Two-phase Composite Materials Research Articles

Micromechanical analysis of magnetoelectric coupling of composites containing nonlinear magnetostrictive and piezoelectric constituents

This paper is a reformulation of the simplified unit-cell and Mori-Tanaka micromechanics theories in their applications to nonlinear magnetoelectric analysis of two-phase composite materials with 0–3, 1–3, and 2–2 connectivity types, respectively. We elucidate the similarity between the two models insofar as concentration-factor matrices are concerned. The representations of the bulk magnetostrictive and piezoelectric phases are based on nonlinear constitutive equations. Due to material nonlinearity, the mathematical frameworks are accomplished via incremental formulation that provides a system of linear algebraic equations at each increment which is obviously a great advantage over nonlinear one. The derived nonlinear composite constitutive relations that govern the hysteresis behavior of composites are implemented to study the composite composed of Terfenol-D and PZT constituents. The responses of this composite to a complete cycle of magnetic field are shown and the micromechanics predictions are compared in light of existing experimental data.

Machine learning-based stiffness optimization of digital composite metamaterials with desired positive or negative Poisson's ratio

Mechanical metamaterials such as auxetic materials have attracted great interest due to their unusual properties that are dictated by their architectures. However, these architected materials usually have low stiffness because of the bending or rotation deformation mechanisms in the microstructures. In this work, a convolutional neural network (CNN) based self-learning multi-objective optimization is performed to design digital composite materials. The CNN models have undergone rigorous training using randomly generated two-phase digital composite materials, along with their corresponding Poisson's ratios and stiffness values. Then the CNN models are used for designing composite material structures with the minimum Poisson's ratio at a given volume fraction constraint. Furthermore, we have designed composite materials with optimized stiffness while exhibiting a desired Poisson's ratio (negative, zero, or positive). The optimized designs have been successfully and efficiently obtained, and their validity has been confirmed through finite element analysis results. This self-learning multi-objective optimization model offers a promising approach for achieving comprehensive multi-objective optimization.

Catalytic Activity of LaFe0.4Ni0.6O3/CeO2 Composites in CO and CH4 Oxidation Depending on Their Preparation Conditions.

LaFe0.4Ni0.6O3/CeO2 (1:1) two-phase composite materials were prepared by mechanochemical (MC) and Pechini routes. The catalytic properties of the composites in methane and CO oxidation reactions strongly depend on their preparation conditions. In low-temperature (<600 °C) catalytic CO oxidation the composites demonstrate a higher activity compared with LaFe0.4Ni0.6O3 perovskite. The highest activity was observed for the composite prepared by mechanical treatment of perovskite and fluorite precursors. There is a correlation between activity and the content of weakly bound surface oxygen species. Catalytic activity in high-temperature (>750 °C) catalytic methane oxidation correlates with the reducibility of samples. The highest activity was observed for the composite prepared by the one-pot Pechini route with higher reducibility of the sample up to 600 °C.

Analysis of electrical conductivity of carbon nanotube-reinforced two-phase composites

This short paper presents a simple approach for calculating the effective electrical conductivity of carbon nanotubes-reinforced two-phase composite materials. The approach is developed by modifying the traditional effective medium approximation to include the effect of percolation threshold. The predicted electrical conductivity from the present approach is validated by using published experimental results. It is shown that the effective electrical conductivity of two-phase composites can be calculated by using the lower bound of the effective medium approximation if the inclusion volume fraction is below its percolation threshold, and the projection of the upper bound of the effective medium approximation if the inclusion volume fraction exceeds its percolation threshold.

Lagrangian Formalism for the Analysis of Acoustic Properties of Two-Phase Composite Materials with Damaged Interfaces

Lagrangian Formalism for the Analysis of Acoustic Properties of Two-Phase Composite Materials with Damaged Interfaces

Numerical computation of the effective thermal conductivity of two-phase composite materials by digital image analysis

We consider the numerical determination of the effective thermal conductivity of 2D, two-phase composite materials, whose microstructural geometries are described by digital images. More specifically, key microstructural data pertaining to the spatial distribution and volume fractions of the constituent phases in the material are extracted, along with the shapes of the interphase boundaries, using computer vision techniques. For inclusions of simple shapes (polygons, circles, ellipses), the extracted interphase boundary data is easily obtained and can be exploited immediately (e.g. polygonal vertices) or can be fitted with smooth curves, using least square error minimization techniques in order to reconstruct parametric representations in the case of circular or elliptical boundaries. For more intricate microstructure geometries characterized by clustered or agglomerated intersecting inclusions, piecewise cubic spline functions are adopted to obtain a least-square fitting of the interphase boundaries. The effective thermal conductivities are then calculated based on a boundary integral formulation defined over the reconstructed inclusion boundaries. They are expressed in terms of power series expansions of a conductivity contrast parameter of the constituent phases in the material. To accelerate the convergence of these expansions, nonlinear transformations (known as Padé Approximants) are used to yield rational approximations of the effective thermal conductivity tensor. Tests conducted on a variety of 2D, two-phase microstructures yielded accurate results over a wide range of microstructure image resolution, regardless of the contrast parameters of the constituent phases, thus, validating the efficacy and robustness of the proposed scheme.

Numerical Computation of the Effective Thermal Conductivity of Two-Phase Composite Materials by Digital Image Analysis

Numerical Computation of the Effective Thermal Conductivity of Two-Phase Composite Materials by Digital Image Analysis

A new model for thermal conductivity of “continuous matrix / dispersed and separated 3D-particles” type composite materials and its application to WC-M (M = Co, Ag) systems

In the present work a new thermal conductivity model is developed for two-phase composite materials, which are consisted of a continuous matrix and dispersed 3D-particles separated from each other by the matrix as a function of grain size and volume ratio of the dispersed particles at different temperatures. The model is applied to reproduce experimental thermal conductivity values of cemented carbide systems WC-Co and WC-Ag. Good agreement was found between measured thermal conductivity data originating from both this work and recent literature and the calculated ones only using semi-empirical parameters for the interfacial thermal resistance (ITR) values at WC/Co, WC/Ag and WC/WC interfaces as a function of temperature. Additionally, the temperature and grain size dependence of the thermal conductivity for WC is established for the first time. The model works well for the case when the matrix (Ag) has a higher thermal conductivity compared to that of the WC particles and also for the case when the matrix (Co) has a lower thermal conductivity compared to that of the WC particles. The new model forms a physically sound basis for further development / materials design of cemented carbides and particle-reinforced composite materials.

Percolation threshold and effective properties of CNTs-reinforced two-phase composite materials

In this paper an analytical prediction model is developed to determine the percolation threshold and effective properties of carbon nanotubes reinforced two-phase composite materials. The model considers the effect of not only volume fraction but also aspect ratio and mixed pattern of fibres in the composites. It is shown that the effect of fibres on the effective properties of the composites can be characterised in terms of three different zones, namely non-percolated zone, partially percolated zone, and fully percolated zone. The formulations for determining percolation threshold and effective properties of the composites in the three different zones are derived. The model is validated by using available experimental data to demonstrate its appropriateness and reliability.

Heat transfer modelling of carbon nanotube reinforced composites

In this paper an analytical prediction model for the heat transfer analysis of two-phase composite materials is developed. Formulations for the effective density, effective specific heat and effective thermal conductivity of the composite materials are derived. The present model considers not only the effect of interfacial thermal resistance between CNTs and polymer matrix but also the influence of fibre aspect ratio of CNTs on the effective thermal conductivity of the composites. The validation of the model is also provided by using available experimental data to demonstrate the appropriateness and reliability of the present model.

Microstructural integrity characterization of cement-based construction materials

In this paper, a new micromechanical framework to characterize the microstructural integrity and predict the effective properties of multi-phase particulate composites is presented. Within the framework, a new scalar micromechanical parameter is identified and used to derive new expressions for the effective elastic properties of particulate composites using the mean-field homogenization technique. The derived equations are then generalized for composites with multiple phase constituents. The generality of the proposed framework is demonstrated by combining the derived equations with the existing homogenization techniques such as the Mori–Tanaka method and the Generalized Maxwell’s Approach (GMA). The results show that the theory delivers consistent estimates of the effective properties of two-phase elastic composite materials. The new scalar micromechanical parameter is also used to characterize the microstructural integrity of both asphalt mixtures and Portland cement concrete. The results show that the new scalar micromechanical parameter correlates well with multiple key fundamental properties of asphalt concrete mixture, including the creep rate, the fracture energy density, the endurance limit, and the damage rate parameters. The results also show that the new micromechanical framework can be used to accurately predict the effective modulus properties of Portland cement concrete mixtures.

Estimation of Local Strain Fields in Two-Phase Elastic Composite Materials Using UNet-Based Deep Learning

Estimation of Local Strain Fields in Two-Phase Elastic Composite Materials Using UNet-Based Deep Learning

Analysis of thermal stresses in FGM-matrix media induced by a constant heat generation

The three-dimensional thermal stress field is derived for an elastic medium that contains a spherical inclusion made of an functionally graded material (FGM) embedded in a matrix phase. The material properties in the inclusion phase are assumed to vary linearly while the material properties in the matrix phase are uniform. The presence of a uniform heat source in the inclusion introduces the temperature distribution which generates thermal stresses. The temperature distribution is derived analytically by solving the heat conduction equation. Based on the temperature distribution, the differential equations for the displacement field are derived for both the inclusion and matrix phases. The displacement for the matrix phase is solved analytically while the displacement for the FGM inclusion phase is solved semi-analytically using the method of weighted residuals. Only a single differential equation needs to be solved. To the authors’ best knowledge, this is the first attempt to express the thermal stress field semi-analytically. Unlike the conventional two-phase composite materials in which the von Mises stress is discontinuous at the interface of the inclusion and the matrix, the von Mises stress in this model shows continuity at the interface.

Effect of silane coupling agents on flowability and compressibility of compound for bonded NdFeB magnet

Based on the difference of the Y-terminal functional group of the silane coupling agent (Y–Si(X)3), four different silane coupling agents were employed to pretreat the surface of the NdFeB powders. The effects of silane coupling agents on the flowability and compressibility of compounds for preparing bonded NdFeB magnets were studied. It is indicated that compounds pretreated by silane coupling agents have weaker friction and meshing force. The apparent density is increased by 0.3 g/cm3 compared with the compound without silane coupling agent, and the radial crushing strength is significantly increased by about 3–4 times. In addition, the epoxy resin is more evenly distributed on the surface of the compounds treated by silane coupling agents observed by scanning electron microscopy, and some agglomerated particles are produced. Also, the compressibility of compounds with silane coupling agents is significantly improved due to the fact that hardening exponents are reduced. However, the addition of silane coupling agents has almost no effect on the magnetic properties of bonded magnets. The special energy was used to manifest the flowability of magnetic powder particles representing the macroscopic performance of the force between powder particles, providing a new direction for the study of the interface compatibility of two-phase or multiphase composite materials.

Fracture of thermo-elastic solids: Phase-field modeling and new results with an efficient monolithic solver

Thermally induced cracking occurs in many engineering problems such as drying shrinkage cracking of concrete, thermal shock induced fracture, micro cracking of two-phase composite materials etc. The computational simulation of such a fracture is complicated, but the use of phase-field models (PFMs) is promising as they can seamlessly model complex crack patterns like branching, merging, and fragmentation by treating the crack discontinuity as thin band of diffuse damage. Despite the success of phase-field models there are two major issues in previous PFMs of thermally induced fracture. Firstly, these models, which are mostly based on a PFM using a simple quadratic degradation function without any user-defined parameters, provide solutions that are sensitive to a length scale. Secondly, they are limited to brittle fracture only. As a solution, we extend the phase-field regularized cohesive zone model (PF-CZM) of Wu [JMPS, 103 (2017)], with a rational degradation function dependent on elasticity and fracture related material parameters, to thermoelastic solids. Furthermore, we present a monolithic BFGS algorithm to solve the three-field (displacements, phase-field and temperature) coupling equations altogether. Multiple thermally induced fracture problems, simulated within the framework of the finite element method, are presented with predictions in good agreement with previous findings and experiments. The proposed model is shown to give better performance in capturing the physics of thermally induced fracture: it provides length scale insensitive responses. And the monolithic solver is 4∼5 times faster than the conventional alternating minimization solver.

Estimation of the efficiency of destroying hard rocks by composites sintered in the diamond-carbonate system

The purpose of this work is to substantiate the possibility of using a new composite sintered in the "diamond-carbonate" system for equippingdiamond drilling tools with high wear resistance and efficiency of rock destruction. The research technique consisted in establishing the influence of the wear resistance of the cutting edge of the samplesof a superhard composite diamond-containing material on the efficiency of rock destruction, assessed by the granulometric composition of its sludge. Research results. The two-phase superhard composite materials diamond – CaMg(CO3)2 and diamond – SrCO3 were obtained as a result of sintering by the method of impregnation of diamond micropowder with carbonate melts under conditions of a high pressure of 8.0 GPa and a temperature of 2100 °C. Wear resistance of the investigated composite sampleswas determined by based on the results of turning the core of granite from the Korostyshevskoye deposit of the X category of drilling. Determination of the size and shape of particles of granite fragments of the Korostyshevskoye deposit, taken during its destruction was carried out by laser diffraction and digital image analysis using a Microtrac Sync analyzer.The relationship between the degree of its wear of the cutting edge of composite samplesand the energy consumption of rock destruction, the size distribution of particles in the cuttings sample and their specific surface was established after analyzing the results of the study of wear resistance and the nature of their wear. Plates of the diamond–CaMg(CO3)2 composite, which have a higher wear resistance compared to other composites, are characterized by an increase in the proportion of large particles in the cuttings sample and a decrease in the value of their specific surface, which indicates a more rational use of energy, which goes to a greater extent for destruction rock and to a lesser extent for friction and wear. Practical value. The research results allow us to make a conclusion about the advisability of equipping a drilling rock cutting tool with samplesof a diamond–CaMg(CO3)2 composite in order to increase its wear resistance and the efficiency of rock destruction.

Effect of shape of inorganic particles on dielectric properties of polymer composites with high energy density

The formation of two-phase composite materials by adding inorganic ceramic particles in the organic matrix is a hot and difficult point in the current study of high energy storage density. The electrostatic energy storage characteristics of the material are determined by its internal electric field distribution. For pure polymer materials, the internal electric field is uniformly distributed in a uniform external electric field environment, but when the inorganic particles are filled to form a composite material, the local electric field of the material will be distorted, which will affect the dielectric properties of the composite material. In this paper, the electric response properties of particles with different shape, including sphere, fiber and disk and its special arrangement has been systematically studied. The results show that both the shape and the spatial arrangement of the particles in the polymer matrix affect the local distribution of electric field. For spherical particles, there will exist be field concentration up and below the particle. For fibers, the field caused by the terminal surface bound charge should not be neglected when the aspect ratio is not large enough. At last, three three-dimensional simulation models of composites with spherical, fiber and disk particles have been established. It is indicated that composites with fiber particle possess the highest effective permittivity, while the disk particle is the lowest under the same concentration. The investigation of this paper is of great significance to understand the microscopic mechanism of energy storage.

The Emergent Behaviour of Thermal Networks and Its Impact on the Thermal Conductivity of Heterogeneous Materials and Systems

The properties of thermal networks are examined to understand the effective thermal conductivity of heterogeneous two-phase composite materials and systems. At conditions of high contrast in thermal conductivity of the individual phases (k1 and k2), where k1 &lt;&lt; k2 or k1 &gt;&gt; k2, the effective thermal conductivity of individual networks of the same composition was seen to be highly sensitive to the distribution of the phases and the presence of percolation paths across the network. However, when the contrast in thermal conductivities of the two phases was modest (k1/k2 ~ 10−2 to 102), the thermal networks were observed to exhibit an emergent response with a low variability in the effective thermal conductivity of mixtures of the same composition. A logarithmic mixing rule is presented to predict the network response in the low variability region. Excellent agreement between the model, mixing rule and experimental data is observed for a range two-phase porous and granular media. The modelling approach provides new insights into the design of multi-phase composites for thermal management applications and the interpretation or prediction of their heat transfer properties.

Crack nucleation and propagation simulation in brittle two-phase perforated/particulate composites by a phase field model

Fracture is a very common failure mode of the composite materials, which seriously affects the reliability and service-life of composite materials. Therefore, the study of the fracture behavior of the composite materials is of great significance and necessity, which demands an accurate and efficient numerical tool in general cases because of the complexity of the arising boundary-value or initial-boundary value problems. In this paper, a phase field model is adopted and applied for the numerical simulation of the crack nucleation and propagation in brittle linear elastic two-phase perforated/particulate composites under a quasi-static tensile loading. The phase field model can well describe the initiation, propagation and coalescence of the cracks without assuming the existence and the geometry of the initial cracks in advance. Its numerical implementation is realized within the framework of the finite element method (FEM). The accuracy and the efficiency of the present phase field model are verified by the available reference results in literature. In the numerical examples, we first study and discuss the influences of the hole/particle size on the crack propagation trajectory and the force–displacement curve. Then, the effects of the hole/particle shape on the crack initiation and propagation are investigated. Furthermore, numerical examples are presented and discussed to show the influences of the hole/particle location on the crack initiation and propagation characteristics. It will be demonstrated that the present phase field model is an efficient tool for the numerical simulation of the crack initiation and propagation problems in brittle two-phase composite materials, and the corresponding results may play an important role in predicting and preventing possible hazardous crack initiation and propagation in engineering applications.

Effective elastic-plastic response of particulate two-phase composite materials under multi-axial loading

In recent papers (Teng, 2014, 2018), an incremental elastic-plastic double-inclusion model was developed to determine the effective elastic-plastic response of two-phase composites of spherical or aligned spheroidal particles. For composites of purely elastic particles and elastic-plastic matrix of von Mises yield criterion with isotropic strain hardening, the double-inclusion model was formulated through the use of an isotropic matrix tangent stiffness tensor. The use of the isotropic tangent stiffness tensor, however, is only suitable for uniaxial loading or pure shear, but not for multi-axial loading. For in general the elastic-plastic tangent stiffness tensor of the matrix is inherently anisotropic, and during plastic deformation normal stress (strain) increment and shear strain (stress) increment are coupled, as a result of the anisotropy of the tangent stiffness tensor. In this paper, the original incremental elastic-plastic double-inclusion formulation presented in the previous papers (Teng, 2014, 2018) for composites of elastic spherical or aligned spheroidal particles and elastic-plastic matrix is modified by adding anisotropic corrections of stress increment defined in terms of the difference between the anisotropic and isotropic tangent stiffness tensors of the matrix. The resulting improved incremental double-inclusion model can be applied to multi-axial loading. Comparison of the model predictions to the results of the direct approach using representative volume elements containing many particles shows that the improved incremental elastic-plastic double-inclusion formulation is capable of predicting the effective elastic-plastic response of two-phase composites of spherical or aligned spheroidal particles under multi-axial loading.