Three-phase Composites Research Articles

Analytical Solution for Chloride Diffusivity of Concrete with Aggregate Shape Effect.

In view of the key role of chloride diffusivity in evaluating concrete durability, it is very important to determine this parameter accurately by an effective approach. This paper establishes an analytical solution for chloride diffusivity of concrete that can consider the aggregate shape. In this approach, the aggregate shape is simulated as an ellipse and the equivalent model is applied to calculate the chloride diffusivity of equivalent aggregate composed of interface transition zone (ITZ) and aggregate. With resort to this model, at the meso scale, the concrete can be reduced from the original three-phase composition to the two-phase one (i.e., equivalent aggregates and cement paste). Based on the mesostructure of concrete that consisted of randomly dispersed equivalent elliptical aggregates and cement paste, the generalized Maxwell’s approach is formed to determine the chloride diffusivity of concrete. The corresponding chloride diffusion test is conducted and the thickness of ITZ is reasonably determined as 0.04 mm by SEM test. By comparing with the experimental data, the accuracy of the analytical solution is confirmed. Finally, the impact of aggregate shape on chloride diffusivity is discussed. The analytical results show that the chloride diffusivity has a reduction with the increase of aggregate content or decrease of aspect ratio.

Cermet materials reinforced with a small addition of spinel nanoparticles for molten salt power systems

This work is devoted to developing of new cermets for molten-salt power systems, promising for use in aviation, rocket and space technology, and power engineering. The production of cermets in the nickel-aluminum alloy system - 35 wt. % aluminum oxide by the method of mechanical activation and spark plasma sintering was carried out. It was found that the addition of 5 wt. % yttrium oxide, as well as small quantities (0.1 wt. %) of aluminum-magnesium spinel nanoparticles, increase the strength of the cermet at elevated temperatures. Cermets have high strength at room and elevated temperatures, which amounted to 480-530 MPa at 20 °C and 430-470 MPa at 750 °C. The micro structure of cermets was characterized by the presence of elliptical regions, the grains in which were significantly smaller than the grains in the surrounding matrix. This structure allows to effectively harden the material because elliptical areas are obstacles to crack propagation. Elliptical zones have length ranged 100 to 200 μm and width 5 to 20 μm. It was found that the material of the NiAl-Al2O3 system at 20 °C and 800 °C contains the phases NiAl, Al2O3, and Ni2Al3. Composite composition NiAl-Al2O3-Y2O3 at 20 °C and 800 °C retains the three-phase composition of NiAl, Al2O3, and Y2O3. Both materials are stable up to 800 °C.

FFT and Equivalent-inclusion approach for effective conductivity of three-phase composites with random coated-ellipse inclusion

Unlike sphere inclusion, every ellipsoid inclusion is anisotropic, but compound-inclusion composite material with random distribution of coated-ellipse inclusion can be considered as isotropic. The paper introduces the Fast Fourier transformation method (FFT) and equivalent inclusion approach to calculate the effective conductivity of the transverse isotropic unidirectional coated-fiber composite with coated-ellipse inclusion. In the equivalent inclusion approximation, the two-phase of coated-ellipse inclusions are substituted by the equivalent homogeneous one of the same size and corresponding mechanical properties, from here we can build a simple approximation formula (EI) to determine effective conductivity of three-phase composites. Beside that, the FFT simulation can be combined with the equivalent inclusion approach to obtain the results FFT-EI.

Low-frequency dispersion in resistor-capacitor networks

In this paper, we modelled the dielectric response of binary disordered materials, which exhibit universal properties, using random RCC’ networks. We used a bimodal distribution for the capacitive values unlike usual networks that are commonly found in the literature. The C value reflects the micro-capacitors formed by relatively large dielectric regions, while the C′ value reflects micro-capacitors formed by small dielectric regions. A low-power law of conductivity σ′ was obtained; its exponent depends on the network’s composition and the C′/C ratio. This was achieved using the well-known Frank and Lobb (FL) algorithm. We also provided an analytical formula of EMA for three-phase composites. Such an agreement of numerical results was obtained between the FL algorithm and EMA except at low and high frequencies, while a good agreement was obtained for low proportions. In addition, we attempted to model low-frequency dispersions (LFDs) using these RCC’ networks. The simulated LFD results were typically good except for the real part of permittivity ε′.

Flexible Daytime Radiative Cooling Enhanced by Enabling Three-Phase Composites with Scattering Interfaces between Silica Microspheres and Hierarchical Porous Coatings.

Daytime radiative cooling has attracted considerable attention recently due to its tremendous potential for passively exploiting the coldness of the universe as clean and renewable energy. Many advanced materials with novel photonic micro/nanostructures have already been developed to enable highly efficient daytime radiative coolers, among which the flexible hierarchical porous coatings (HPCs) are a more distinguished category. However, it is still hard to precisely control the size distribution of the randomized pores within the HPCs, usually resulting in a deficient solar reflection at the near-infrared optical regime under diverse fabrication conditions of the coatings. We report here a three-phase (i.e., air pore-phase, microsphere-phase, and polymer-phase) self-assembled hybrid porous composite coating, which dramatically increases the average solar reflectance and yields remarkable temperature drops of ∼10 and ∼ 30 °C compared to the ambient circumstance and black paint, respectively, according to the rooftop measurements. Mie theory and Monte Carlo simulations reveal the origin of the low reflectivity of as-prepared two-phase porous HPCs, and the optical cooling improvement of the three-phase porous composite coatings is attributed to the newly generated interfaces possessing the high scattering efficiency between the hierarchical pores and silica microspheres hybridized with appropriate mass fractions. As a result, the hybrid porous composite approach enhances the whole performance of the coatings, which provides a promising alternative to the flexible daytime radiative cooler.

Investigation on mechanical properties and deformation behavior of copper-based three-phase metal matrix composite: Experimental and micro-macro-mechanical finite element analysis

The present study involved development of copper-based metal matrix composite, reinforced with waste EN 31 steel chips and TiB2 ceramic particles. Waste EN 31 steel chips and TiB2 ceramic particles were ball-milled for 100 h to obtain a single entity. The composite material was produced with a stir-casting technique, followed by a squeeze pressure process. The addition of Cu + 10 wt% of waste steel chips + 5 wt% of TiB2 improved the tensile strength of the copper matrix by about 68.35%. Furthermore, the addition of Cu + 5 wt% of waste steel chips + 10 wt% of TiB2 and Cu + 12.5 wt% of waste steel chips + 2.5 wt% of TiB2 increased the hardness and toughness of the copper matrix by about 133.33% and 28.57%, respectively. The addition of Cu + 10 wt% waste steel chips + 5 wt% of TiB2 ensured minimal corrosion weight loss in the metal matrix composite as a result of low porosity and a strong bond between the molecules. Further, representative volume element (size: 225 × 225 × 225 nm)-based finite element analysis was done to explain the micro-mechanical deformation, interfacial strength of matrix-particle interaction and damage behavior of Cu + 10 wt% of waste steel chips + 5 wt% of TiB2 metal matrix composite. A user material sub-routine model was also written and implemented with the help of FORTRAN subroutines to simulate the macro-mechanical tension test process of Cu + 10 wt% waste steel chips + 5 wt%TiB2 metal matrix composite. The results revealed a good agreement between the micro-mechanical and macro-mechanical finite element analysis models on the one hand and the experimental results on the other. Further, the representative volume element (with matrix and particles) showed about 59% and 66.5% higher tensile strength compared to the matrix–particle interface and the matrix (without particles), respectively. The percentage difference between the micro-mechanical finite element analysis and the experiments as well as the macro-mechanical finite element analysis and the experiments was found to be 5.58% and 9.64%, respectively. The finite element analysis results established that the waste steel chip powder particles exhibited greater stress than the TiB2 powder particles.

Specimen size effect on the splitting-tensile behavior of coral aggregate concrete: A 3D mesoscopic study

The paper presents a mesoscopic investigation into the effects of specimen size and strain rate upon the strength and failure modes of coral aggregate concrete (CAC) subjected to splitting-tensile load. A three-dimensional (3D) mesoscale model that assumes concrete as a three-phase composite, i.e., aggregate, mortar and interfacial transitional zone (ITZ), was established for simulating the splitting-tensile behaviors of CAC at different strain rates (10−5 ∼ 200 s−1). The mesoscopic deformation and failure patterns of CAC cylinders with different sizes were exhibited through the 3D mesoscale modelling. Emphasis was set on the specimen size- and strain-rate effect on the tensile strength of CAC and corresponding effect laws were finally expressed by the mathematical statistical method. The numerical results suggest that there is a rate-hardening effect on the tensile strength of CAC, and the strain-rate effect is more noticeable when the critical strain-rate (1 s−1) is reached. Taking into the varying strengths at low- and high strain rate, the piecewise formulas were determined by the numerical and available test results to represent the strain-rate effect on CAC. In accordance with the relationship between the splitting-tensile strength and fracture area of specimen, the size-effect law of CAC at various strain rates was mathematically expressed using a series of power functions, which is of great significance for future research and application of CAC.

Microwave shielding and absorbing properties of single- and multilayered structures based on two-phase filler/epoxy composites

The microwave absorbing and shielding properties of epoxy composites with multiphase filler were studied in a wide frequency range of electromagnetic radiation (EMR) (1–67) GHz. The multiphase filler consists of carbon nanotubes (CNTs) and dielectric (titanium dioxide TiO2) or ferromagnetic (carbonyl iron Fe) particles. The content of TiO2 or Fe was fixed and equal to 35 wt% and 30 wt%, respectively, while the CNT content was varied from 1 to 5 wt%. It was found that EMR shielding efficiency SET is sufficiently increased with carbon nanotubes content and thickness of the composite especially for epoxy CMs filled with carbon nanotubes and carbonyl iron. The measured complex permittivity data (and permeability for CNT/Fe/epoxy CMs) were used for simulation of the reflection loss RL for studied composites. The simulated data have shown that more pronounced reflection loss $$\left| {\text{RL}_{\min } } \right|$$ = (30–44) dB is observed for 2–3 wt% CNT content in ternary epoxy CMs (sample thickness is 0.5–0.7 mm). For the higher CNT content (4–5 wt%), especially for CNT/Fe/epoxy CMs, the reflection loss $$\left| {\text{RL}_{\min } } \right|$$ was decreased, i.e., the large contribution in EMR attenuation is provided due to EMR reflection on the first air-composite boundary. It was shown that effective bandwidth of $$\left| {\text{RL}_{\min } } \right|$$ at level 10 dB can achieve (8–12) GHz and its position and $$\left| {\text{RL}_{\min } } \right|$$ value can be manipulated by varying the composition and thickness of the composite sample. The absorbing performance of 4-layered composite structures was modeled using electromagnetic parameters of single-layer absorbers based on the three-phase composites and optimal layers composition and thickness were found.

Analyzing the behavior of GPR wave propagation in zinc contaminated soil combining the dielectric properties—experimental study

There is a very strong link between the behavior of ground penetrating radar (GPR) wave propagation in zinc-contaminated soil and the dielectric properties of soil. This relationship can be of significant use in the practices of quick detecting the degree of pollution in zinc-contaminated soil. In this research, measurements were conducted on the zinc-contaminated soil samples with different soil index properties (i.e., zinc ion concentration, wet density and moisture content). The radar reflection wave data of the common midpoint and common-offset sounding mode were obtained by using the 600 MHz antenna, and the relative permittivity was measured using the vector network analyzer. The attribute analysis of radar reflection wave shows that the wave velocity is affected by wet density and moisture content, but independent of zinc ion concentration. Both the amplitude and the peak frequency decrease with the increase in zinc ion concentration, wet density and moisture content. For the soil dielectric properties, the metal ions can change the conductivity of solution in soil, affecting the imaginary part of relative permittivity, but with little effect on the real part. The positive correlations between the relative permittivity with density and moisture content are caused by the variation of three-phase composition of soil. Besides, the measured soil dielectric properties and the radar reflected wave attributes confirm each other, which can well explain the change rules of electromagnetic wave velocity, amplitude and central frequency. The presented results can increase understanding and confidence on GPR for quantitative monitoring and detecting of zinc-contaminated soil.

Linear aeroelastic analysis of cantilever hybrid composite laminated plates with curvilinear fibres and carbon nanotubes

In this paper, cantilever laminated composite plates, subjected to supersonic airflow, are studied in the linear elastic regime. The considered material is a multiscale three-phase composite, constituted by epoxy resin reinforced with multi-walled carbon nanotubes and curvilinear carbon fibres. The orientation of the fibres is defined using three different functions. A model based on a third-order shear deformation theory and a p-version finite element is applied. Furthermore, a hierarchical approach is applied to characterise the mechanical properties of the composite material. A combination of adequate micromechanics based models, including a modified version of the Halpin-Tsai model, the Rule of Mixtures, a unit cell-based model, and the Chamis model, is implemented. The aeroelastic analysis is performed considering the linear piston theory to evaluate flutter (dynamic instability) and divergence (static instability) in such structures. The improvements achieved through the combination of carbon nanotubes and curvilinear fibres on the instabilities are explored.

Towards Next-Generation Sustainable Composites Made of Recycled Rubber, Cenospheres, and Biobinder.

The utilisation of industrial residual products to develop new value-added materials and reduce their environmental footprint is one of the critical challenges of science and industry. Development of new multifunctional and bio-based composite materials is an excellent opportunity for the effective utilisation of residual industrial products and a right step in the Green Deal’s direction as approved by the European Commission. Keeping the various issues in mind, we describe the manufacturing and characterisation of the three-component bio-based composites in this work. The key components are a bio-based binder made of peat, devulcanised crumb rubber (DCR) from used tyres, and part of the fly ash, i.e., the cenosphere (CS). The three-phase composites were prepared in the form of a block to investigate their mechanical properties and density, and in the form of granules for the determination of the sorption of water and oil products. We also investigated the properties’ dependence on the DCR and CS fraction. It was found that the maximum compression strength (in block form) observed for the composition without CS and DCR addition was 79.3 MPa, while the second-highest value of compression strength was 11.2 MPa for the composition with 27.3 wt.% of CS. For compositions with a bio-binder content from 17.4 to 55.8 wt.%, and with DCR contents ranging from 11.0 to 62.0 wt.%, the compressive strength was in the range from 1.1 to 2.0 MPa. Liquid-sorption analysis (water and diesel) showed that the maximum saturation of liquids, in both cases, was set after 35 min and ranged from 1.05 to 1.4 g·g −1 for water, and 0.77 to 1.25 g·g−1 for diesel. It was observed that 90% of the maximum saturation with diesel fuel came after 10 min and for water after 35 min.

Three-phase composites of NiFe2O4/Ni@C nanoparticles derived from metal-organic frameworks as electrocatalysts for the oxygen evolution reaction

Composite electrocatalysts of carbon and metals or metal compounds with homogeneous active sites can be obtained through the carbonization of metal organic framework (MOF) materials under inert atmosphere. In this work, a three-phase composite electrocatalysts NiFe2O4/Ni@C were prepared via pyrolysis from self-assembled MOF nanosheets aggregates. The excellent electrocatalytic activity of the obtained electrocatalysts with various Ni:Fe ratios is demonstrated. Especially, the NiFe2O4/Ni@C sample with the mole ratio of Ni:Fe = 1:1 can use the overpotential (η) of 330 and 423 mV to drive 10 and 50 mA cm−2 respectively. After 80 000 s/22 h, the current density could retained 90% of the initial current density. The excellent activity and stability of the electrocatalysts are attributed to nickel and iron ions with uniform dispersion at atomic level in the NiFe2O4 phase and the synergistic effect of nickel and NiFe2O4 nanoparticles with amorphous carbon atoms or nanoparticles around.

Porous materials reinforced with short fibers: Unbiased full-field assessment of several homogenization strategies in elasticity

This work is concerned with the micromechanical modeling of porous short fiber-reinforced composites considered as three-phase microstructures: cavities and short fibers embedded in a matrix phase. Several homogenization strategies are evaluated in isothermal linear elasticity: two-level, two-step and direct Mori-Tanaka (MT) models. Unbiased evaluation of the methods is conducted based on full-field finite element (FE) analyses. No Eshelby-based analytical mean-field models are used. A parametric study for a porous thermoplastic polymer matrix reinforced with short glass fibers is carried out, for both fixed and distributed fiber orientations. The predictions of the various homogenization strategies are compared against reference FE results of the original three-phase composites. The reported numerical simulations are in 2D plane stress, but provide nevertheless insight into 3D situations. There are three main findings. (1) The best predictions are obtained with a two-level strategy, where in the lower level the actual porous matrix is homogenized, and in the upper level, fibers are embedded in the homogenized matrix. (2) The direct MT model can generate nonphysical predictions: effective properties outside the Voigt and Reuss estimates, and non-symmetric effective stiffness matrix. (3) For misaligned fibers, two-step homogenization methods can be used at the upper level in combination with the recommended two-level strategy. Acronyms and abbreviations: FE: finite element, BC: boundary condition, PBC: periodic BC, MF: mean-field, MT: Mori-Tanaka, ODF: orientation distribution function, OT: orientation tensor, RVE: representative volume element, SFRC: short fiber-reinforced composite, UC: unit cell, UD: unidirectional.

Constructing highly active Co sites in Prussian blue analogues for boosting electrocatalytic water oxidation.

High-valence cobalt sites are considered as highly active centers for the oxygen evolution reaction (OER) and their corresponding construction is thus of primary importance in the pursuit of outstanding performance. Herein, we report the design and facile synthesis of abundant high-valence cobalt sites by introducing Zn2+ into CoFe Prussian blue analogues (PBAs). The modification results in the drastic morphological transformation from a pure phase (CoFe-PBA) to a three-phase composite (CoFeZn-PBA), with a significant increase not only the amount of highly oxidized Co sites but the specific surface area (by up to 4 times). Moreover, the obtained sample also exhibits outstanding electric conductivity. Consequently, an excellent OER performance with an overpotential of 343 mV@10 mA cm-2 and a Tafel slope of 75 mV dec-1 was achieved in CoFeZn-PBA, which outperforms the commercial IrO2 catalyst. Further analysis reveals that CoFeZn-PBA becomes (oxyhydr)oxides after the OER.

Study on Mechanic Parameters Selection of Rock Slope Based on BP Neural Network Displacement Back Analysis

Natural rock mass is a complex three-phase composition, and its internal structure, physical characteristics such as fragmentation and water content have significant temporal and spatial variability. The method of assigning the mechanical parameters of rock mass according to the code ignores this important feature. In order to obtain the mechanical parameters of natural rock mass more accurately, based on a rock slope in NO.2 section of Ganxian-Xingguo expressway, a method for calculating mechanical parameters based on displacement back analysis of BP neural network was proposed on the basis of traditional code assignment. The back analysis model was optimized by neuron weight, inertia correction and algorithm step control, and then the mechanical parameters of the whole slope were back analyzed. Fatherly, the finite element numerical simulation software ANSYS was used to establish the grid model of the slope to judge the whole stability of the slope. The field monitoring was used to verify the calculation results. Facts and figures showed that the mechanic parameters gotten from the back analysis is more reliable than those in the code. The study can provide reference for mechanic parameters assignment of the rock slope.

On the effect of stiffness/softness and morphology of interphase phase on the effective elastic properties of three-phase composite material

In the present study, Composite material consisting of an elastic homogeneous isotropic matrix in which are embedded coated elastic isotropic inclusions, widely used in many applications is investigate by homogenization approach coupled to the finite elements method. A finite element model is proposed to predict the Young and Shear modulus of the three-phase composite containing spherical inclusions surrounded by a spherical or ellipsoid interphase layer. Three cases of particles volume fractions and interphase was considered with addition of two interphase morphology. Young modulus of interphase region was varied from soft to hard than the matrix properties. We note that interphase morphology and properties plays an important role in the elastic properties of composite with increasing the volume fraction of inclusions and interphase. The results were compared to the first order bounds Voigt and Reuss, and the mean field homogenization techniques. A sensitive study of the effect of mesh density on the results of the von Mises stresses and elastic properties has been made.

Thermo-mechanical modeling and characterization of three-phase shape memory alloy hybrid composites

The thermo-mechanical properties of shape memory alloy hybrid composites (SMAHCs) are characterized, and their three-phase constitutive relationship in the form of a lamina embedded with shape memory alloy (SMA) wires is established by micromechanics. Considering large beam deflection, a theoretical bending model of SMAHC beams with different fiber volume fractions and arbitrary ply schemes is proposed. The Runge–Kutta method is employed to solve the nonlinear ordinary differential equations, and the quantitative relations of curvature, rotation and deflection under thermal load are obtained from the model by directly using the original three-phase material parameters without the need of the experimental measurement in single layer. The SMAHC beams with different fiber orientation, number of layers, and volume fraction of SMA are fabricated, and their thermo-mechanical behavior is experimentally evaluated. Good agreements between the theoretical predictions and experimental results demonstrate that the proposed model is capable of predicting the thermo-mechanical behavior of three-phase SMAHC beams. The generic model developed can be used as an analytical tool in design analysis and optimization of SMAHC structures for effective shape, tracking, and vibration control.

Tunable Electrical Properties of Embossed, Cellulose-Based Paper for Skin-like Sensing.

This article describes a process of fabricating highly porous paper from cellulosic fibers and carbon black (CB) with tunable conductivity. By embossing such paper, its porosity decreases while its conductivity increases. Tuning the porosity of composite paper alters the magnitude and trend of conductivity over a spectrum of concentrations of conductive particles. The largest increase in conductivity from 8.38 × 10-6 to 2.5 × 10-3 S/m by a factor of ∼300 occurred at a percolation threshold of 3.8 wt % (or 0.36 vol %) with the composite paper plastically compressed by 410 MPa, which caused a decrease of porosity from 88% to 42% on average. Our composite paper showed stable piezoresistive responses within a broad pressure range from 1 kPa up to 5.5 MPa for 800 cycles. The piezoresistive sensitivities of the composite paper were dependent on concentration and decreased with pressure. Composite paper with 7.5 wt % CB had sensitivities of -0.514 kPa-1 over applied pressures ranging from 1 to 50 kPa and -0.215 kPa-1 from 1 to 250 kPa. This piezoresistive paper with embossed patterns enabled touch sensing and detection of damage from darts and punches. Understanding the percolation behavior of three-phase composites (cellulosic fibers/conductive particles/air) and their response to damage, pressure, and processing conditions has the potential to enable scalable applications in prosthetics and robotics, haptic feedback, or structural health monitoring on expansive surfaces of buildings and vehicles.

3D Mesoscale Finite Element Modelling of Concrete under Uniaxial Loadings.

Concrete exhibits a complex mechanical behavior, especially when approaching failure. Its behavior is governed by the interaction of the heterogeneous structures of the material at the first level of observation below the homogeneous continuum, i.e., at the mesoscale. Concrete is assumed to be a three-phase composite of coarse aggregates, mortar, and the interfacial transitional zone (ITZ) between them. Finite element modeling on a mesoscale requires appropriate meshes that discretize the three concrete components. As the weakest link in concrete, ITZ plays an important role. However, meshing ITZ is a challenging issue, due to its very reduced thickness. Representing ITZ with solid elements of such reduced size would produce very expensive finite element meshes. An alternative is to represent ITZ as zero-thickness interface elements. This work adopts interface elements for ITZ. Damage plasticity model is adopted to describe the softening behavior of mortar in compression, while cohesive fractures describe the cracking process. Numerical experiments are presented. First example deals with the estimation of concrete Young’s modulus. Experimental tests were performed to support the numerical test. A second experiment simulates a uniaxial compression test and last experiment simulates a uniaxial tensile test, where results are compared to data from the literature.

Stiffness of Three-Phase Concentric Composite Solids

There are numerous examples of three-phase concentric composites, including coated fiber-reinforced materials and syntactic foams. The stiffness of such three-phase materials is usually investigated by micromechanical methods specified for this particular case. For example, Luo and Weng presented solutions for three-phase concentric spheres [1] and for three-phase concentric cylinders models [2] of an inclusion, a coating (“intermediate matrix”), and a matrix using the Mori–Tanaka method. Among numerous studies of three-phase or multi-phase composites one can mention [3-6].