Narrow Results

This work investigates the development and tribological performance of aluminum (Al) matrix composites reinforced with boron carbide (B₄C) particles at 2, 4, and 6wt.%. These composites were fabricated using a novel ultrasonic-assisted stir-casting approach. The inclusion of B₄C, a ceramic material known for its hardness and thermal stability, aimed to enhance the wear resistance of the Al matrix. Ultrasonic-assisted stirring ensured uniform dispersion of B₄C particles and reduced agglomeration, addressing a common issue in composite production. The developed composites with varying B₄Cwt.% were subjected to dry sliding wear testing using a pin-on-disc device and a Box-Behnken design of response surface methodology, incorporating variables such as load, sliding distance, and reinforcement wt.%. XRD analysis confirmed the presence of B₄C in the Al–B₄C composite. A slight peak shift was observed as the weight percentage of B₄C increased. The 2% Al–B₄C composite exhibited a 29% decrease in porosity compared to cast Al 6061. The inclusion of 2wt.% B₄C resulted in a significant 33% improvement in the composite’s hardness, reaching 86.6HV. Severe plastic flow and subsequent strain hardening were responsible for this increase in hardness. The ANOVA results primarily influenced the wear rate, with sliding distance and reinforcement weight percentage following closely behind. This study highlights the potential of Al–B₄C composites in applications requiring exceptional wear performance, such as the automotive and aerospace industries.

Crack initiation and propagation analysis in brittle two-dimensional isotropic materials are conducted using the damage Phase Field Method (PFM) following the variational approach. Here, we study two-dimensional (2D) structures that contain material heterogeneities (e.g., interfaces and inclusions) as well as geometric ones (e.g., cracks and voids) when subjected to quasi-static uniaxial tensile loading. The adopted methodology combines Extended Finite Element Method (XFEM) and Level-Set couple with PFM in order to investigate both the case of heterogeneous materials (composite or porous) as well as the case of interfacial cracks between two different materials for their interest and relevance as practical examples. Among many others, one can, for example, argue that: (a) the regular hexagonal arrangement of heterogeneities leads to a significantly higher strength than any random arrangement, for both the composite material (containing fibers) and the porous material (containing voids), (b) the effects of contrasting stiffness and toughness between two materials along with their respective impacts on the interfacial crack trajectory, on energy balance and on reaction force are in favor of toughness.

It is of great significance to sort specific types of cells through a fast and efficient technology in biomedical research and clinical applications. In this study, commercial hollow glass beads were modified with 3-aminopropyltriethoxysilane (ATPES) and hyaluronic acid (HA) sequentially, which can capture HeLa cells with nearly 100% efficiency within 10min. The beads can specifically recognize and sort HeLa cells from a cell coculture of HeLa and L-929 depending on their strong buoyancy and good affinity with cancer cells. The job provides a facile, quick and low-cost cell sorting method, which has potential application in the fields of specific and efficient cell isolation.

Fiber-reinforced composites are a class of material with increasing industrial applications. Computer simulations have been used in order to understand the microscopic mechanism which can explain their mechanical behavior and several models have been introduced in the last decade. In this paper we introduce a criterion to define the brittle-ductile transition region in unidirectional fiber-reinforced composites. In order to simulate a fiber bundle, a recently introduced stochastic model is used. The results obtained with our criterion are compared with those obtained by using a self-organized criticality (SOC) approach.

Considering the interface effect between two phases in composite, we present a novel model of dielectric constant of two-phase composites with interfacial shells. Starting from Maxwell theory and average polarization theory, the formula of calculating the effective dielectric constant of two-phase random composites with interfacial shells is presented. The theoretical results on effective dielectric constant of alkyd resin paint/Barium titanate random composites with interfacial shells are in good agreement with the experimental data.

Recently the thick open section composite beams are extensively used to replace conventional metal load carrying members and stiffeners of structural elements. However, most of studies on the open section composite beams are confined to the thin composite beams. There are some works focused on the thick composite beams but they are limited only to closed section beams. Therefore, it is required to develop an appropriate model to analyze the thick open section composite beams. In this study, the cantilever beams of two specific lay-up configurations are considered which are the circumferentially asymmetric stiffness (CAS) and circumferentially uniform stiffness (CUS) beams. Under the vertical loading at the free end, loading induced deformations are obtained for the thick beams using the suggested model. The model includes coupled stiffness and secondary warping effects. The results are compared with those obtained using thin beam model to observe the thickness effects. Those results are also compared with the finite element analysis results for the verification of the suggested model. A good agreement is obtained between the results from the suggested model and those from finite element analysis.

Quasi-static contact behavior of an inflated MAXXIS VICTRA MA-Z1 (235/45/R17) radial tire is reported in this work. Compressional response of the inflated tire with a prescribed weight loaded quasi-statically was examined. Both experimental and numerical results were obtained and compared. In addition, dynamic contact simulation of the tire rolling on a dry-flat roadway was also studied. A commercial finite element commercial Code (LS-DYNA) was used to construct the complex tire model and to perform both quasi-static contact and dynamic rolling simulations. The Mooney-Rivlin constitutive relationship was adopted to describe the non-linear elastic behavior of rubber material, and the classical laminated theory was used to model the stress-strain behavior of the fiber reinforced composite layers of tire. Quasi-static contact force and compression displacement of tire were measured and numerically simulated. Contact pressure distribution of the tire tread in touch with simulated rigid dry-flat road surface was also numerically and experimentally obtained. Good relationship between the test findings and simulated results were reported. In addition, the dynamic contact simulations of the inflated tire rolling on a dry-flat rigid roadway with a prescribed weight loaded are presented, and the deformation pattern and local contact stress distribution are also reported.

Fuel cell is undoubtedly widespread energy conversion technology, which can convert fuel (biogas) energy into electricity. Solid oxide fuel cell (SOFC) is one of the best choices among the fuel cell’s family due to high efficiency and fuel flexibility. In this study, zinc-based nanostructured ${\mathrm{\text{Mn}}}_{0.20}{\mathrm{\text{Fe}}}_x{\mathrm{\text{Zn}}}_{0.80-x}{\mathrm{\text{O}}}_{\delta }$ electrode materials were successfully developed by solid state reaction. The proposed materials have been characterized by XRD and SEM. The electrical conductivities have been examined by four-probe DC method in the temperature range of 300–600${}^{\circ }$C, the maximum values were recorded and found to be 12.019 and 5.106 S/cm at natural gas and air atmosphere, respectively. The electrochemical performance has been measured employing NK-SDC electrolyte material and their current density versus voltage and current density versus power density (I-V and I-P characteristics) have been drawn. The maximum power density was found to be 170 mW/cm² using natural gas as a bio-fuel over a temperature of 600${}^{\circ }$C.

A composite mechanoluminescent layer has been produced on the surface of polymethylmethacrylate by liquid-phase embedding of ${\mathrm{\text{SrAl}}}_2{\mathrm{\text{O}}}_4:({\mathrm{\text{Eu}}}^{2+},{\mathrm{\text{Dy}}}^{3+})$ phosphor microparticles into the polymethylmethacrylate surface layer. The photoluminescence and mechanoluminescence of the obtained layer have been investigated. The mechanoluminescence was excited by the short acoustic pulses and by the dynamic pressure of the stylus sliding over the mechanoluminescent layer surface. A possible mechanism of mechanoluminescence excitation is under discussion. The produced composite layer is shown to exhibit high efficiency of “mechano-optical” transformation.

The paper presents results of studying temperature dependences of the specific volume resistance of nonirradiated and irradiated $\gamma$-rays with a different dose of $\mathrm{\text{LDPE}}+x$ vol.%TlInSe₂ composites in the temperature range 300–380 K. The technique for modifying the structure of composites with semiconductor filler was carried out on a ${}^{60}$Co-type MPX $\gamma$-25 M isotope $\gamma$-emitter at a temperature of 300 K in vacuum ampoules at doses of $0$–$10^6$ Gy. The electrical properties of the composites were studied before and after irradiation with $\gamma$-rays. Samples were prepared by mechanically mixing the filler ${\mathrm{\text{TlInSe}}}_2$ powder with a low density polyethylene powder until obtaining a uniform mixture. The mixture is kept for 5 min at the melting temperature of the polymer under a pressure of 5 MPa. At the same temperature, by pressing a homogeneous mixture, the pressure rises to 15 MPa, at this pressure the sample is held for another 5 min, and then quickly cooled in water. The specific volume resistivity of the composites was measured using a DC bridge of the P-4053 type with additional measuring electrodes. Samples before testing are aged for 24 h at a temperature of $20\pm 2^{\circ }$C and a relative humidity of $65\pm 5$%. It was revealed that with an increase in the volume content ${\mathrm{\text{TlInSe}}}_2$, the specific volume of resistivity of composites decreases. Under the action of $\gamma$-radiation and a change in the filler content, the magnitude and nature of ${\rho }_V(T)$ dependence changes, and this allows to manage the physical parameters of studied composites by varying the filler content and $\gamma$-radiation dose.

In this study, ion-beam-sputtering technique is used to prepare nanocomposite films, consisting of deposited copper nanoparticles (CuNPs) on polyethyleneterephthalate (PET). The successful formation of the flexible Cu/PET composite films is confirmed by X-ray diffraction (XRD). The surface morphology of Cu/PET is studied by atomic force microscopy (AFM). The results show that the surface roughness increased from 22.6 nm for PET to 45.3 nm after 40 min of deposited Cu/PET. The sheet resistance decreases from $5.16\times 10^4\mathrm{\Omega }$ to $1.3\times 10^4\mathrm{\Omega }$ and resistivity decreases from $2.3\times 10^{-2}\mathrm{\Omega }\cdot \mathrm{\text{cm}}$ to $1.77\times 10^{-2}\mathrm{\Omega }\cdot \mathrm{\text{cm}}$, as the Cu deposition time increases from 20 min to 60 min. Moreover, Young’s modulus increases from 2.82 GPa to 2.96 GPa and the adhesion force enhances from 14.7 nN to 29.90 nN after 40 min of Cu deposition. The DC electrical conductivity at 300 V is improved from $1.75\times 10^{-8}$ S.cm${}^{-1}$ to $3.57\times 10^{-8}$ S.cm${}^{-1}$ after 60 min of Cu deposition. The results show the deposited Cu on flexible PET platform clearly exhibits improvement over pristine PET in the mechanical and electrical properties which render it useful for a broad range of dielectric applications.

This paper is devoted to the analysis of physical processes in composite matrix materials whose properties are greatly affected by the interphase interaction of the matrix and the modifier. Contribution of this interaction to thermodynamic and dielectric properties of such materials is investigated by the example of a model system which is a colloid solution of solid particles with charged surface in a polar liquid. Mechanisms underlying formation and stabilization of specific structures near the interphase boundaries of the examined system are discussed. Special attention is paid to the assessment of additional contribution to the internal energy and heat capacity related to the electric interaction of solid and liquid components. Results obtained within the proposed model show that for a certain concentration of liquid (about several percent) the interphase energy in a unit of volume magnificently increases to the values of about 10⁷–10⁸ J/m³ and therefore exceeds heat motion energy of polar molecules. Moreover it was revealed that the electrical part of heat capacity is comparable to self-capacity of the liquid matrix provided that the surface charge density of solid particles is high enough.

To meet the requirement of next-generation multilayer ceramic capacitors, the synthesis and characterization of Ba_0.985Bi_0.01TiO₃-based high-k dielectric compositions are reported. Solid solutions with a nominal composition of 0.4Ba_0.985Bi_0.01TiO₃–0.6BaTi_1-xZr_xO₃ (x = 0.001, 0.005, 0.01, 0.02, 0.04, 0.06, 0.1) was synthesized by distillation method. Room-temperature X-ray diffraction patterns showed an increase and then a decrease in the tetragonality of Ba_0.985Bi_0.01TiO₃ after modifying with BaTi_1-xZr_xO₃. The decrement in tetragonality (c/a ratio) was accompanied by lowering of Curie temperature. 0.4Ba_0.985Bi_0.01TiO₃–0.6BaTi_0.995Zr_0.005O₃ was found to exhibit diffuse phase transition accompanied by an ultrahigh dielectric constant of 77,619, a loss tangent < 1 and a grain size < 1 μm.

This work reports, microwave characterization of nanocrystalline nickel-polyvinylidene fluoride (n-Ni/PVDF) composites with an aim to explore their electromagnetic interference (EMI) shielding and absorption properties. The composites were fabricated using compression hot molding process at an optimum level of temperature and pressure. The electrical properties of the samples are computed using the measured scattering parameters in the X-band. The wave absorption capability of a single layer absorbing structure is theoretically evaluated by employing the computed electrical parameters. Besides, the shielding effectiveness (SE) of free standing samples are also calculated using transmission line model and compared with the experimentally obtained results to validate the theoretical model. High SE (42.87 dB) and absorption (−14.37) obtained in this work, suggest futuristic applications of n-Ni/PVDF composites for EMI shielding and wave absorption.

This paper presents a new design procedure for large wind turbine blades, which can be used in various case studies. The structural design of 2MW CFRP blade was performed using a verified 2MW GFRP blade model. The structural integrity assessment of the CFRP model demonstrated that the design criteria for tip deformation, buckling failure, and laminate failure in normal wind turbine operating conditions were met. The existing aero-elastic analysis code was not used to estimate the blade load, but the blade’s surface pressure was calculated using CFD. The conventional load analysis code necessitates the establishment of a turbine system and the input of structural characteristics with changes in the structural design specifications. However, when CFD was used to estimate the load, the turbine system was not required and the structure was evaluated against various design cases, making this a useful approach in preliminary design. This new structural design and evaluation procedure for wind blades can be used to review diverse design specifications in the initial design stage.

Alloys of the As₂Se₃–CuCr₂Te₄ system were synthesized in a wide range of concentrations, and their physico-chemical properties were studied by differential thermal analysis (DTA), X-ray diffraction (XRD), microstructural (MSA) analysis, as well as by determining the microhardness and density, and its $T$–$x$ phase diagram was constructed. It has been established that the phase diagram of the As₂Se₃–CuCr₂Te₄ system is quasi-binary of the eutectic type. The system has small single-phase fields based on the original components. In the As₂Se₃–CuCr₂Te₄ system, the area of the solid solution based on the As₂Se₃ compound at room-temperature is 2 mol%, and the area of the solid solution based on the CuCr₂Te₄ compound is 6 mol%. Joint crystallization of As₂Se₃ and CuCr₂Te₄ ends at the double eutectic point with a composition of 15 mol% CuCr₂Te₄. With slow cooling in the As₂Se₃–CuCr₂Te₄ system based on As₂Se₃, the glass formation region reaches 10 mol% CuCr₂Te₄. The magnetic properties of the obtained solid solutions (CuCr₂Te${}_4{)}_{1-x}$(As₂Se${}_3{)}_x$ ($x$–0.03; 0.05) were studied.

We characterize the functionals which are Mosco-limits, in the L²(Ω) topology, of some sequence of functionals of the kind

This paper is motivated by modeling the procedure of formation of a composite material constituted of solid fibers and of a solidifying matrix. The solidification process for the matrix depends on the temperature and on the reticulation rate which thereby influence the mechanical properties of the matrix. The mechanical properties are described by a viscoelastic medium equation of Kelvin–Voigt type with rapidly oscillating periodic coefficients depending on the temperature and the reticulation rate. That is modeled as an initial boundary value problem with time-dependent elasticity and viscosity tensors to account for the solidification, and the mechanical and/or thermal forcing. First we prove the existence and uniqueness of the solution for the problem and obtain a priori estimates. Then we derive the homogenized problem, characterize its coefficients including explicit memory terms, and prove that it admits a unique solution. Finally, we prove error bounds for the asymptotic solution, and establish some related regularity properties of the homogenized solution.

A fluid–structure interaction (FSI) validation study of the Micon 65/13M wind turbine with Sandia CX-100 composite blades is presented. A rotation-free isogeometric shell formulation is used to model the blade structure, while the aerodynamics formulation makes use of the FEM-based ALE-VMS method. The structural mechanics formulation is validated by means of eigenfrequency analysis of the CX-100 blade. For the coupling between the fluid and structural mechanics domains, a nonmatching discretization approach is adopted. The simulations are done at realistic wind conditions and rotor speeds. The rotor-tower interaction that influences the aerodynamic torque is captured. The computed aerodynamic torque generated by the Micon 65/13M wind turbine compares well with that obtained from on-land experimental tests.

We identify the restricted class of attainable effective deformations in a model of reinforced composites with parallel, long, and fully rigid fibers embedded in an elastic body. In mathematical terms, we characterize the weak limits of sequences of Sobolev maps whose gradients on the fibers lie in the set of rotations. These limits are determined by an anisotropic constraint in the sense that they locally preserve length in the fiber direction. Our proof of the necessity emerges as a natural generalization and modification of the recently established asymptotic rigidity analysis for composites with layered reinforcements. However, the construction of approximating sequences is more delicate here due to the higher flexibility and connectedness of the soft material component. We overcome these technical challenges by a careful approximation of the identity that is constant on the rigid components, combined with a lifting in fiber bundles for Sobolev functions. The results are illustrated with several examples of attainable effective deformations. If an additional partial second-order regularization is introduced into the material model, only rigid body motions can occur macroscopically.