Volume 24, Issue 2

Four polycarbonate (PC)-based composites with 1, 2.5, 5, and 10 wt.% raw multiwalled carbon nanotubes (MWCNTs) were prepared using extrusion process followed by injection molding. The effects of MWCNT mass fraction ( W ) on composite mechanical, thermal, and electrical properties were examined. The mechanical properties suggested that the tensile strength of the composites with 2.5 wt.% raw MWCNTs exhibited an increase of ~5 MPa (~8.6%) at a particular injection condition. Besides, thermogravimetric analysis (TGA) indicated that the addition of 1 wt.% MWCNTs improved the thermal stability of PC by approximately 100°C. Aside from mechanical and thermal properties, the electrical resistivity of the 5 wt.% raw MWCNT composites was considerably decreased to 10 2 Ω/sq, a value approximately 15 orders of magnitude lower than that of PC. Furthermore, the effects of injection conditions on composite electrical properties were emphatically discussed, and it was found that electrical resistivity was sensitive to injection temperature and speed. Low electrical resistivity was achieved at high injection temperature and low injection speed. Scanning electron microscopy images revealed that electrical resistivity relied on the microstructure of the prepared MWCNT/PC composites.

Carbon nanotubes (CNTs) were successfully prepared using chemical vapor deposition method on nickel-coated silicon substrates. The CNTs were then modified to obtain functionalized ends. Afterward, acrylate polymers were successfully grafted on the surface of CNTs by atom transfer radical polymerization method. The synthesis process was optimized by studying the surface properties of the composite films. It revealed the existence of chemical bonding between CNTs and polymers. The introduction of CNTs into polymers could improve the water resistance of films. Micro/nano and papillary structures similar to that of lotus leaf were obtained when the polymer matrix was partly etched. The excellent fluid drag reduction performances of film surfaces were expected to be applied in microfluid devices and packaging field.

Nylon 6,9/CaCu 3 Ti 4 O 12 (CCTO) nanocrystal composites with relatively high dielectric permittivity (220 at 100 Hz) were fabricated by melt mixing followed by hot pressing. The CCTO nanoceramics were synthesized using the oxalate precursor route, and the transmission electron microscopy studies exhibited that the crystallites are in the range of 20–200 nm. The nanocomposites were characterized using X-ray diffraction, scanning electron microscopy, thermogravimetric analysis, differential scanning calorimetry, and impedance analyzer to study their structural, thermal, and dielectric properties. The introduction of CCTO nanoparticles into the matrix had influenced the thermal properties. The effective dielectric permittivity of the nanocomposite increased by the augmentation of CCTO content in the Nylon 6,9. Our experimental outcomes showed that the fixed dielectric permittivity of such two-phase composite was established above 200 when the CCTO concentration was closer to its percolation threshold. The room temperature dielectric permittivity as high as 220 at 100 Hz has been achieved when the CCTO content increased to 58 vol% in the polymer and this was increased to 3845 at 150°C. The increase in AC conductivity with the increase in the CCTO content in the polymer matrix supported the hopping of the charge carrier conduction mechanism.

The volume fraction, dissolution, and segregation of WC particles in metal-matrix composites (MMCs) are critical to their wear resistance. Low carbon steel substrates were precoated with NiCrBSi coatings and processed with gas tungsten arc melt injection method to fabricate MMCs with high volume fraction of WC particles. The microstructures and wear resistance of the composites were investigated. The results showed that the volume fraction of WC particles increased with decreasing hopper height and was as high as 44% when hopper height was 100 mm. The dissolution of WC particles was minimal. The content of the alloying elements decreased from the top to the bottom of the matrix. More WC particles dissolved in the overlapping area, where Fe 3 W 3 C carbide blocks could be found. The wear loss of the MMCs after 40 min was 6.9 mg, which is 76 times less than that of the substrate after the 4 min test.

Polypropylene composite multifilaments filled with surface-treated jute microparticles were successfully spun by melt spinning. To enhance the particle distribution, jute particleos were treated with 5–20% (w/v) aqueous solutions of sodium perborate trihydrate (SP). X-ray photoelectron spectroscopy (XPS) was used to confirm the surface treatment. XPS analysis indicated that the treatments improved the hydrophobicity of the jute by means of increasing the carbon/oxygen ratio of the surface; thus, the maximum increment was achieved after 10% (w/v) SP treatment. After determining the optimum SP concentration, the spinning of polypropylene composite multifilaments containing 0.3–1.4 wt% jute particles was employed. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) revealed the nucleating agent effect of the particles during crystallization in the filaments. The addition of fillers did not result in significant changes in the functional groups of polypropylene. The main output of this research is that polypropylene multifilaments incorporating 1.4 wt% jute particles presented the highest moisture absorption and hydrophilic character as determined by TGA, moisture content, and vertical wicking tests. It was concluded that particle content >0.3 wt% showed a tendency to agglomerate in the filament. Consequently, this study provided a new polypropylene filament having moisture absorbability performance, which can create potential applications in the textile industry.

Structural health monitoring (SHM) takes advantage of the recent advances in structural behavior monitoring to assess the performance of a structure, identifying the damage in the early stage. In this study, a carbon nanotube thread strain sensor was fabricated into a three-dimensional (3D) braided composite preform for the strain sensing of SHM. We present the results of an investigation on a carbon nanotube thread network in 3D composites for damage detection, in which the variation of the electrical resistance of the carbon nanotube thread embedded into 3D composites was recorded. Based on the variation of the electrical resistance, the location and size of damages were estimated by the response surface method, providing an effective solution for the estimation of the location and size of damages in 3D composites.

A two-dimensional analytic solution based on linear elasticity theory is used to investigate the effect of using a functionally graded material (FGM) as an inter-layer in reducing the stress concentration in non-axisymmetric loaded metal-composite joints. The geometry of the joint consists of a metal cylinder surrounded in a composite thick plate and loaded arbitrarily by in-plane radial force profile, the condition of which occurs in double-lap pins, bolt joints, and T-bolt joints. The significant difference between the mechanical properties of the adjacent materials induces a stress concentration in the flexible part of the joint. In this work, an analytic solution based on the Airy stress function is used and derived into the strain compatibility equation in two-dimensional problems. The power law model is used for the FGM property variation, and a transversely isotropic model is considered for the composite plate. A two-dimensional condition is assumed for the structure. The results of several models are compared with the finite-element method and show good conformity between the two methods. In some cases, by using the FGM inter-layer, the stress level in the surrounding plate would be decreased significantly.

The present paper deals with a study of the thermal properties of bagasse fiber (BF)-reinforced epoxy composites. BFs are subjected to untreated and chemical treatments with 1% sodium hydroxide followed by 1% acrylic acid at ambient temperature before the composites are made. The thermal stability of the components was studied by thermogravimetric analysis and differential scanning calorimetry, as well as by differential thermal gravimetric analysis. Thermal analysis results of untreated BF-reinforced epoxy composite were compared with treated BF-reinforced epoxy composite. The chemical treatment of BF induces reasonable changes in the thermal stability of the polymer composites.

This paper studied the effect of extrusion on the microstructures and tensile properties of 4 vol.% 5 μm SiC p /Al2014 composites fabricated by stir casting. It has been found that extrusion could refine the α-Al grains, increase the distributed homogeneity of SiC particles, decrease the porosity of the composites, and improve the interfacial bonding strength. The tensile properties, especially the ductility, of the fine SiC p /Al2014 composites were significantly improved by extrusion. Compared with the as-cast 4 vol.% 5 μm SiC p /Al2014 composites, the yield strength, ultimate tensile strength, and fracture strain of the extruded composites increased from 242 MPa, 367 MPa, and 3.8% to 304 MPa, 530 MPa, and 11.2%, which were increased by 25.6%, 44.4%, and 195%, respectively.

TiO 2 film was applied to graphite substrate through chemical bath deposition (CBD) method with TiCl 4 as precursor. CdS was deposited on TiO 2 /graphite (TiO2/G) by CBD with precursors of CdSO 4 . A UV-Vis diffuse reflectance (UV-Vis DR) analysis was used to analyze the optical properties and band gap energy. Meanwhile, photocatalytic activity was determined from the quantum yield (QY) value of isopropanol degradation. The X-ray diffraction pattern shows that the TiO 2 film contains rutile and anatase phases. UV-Vis DR spectrum shows the photoactivity in the visible light area and provides lower band gap value due to CdS deposition. TiO 2 /G provide energy gap at 3.0 eV, which indicates that rutile phase is dominant. Meanwhile, CdS-TiO 2 /G shows multiple energy gaps representing CdS at 2.4 eV, rutile at 3.0 eV, and anatase at 3.2 eV. The QY values of CdS-TiO 2 /G are 7.98×10 -3 and 8.62×10 -4 at 450 and 380 nm of radiation light, respectively. These values are higher than the QY of TiO 2 /G and TiO 2 -P25/graphite (TiO2-P25/G), which are 1.19×10 -4 and 5.0×10 -4 , respectively. The photocatalytic reaction follows the first-order reaction. CdS deposition allows the rate constant to increase from 2×10 -3 to 13×10 -3 under UV radiation.

Abrasion resistance is one of the most important durability properties of concrete. Especially, highway, airport and industrial floor pavements should be resistant to abrasion. Recently, many research studies have been carried out on the utilization of industrial by-products in concrete. Granulated blast-furnace slag (GBFS) and bottom ash (BA) are two of these by-products. BA is not generally utilized in concrete and has a limited usage. It is mostly dumped, leading to additional costs and environmental problems. On the other hand, both GBFS and BA have potential for concrete production to provide sustainability. They can substitute fine aggregate thanks to their positive effects on concrete durability. Therefore, the aim of this study was to investigate the abrasion resistance of concretes produced with GBFS and BA substituting fine aggregate. Three different concrete series were produced by replacing fine aggregate with GBFS, BA and both of them by mixing them at equal ratios. The replacement ratios of by-products were 10%, 20%, 30%, 40% and 50% by volume. Compressive strength and Bohme abrasion tests were conducted on series. Results were compared to each other. It can be said that abrasion resistance can be improved by these by-products.

This work contributes to the extant literature by providing experimental results showing an improvement in the interfacial adhesion between diamond and epoxy resin by modifying the surface properties of diamond using KH550 silane coupling agent in (i) aqueous alcohol solvent (KH550:H 2 O:C 2 H 5 OH=1:1:8) and (ii) toluene solvent (KH550:C 7 H 8 =1:9), and the weight ratio of diamond to the above-mixed solution was 1:4. This in turn has been demonstrated to provide improved mechanical properties of the corresponding diamond/resin composite material synthesized from this study. The results obtained from this study were analyzed by using Fourier-transform infrared spectroscopy, X-ray photoelectron spectra, field emission scanning electron microscopy. and scanning electron microscopy. Besides these examinations, bend strength and hardness tests were also conducted, which lend further credence to this study. Finally, toluene solvent was observed to provide better adhesion at the interface of diamond and epoxy resin, and consequently, this resulted in improved bend strength of the corresponding diamond/resin composite by 14.3%.

The primary goal of this paper is to investigate the combined effects of strain rate and microscopic parameters (fiber off-axis orientation, array pattern and cross-sectional shape) on the mechanical behavior of metal matrix composites (MMCs). To this end, a rate-dependent micromechanical model by the combination of finite-volume theory and Bodner-Partom viscoplastic model is developed to analyze the inelastic response of MMCs. In the simulations, the fibers are modeled as linearly elastic while the metal matrix exhibits viscoplasticity. The macroscopic stress-strain response, local stress and strain fields are obtained simultaneously. An acceptable agreement has been found between the model’s prediction and finite-element results, which demonstrates the good predictive capabilities of the proposed method. It is concluded that the composite response is strongly affected by strain rate, fiber array pattern and cross-sectional shape in the elastic-plastic region but to a lesser extent in the elastic region. Furthermore, the clustering array provides stiffer response than random and square ones; the square fiber predicts stiffer response than circular and elliptical ones. However, increasing the strain rate will weaken the influence of clustering array and square fibers.

In this study, multilayer graphene (Gr)-reinforced cellulose composites were synthesized by using 1-ethyl-3-methylimidazolium diethylphosphonate ionic liquid. The composites were fabricated via dissolving the cellulose in 1-ethyl-3-methylimidazolium diethylphosphonate and Gr loading at different ratios (0.2, 0.4, and 0.6 wt.%). Both sides of the composites were coated with gold leaf to generate electrodes. The effect of Gr loading on chemical functional groups, crystallographic properties, thermal stability, and morphological and mechanical properties of cellulose film was investigated by Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, scanning electron microscopy, and tensile test, respectively. Electromechanical behavior of the cellulose composite films reinforced with Gr (0.2, 0.4, and 0.6 wt.%) was investigated under DC excitation voltages of 1, 3, 5 and 7 V. Gr loading of 0.2 wt.% increased maximum tip displacement by 400% when the actuator is excited with 3 V.

Magnesium composites with suitable reinforcement such as hydroxyapatite (HA) or tricalcium phosphate can offer improved mechanical and also biological properties, which points to them as possible candidates in medicine as biodegradable materials. The present paper deals with structure and mechanical properties of Mg- x HA ( x =0, 2, 5, 10 wt.%) composites prepared from coarse Mg powder and nanoparticles of HA. Different preparation methods (milling, stamping, extrusion, spark plasma sintering) and process temperatures are combined to avoid the creation of agglomerates in structure and to reach improved mechanical properties. Hardness, compressive and three-point bending tests are performed for material characterization. On the basis of these results, authors confirm the clear effect of the volume fraction of reinforcement in composite on final properties, but authors also show even stronger effect of the preparation method on the mechanical properties of Mg-HA composites. Measured properties of selected final products, which reached about 500 MPa in ultimate compressive strength and flexural strength, slightly exceed values reported in literature and fulfil general requirements on mechanical properties for applications in medicine such as bone fixations.

The Al layer with α-Al 2 O 3 seed crystals and the rare earth element Y were deposited directly onto a 316L stainless steel substrate and then oxidized at a temperature as low as 580°C using the double glow plasma technique. The complex Al target material containing 10 wt% α-Al 2 O 3 seed crystals and 10 wt% Y was used in the experiment. The results indicated that the coatings were very dense and uniform. The field emission transmission electron microscopy observation indicated that element Y was discontinuously distributed, which was mainly concentrated at the grain boundary of the coating. After plasma oxidation, Y was oxidized to Y 2 O 3 . Under the action of coupled multiple factors (ion bombardment, α-Al 2 O 3 seed crystals, and rare earth element Y), the AlYα oxide coatings contained large amounts of α-Al 2 O 3 crystals. The increase of the Y content improved the adhesive force of the coatings. The corrosion current of the oxide coatings was reduced by three orders of magnitude.