generalized dipole-enhanced approximation, considering the interactions among particles in a dielectric mixture, to calculate the electric field distributions at the surface of an arbitrarily selected spherical particle in a uniform external field. An approximate formula whose calculated results agree well with the exact numerical solutions obtained by the finite-element method is derived. This formula provides analytic solutions for the dielectric mixtures with high-volume fraction particles because it truly reveals the perturbations due to all the other particles. As the difference between the exact solutions and the ideal dipole approximations reflects the perturbations due to all the other particles, the difference calculated based on the dipole-enhanced approximation is applied to the prediction of effective permittivity for dielectric mixtures, and a modified mixing formula is presented.

Comparison of ceramic material effects on the flexural Weibull statistics and fracture of high volume fraction particle reinforced aluminum

The effects of the ceramic particle material on the flexural Weibull modulus, characteristic flexural strength, and damage parameters of particulate-reinforced metal-matrix composites were studied. Three high volume fill composites were fabricated using the pressure infusion casting technique: they were reinforced with SiC, B4C, and α-Al2O3 particles. Four-point bend testing determined the effects of particle material on flexural strength and elastic modulus. It was found the B4C and SiC composites had similar flexural Weibull modulus, low deflection, and similar damage parameters. The α-Al2O3 reinforced composite had the largest flexural Weibull modulus, highest deflection at failure, and largest damage parameter. Extensive microstructural and SEM fractographs were taken of the as-processes and fractured specimens. The mechanisms leading to the dominant failure modes are discussed.

Aging behavior and precipitation kinetics of SiCp/6061AI composites

The aging behavior of SiC particle reinforced 6061 aluminum matrix composites was investigated with Brinell hardness measurement, differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). For 40 vol%SiCp/6061Al composite, the age-hardening efficiency was lower than that of monolithic 6061Al alloy and its high strength was mainly attributed to the introduction of high volume fraction particles. At low aging temperature, the aging process of composite was more accelerated than that of 6061Al alloy. With temperature increasing, the time to reach the peak hardness was shortened and the precipitation processes became accelerated. Moreover, precipitation process observed in the matrix alloy was altered by the addition of SiC particles. Formation of G.P. region was severely suppressed and the activation energy of β′ phase decreased, which made the precipitation of β′ phase easier than that of 6061Al alloy.

A dipole-enhanced approximation for a dielectric mixture

This paper presents a dipole-enhanced approximation to calculate the saturation charge of particles for high-volume fraction particles. An approximate formula for calculating the maximum field strength at the surface of one sphere is derived. It shows the variation of the maximum field strength with the difference in permittivity and the ratio of the particle radius to the distance between particles. The maximum field strengths calculated using this formula are compared with those obtained with the dipole model and the finite-element method, the calculated result shows that the formula is acceptable. A formula for calculating saturation charge of particles is derived, which depends on the volume fraction of particles.

Quantification of microdamage phenomena during tensile straining of high volume fraction particle reinforced aluminium

Particle reinforced composites are produced by infiltrating ceramic particle beds with 99.99% Al. Resulting materials feature a relatively high volume fraction (40–55 vol. pct) of homogeneously distributed reinforcement. The evolution of damage during tensile straining of these composites is monitored using two indirect methods; namely by tracking changes in density and in Young's modulus. Identification and quantification of the active damage mechanisms is conducted on polished sections of failed tensile specimens; particle fracture and void formation in the matrix are the predominant damage micromechanisms in these materials. The damage parameter derived from the change in density at a given strain is found to be one to two orders of magnitude smaller than the parameter based on changes in Young's modulus. A simple micromechanical analysis inspired by the observed damage micromechanisms is used to correlate the two indirect measurements of damage. The predictions of this analysis are in good agreement with experiment.