Volume 23, Issue 4

The aim of the present article is to investigate the influence of the amount of bis(triethoxysilylpropyl) tetrasulfide on the curing characteristics and mechanical and dynamic properties of rubber composites based on epoxidized natural rubber (Epoxyprene 50) filled with 70 phr silica. The obtained results showed that although the interaction between the epoxy groups of epoxidized natural rubber and the silanol groups of silica through hydrogen bonds improves the dispersion of filler in the rubber matrix, the presence of silane coupling agents is necessary to obtain rubber compounds and vulcanizates with good vulcanization characteristics and mechanical and dynamic properties.

Using image processing and recognition, a microstructure-based finite element model (FEM) was established to predict the dynamic properties of SiCp/Al composites at different strain rates ranging from 200 to 14,000 s -1 . In the microstructure-based FEM, the irregular SiC particles were randomly distributed in the matrix, and its configurations did not change. The results showed that the flow stress of SiCp/Al composites with low particle volume fraction first increases and then decreases with the increasing of strain rate during the adiabatic compression. The reducing flow stress of SiCp/Al composites is caused by the inner damage and the heat softening of composites. The angular particles in SiCp/Al composites provide more strengthening effect than the circle particles when the strain is <0.62, while the circle particles provide more strengthening effect than the angular particles for strain >0.62.

A preliminary investigation on the impact properties and morphologies of unsaturated polyester reinforced with jute woven fabric recycled from used coffee bags with different moisture contents was conducted. The laminated structural effect of hybridization with glass woven fabric was also investigated. Jute/jute-laminated composites, and jute/glass/jute- and jute/jute/glass-laminated hybrid composites were fabricated by the hand lay-up method. Their impact properties were compared by drop-weight and the Izod impact tests. The acoustic emission (AE) technique was applied under a tensile load to detect micro-failure processes in the jute and jute/glass hybrid composites. The number of AE signals and the AE energy were monitored using two transducers with resonant frequencies of 140 kHz and 1 MHz. The results showed that the moisture content affected the mechanical properties of the composites. The strength and elongation at break of the jute yarn decreased with a decrease in moisture content. The AE characteristics and observations of the fracture surfaces revealed that the composites fabricated from jute fabric with low moisture content had a relatively higher initial fracture stress and higher resistance to micro-fractures. Moreover, the mechanical properties of the hybrid composites were significantly affected by the laminating structure.

Sodium calcium silicate (Na 2 CaSiO 4 ) is a bioactive silicate with Na 2 O, CaO and SiO 2 as its basic components, which is similar to that of the composition of bioactive glasses. In the present study, pure sodium calcium silicate was synthesized by rapid combustion technique, and the synthesized sample was characterized by powder X-ray diffraction to check the phase purity. The scaffolds were prepared by varying the ratio of sodium calcium silicate and polyvinyl alcohol, and the apatite-formation ability of the scaffolds was examined by soaking them in a simulated body fluid. The results revealed the formation of hydroxyapatite on the surface of the scaffold after 5 days, which is found to be rapid when compared with the bioactivity of the calcium silicates and calcium magnesium silicates. The scaffolds were also loaded with ciprofloxacin as a model drug and analyzed for its drug release profile using UV spectrophotometer. The release profile did not vary with the change in bioceramic-to-biopolymer ratio, and 60% of the drug was released in 10 days, which is within the appreciable range for a targeted drug delivery system. Moreover, the experimental and simulated values of the release kinetics were compared by applying the existing mathematical model.

In this research, synthesis of Fe-TiC nanocomposites from activated ilmenite concentrate and carbon black was investigated. Ilmenite and carbon black as raw materials were milled in a planetary ball mill and sampled after different milling times. The activated powder was heat treated at different temperatures in an atmosphere control tube furnace and analyzed by X-ray diffraction technique. The X-ray diffraction results showed that increasing the milling time would lower the synthesis temperature of final products. Furthermore, the lattice parameter showed deviation from standard size, and mean grain size was decreased. In contrast, the strain of the system was increased based on the calculations.

The effect of the amount of carbon nanotubes on the electrical and optical properties of carbon nanotube (CNT)-zinc oxide nanocomposites was investigated. In this study, carbon nanotubes were prepared by chemical vapor deposition in a fluidized reactor. The diameters and lengths of the carbon nanotubes that were synthesized were determined by high-resolution transmission electron microscopy to be 20–30 nm and a few micrometers, respectively. Then, CNTs were added to commercial zinc oxide powder to prepare the nanocomposite. The structural, optical, and electrical properties of the samples were characterized by various techniques, such as scanning electron microscopy (SEM), UV-vis absorption, and electrical transport measurements. The room temperature conductivity σ 25 values of the undoped ZnO and ZnO doped with 0.1% CNTs, 0.2% CNTs, and 5% CNTs were found to be 6.55×10 -5 , 5.46×10 -4 , 1.23×10 -3 , and 2.83×10 -2 S/cm, respectively. The optical band gaps of the composites were determined by the Kubelka-Munk theory based on the analysis of diffuse reflectance. The results that were obtained indicated that the electrical and optical properties of ZnO semiconductors can be improved by the incorporation of CNTs. However, the ZnO lost some of its distinctive properties when excess amounts of CNTs were used in the ZnO-CNT composites.

Ni-AlN thin films were successfully fabricated via direct-current (DC), pulse-current (PC), and ultrasonic-assisted pulse-current (UAPC) deposition. The microstructure, microhardness, and erosion characteristics of the Ni-AlN thin films were determined with the use of scanning probe microscopy (SPM), X-ray diffraction (XRD), Vickers hardness test, electrochemical station, and scanning electron microscopy (SEM). SPM results revealed that the Ni-AlN thin films synthesized by UAPC deposition have a compact and fine morphology with average grain diameters of the Ni and AlN particles of approximately 97.7 and 40.2 nm, respectively. Based on the XRD results, the Ni-AlN thin films consist of Ni and AlN phases. The Ni-AlN thin films prepared by DC, PC, and UAPC deposition at 4.5 A/dm 2 current density exhibited an optimum microhardness value of 904, 943, and 987 HV, respectively. Based on the erosion test results, the films prepared by UAPC deposition possesses the best corrosion resistance among the prepared thin films. The corrosion potentials of the DC-, PC-, and UAPC-deposited films were -0.552, -0.473, and -0.446 V vs. SCE, respectively.

This article reports on experiments aimed at modifying nanosilica powder by adding a silane coupling agent, KH570, to achieve high dispersibility and strengthen the compatibility and interface bonding between it and the organic phases. Experiments were first done to prepare the common nanosilica powder, dried at 120°C for 4 h in a drying oven; second, an ethanol/water solution (volume ratio 11:1, total volume not more than two-thirds of the capacity of the flask) was blended in a three-necked flask with a reflux condenser and magnetic stirring; third, appropriate amount of dried nanosilica powder and appropriate mass fraction ratio of the silane coupling agent KH570 were added into the ethanol/water solution, and the pH of the mixture was adjusted to about 4–5 by adding acetic acid solution; fourth, the three-necked flask was placed in a water bath, and the modification reaction of the above mixing solution was sustained for an appropriate time in the appropriate temperature with magnetic stirring; fifth, the above mixing solution was separated by using a centrifuge (10,000 rpm) for 3 min, and the precipitate at the bottom of the flask was obtained after the supernatant was poured out; sixth, the precipitate was dried at 120°C for 48 h in a drying oven after it was washed with acetone several times, finally yielding the high-dispersibility nanosilica powder. The orthogonal test method was adopted to optimize three key test parameters: mass fraction ratio of the silane coupling agent KH570, modification reaction temperature, and modification reaction time. The dispersion effect of the high-dispersibility nanosilica powder was characterized by using infrared, X-ray diffraction, and scanning electron microscopic analyses from different views. The results revealed that the best dispersibility effect was achieved when the mass fraction ratio of the silane coupling agent KH570 was 3%, the modification reaction temperature was 80°C, and the modification reaction time was 2 h. Furthermore, the modification reaction resulted in chemical bonding, but not simple physical adsorption, owing to the presence of organic bond groups in the nanosilica modified by the silane coupling agent. The crystal structure of the nanosilica powder remained amorphous after the modification reaction.

This paper compared the influence of fused zirconia-corundum (AZ40), monoclinic zirconia (m-ZrO 2 ), and 3 mol% yttria-stabilized zirconia (3Y-ZrO 2 ) on physical properties at room temperature, hot modulus of rupture, and thermal shock resistance of Al 2 O 3 ceramics, and their relationships with microstructure changes were investigated. It was found that m-ZrO 2 or 3Y-ZrO 2 addition promoted the process of sintering densification and enhanced the room temperature strength and the hot modulus of rupture of Al 2 O 3 ceramics, and the effect of the latter was more distinct, while those of the sample with AZ40 addition decreased. In addition, the three kinds of ZrO 2 were beneficial to improving the thermal shock resistance of Al 2 O 3 ceramics. All these changes had close relationships with the changes of corresponding microstructure characteristics (including distribution of particles, degree of contact between crystals, grain boundary solid solution, microcrack density) and phase composition.

We prepared intercalated organic montmorillonite (OMMT) from a pristine MMT and long-alkyl-chain quaternary ammonium salts (LACQAS). X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and thermogravimetric analyses revealed that the amount, carbon atoms, and alkyl chains of LACQAS influenced the large value of d (001) of OMMT significantly. The d (001) stabilized at 100–150 mmol·(100 g) -1 of LACQAS/MMT. The single LACQAS cations arranged in the form of a lateral layer or half-paraffin-type molecular structure between MMT layers, whereas the dual and triple LACQAS cations arranged in the form of a paraffin-type molecular structure. The pyrolysis temperature and maximum pyrolysis rate of OMMT increased greatly compared with those of MMT. The thermal weight loss of MMT was caused by the removed absorbed and structural water, whereas that of OMMT was by the pyrolysis of LACQAS. With the help of the Agrawal integral equation, the pyrolysis kinetics of MMT and OMMT were obtained using a trial-and-error method.

Multilayer feed forward network, radial biased function network, generalized regression neural network and adaptive network-based fuzzy inference system (ANFIS) were used to predict the surface roughness of Ti-13Zr-13Nb alloy in etching sulfuric acid. Subsequent processes – polishing, sandblasting and acid etching or SLA – were employed to modify the surface. Alumina particles for surface blasting and concentrated sulfuric acid for acid etching were utilized in this experiment. This was performed for three different periods of time (10, 20 and 30 s) and temperature (25, 45 and 60°C). Correspondingly, the Ti-13Zr-13Nb surfaces were evaluated using a field emission scanning electron microscope for roughening and a contact mode profilometer for the average surface roughness (Ra) (nm). Different configurations of neural networks and ANFIS approaches are examined in order to minimize the root mean square error. Consequently, the ANFIS model is selected by dividing the time and temperature into one and three spaces, respectively, using the Gaussian-shaped membership function. A mathematical model is attained from the best approach in terms of root mean square error to realize the relation of the surface roughness of Ti-13Zr-13Nb alloy in etching sulfuric acid and time and temperature as the effective parameters.

In this study, the effects of machining parameters on the material removal rate (MRR) and surface roughness (Ra) were investigated during the cutting of Al/B 4 C/Gr hybrid composites by wire electrical discharge machining (WEDM). Wire speed (W S ), pulse-on time (T on ) and pulse-off time (T off ) were chosen as the control factors. The L 27 (3 3 ) orthogonal array in the Taguchi method was used in the experimental design and for the determination of optimum control factors. Response surface methodology was also used to determine interactions among the control factors. Variance analysis (ANOVA) was applied in the determination of the effects of control factors on the MRR and Ra. According to the ANOVA results, the most effective parameters on MRR and Ra were wire speed with a 85.94% contribution ratio, and pulse-on-time with a 47.7% contribution ratio. The optimum levels of the control factors for MRR and Ra were determined as A 3 B 3 C 3 and A 1 B 1 C 2 . In addition, second-order predictive models were developed for MRR and Ra; correlation coefficients (R 2 ) were calculated as 0.992 and 0.63.

The design analysis and prototype of a compact 8×10-mm 2 planar microstrip line-fed patch antenna on a readily available, low-cost, reinforced-fiberglass polymer resin composite material substrate is presented in this article. The proposed compact-size antenna has been configured and numerically analyzed using the finite element method-based three-dimensional full-wave electromagnetic field simulator. The optimized design of the antenna has been fabricated on a printed circuit board (PCB), and experimental results have been collected for further analysis. The measurement results affirm the fractional impedance bandwidths of (return loss of less than -10 dB) of 38.78% (2.03–2.98 GHZ) and 16.3% (5.38–6.35 GHz), with average gains of 2.52 and 3.94 dBi at both lower and upper bands, respectively. The proposed dual resonant antenna shows the radiation efficiencies of 91.3% at 2.45 GHz and 87.7% at 5.95 GHz. The stable and almost symmetric radiation patterns and performance criteria of the antenna can successfully cover IEEE 802.11b/g/n, Bluetooth, WLAN, and C-band telecommunication satellite uplinks.

Free vibration behavior of short beams made of axially layered functionally graded material (FGM) was investigated experimentally and numerically. Beams, which have gradation of the material properties in the axial direction, are fabricated by powder metallurgy technique using different weight fractions of aluminum and silicon carbide powders. In order to determine elasticity modulus of axially layered functionally graded (FG) beams, homogeneous beams containing different weight fractions of Al (aluminum) and SiC (silicon carbide) are produced, and these homogeneous beams are subjected to tensile tests. Density of each homogeneous layer is also calculated experimentally. After determination of the mechanical properties of each layer of the FG beams, they are modeled in a finite element program (ANSYS) according to Timoshenko beam theory, and free vibration analyses are performed. Fundamental frequencies of the axially layered FG beams produced are also calculated experimentally. FG beams with clamped-free boundary conditions are considered. Layers of the axially FG beams are considered to have symmetric configurations. Effect of the change in weight fractions of SiC particles and sorting order of layers to fundamental frequency of the beam is investigated. Experimental results obtained are compared with numerical results.

An amorphous-nanocrystal reinforced composite coating was fabricated on a TA15 alloy by laser cladding of BN-NiCoCrAlY mixed powders. Experimental results indicated that a portion of the amorphous phases just began to crystallize when the laser molten pool had completed the solidification process. The nucleation and growth of the amorphous phases were retarded by the nanocrystalline phases to a certain extent during the crystallization process. Due to the rapid solidification process of the laser molten pool, a number of the fine precipitates were produced. The production of eutectics, such as Co-Ti and Ti-Si compounds, in such a coating greatly promoted the formation of amorphous phases.