Volume 20, Issue 4

In this work, contact angle, spreading area, and isothermal aging tests were conducted to study the difference between Sn-3Ag-0.5Cu lead-free solder and its composite solder at different multiwalled carbon nanotube reinforcement volume fractions. The material interaction between the solder and the substrate at different aging temperatures and times was investigated using scanning electron microscopy elemental analysis. The experimental results indicated that the composite solder had a lower contact angle as well as good spreading area. An intermetallic compound layer was found between the solder and the copper substrate, and the thickness of this reaction layer increased with increasing aging temperature and time. Meanwhile, the intermetallic compound layer of multiwalled carbon nanotube reinforcement composite solder was thicker than that of the Sn-3Ag-0.5Cu lead-free solder. The composite solder with 0.1 vol% multiwalled carbon nanotube reinforcement addition exhibited better comprehensive properties than composite solders with other reinforcement volume fractions.

A hard SiC-B 4 C reinforced composite coating was fabricated by laser alloying of SiC-B 4 C+Al-Sn-Mo-Y 2 O 3 mixed powders on a Ti-3Al-2V alloy. Al-Sn-Mo mixed powders were first used in the laser alloying technique to improve the wear resistance of titanium alloys. Proper selection of the laser alloying process parameters allows us to obtain a composite coating with a metallurgical combination with substrate. Under the action of Mo, fine particles with high microhardness were produced in the coating matrix and also hindered the formation of adhesion patches and deep plowing grooves during the sliding wear process, leading to the improvement of wear resistance of a titanium alloy substrate surface.

Metal matrix composites (MMCs) are characterized by high specific strength and stiffness. Light metal alloys are reinforced with hard ceramic particles, which show better properties compared to monolithic alloys. ZA43 MMCs are fabricated by stir casting technique by reinforcing preheated silicon carbide particles (SiCp). Wear behavior of ZA43 MMCs is evaluated by conducting dry sliding wear test using a pin-on-disc wear test rig. The tests were conducted for varying loads of 9.81, 19.62, 29.43 and 39.24 N and sliding disc speeds of 2.12, 2.93, 3.66, 4.39 and 5.13 m/s at constant time of 15 min. The results reveal that the wear resistance property of the composite increases as the percentage of reinforcement increases. It was also observed that volume loss increases with increasing applied load and sliding speed. The tested samples were examined and analyzed by taking scanning electron micrographs. The dominating wear mechanisms observed were delamination, scissoring of the abrasive particle, pullout of particle, smearing of the surface and abrasion.

The effect of various process parameters on the stability of TiO 2 nanofluid, which can mostly be defined as zeta potential and particle size, was studied using response surface methodology (RSM) by the design of experiments and was predicted through a trained artificial neural network (ANN). The process parameters studied were weight percentage of surfactant (sodium lauryl sulfate) (0.01–0.2 wt%) and the value of pH (10–12). Central composite design and the RSM were employed to develop a mathematical model as well as to define the optimum condition. A three-layered feed-forward ANN model was designed and used for the prediction of the stability parameters. From the analysis of variance, the significant factors that affected the experimental design responses were also identified. The predicted stability parameters using the RSM and ANNs were compared using figures and tables. It is shown that the trained ANN outperformed the RSM in terms of accuracy and prediction of obtained results.

A ferric oxide (Fe 2 O 3 )/silicone rubber (SR) composite was prepared to produce a magnetic rubber with good heat-resistant and friction properties: SR and nano-Fe 2 O 3 were used as its raw materials. The heat-resistant, antiflaming, magnetic, and mechanical properties of such composites with different proportions of nano-Fe 2 O 3 were studied. The results showed that the Fe 2 O 3 nanoparticles were uniformly distributed throughout the composites. The physical and mechanical properties of SR were improved when Fe 2 O 3 nanoparticles were added. The maximum elongation and tensile strength of the composites were relatively good when the ratio of Fe 2 O 3 was 20 phr. The heat-resistance and antiflaming properties of SR were improved by adding nano-Fe 2 O 3 , which had good combined heat resistance. The friction properties of these composites were optimal at 20 phr addition of nano-Fe 2 O 3 , which laid the foundation for further applications of this type of composite in high-temperature sealing and shock absorption environments.

Apple and cherry pruning with red pinewood particles in various proportions were used as the raw material for the experimental particleboard manufacturing in laboratory conditions. The results showed that there were no considerable differences in the main chemical constituents of carbohydrate and lignin content, although there were some differences found for extractives that are considerably higher for both cherry and apple pruning. The mean modulus of rupture values of boards were found to ranged from 12.4 to 18.48 MPa. These indicated that all the boards, except for the board type F (prepared from 100% apple pruning), met the minimum bending strength required in standard for general-purpose particleboards. The modulus of elasticity and internal bond of the experimental particleboards usually decreased as red pinewood particle content decreases in proportion. However, all the boards produced in this study met the minimum modulus of elasticity, internal bond, and surface strength required in standard for general-purpose particleboards. However, the thickness swelling for 24 h was considerably higher than the required in standard value of 14% for all boards.

Mechanical properties of fiber reinforcement that can be obtained by the introduction of basalt fibers in jute fiber-reinforced polyester composites have been analyzed experimentally. Basalt/jute fiber-reinforced hybrid polymer composites were fabricated with a varying fiber percentage by using compression molding techniques. The fabricated composite plates were subjected to mechanical testing to estimate tensile strength, flexural strength and impact strength of the composites. The effect of fiber content on basalt/jute fiber in the composites has been studied. Addition of jute fiber into basalt fiber composite makes it a cost-effective one. Incorporation of basalt fiber into the composites was at approximately 10%, 20%, up to 90%, and the jute fiber percentage was reduced from 90%, 80%, to 10% correspondingly. Mechanical properties were investigated as per ASTM standards. Tensile and flexural strengths were tested by using a computer-assisted universal testing machine, and impact strength by using an Izod impact tester. It has been observed that the addition of jute fiber to the basalt fiber polyester composites enhanced the mechanical properties. Water absorption of hybrid composites was also analyzed and was found to be proportional to fiber percentage.

In this study, the effect of fungal decay on the long-term water absorption of bagasse fiber/polypropylene composites at different exposure times was studied. For this purpose, the blend composites were prepared through the melt mixing of bagasse fiber with polypropylene at 40:60% weight ratios, with 2% coupling agent for all formulations. Then, the samples were exposed to brown-rot ( Coniophora puteana ) and white-rot ( Trametes versicolor ) fungal treatments for 8, 12 and 16 weeks with the Kolle flask method. The long-term water absorptions of samples were evaluated by immersing them in water at room temperature for several weeks, and water diffusion coefficients were also calculated by evaluating the water absorption isotherms. Also, the morphology of composites was characterized using scanning electron microscopy (SEM). The results showed that the water absorption of samples was actually much higher after both types of rotting and was significantly higher than that of control samples. Also, the water absorption of white-rotted samples was higher than that of brown-rotted and control samples for all weeks of fungal exposure times. In addition, the control sample and composite after 16 weeks of exposure to white-rot fungi exhibited the lowest and highest water diffusion coefficients, respectively. The mechanism of water absorption of samples against fungal decay at different exposure times followed the kinetics of a Fickian diffusion process. Furthermore, the SEM micrographs showed that the extent of degradation increased with increasing exposure time to fungus.

In this study, free vibration behavior of a multilayered symmetric sandwich beam made of functionally graded materials (FGMs) with variable cross section resting on variable Winkler elastic foundation are investigated. The elasticity and density of the functionally graded (FG) sandwich beam vary through the thickness according to the power law. This law is related to mixture rules and laminate theory. In order to provide this, a 50-layered beam is considered. Each layer is isotropic and homogeneous, although the volume fractions of the constituents of each layer are different. Furthermore, the width of the beam varies exponentially along the length of the beam, and also the beam is resting on an elastic foundation whose coefficient is variable along the length of the beam. The natural frequencies are computed for conventional boundary conditions of the FG sandwich beam using a theoretical procedure. The effects of material, geometric, elastic foundation indexes and slenderness ratio on natural frequencies and mode shapes of the beam are also computed and discussed. Finally, the results obtained are compared with a finite-element-based commercial program, ANSYS ® , and found to be consistent with each other.

Some panels and particleboards were made from reed mats and blends of reed-wood chips to be used inside buildings for sound and heat insulations. It was seen that the outer layers of the reed body (spike) was almost water resistant and exceptionally resistant to the penetration of common adhesives. Therefore, the panels from stitched reed mats exhibited very poor mechanical strength. The sound transmissions of such panels (1–3 km/s) made with various combinations, however, were recorded to be excellent compared with that of particleboards made of wood (17 km/s). Blends of reed chips (2 cm) and wood chips, however, gave particleboards with better mechanical properties (5–17 MPa) than that of panels made from reed mats (2 MPa). An increasing amount of reed chips in tested particleboards was recorded to be improving both sound and heat insulations from 17 to 6 km/s and from 0.34 to 0.27 W/mK, respectively. The bending strength of samples, however, was reduced from 26 to 5 MPa. Thickness swelling was also noted to increase from 18% to 85% due to reed chips addition. It was concluded that the outer layers of water reeds should be modified via chemical and/or enzymatic methods to increase the interfacial bounds between adhesives.

In this paper, an interpenetrating network of acrylic acid (AA)-based superabsorbent resin (SAR) with polyvinyl acetate (PVA) and acrylamide (AM) was synthesized by copolymerizing partly neutralized AA, AM and PVA with ammonium persulfate/sodium hydrogen sulfite (APS/SHS) as the radical initiating system and N , N -methylene bisacrylamide as cross-linking agent in an aqueous copolymerization system at 60°C. This type of SAR exhibited excellent properties such as higher water and saline absorbency compared with AA-based SAR. The maximum water and saline absorbency of SAR was 1050 and 125 ml/g, respectively. Those effects were well explained by photographic morphologies obtained using scanning electron microscopy.

Since the focus on the energy crisis and environmental issues due to excessive fossil fuel consumption, wind power has been considered as an important renewable energy source. Recently, several megawatt-class large-scale wind turbine systems have been developed in some countries. Even though the large-scale wind turbine can effectively produce electrical power, the small-scale wind turbine has been continuously developed due to some advantages; for instance, it can be easily built at a low cost without any limitation of location, i.e., even in the city. In case of small-scale wind turbines, the vertical axis wind turbine (VAWT) is used in the city despite having a lower efficiency than the horizontal axis wind turbine. Furthermore, most small-scale wind turbine systems have been designed at the rated wind speed of around 12 m/s. This aim of this work is to design a high-efficiency 500W class composite VAWT blade that is applicable to relatively low-speed regions. With regard to the aerodynamic design of the blade, parametric studies are carried out to decide an optimal aerodynamic configuration. The aerodynamic efficiency and performance of the designed VAWT is confirmed by computational fluid dynamics analysis. The structural design is performed by the load case study, initial sizing using the netting rule and the rule of mixture, structural analysis using finite element method (FEM), fatigue life estimation and structural test. The prototype blade is manufactured by hand lay-up and the matched die molding. The experimental structural test results are compared with the FEM analysis results. Finally, to evaluate the prototype VAWT including designed blades, the performance test is performed using a truck to simulate various ranges of wind speeds and some measuring equipment. According to the performance evaluation result, the estimated performance agrees well with the experimental test results in all operating ranges.

Dispersive and expansive soils are considered problematic, and these soil properties cause serious problems for many engineering structures. For many years, comprehensive studies have been carried out with the aim of improving the swelling and dispersive qualities of soils by using additives. Each feature in the literature associated with the improvement of the dispersive and swell properties of clay soil with additives was separately evaluated. In this study, the effect of cement and natural zeolite additives on the characteristics of dispersibility and swelling potential of clay soils were investigated. A fixed percentage of cement (3%) plus different percentages of natural zeolite (1%, 3%, 6%, 10%, 15%, and 20%) were mixed with four different clay soil samples. In this context, first, the physical and chemical properties of the soil samples were determined. Next, the swell percentage, swell pressure, crumb, pinhole and unconfined compressive strength tests at different curing times were performed on samples with and without the additive by compressing the sample to achieve particular compaction characteristics. Significant strength value increases depended on curing time, and the properties were improved with the mixture of cement and zeolite additives, depending on the sodium adsorption ratio (SAR) and exchangeable sodium percentage (ESP) values of clay soil samples with different plasticity characteristics that exhibit dispersive and swell properties. This study not only showed that a mixture of cement and zeolite additives improved the dispersive and swell properties of clay soil samples with four different plasticity characteristics, depending on their SAR and ESP values, but also significant increases in strength values were observed.