Band 25, Heft 1

The room-temperature shape of unsymmetric laminate due to the residual stress developed during the curing process has been investigated in the past decades. The factors influencing the residual stress of unsymmetric laminate, including moisture, fiber orientation, aspect ratio and ply thickness, have been widely investigated. Another mechanism that can generate residual stress is the interaction between the tool and the composite part during heating-up process. In this work, the effects resulting from the interaction between laminate and tool during the heating-up phase were considered. By introducing an interfacial shear stress due to tool-part interaction, an analytical model based on the Extended Classical Lamination Theory of Dano and Hyer was proposed to predict the room-temperature shapes of cross-ply unsymmetric laminates. The interfacial shear stress, which was correlated with experimental results, was introduced to tailor the amount of residual stress transferred from the tool. The model was validated with experimental data provided in the literature. It is shown that this model which takes the tool-part interaction into consideration could predict part processing deformations more accurately.

Carbon nanotubes/akaganeite composite photocatalysts (CNTs/β-FeOOH) with different weight addition ratios of CNTs have been synthesized by a very simple hydrothermal method. X-ray diffraction, Fourier transform infrared spectrum, UV-vis diffuse reflectance spectra, scanning electron microscopy, and transmission electron microscope were used to characterize the composite photocatalysts. This study investigates the oxidative degradation of methyl orange, a probe contaminant, by a heterogeneous photo-Fenton-like process over the prepared composite photocatalysts. The CNTs/β-FeOOH composites exhibit remarkably enhanced photocatalytic activity toward the degradation of methyl orange in water under visible light irradiation as compared with bare β-FeOOH. The added CNTs have triple crucial roles in the promotion of photocatalytic activity of β-FeOOH. One is to trap electrons and effectively hinder recombination of the photoexcited carriers. Two is to act as a dispersing support to control the particle size of β-FeOOH in the CNTs/β-FeOOH composites. Three is to enhance the visible light absorption intensity. Finally, the catalytic mechanism of CNTs/β-FeOOH composite is proposed.

W75-Cu and W55-Cu alloys were brazed with a Cu-based filler metal under the process parameters of a brazing temperature of 1060°C and a holding time of 30 min in a vacuum furnace with a vacuum level >6×10 -3 Pa. The microstructure, element distribution, phase constituents, four-point bending strength, and fracture morphology of the brazed joint were studied with a series of standard methods. The results indicated that the main microstructure of the brazing seam region was a Cu-based solid solution of Mn and Co dissolved in the Cu phase. The element Cu and a little element W from two sides of the base metals transited into the brazing seam region, and the elements Cu, Mn, and Co contained in the brazing filler metal diffused into the interface or even substrates. The main phases that existed in the brazed joint were Cu-rich phase Cu(Mn,Co), simple substance of W, simple substance of Cu, and trace amounts of Cu 0.4 W 0.6 . The four-point bending strength was about 950 MPa, and fracture occurred at the interface near the W75-Cu alloy side. The fracture morphology of the W75-Cu/W55-Cu brazed joint was identified as mixed ductile-brittle.

Poly(arylene ether nitrile) (PEN)-functionalized multiwalled carbon nanotube (MWNT) composites were successfully prepared via an in situ polymerization method based on the combination of nucleophilic aromatic substitution polymerization with simple acylate-functionalized MWNTs (MWNTs-COCl) in the presence of nitrile monomers. The structure and morphology of PEN-MWNT composites were characterized using Fourier transform infrared spectroscopy and scanning electron microscopy, respectively. The improvement in the thermal stability and mechanical properties of PEN-MWNT films was achieved because of the good-quality dispersion of MWNTs and strong interfacial interaction between the PEN matrix and MWNTs. The most important result is that the dielectric constant and electrical conductivity can be remarkably enhanced by a high MWNT content.

Polypropylene/polycarbonate (PP/PC) nanocomposites containing various proportions of the organically modified montmorillonite were prepared by extrusion and injection molding process. The morphology of PP/PC nanocomposites was characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray diffraction (XRD). The nanocomposites with 3 or 5 wt% of nanoclay (NC) show a uniform dispersion of the NC as pointed out by two different methods, TEM and XRD. It was shown that the morphology of dispersed phase (PC) is highly dependent on the content of minor phase, which was correlated with the balance of drop breakup and coalescence. The mechanical properties have been investigated by tensile test and Izod impact test. The virgin PP/PC samples showed a reduction in impact strength and elongation at break and up to 50% increase in Young’s modulus by increase in PP content comparing with the pure PP. Investigating the effect of NC and PC content on the mechanical behavior of PP/PC nanocomposites showed increased Young’s modulus and decreased impact strength with increasing PC and NC loading. An obvious ductile to brittle behavior transition at a high content of PC or NC was supported by notched Izod impact strength experiments and SEM results.

The present study deals with the free torsional vibration of a composite conical shell made of a polymeric matrix reinforced with carbon nanotubes (CNTs). Distribution of CNTs across the thickness of the conical shell may be uniform or functionally graded. Five different cases of functionally graded reinforcements are considered. First-order shear deformable shell theory compatible with the Donnell kinematic assumptions is used to establish the motion equations of the shell. These equations are two coupled equations which should be treated as an eigenvalue problem. The generalized differential quadrature method is used to obtain a numerical solution for the torsional frequency parameters and the associated mode shapes of the shell. After validating the results of this study for the cases of isotropic homogeneous cone and annular plates, parametric studies are carried out to analyze the influences of geometrical characteristics of the shell, volume fraction of CNTs, and grading profile of the CNTs. It is shown that volume fraction of CNTs is an important factor with regard to torsional frequencies of the shell; however, grading profile does not change the torsional frequencies significantly.

In this paper, cationic organic montmorillonites (OMts) were prepared by dry, semi-dry, and wet methods. The structures and properties of these OMts according to the modification methods were studied. By the characterization of XRD, TG-DTA, lipophilicity, and thixotropy, the results showed that cationic OMt prepared by wet method with sufficient surfactants had better properties, including contact angle, swelling capacity, thixotropic loop area, and thermal stability compared with cationic OMt prepared by dry and semi-dry methods. Attention should be paid that with low ratio amount of surfactants used, cationic OMt prepared by the semi-dry method had favorable properties compared with cationic OMt prepared by wet method, and it had the potential to be applied in industrial field due to its environment-friendly and modification efficiency characteristics.

In this paper, we are presenting a new metamaterial unit cell for satellite applications. The unit cell of the metamaterial was designed on FR-4 substrate material. The transmission characteristics of the unit cell display resonance at the frequency of 3.45 GHz of S-band of microwave region, which is usually suited for satellite communications. We did further analysis on the material’s effective medium properties by replacing the substrate material with Rogers RT 6010, lossy polyimide and aluminum nitride substrate materials, and we achieved different promising electromagnetic properties including double negative characteristics within the same band as well. For all these analyses, the popular “CST Microwave Studio” simulation software was adopted. The proposed design gives fine controllability in different types of metamaterial just by changing the substrate material, and all are working in the same S-band microwave spectrum.

In this study, the effect of Mg alloying addition (1–4 wt.%) on dry sliding wear behaviour of AA1050 matrix composites was investigated. Composites were produced by the pressure infiltration technique at 800°C and had a B 4 C particle volume fraction of 60%. Reinforcement particles were uniformly distributed in the aluminium matrix. Compared with the AA1050 matrix, the weight loss of the composites decreased with increasing Mg content. The wear rate of the composites increased when the applied load and sliding distance were increased. The results show that when the applied load reaches critical values (30 N), the weight loss increases significantly.

Four different local reinforcement schemes used in composite bolted joints were studied. In numerical study, a set of 3-D failure criteria was used and the progressive failure analysis was implemented via user-defined subroutine vectorized user-material (VUMAT), which was programmed by the commercial finite element (FE) software ABAQUS. In the experiment, test specimens were manufactured with different local reinforcement schemes, and the mechanical performances of these specimens were tested under tensile loads. Failure modes of these specimens were observed and mechanical performances of test specimens with local reinforcement were studied. It was found that the numerical results agreed well with the experiment. It was also found that local reinforcement schemes influenced the mechanical performances of bolted joints obviously and that the tensile strength of composite bolted joints could be improved significantly by burying laminate slices.

This experimental study was conducted to investigate the effect of NaOH concentration and treatment time on the flexural properties of Luffa cylindrica fiber-reinforced epoxy composites. Significant improvement (up to 84.92%) in the flexural properties for the treated fiber composite compared with the untreated fiber composite was observed. Both treated and untreated fiber composites were then subjected to different environmental treatments (saline water, distilled water, and subzero temperature). To find out the changes in flexural strength immediately after treatment, the same test was carried out on the composites. Degradation in the flexural strength of both treated and untreated fiber composites, when subjected to environmental treatments, was observed. They were found within the range of 2%–20% and were found to be least in subzero treatment. The SEM micrograph indicates that alkali treatment is effective in improving the adhesion between the fiber and matrix.

Mn 3 Zn 0.5 Sn 0.5 N/Al composites were successfully prepared by sintering at 623 K and 723 K. It is found that the thermal expansion of Al is effectively decreased with the addition of negative thermal expansion material Mn 3 Zn 0.5 Sn 0.5 N, which plays the role of the thermal expansion compensator in the composite system. The thermal expansion of composites can be tailored by adjusting the volume fraction of Mn 3 Zn 0.5 Sn 0.5 N. In particular, 40 vol.%-Mn 3 Zn 0.5 Sn 0.5 N/Al composite sintered at 723 K has a low thermal expansion coefficient of 2.38×10 −6 K −1 . The thermal expansion of Mn 3 Zn 0.5 Sn 0.5 N/Al composites matches well with those calculated from the rule of mixture (ROM) estimation. The ROM model can be used to predict the thermal expansion of Mn 3 Zn 0.5 Sn 0.5 N/Al composite and design Mn 3 Zn 0.5 Sn 0.5 N/Al composite with a particular thermal expansion. Mn 3 Zn 0.5 Sn 0.5 N/Al composites exhibit excellent electrical conductivities at the level of 10 4 S/cm. The hardness of the as-prepared composites increases by adding Mn 3 Zn 0.5 Sn 0.5 N in Al.

Copper-aluminum layered double hydroxides (Cu-LDHs) and nickel-aluminum layered double hydroxides (Ni-LDHs) were synthesized using co-precipitation method. LDHs were organically modified by long chain sodium stearate. Polypropylene (PP)/layered double hydroxides (LDHs) and polypropylene (PP)/organically-modified layered double hydroxides (m.Cu-LDHs or m.Ni-LDHs) were prepared through the melt bending of the PP with either nanosized LDHs or m.LDHs without any other additives. The effect of stearate on the dispersibility of LDHs was investigated by X-ray diffraction (XRD). The surface morphology of LDHs was also studied using scanning electron microscope (SEM), and the thermal stability properties of PP/LDHs composites were studied by thermogravimetric analysis (TGA). The mechanical properties of the PP/LDH composites, tensile strength, and modulus of elasticity were investigated. The flammability properties were investigated using the cone calorimeter test. The intercalation of modified LDHs was determined by XRD in the presence of stearate. Results showed that modified LDHs presented good disperasbility in the PP matrix. The thermal stability of PP has been improved by up to 6% using m.Ni-LDHS. Unmodified and modified nanosized LDHs decreased the fire growth rate of PP from 10.8 kW/m 2 .s to 4.1 kW/m 2 .s and 4.5 kW/m 2 .s, respectively.

A simple, accurate, and unified formulation for the free vibration analysis of functionally graded (FG) plates is introduced. New four-variable first-order and higher-order shear deformation theories together with the classical FG plate theory can be easily achieved. The only assumption is that the transverse displacement consists of bending and shear components, and hence the theory has the potential to be used for modeling of the nonlinear FG plate problems. To validate the proposed formulation, the free vibration analysis of FG plates on two-parameter elastic foundation is conducted. The material properties vary continuously through the plate thickness. Analytical solutions for simply supported and approximate solutions for FG plates with arbitrary boundary conditions are extracted by extending the application of the conventional differential quadrature method as an accurate and efficient numerical tool. Comparison studies with existing two- and three-dimensional results available in open literature are performed. Excellent agreement between the results of the present formulation and the other theories is observed.

The fabrication of a durable and usable aluminum matrix composite poses a challenge because it is hard to obtain defect-free welds by using conventional fusion welding methods. The development of friction-stir welding (FSW) provides improved microstructure modification. As there are no melting problems associated with it, liquid-solid reactions are eliminated. The objective of this study was to attempt FSW of an AA6061 alloy reinforced with an iron-based metal and to determine the properties of the joints. The effects of FSW parameters, especially the tool rotation speed, are presented first. Then, the application of the technique in manufacturing and microstructure modification of particle-reinforced composite materials is discussed. Finally, interfacial microstructural changes and the associated mechanical properties are evaluated.

In this paper, an attempt has been made to investigate the effect of coir fiber addition along with the banana fiber in low-density polyethylene (LDPE) to develop cost-effective and high-performance composite material. The composite samples were prepared at fixed fiber content (25 wt%) and with varying relative weight fraction of banana and coir fiber using compression molding technique. The effect of hybridization was analyzed through the mechanical properties (tensile, flexural, and impact), thermal stability, morphological behavior, and water absorption behavior. Additionally, scanning electron microscopy studies had been carried out on the tensile fractured surface for all composite samples to examine the fracture behavior of the composite samples. The results showed that the incorporation of coir fiber into the banana fiber composites of up to 50% by weight led to enhancement of the mechanical properties and thermal stability and to reduction of the water absorption capacity of the banana fiber/LDPE composites.

Computational micromechanics provides an efficient strategy to optimize composite materials by addressing the effect of different material and geometric parameters involved. In the present paper, the effective transverse elastic properties for periodic composite materials reinforced with single and clustered polygonal fibers are evaluated using the micromechanical finite element formulation subject to periodic displacement boundary conditions. The cross-sectional shapes of polygonal fibers are assumed to be triangular, square, pentagonal, hexagonal, octagonal, and circular to perform comprehensive investigation. By applying a periodic displacement constraint along the boundary of the representative unit cell of the composite to meet the requirement of straight-line constraint during the deformation of the unit cell, the computational micromechanical modeling based on homogenization technology is established for evaluating the effects of fiber shape and cluster on the overall properties. Subsequently, the micromechanical model is divided into four submodels, which are solved by means of the finite element analysis for determining the traction distributions along the cell boundary. Finally, the effective orthotropic elastic constants of composites are obtained using the solutions of the linear system of equations involving traction integrations to investigate the effects of fiber shape and cluster on the overall properties.

Colloid composition based on the nanosized carbon powder, dispersed in complex mineral solvent, was elaborated. It was found that the composition can be used both as surface coating and as filler for an ultra-high molecular weight polyethylene matrix. A study of electromagnetic wave absorption showed that the coatings and composites thus obtained possess high microwave protection properties. Wave absorption of a coating 50 μm thick varies from −5 to −25 dB depending on frequency. A study of polymer composites filled with colloid composition, showed that increase in the filler content leads to the transition from chaotically dispersed to the oriented distribution of colloid composition particles in the polymer matrix. Tensile test showed that the polymer filled with colloid composition retains the mechanical properties close to those of pure ultra-high molecular weight polyethylene (UHMWPE). Microwave absorption gradually increases with increasing filler content in UHMWPE-based composites.

Being newly advanced materials, metal matrix composites enjoy the properties of high service temperature, light weight, high specific strength, good wear resistance, high stiffness, and a low thermal expansion coefficient. However, machining these materials by conventional methods is difficult. A key machining process for difficult-to-machine materials like composites is electro-discharge machining, which is widely used in non-conventional material removal processes. The current work aims to identify different parameters, such as voltage, current, pulse on-time, and pulse off-time, which influence the material removal rate (MRR), tool wear rate (TWR), and surface roughness (SR). By applying regression equations, a mathematical model is adopted to estimate MRR, TWR, and SR. The optimum machining parameters are investigated using the Taguchi method with L9 orthogonal array. The optimum values are also analyzed by multi-objective Taguchi method with calculation of total normalized quality loss (TNQL) and multi-signal to noise ratio (MSNR) included. Analysis of the Taguchi method introduced voltage and pulse off-time as the two main significant factors that influence the value of the material removal rate. The discharge current and pulse off-time also have a statistically significant impact on both tool wear rate and surface roughness.

An innovative load-bearing sandwich wall panel with glass fiber-reinforced polymer (GFRP) skins and a foam-GFRP web core (GSFW wall panels, where “GS” denotes GFRP skin and “FW” denotes foam-GFRP web core), which was manufactured using a vacuum-assisted resin infusion process, was developed in this paper. An experimental study involving nine specimens was conducted to validate the effectiveness of this panel for increasing the axial strength under edgewise compression loading. The effects of web thickness, web spacing, web height, and skin thickness on axial stiffness, displacement ductility, and energy dissipation were also investigated. The test results demonstrated that axial strength, axial stiffness, displacement ductility, and energy dissipation could be improved by increasing the web thickness, web height, and skin thickness. An analytical model that considers the confinement effect of foam and the local buckling of GFRP skin was proposed to predict the ultimate axial strength of GSFW panels. A comparison of the analytical and experimental results showed that the analytical model accurately predicted the ultimate axial strength of GSFW wall panels under edgewise compression loading. To simulate the low velocity impact by blindings that are rolled by the wind, an impact test was conducted and the residual axial strength of the wall panels after impact was also investigated.

Polymer nanocomposites of various concentrations were prepared using iron oxide (Fe 2 O 3 ) nanoparticles as filler in an 80:20 ratio of the polyurethane diol and polycaprolactone hybrid. Fourier transformed infrared spectroscopy studies were performed to find out the interaction of the nanoparticles with the polymer blend. Fe 2 O 3 in the polymer composites was in the nanoscale and uniform dispersion was achieved, as revealed by X-ray diffraction. The thermal stability of the blend was assessed through thermogravimetry analysis and dynamic mechanical analysis. High-resolution scanning electron microscopy and transmission electron microscopy images ensured the development of the polymer hybrid around Fe 2 O 3 nanoparticles and the prepared composites were indeed in the nanoscale. The magnetic behavior of the prepared nanocomposites is superparamagnetic with high magnetization values, as assessed by vibrating sample magnetometry analysis.

In this study, fly ash cenospheres were added to semisolid AZ91D Mg alloy to prepare fly ash cenosphere/AZ91D (FAC/AZ91D) composites by means of compo-casting. The high-temperature damping capacity of FAC/AZ91D composites was investigated as compared with AZ91D Mg alloy. The results show that the damping capacities of FAC/AZ91D composites and AZ91D Mg alloy strongly depend on the measuring temperature. The FAC/AZ91D composites show better damping capacity than AZ91D Mg alloy. The 10 wt.% FAC/AZ91D composites exhibit the best damping capacity from room temperature to 125°C, whereas the 2 wt.% FAC/AZ91D composites show the highest damping capacity at 125°C–320°C. The damping mechanism was analyzed by microstructure observation at elevated temperatures. The damping-temperature curves exhibit a damping peak at approximately 150°C, and the activation energy of the damping peak was calculated according to the Arrhenius equation. Furthermore, the peak temperature increases with increasing frequencies. The damping peak is related to the thermal activation relaxation process, and its mechanism is the dislocation-induced damping.

In this paper, the effect of weight fraction of nano silica (hydrophilic fumed silica particles) and molecular mass of polyethylene glycol (PEG) on the rheological properties such as the critical shear rate of fluids has been studied. Dynamic moduli based on strain and the effects of increasing the molecular weight are presented. Constructed samples with high-molecular-weight PEG have higher initial, final and critical viscosities. Also, higher molecular chains in the polymer and preventing the movement of most of these chains against the relative motion of liquid (viscosity) will cause higher viscosity in samples. Critical shear rate is lower in the provided samples with high-molecular-weight PEG. Polymer branches in these suspensions are absorbed by the surface of the particles. Due to OH bonds in the silica particles and also due to the presence of this bond in PEG, creating a hydrogen bond is likely. Such a hydrogen bond between the polymer yarn and the particle surface causes surface absorption of the particles. To show the effect of molecular weight on fibers, woven fabric specimens impregnated with shear thickening fluid (STF) have been examined by penetration and pressure test diagrams have been investigated. In a sample with higher molecular weight, displacement to yield point is higher and residence to penetration does not show much difference.