Random Particle Dispersion Research Articles

Simulation of Microscale Features Effect on Mechanical Properties of PTFE-Al Composites

The compression behavior of polytetrafluoroethylene (PTFE)–aluminum (Al) is studied by the means of the two-dimensional finite element analysis of mesoscale model containing a random dispersion of particles. The results show that for composite materials with a single particle size the strength of the material increases first and then decreases with the increase of the content of metal particles. When the particle content is high the strength of the material can be improved by a reasonable particle gradation. The influence of particle content and size on the strength of particle composites is obtained and theoretical analysis is carried out from the perspective of the formation and evolution of force chains.

A method for quantitative characterization of agglomeration degree in nanocomposites

Dispersion and agglomeration control the macroscopic properties of nanocomposites; thus, quantitative characterization of particle dispersion and agglomeration is crucial. So far, methods such as image analysis or measurement of macroscopic properties have been insufficient. So, a novel methodology is introduced to predict particle dispersion and agglomeration degree quantitatively through the measurement of effective dielectric constant. This is done by taking into account the impact of inter-particle interactions in respect to microstructure for the calculation of effective dielectric constant. Inter-particle interaction is calculated as a function of inter-particle distance for random dispersion of particles in composites and as a function of agglomerate size and packing density for nanocomposites with agglomerated microstructure. The inter-particle interactions increase with increase in filler content and agglomeration. This increment is abrupt at percolation where inter-particle distance is significantly reduced. Experimental data from ZnO/PS composites with controlled inter-particle distance and agglomeration confirm the theoretical results.

Dispersion Morphology of Poly(methyl acrylate)/Silica Nanocomposites

Nearly monodisperse poly(methyl acrylate) (PMA) and spherical SiO2 nanoparticles (NP, d = 14 ± 4 nm) were co-cast from 2-butanone, a mutually good solvent and a displacer of adsorbed PMA from silica. The effects of NP content and post-casting sample history on the dispersion morphology were found by small-angle X-ray scattering supplemented by transmission electron microscopy. Analysis of the X-ray results show that cast and thermally annealed samples exhibited a nearly random particle dispersion. That the same samples, prior to annealing, were not well-dispersed is indicative of thermodynamic miscibility during thermal annealing over the range of NP loadings studied. A simple mean-field thermodynamic model suggests that miscibility results primarily from favorable polymer segment/NP surface interactions. The model also indicates, and experiments confirm, that subsequent exposure of the composites to the likely displacer ethyl acetate results in entropic destabilization and demixing into NP-rich and NP-le...

Indentation behavior of functionally graded Al–SiC metal matrix composites with random particle dispersion

This study addresses the effects of number of layers, compositional gradient exponent (material composition) and random particle dispersion on the indentation behavior of a functionally graded metal matrix composite. The ceramic particles in a certain volume fraction were randomly distributed within each layer depending on the compositional gradient exponent in order to have a similar structure to an actual microstructure as possible. Increasing the number of layers caused an evident increase in indentation depths for all compositional gradient exponents. The compositional gradient exponent had an important effect on the indentation depth. The random particle dispersion also played an important role on the central indentation depth ( n < 3) as well as on the deformed surface profiles for both high layer numbers ( N = 75 and 150 layers) and the material compositions approaching to a metal-rich structure resulted in some fluctuations in the deformed surface profiles. Increasing the number of layers at a certain compositional gradient exponent resulted in larger mean residual stresses and plastic deformations. Increasing the compositional gradient exponent at a certain layer number decreased mean residual stresses and strains since the ceramic volume fraction is increased. The random particle dispersion also resulted in non-uniform residual stress and strain levels and distributions.

Effects of random particle dispersion and size on the indentation behavior of SiC particle reinforced metal matrix composites

This study investigates the effects of particle size, volume fraction, random dispersion and local concentration underneath a spherical indenter on the indentation response of particle reinforced metal matrix Al 1080/SiC composites. The ceramic particles in certain sizes and volume fractions were randomly distributed through the composite structure in order to achieve a similar structure to an actual microstructure as possible. The particle size and volume fraction affected considerably indentation depths and deformed indentation surface profiles. The indentation depth increases with increasing particle size, but decreases with increasing particle volume fraction. The experimental indentation depths were in agreement with numerical indentation depths in case the local particle concentration effect is considered. The local particle concentration plays an important role on the peak indentation depth. For small particle sizes and large volume fractions the random particle distribution affects the deformed surface profiles as well as the indentation depths. However, its effect is minor on residual stress and strain distributions rather than levels in the indentation region.

Effects of Random Particle Dispersion and Particle Volume Fraction on the Indentation Behavior of SiC Particle-Reinforced Metal-Matrix Composites

The present composite structure models assume that reinforcement particles are located in a repeated arrayed order through metal matrix. This study investigates the effect of both random particle distribution and particle volume fraction on the indentation behavior of Al 1080/SiC particle reinforced metal—matrix composites under a spherical indenter. The ceramic particles were distributed randomly in a certain particle volume fraction through aluminum matrix in order to achieve a similar structure to a real particulate composite structure as possible. The particle volume fraction strongly affects permanent indentation surface profiles and indentation depths. The indentation profile becomes smoother, and the peak indentation depth increases as the particle volume fraction decreases. The random particle distribution has a small effect on the peak indentation depth but affects strongly the permanent indentation profiles as well as the residual stress and strain fields in the indentation region. A small increase appears in the local particle concentration in the indentation region and is affected considerably by the random particle distribution. The hardness tests as well as the scanning electron microscopy micrographs of the indentation regions of specimens with different particle volume fractions are in good agreement with theoretical analysis.

Multi-step 3-D finite element modeling of subsurface damage in machining particulate reinforced metal matrix composites

A multi-step 3-D finite element model using the commercial finite element packages Third Wave Systems AdvantEdge © and ABAQUS/Explicit © is developed for predicting the sub-surface damage after machining of particle reinforced metal matrix composites. The composite material considered for this study is an A359 aluminum matrix composite reinforced with 20 vol% fraction silicon carbide particles (A359/SiC/20p). The effect of machining conditions on the measured cutting force and damage is modeled by means of a multi-step fully-coupled thermo-mechanical model. Material properties are defined by applying the Equivalent Homogenous Material (EHM) model for the machining simulation while the damage prediction is attained by applying the resulting stress and temperature distribution to a multi-phase sub-model. In the multi-phase approach the particles and matrix are modeled as continuum elements with isotropic properties separated by a layer of cohesive zone elements representing the interfacial layer to simulate the extent of particle–matrix debonding and subsequent sub-surface damage. A random particle dispersion algorithm is applied for the random distribution of the particles in the composite. Experimental measurements of the cutting forces and the sub-surface damage are compared with simulation results, showing promising results.

Nonlinear viscoelasticity, percolation and particles dispersibility of PVA/aluminum hydroxide composite gels

We investigated the rheological properties of a composite gel consisting of poly(vinyl alcohol) and aluminum hydroxide particles, and discussed the relation among nonlinear viscoelasticity, percolation and particles dispersibility. The dynamic viscoelastic measurements revealed that the storage modulus at volume fractions ϕ < 0.04 satisfied with the Krieger–Dougherty equation representing random dispersion of particles. The storage modulus did not show any nonlinear viscoelastic response at ϕ < 0.04. However, the storage modulus at ϕ > 0.06 took a value which is far larger than that expected by the equation, indicating heterogeneous distribution of particles. Additionally, the nonlinear viscoelastic response was recognized clearly at ϕ > 0.06, suggesting a partial contact between particles. The storage modulus at ϕ > 0.18 showed a further increase satisfied with the percolation theory, therefore, the volume fraction is considered to be the percolation threshold of 3-dimension. Microscopic observations of the gel showed a clear network with a mesh size of few μm that is considered to be a partial network of particles.

A statistical approach for estimating uncertainty in dispersion modeling: An example of application in southwestern USA

A method based on a statistical approach of estimating uncertainty in simulating the transport and dispersion of atmospheric pollutants is developed using observations and modeling results from a tracer experiment in the complex terrain of the southwestern USA. The method takes into account the compensating nature of the error components by representing all terms, except dispersion error and variance of stochastic processes. Dispersion error and the variance of the stochastic error are estimated using the maximum likelihood estimation technique applied to the equation for the fractional error. Mesoscale Model 5 (MM5) and a Lagrangian random particle dispersion model with three optional turbulence parameterizations were used as a test bed for method application. Modeled concentrations compared well with the measurements (correlation coefficients on the order of 0.8). The effects of changing two structural components (the turbulence parameterization and the model grid vertical resolution) on the magnitude of the dispersion error also were examined. The expected normalized dispersion error appears to be quite large (up to a factor of three) among model runs with various turbulence schemes. Tests with increased vertical resolution of the atmospheric model (MM5) improved most of the dispersion model statistical performance measures, but to a lesser extent compared to selection of a turbulence parameterization. Method results confirm that structural components of the dispersion model, namely turbulence parameterizations, have the most influence on the expected dispersion error.

A micromechanical damage model for effective elastoplastic behavior of partially debonded ductile matrix composites

A micromechanical damage model considering progressive partial debonding is presented to investigate the effective elastoplastic-damage behavior of partially debonded particle reinforced ductile matrix composites (PRDMCs). The effective, evolutionary elastoplastic-damage responses of three-phase composites, consisting of perfectly bonded spherical particles, partially debonded particles and a ductile matrix, are micromechanically derived on the basis of the ensemble-volume averaging procedure and the first-order effects of eigenstrains. The effects of random dispersion of particles are accommodated. Further, the evolutionary partial debonding mechanism is governed by the internal stresses of spherical particles and the statistical behavior of the interfacial strength. Specifically, following Zhao and Weng (1996), a partially debonded elastic spherical isotropic inclusion is replaced by an equivalent, transversely isotropic yet perfectly bonded elastic spherical inclusion. The Weibull's probabilistic function is employed to describe the varying probability of progressive partial particle debonding. The proposed effective yield criterion, together with the assumed overall associative plastic flow rule and the hardening law, forms the analytical framework for the estimation of the effective elastoplastic-damage behavior of ductile matrix composites. Finally, the present predictions are compared with the predictions based on Ju and Lee's (2000) complete particle debonding model, other existing numerical predictions, and available experimental data. It is observed that the effects of partially debonded particles on the stress–strain responses are significant when the damage evolution becomes rapid.

Analysis of Thermal Stresses in Graded Thermal Barrier Coatings Using Particle Dispersion Modeling.

This paper presents an analytical method of thermal stresses in ZrO2-8%Y2O3/MCrAlY graded thermal barrier coatings produced by plasma spraying. The formation of sprayed particles in graded coatings is investigated in order to construct the analytical model. The model is characterized by random dispersion of particles which have each physical properties in graded coatings. The validity of this methodology is investigated by comparison with more detailed stress analysis on a simple pattern with MCrAlY particle in ZrO2 matrix. This analytical method is applied to graded thermal barrier coatings on gas turbine blades to determine the thermal stresses. Meanwhile the vertical crack in the 100% ZrO2 top coat of the coating surface layer and the delamination in the ZrO2 rich area of ZrO2/MCrAlY graded layer in graded coating specimens are generated in heat cycle tests. The relationship of thermal stresses to these fractures in graded coatings is discussed.