Homogenization Of Composite Materials Research Articles

Defect introduction and interfacial strategies for enhancing microwave absorption in carbon-based materials

Poor impedance matching and a single loss mechanism are typical challenges for carbon-based materials to become efficient microwave absorbers. To address these issues, defect introduction and interfacial strategies are effective methods for enhancing microwave absorption through the micro-mechanism of material interaction with microwaves. Additionally, forming a homogeneous composite material is crucial for achieving good impedance matching. In this study, we used a controlled solvent-thermal method to achieve self-assembled interfacial intercalation, yielding amorphous VOPO4/rGO nanohybrids, which show significantly enhanced microwave absorption properties. The abundant defects introduced by VOPO4 within the amorphous layered composites disrupt the charge distribution, contributing to polarization loss. The graphene nanosheets expose more VOPO4 structural units, facilitating increased conductivity and enriching the microwave absorption mechanism. As a result, the prepared VOPO4/rGO nanohybrids demonstrate outstanding microwave absorption, with the effective absorption bandwidth covering the entire Ku-band (11.6–18.0 GHz) at a thickness of 2.3 mm. This research provides an important reference for understanding the mechanisms that enhance the electromagnetic wave absorption of carbon-based materials.

Vitrification as a Key Solution for Immobilisation Within Nuclear Waste Management

AbstractVitreous materials in the form of both relatively homogeneous glasses and composite glass crystalline materials (GCM) incorporating disperse crystalline phases are currently the most reliable wasteforms effectively used on industrial scale for nuclear waste immobilisation. Glasses are stable solid-state materials with a topologically disordered atomic structure in the form of solid solutions, i.e. solutions frozen via vitrification to a solid state without forming regular crystalline phases. Nuclear waste vitrification is attractive because of technological and compositional flexibility enabling hazardous elements to be safely immobilised and providing a glassy material characterised by high corrosion resistance, mechanical and radiation durability, as well as effectively reducing the volume of the resulting wasteform.

Synthesis of novel hollow carbon nanotubes @ Co-Fe alloy/iron phthalocyanine electrocatalyst by self-assembly method for OER and ORR study

The exploration of an inexpensive catalyst with effective oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) activities to replace precious metal electrocatalysts has been of great interest in recent years. In this paper, CNT@Co-Fe/FePc composites were synthesized with high efficiency using a self-assembly strategy. In the synthesis process, carbon nanotubes (CNTs) were synthesized as the base material using crab shells as templates and honey as the carbon and nitrogen source. CoFe alloy nanoparticles derived from CoFe-based prussian blue analogs were self-assembled and anchored on CNTs, and then iron phthalocyanine with Fe-N4 portion was coupled with CNTs by π-π stacking. Finally formed a homogeneous and stable composite material. The self-assembly method is simple and efficient to achieve good metal loading. The prepared CNT@Co2-Fe1/FePc exhibits excellent catalytic performance and stability for OER and ORR in alkaline electrolyte. The overpotential at 10 mA cm−2 of CNT@Co2-Fe1/FePc for OER is 343 mV with a very small Tafel slope of 43.59 mV dec−1. CNT@Co2-Fe1/FePc has high methanol tolerance and persistence for ORR. This work provides a strategy for the construction of transition metal-carbon composite electrocatalytic materials with excellent catalytic performance and stability for OER and ORR reactions.

Envelope enrichment method for homogenization of non-periodic structures

The homogenization of composite materials is critical for accurately predicting their mechanical performance, particularly when complex reinforcement arrangements are involved. Microstructural characteristics exert a substantial influence on the composite’s properties during practical applications. A widely adopted approach for analyzing composites is the numerical simulation of a Representative Volume Element (RVE). Although this method is well-established for periodic RVEs, it encounters difficulties when applied to non-periodic meshes, which complicates the imposition of classical boundary conditions on nodes exhibiting varying properties. To address this challenge, we propose a novel methodology that involves modeling an envelope surrounding the RVE, to which periodic boundary conditions are applied. By defining the envelope as a homogeneous material, stress transmission to the RVE is facilitated. The stiffness tensor of the envelope is updated iteratively through a homogenization process, ultimately converging to the effective properties of the RVE. The method is validated on a non-periodic arrangement of spherical inclusions embedded within a matrix. Convergence is observed in the different cases studied within ten iterations and the results are found within the Voigt and Reuss bound.

Soil–Geosynthetic Interaction Under Triaxial Conditions: Shear Strength Increase and Influence of the Specimen Dimensions

Geosynthetics are extensible reinforcements used to enhance the engineering performance of a soil. The transfer of stresses from the soil to the reinforcement is achieved through soil–geosynthetic interaction. The proposals from the literature to assess the shear strength of the reinforced soil under triaxial conditions use three different approaches. These involve analysing the reinforced soil: (i) as a homogeneous composite material (Approach A), (ii) as two different materials (Approach B), or (iii) as soil having the same fundamental shear strength, with the effect of the reinforcement represented as an additional lateral or confining stress (Approach C). In this paper, triaxial tests data of a soil reinforced with a geosynthetic, and specimens with different dimensions (diameters 70 and 150 mm) were used to assess changes in shear strength and to carry out a statistical analysis. The increases in shear strength of the reinforced soil and of the soil–geosynthetic interface were analysed using equations from the literature. The difference between the triaxial results obtained from specimens of different sizes was assessed using an Analysis of Covariance (ANCOVA). When the joint term of the regression model was not statistically significant, the characterisation from different specimen sizes was used to generate soil failure envelopes. Thus, a new methodology to obtain a failure envelope with different specimen sizes is presented.

Transformation field analysis as a background of clustering discretization methods in micromechanics of composites

A linear composite material (CM) consisting of a homogeneous matrix with either the periodic or random set of heterogeneities is considered. One of the first reduced-order models (ROMs), Transformation Field Analysis (TFA) by Dvorak for the pair strain-eigenstrain (or stress-eigenstress) is modified in terms of the “mixed” pair strain-eigenstress (or stress-eigenstrain) for implementation to clustering-based ROMs initiated by the self-consistent clustering analysis (SCA) by WK Liu. A set of consistency conditions are obtained for both the effective properties and modified eigenfield concentration factors. It is found that modified TFA represents a unified background of all three central clustering-based ROMs: the SCA, virtual clustering analysis (VCA), and finite element analysis–clustering analysis (FCA). One presents the scheme of estimation of inhomogeneous strain concentration factors in some prescribed clusters analyzed by the SCA (nonlinear problem). For statistically homogeneous CMs, a localized version of the modified TFA is proposed for clustering of the matrix (coating) in the vicinity of inclusions. VCA used for the analysis of a finite size inclusion can be modified for the implementation of a combination of both the modified TFA and functional gradient theory.

Magneto-Mechanical and Thermal Properties of Nd-Fe-B-Epoxy-Bonded Composite Materials.

Polymer-bonded magnets are a class of composite material that combines the magnetic properties of metal particles and the molding possibility of a polymeric matrix. This class of materials has shown huge potential for various applications in industry and engineering. Traditional research in this field has so far mainly focused on mechanical, electrical or magnetic properties of the composite, or on particle size and distribution. This examination of synthesized Nd-Fe-B-epoxy composite materials includes the mutual comparison of impact toughness, fatigue, and the structural, thermal, dynamic-mechanical, and magnetic behavior of materials with different content of magnetic Nd-Fe-B particles, in a wide range from 5 to 95 wt.%. This paper tests the influence of the Nd-Fe-B content on impacting the toughness of the composite material, as this relationship has not been tested before. The results show that impact toughness decreases, while magnetic properties increase, along with increasing content of Nd-Fe-B. Based on the observed trends, selected samples have been analyzed in terms of crack growth rate behavior. Analysis of the fracture surface morphology reveals the formation of a stable and homogeneous composite material. The synthesis route, the applied methods of characterization and analysis, and the comparison of the obtained results can provide a composite material with optimum properties for a specific purpose.

Development and evaluation of osteogenic PMMA bone cement composite incorporating curcumin for bone repairing

Acrylic resin (PMMA - polymethylmethacrylate) is a material widely used in orthopedics to fill gaps or cavities in the bone marrow, bone defects, and implants fixation. However, even if it possesses high mechanical strength and is considered bioinert, its use has various limitations related to the lack of positive additional bioactive effects, such as osteogenesis stimulation. This work reports a preliminary assessment of the effects of curcumin incorporated in PMMA bone cements at different concentrations (4, 5, 7.5, and 10 wt%), and in particular, its osteoinductivity and osteoconductivity in vitro, tested with KUSA-A1 cells. The different samples were characterized using a combination of microscopic and spectroscopic techniques before and after in vitro testing. Results showed that curcumin and PMMA can produce a homogeneous composite material in a wide range of concentrations, up to at least 10 wt%. By increasing the percentage of curcumin both cellular adhesion and bone production are improved, without sacrificing the quality of the bone tissue formed. Addition of curcumin over a threshold of about 5% results in a sudden loss of ultimate strength with an increase of the elongation to failure. Samples containing about 5% of curcumin proved to have good in vitro performances without compromising the mechanical properties. This suggests how curcumin can be considered as a low-cost additive useful not only for its well-known antimicrobial activity but also in the bone regeneration improving the bioactive properties of the PMMA.

On Bhattacharyya relative entropy in a homogenization of composite materials

AbstractThe main idea of this work is an application of relative entropy in the numerical analysis of probabilistic divergence between original material tensors of the composite constituents and its effective tensor in the presence of material uncertainties. The homogenization method is based upon the deformation energy of the representative volume elements for the fiber‐reinforced and particulate composites and uncertainty propagation begins with elastic moduli of the fibers, particles, and composite matrices. Relative entropy follows a mathematical model originating from Bhattacharyya probabilistic divergence and has been applied here for Gaussian distributions. The semi‐analytical probabilistic method based on analytical integration of polynomial bases obtained via the least squares method fittings enables for determination of the basic probabilistic characteristics of the effective tensor and the relative entropies. The methodology invented in this work may be extended toward other probability distributions and relative entropies, for homogenization of nonlinear composites and also accounting for some structural interface defects.

Mechanical and tribological properties of electrical corrosion resistance-glass reinforced polyimide composites for high voltage applications

In recent times, glass fiber reinforcements are extensively used in the development of polymer matrix composites to improve their performance especially when used for engineering applications. As such, the focus of the present study remains on the effects of electrical corrosion resistance (ECR) glass particles on the mechanical and tribological properties of polyimide (PI) composites fabricated by the spark plasma sintering (SPS) process. SPS is a novel powder metallurgy method in producing homogeneous composite materials in short sintering time with finer microstructure. However, the PI composites were produced at different contents of ECR-glass reinforcement particles (5, 10, 15, and 20 wt %). The microstructural characterization of the samples was conducted using scanning electron microscope (SEM). Nanoindentation tests and pin-on-disc wear tests (under dry condition) were conducted to evaluate the mechanical and tribological properties of the composites. The SEM results revealed that the reinforcement’s particles were well distributed in the PI matrix phase. Incorporation of ECR-glass particles into the PI composites improved its hardness and elastic modulus. The ECR-glass/PI matrix composite loaded with 15 wt% ECR displayed a significant reduction in coefficient of friction from 0.091 to 0.015 and wear rate from 0.81 × 10−4 to 0.14 × 10−4 mm3/Nm. In addition, the ECR/PI composites exhibited improved dielectric properties over the pure PI. Hence, corroborating the potential of this ECR-glass reinforced PI for industrial (automobile and power) applications requiring high hardness, elastic modulus, good wear resistance, and low dielectric constant.

Effective nonlocal behavior of peridynamic random structure composites subjected to body forces with compact support and related prospective problems

We consider a static problem for statistically homogeneous matrix linear bond-based peridynamic composite materials (CMs) subjected to body force with compact support. Estimation of the effective displacements is performed by the exploitation of the most popular tools and concepts used in conventional local elasticity of composite materials (CMs) with their adaptation to peridynamics. The method is based on estimation of a perturbator introduced by one inclusion inside the infinite peristatic matrix subjected to the body force. The statistical averages of both the displacements and stresses are estimated by summation of these perturbators for all possible locations of inclusions. It leads to obtaining of a new general integral equation (GIE) where a renormalizing procedure is not required for the involved absolutely convergent integrals. It allows us to estimate not only the effective nonlocal constitutive equation but also to evaluate the statistical field averages (inhomogeneous and nonlocal) inside the phases at the fine scale that is critically important for advanced modeling (e.g. for any nonlinear phenomena potentially considered in the future). In particular, in the generalized effective field method (EFM) proposed, the effective field is evaluated from self-consistent estimations using closing of a corresponding integral equation in the framework of the quasi-crystalline approximation. In so doing, the classical effective field hypothesis is relaxed, and the hypothesis of the ellipsoidal symmetry of the random structure of CMs is not used. The method proposed is a promising ingredient at the construction of provably robust data-driven surrogate equations describing both the effective behavior and effective displacement concentration operator inside inclusions. Some opportunities for generalizations of the method proposed are considered. Numerical results for the estimation of effective deformations are obtained for one-dimensional (1D) statistically homogeneous peridynamic composite bar with the prescribed self-equilibrated body forces.

Optical composites based on organic polymers and semiconductor pigments

The aim of the work was the development of optical organic-inorganic composite materials with high absorption of light the visible part of the spectrum and high reflection in the near infrared region of the spectrum. Such materials are used in industry and construction as coatings. To create these optical composites, epoxy and epoxy-polyurethane polymer matrices containing inorganic semiconducting particles (CuS, PbS, Fe3O4) were used. Highly dispersive powders of inorganic pigments were used for the preparation of homogeneous composite materials. The wet precipitation method with the application of organic stabilizing additions was applied for the preparation of dispersive CuS and PbS powders. Optical microscopy and X-ray diffraction analysis helped to study the crystal structure and morphology of the obtained semiconductor pigments. PMT-3 device was applied for microhardness measurements of the prepared composite materials. Based on the data of X-ray diffraction analysis, the average crystallite size was calculated using the Scherrer formula. It was found that freshly precipitated CuS and PbS powders consist of nanocrystals with a size of 11–20 nm. Optical microscopy data indicate the formation of aggregates of semiconductor nanocrystals in powders. Experiments have shown that all synthesized composites have low light reflection coefficient (less than 0.06) in the visible part of the spectrum and an increased light reflection coefficient in the near infrared region of the spectrum (0.13–0.15 and more). The results of the study showed that the use of epoxy-polyurethane polymer matrices provides greater microhardness of composite materials, compared to the composites based on epoxy polymers. The highest microhardness values were observed in composite materials based on epoxy-polyurethane polymers containing highly dispersed Fe3O4 particles. Obtained organic-inorganic composites could be used as materials for light-absorbing coatings in different industrial applications.

Preparation and characterization of CQDs/SBS composites and its application performance as asphalt modifier

This research aims to use the prepared bio-base carbon quantum dots/styrene–butadiene styrene block copolymer (CQDs/SBS) composite materials as asphalt modifiers based on Pickering emulsion polymerization. The physical and chemical properties of CQDs/SBS composite modifier and its effect on asphalt modification were researched and contrasted it with SBS modifier. The results show that strong van der Waals forces and chemical covalent bonds are formed between CQDs and SBS polymer chains through a series of physicochemical reactions, resulting in strong interactions. Thus CQDs are uniformly dispersed in the SBS phase to form a homogeneous composite material. With the addition of CQDs, the CQDs/SBS composite modifier with slightly lower molecular weight than SBS modifier and can be better dispersed in asphalt. In addition, CQDs/SBS composite modifier has better thermal stability. Furthermore, CQDs and SBS have a synergistic impact in progressing the high-temperature property of polymer modified asphalt (PMA), which is showed by the improvement in softening point, viscosity, rutting resistance, and elastic recovery rate of CQDs/SBS PMA. However, the low-temperature property of CQDs/SBS PMA decreased, which is manifested by decreased penetration and ductility, increased creep stiffness modulus (S), and decreased the rate of change of stiffness with time (m). Further, CQDs/SBS PMA appears superior better storage stability than SBS PMA. It has the preferences of facile preparation procedure and low cost too, making it a beneficial choice for asphalt modifiers.

A novel manufacturing method and structural design of functionally graded piezoelectric composites for energy-harvesting

The power supply to the sensors becomes increasingly critical as the Internet of Things (IoT) evolves. Hence, our goal is to transform ambient environmental energy in our daily lives into electrical energy and then give power to IoT sensors. In this work, we developed and manufactured functionally-graded piezocomposite using poly(vinylidene fluoride-co-trifluoroethylene) [P(VDF-TrFE)] and barium titanate (BaTiO3, BTO) particles. Functionally graded materials offer better specific strength, toughness, and fatigue resistance than homogeneous composite materials, making them appropriate for energy-harvesting. Spin coating and hot-pressing methods were used to create BTO/P(VDF-TrFE) composites with varying BTO particle fractions and structures. After determining the optimal spin coating and hot-pressing conditions, the composites were polarized using the corona poling technique. The structure and properties of the composites were determined by scanning electron microscopy, differential scanning calorimetry, and X-ray diffraction. Then the piezoelectric characteristics were tested, and impact and vibration energy production tests were devised and carried out. This research provides a feasible manufacturing method for functionally graded piezocomposites and investigates the material energy-harvesting potential. Meanwhile, guidance is offered for the construction of functionally graded piezoelectric composites structures for use in various types of energy-harvesting applications.

In situ CaCO3 mineralization controlled by carbonate source within chitosan-based cryogels

Designing of multifunctional hydrogel/CaCO3 composites has received great interest in the modern tissue engineering. Herein, four chitosan-based cryogel samples as monoliths, prepared by ice-segregation technique and which differ by structural porosity, are proposed as possible matrix for CaCO3 crystal growth, aiming the formation of homogeneous composite materials. Also, four types of carbonate sources were applied as modulators for crystal growth: Na2CO3 in an alternate dipping process, dimethyl- or diethyl-carbonate (DMC or DEC) hydrolysis, and ammonium bicarbonate diffusion. The morphology of the composites was investigated by scanning electron microscopy and the polymorphs characteristics by X-ray diffraction and FTIR-ATR spectroscopy. The crystal growth applied methods were effective for composite formation, tuning the inorganic formation in the whole cryogels 3D pattern. Thus, increasing the number of alternate sorption steps, the amount of CaCO3 crystals increased but keeping the pores open for further specific applications. Also, CaCO3 polymorphs formed by DMC or DEC hydrolysis show mainly the formation of calcite rhombohedral crystals arranged in large polycrystals. The ammonium diffusion method generated the most uniform structures, in the whole investigated cryogels samples, MTS test showing samples biocompatibility.

An impedance sensor based on chitosan-carbon quantum dots for the detection sialic acid in humuan serum

Here, we introduce an ultra-sensitive electrochemical impedance sensor for the detection of sialic acid (SA) in human serum. We synthesized carbon quantum dots (CQDs) by a simple hydrothermal method. By dispersing CQDs in chitosan (CS), a homogeneous CS-CQDs composite material can be obtained. CS-CQDs composite material has good biocompatibility and high stability, and can form a stable film on the surface of the glassy carbon electrode (CS-CQDs/GCE). In addition, based on the principle that boronic acid groups specifically recognize sialic acid, 3-aminophenylboronic acid (ABA) is used as a specific recognition molecule for sialic acid to improve the sensitivity and selectivity of the prepared modified electrode (ABA/CS-CQDs/GCE). The morphology of the CS-CQDs composite material was characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM) and Fourier transform infrared spectroscopy (FTIR). At the same time, the electrochemical behavior of CS-CQDs composite materials was discussed through electrochemical technology. Studies have shown that the linear response range of the prepared ABA/CS-CQDs/GCE to SA is 0.02 ~ 3 mM. The detection limit is 5 μM (S/N = 3). The proposed ABA/CS-CQDs/GCE has high sensitivity, good repeatability and strong selectivity, and has achieved good results in the detection of real samples (human serum samples). Therefore, a practical detection platform for rapid, simple, selective and reliable detection of SA is provided.

Feasible preparation of Cu6Sn5 alloy thin-film anode materials for lithium-ion batteries from waste printed circuit boards by electrodeposition

Homogeneous and three-dimensional structural Cu6Sn5 alloy thin-film composite materials are successfully fabricated by efficiently electrodepositing the acidic leaching solution of waste printed circuit boards with the pH value adjusted to 10 at different current densities, which are confirmed by inductive coupled plasma-optical emission spectrometer, scanning electron microscope, and X-ray diffraction. When the Cu6Sn5 alloy thin-film composite materials electrodeposited at 5 mA/cm2 are employed as anode materials for lithium-ions batteries, the assembled coin cells can deliver initial discharge and charge specific capacity of about 617 and 502 mAh/g at 100 mA/g, respectively, and can retain a discharge specific capacity of 448 mAh/g after 25 cycles. Moreover, the cells assembled with Cu6Sn5 alloy anodes can exhibit an enhanced lithium-ion diffusion coefficient of 5.045 × 10−16 cm2/s with a lower transfer resistance of 63.43 Ω. Those results may provide an effective strategy for the resource utilization of low-value wastes into copper‑tin alloy thin-film electrode materials.

New Reduced‐Order Lithium‐Ion Battery Model to Account for the Local Fluctuations in the Porous Electrodes

Numerical simulations of microscopic transport processes in porous electrodes of lithium‐ion batteries demonstrate the presence of spatially localized fluctuations of physical quantities on the microstructure scale. They can influence the macroscopic battery characteristics (for example, the degradation rates). These fluctuations cannot be captured in a straightforward manner by the widely used porous electrode theory by Doyle, Fuller, and Newman (DFN model). The latter treats the porous electrodes as macroscopically homogeneous composite materials; it reduces the computational costs of numerical simulations. Herein, a modification of the DFN model that incorporates the local fluctuations but preserves the computational efficiency is proposed. Numerical simulation examples are presented that test the accuracy of the reproduction of the local fluctuations. The main new feature lies in the mathematical representation of the slow transport processes in the active material and their influence on the macroscopic reaction rates. The model is rooted in the rigorous mathematical analysis of the transition from a microscopic, microstructure‐resolving transport and reaction description to a macroscopic, volume averaging‐based one. The model construction methodology is open for further modifications for the applications in which some of the assumptions should be dropped, or description of new processes, reactions, phases, etc. should be incorporated.

A study of magnetic and magnetocaloric properties of 0.95 (La0.45Nd0.25Sr0.3MnO3)/0.05CuO composites prepared by spray drying

This study presents an investigation of the structural, magnetic and magnetocaloric properties of the 0.95(La0.45Nd0.25)Sr0.3MnO3/0.05CuO polycrystalline composite. The investigated composite materials are elaborated by combining both solid-state reaction and spray-drying method at the pilot-scale aiming to obtain a homogeneous composite material with controlled morphology and regular particles size. The structure, microstructure, magnetism and magnetocaloric features of the synthesized materials are investigated by using several techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM) and Magnetic measurements. The XRD and SEM data confirm the co-existence of perovskite and copper oxide phases. The magnetization data unveil that the studied composite exhibits a ferromagnetic to paramagnetic transition close to room-temperature (TC = 295 K). More importantly, its magnetocaloric effect in terms of the entropy change remains similar to that of (La0.45Nd0.25)Sr0.3MnO3/0.05CuO only synthesized by the conventional solid-state reaction technique. This points out the possibility of upscaling the production of magnetocaloric oxides to industrial levels using the spray-drying technique.

Generalized effective fields method in peridynamic micromechanics of random structure composites

We consider a static problem for statistically homogeneous matrix linear bond-based peridynamic composite materials (CMs). For the media subjected to remote homogeneous volumetric boundary loading, one proved that the effective behavior of this media is governed by conventional effective constitutive equation as in the local elasticity theory. It was made by the most exploitation of the popular tools and concepts used in conventional elasticity of composite materials (CMs) with their adaptation to peridynamics. This is extraction from the material properties a constituent of the matrix properties. Effective moduli are expressed through the introduced new notion of the average local polarization tensor. The average is performed over the surface of the extended inclusion phase rather than over an entire space. Any spatial derivatives of displacement fields are not required. The basic hypotheses of locally elastic micromechanics are generalized to their peridynamic counterparts. In particular, in the generalized effective field method (EFM) proposed, the effective field is evaluated from self-consistent estimations by the use of closing of a corresponding integral equation in the framework of the quasi-crystalline approximation. In so doing, the classical effective field hypothesis is relaxed, and the hypothesis of the ellipsoidal symmetry of the random structure of CMs is not used. One demonstrates some similarity and difference with respect to other methods (the dilute approximation and Mori-Tanaka approach) proposed before in micromechanics of peridynamic CMs. Comparative numerical analyses of these methods are performed for 1D case.