Narrow Results

The development of composite materials is a key area of research for enhancing the electrochemical performance of electrode materials. In this study, NiCo–S nanostructured hybrid electrode materials were prepared on nickel foam (NF) by using binary metal–organic frameworks (MOFs) as the sacrificial template through a two-step hydrothermal method. Ni–MOF was then deposited on the surface of NiCo–S/NF through the hydrothermal method and subsequently converted into Ni(OH)₂ through a subsequent alkalization treatment. The duration of the Ni–MOF hydrothermal process was varied as a parameter. NiCo–S@Ni–MOF/NF was prepared through hydrothermal reaction for 6h, 9h and 12h, followed by heating in a 6M KOH solution at 75${}^{\circ }$C for 6h in a water bath. The electrode materials with the best morphology and electrochemical properties were obtained when the hydrothermal reaction time was 6h. The optimized electrode had a specific capacity of 2533.2F$\cdot$g${}^{-1}$ at 1A$\cdot$g${}^{-1}$ and a capacity retention rate of 60.8% at 10A$\cdot$g${}^{-1}$, which indicated good rate performance. Additionally, the electrode material demonstrated excellent cycling stability, with a capacity retention rate of 95.3% after 5000 cycles at 50mV$\cdot$s${}^{-1}$. The energy density of the hybrid supercapacitor device assembled from this electrode material was 33.5Wh$\cdot$kg${}^{-1}$ when the power density was 849.89W$\cdot$kg${}^{-1}$ at a current density of 1A$\cdot$g${}^{-1}$.

Crashworthiness research has attracted significant attention, focusing on evaluating deformation behavior and selecting composite material components that act as energy-absorbing devices. Among the available composite materials, carbon fibers can absorb high energy during a crash. This paper presents the initial concept of the design application of a carbon fiber Belleville spring. The proposed design of the mechanism is directed to reduce the extent of the impact. An analytical approach is followed to calculate the energy absorbed during a crash. The parametric study is conducted for a different range of load $22250\le F\le 27000$N to predict which spring material absorbs maximum energy. The impact on the occupant side is minimum by the finite element approach. A brief overview of the spring’s energy absorption capability is provided through Ansys, and a correlation is proposed, which helps predict the value of Energy for different loads.

Silicon nitride bonded silicon carbide (Si₃N₄-SiC) refractories are commonly used as the sidewall of aluminum electrolysis cells. They have to withstand an extremely corrosive molten electrolyte bath for long periods. The sidewall is normally protected with a layer of solidified electrolyte (called frozen ledge), which is sensitive to the thermal conductivity of the sidewall. In this work, through review of the literature on modeling methods for predicting the effective thermal conductivity of dense composites and porous materials, some selected methods were applied to calculate the effective thermal conductivity of Si₃N₄-SiC refractories. The model predictions were compared with the thermal conductivity of a commercial Si₃N₄-SiC refractory measured by using laser flash technique. The present study showed that, due to multi-phase nature and complex microstructure of Si₃N₄-SiC refractories, most of the selected modeling methods individually do not give satisfactory predictions in one step. Recursive applications of one method or combinations of different methods are capable of giving satisfactory predictions.

BaZrO₃ submicron powder obtained from chemical route was added to YBCO for preparation of YBCO + xBZO (x = 0, 1, 2.5, 5, 10 rm wt%) composites samples. The X-ray peak profile analyses and the scanning electron microscopy have indicated that the mean powder size for BZO ranges from 500 to 800 nm. In fact, the presence of BZO brings about a significant modification in the microstructure of the composites. The resistive transition in presence of magnetic field (0–8 T) was investigated. With application of magnetic field, T_c0 decreases significantly, suggesting that grain boundaries (Josephson junctions) are affected more than the grains (Abrikosov junctions). Activation energy is found dependent not only on the particle size, but also on penetration depth and decreases with increasing doping concentration of BZO submicron size particles in contrast to what has been recently observed by M. Safonchik et al. with grain sizes of 40 nm BZO. It has also been observed by H. Shakeripour, M. Akhavan [Supercond. Sci. Technol.14, 234 (2001)] and Gamchi et al. [Phys. Rev. B50, 12950 (1994)] that the activation energy depends not only on the temperature and magnetic field, but also on the doping concentration.

The LPG gas sensing response of polyethylene oxide (PEO)-Cu (Cu = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 and 1.0 wt. %) composite thick films prepared on alumina substrates by using novel screen printing technique are reported in present paper. The gas sensing responses of films were tested at 1000 ppm of LPG by using home-built static gas sensing system [between room temperature - 50 °C]. A very high value of SF = 1400 was obtained at an optimum temperature of 47 °C for a film with Cu = 0.7 wt.%. Further, better LPG sensing response, SF = 700 was obtained at low operating temperature = 36 °C for a film with Cu = 0.2 wt. %. The LPG sensing responses of the films were found to be strongly influenced by concentration level of Cu additive.

[X]%BaTiO₃[100-x]%CoFe₂O₄ composites (x = 0, 20, 40, 60, 80, and 100) were prepared by the general ceramic method. X-ray diffraction patterns and IR spectra confirmed the presence of two phases beside identified phase in the composites with (x% = 40-80%BaTiO₃).

The temperature variation of conductivity was mainly attributed to change of the drift mobility rather than to the variation of charge carrier concentration. All the composites showed p-type behaviors in the range of temperature 300–400 K. For T > 400 K all composites showed n-type behavior. At this high temperature, the conduction is mainly due to Fe³⁺→Fe²⁺. Hence, there is a p–n transition.

The variation of dielectric constant as a function of temperature showed a peak value at the Curie temperature (around 390 K) of ferroelectric phase in composites. It is also noted that the phase transition temperature T_c varied for different composites.

The relation between charge carrier mobility log(μ_d) versus (1/T) is nearly linear supporting the polaron hopping model for the conduction. The activation energies calculated from resistivity and that from mobility are in close agreement indicating localized model of charge carrier.

The initial permeability increased with increasing temperature which is due to the activation of hopping electrons between Fe³⁺ and Fe²⁺ giving rise to the magnetic moment of the composites.

The paper deals with low-temperature photoluminescence and deformation luminescence (mechanoluminescence) of a composite material based on fine disperse powder of phosphor SrAl₂O₄:(Eu²⁺, Dy³⁺) and photopolymerizing resin that is transparent in the visible region. New information about the energy levels of impurities and defects was obtained. It has been found that at low temperatures (T = 15 ÷ 200 K) the photoluminescence spectrum of SrAl₂O₄:(Eu²⁺, Dy³⁺) presents two partially overlapping wide bands with the maxima at λ_1max = 446 nm and λ_2max = 517 nm. The strong interaction of energy states of the bands results in temperature quenching of the short-wave band of luminescence (λ_1max = 446 nm) and its complete attenuation at T ≥ 200 K. The results were used to describe the mechanism of persistent luminescence and mechanoluminescence of SrAl₂O₄:(Eu²⁺, Dy³⁺).

In this study, the CFRP shafts made up of T700-SC multilayered composites have been designed to replace the steel shaft of a ship. An important design variable to be considered when designing composite material intermediate shafts is the natural frequency for resonance avoidance at critical rotational speed and torsional strength for axial load. In order to satisfy these, strength and modal analysis were performed. In order to minimize the deformation of the shape due to the residual stress after mandrel removal, it was laminated by axial symmetry. The fibers orientation angle has a great influence on the natural frequency of the drive shaft. The carbon fiber should be closely oriented at $30^{\circ }$ to improve the modulus of elasticity in the direction of length of the intermediate shaft and to increase the natural frequency. Also, the optimum fiber orientation for maximum torsional strength should be close to $45^{\circ }$. The stacking pattern and the stacking order were finally decided considering the results of the finite element analysis (FEA).

This study mainly aimed to make 3D printing technologies serve as the guidelines for the development of technology-oriented industries. The most important one was tasked to establish modeling technology applicable to 3D printing in view of technological development. For the substrate material of 3D printers, aside from commonly usable plastic, new carbon fiber composite substrates have been proposed. Substrates were selected for manufacturing dependent on different object characteristics. The components were manufactured mainly by focusing on small-sized aircraft components. Additionally, potential problems encountered during 3D printing were explored with feasible suggested solutions. In the aerospace industry, because of the extreme requirements for the weight reduction of aircraft components, in the past, this was limited by manufacturing difficulties. If specific shapes were required, it was highly difficult to produce a component in a single-cast production or cut from a single metal piece. Component manufacturing often had to be divided into several planning blocks, and then welding, assembly, or rivet connection was conducted. This situation was not only flawed with structural weaknesses but also extra weight. If metal powder was operable with 3D printing for integral molding, the above disadvantages could be avoided.

This paper presents the stability analysis of a perforated plate with sector geometry made of composite materials. The sector of concern is a compound of graphite-epoxy and glass-epoxy with identical ply thickness but different fiber angles for each layer. The mechanical load conditions considered include uniform axial, circumferential, and biaxial pressure, while the thermal loading is specified to be uniform temperature increase over the whole sector. The existence of one or two circular holes has increased the complexity of analysis. To obtain solutions of high accuracy, the three-dimensional elasticity theory relations have been employed. Using the finite element method along with the stability condition of Trefftz, the buckling equation of the structure is derived. Green nonlinear strain-displacement relations are used to form the geometrical stiffness matrix. Unlike the finite element method used by other researches, a novel curved 3D B-Splined element is used to more accurately trace the displacement and stress variations of the structure. This element can be used in solution domains with geometric discontinuities, such as perforated plates and also meshed in the thickness direction. Moreover, instead of using the common von Karman assumptions, the most general form of the strain tensors in the curvilinear coordinates is adopted. The buckling load is obtained by extremizing the second variations of the total potential energy. The finite element formulation is coded in the MATLAB software. The effects of various parameters such as sector dimensions, dimensions of the hole, mechanical load directions, and fiber angles of each layer on the thermomechanical buckling is investigated.

The Cs${}_{0.3}$WO₃/WO₃ composite with near-infrared shielding properties was synthesized by the solvothermal method using tungstic acid and cesium salt as raw materials. The as-prepared composites were tested by X-ray powder diffraction, scanning electron microscopy, energy spectrum analysis, transmission electron microscopy, electron energy loss spectroscopy, and ultraviolet-visible near-infrared spectroscopy. The effects of different reaction conditions on the structure and near-infrared shielding properties of the synthesized composites were investigated. The best near-infrared light transmittance of as-prepared composites can reach up to 9%, which provides a feasible solution for the near-infrared shielding material. The new homogeneous composites of cesium tungsten bronze and tungsten oxide are good candidates for solar filters.

To improve the safety performance and maintain light weight of composite automotive bumper beams subjected to low-velocity impacts, a structural optimization and a novel reliability analysis procedure for multi-objectives are established in this paper. Both longitudinal and corner pendulum impacts are considered, and the optimized bumper beam has significant improvements. Compared with the original composite bumper beam, the section force of the crash box in the corner pendulum impact and the mass of the optimal bumper beam are decreased by 9.6% and 20.3%, respectively. The novel reliability analysis results show that the knee point may be less reliable whereas the design with inferior knee point is of higher reliability. Therefore, a design on an inferior knee point may be more attractive in engineering design practices. Our numerical results have demonstrated that the optimization procedure established in this paper to improve the performance of composite bumper beams and our proposed reliability analysis method considering multi-objectives are effective and useful in the engineering design of bumper beams. These techniques are also useful for the design of other types of structural components where weight and safety are of importance.

Development of high-toughness composite materials requires careful microstructure design as geometric distribution of phases, constituent properties and interface attributes combine to influence the deformation and failure behavior of composites. In two-phase composite materials, reinforcement cracking and interface debonding are two competing fracture mechanisms observed during the crack–microstructure interactions. The activation of each fracture mechanism largely depends on the microstructure and ultimately determines the fracture toughness of composites. The objective of this study is to quantify the competition of the two fracture mechanisms as function of microstructure and find their intricate coupling with material fracture toughness. The multiscale material design framework developed here allows fracture toughness to be predicted through cohesive element-based fracture simulation and digital image correlation measurement. Based on the numerical and experimental results, two analytical models are developed for fracture mode determination of both brittle and ductile composites. Although calculations carried out concern ceramic composites Al₂O₃/SiC and metal matrix composites Al/SiC, the approach developed can be applied to other composite material systems.

Modern planetary rovers are based on aluminum chassis, but thanks to carbon fiber composites, the weight of such mobility platforms can be dramatically lowered. This paper describes the design of a 6-wheeled rover with a rocker-bogie suspension, adopting carbon fiber laminates and short-fiber-reinforced polymers. This last feature is an innovative approach that fits well with the use of additive manufacturing, allowing for both highly optimized parts and rapid fabrication of spares in future manned missions on the Lunar surface. The structural design was validated against a set of boundary conditions (static analyses) and requirements of launch and space environments (dynamic analyses) as prescribed by European Cooperation for Space Standardization standards. The composite rover was designed to lighten the structure itself and increase the payload-to-total-mass ratio: the composite solution offers a ratio three times higher than the typical rover (ratio from 0.12 to 0.38).

This work proposes the functional characterization of a composite material, suitable for passive suppression of flexural vibration of beams and shells. Two patterned thin sheets of CuZnAl Shape Memory Alloy (SMA) are embedded into a layered beam of glass fiber. The composite combines the density and stiffness of the glass fiber with high damping properties of SMA in martensitic state. Properly shaped patterning of the SMA sheets, for improving adhesion between the SMA and glass fiber, is performed by means of laser technology. The effect of the laser micromachining on transformation temperatures and internal friction properties of the SMA elements are analyzed. Finally, measurements of the structural damping of the layered glass fiber/SMA composite are reported and the flexural vibration suppression, due to the embedded CuZnAl sheets, is shown.

Purpose- This paper describes finite element fatigue damage modeling.

Design/Methodology/Approach- Fatigue life prediction and damage progressive evaluation are analytically studied. We present a numerical implementation of the studied models into the home made finite element code MPEF. Numerical simulations are performed on composite and metallic material. We carried out a parametric study to investigate the influence of model's parameters on the damage accumulation and their sensitivity on its kinetics. Simulations are conducted for two different loading levels to characterize cumulative damage and to study loading sequence effect. A comparative study is performed to characterize the efficiency of the two models to describe the damage evolution for the two different materials.

Findings- Numerical examples are presented to illustrate its performance.

Originality/value- This paper intends to present a comparative study of the damage evolution for metallic and composite material under uniaxial loading. The effect of the loading sequence will be investigated.

In this work, the Eshelby tensor of a finite spherical domain is employed to construct an interphase model to evaluate elastic properties of concrete composites. Explicit formulations of the interphase model via multi-inclusion method for a class of concrete composites are derived. The theoretical estimate based on an improved Hashin–Shtrikman bounds for the Young’s modulus of two-phase concrete composite material are used as a comparison result in the analysis, and the influence of the interfacial transition zone (ITZ) on elastic properties of three-phase concrete composite is studied. Moreover, the homogenization results predicted by the proposed interphase model are compared with the published experimental data. Results obtained in this work show that the proposed interphase model can provide a very accurate estimate of the effective elastic properties of complex concrete composite materials.

Thermal residual stresses (TRS) in hybrid materials and structures occur by the mismatch of thermal expansion of different materials. Especially when combining metals with carbon fiber reinforced plastics (CFRP), a significant level of internal stresses can be reached. High processing temperatures and high stiffness of the constituents are also responsible for high stress levels. Laminates of thermoplastic CFRP (unidirectional carbon fiber reinforced polyamide 6) and stainless steel foils are a suitable material system to examine the TRS in detail. Since TRSs in the steel fraction are of tensile nature, these superpose to externally applied loads, resulting in higher efforts for the material and thus reduced lifetimes under cyclic fatigue loading. Therefore, a reduction of TRS is desired. Two methods for TRS reduction were applied, and its influence on fatigue lifetime was investigated. Firstly, specimens were stretched by a preloading to reduce TRS by yielding of the metal. Secondly, non-symmetric laminates were gradually cooled down after consolidation to compensate TRS formation by non-symmetric shrinkage. While preloading of materials and structures is known for TRS modification, the gradually cooling is not established, yet. Both modification principles were numerically investigated before experimental validation. A significant increase of lifetime was reached by TRS reduction.

Laminar composite materials widely used in engineering usually emerge delaminations because of manufacturing technique and other factors. Delaminations will take place buckling. The particular circumstance buckling is often related to time under constant load. In this paper, the buckling time-delay characters of a circular delamination with elastic bridge were studied by considering laminar composite material as viscoelastic material. The relationship between critical pressure and time of delamination buckling was gained. The effect of cohesion between layers on delaminations time-delay buckling was discussed. Theoretic analysis showed that the creeping buckling of viscoelastic delamination is related to mechanic performances of material, delamination dimension and cohesion between layers. The critical pressure is not a constant value and is related to time. After a period of time, time-delay buckling occurs to delaminations under constant load, and layers cohesion affect the shape of buckling surface if the load is heavy enough.

This thesis analyzes the main factors which cause sand corrosion of wind turbine based on the erosion of practical engineering; it presents how to reduce sand corrosion by hierarchical coating according to the aerodynamic characteristics of wind turbine blade.