Volume 22, Issue 5

The adsorption isotherms and structural evolution of alkyl quaternary ammonium bromide (C n TAB) on graphite oxide (GO) were measured by means of an elemental analyzer, X-ray diffraction and Fourier transform infrared spectroscopy. In order to interpret the adsorption mechanism of surfactants onto GO, the adsorption kinetics and thermodynamics were further investigated. It was found that GO is a relatively efficient adsorbent within a wide range of temperatures (297–353 K), and the C n TAB was intercalated and then agglomerated into the interlayer spacing of GO via ionic bonding and hydrophobic bonding. The saturation amount of alkyl ammonium adsorbed on GO was decreased with the rise in temperature, and the experimental data fitted well into the modified Langmuir (Langmuir-Freundlich) equation. In addition, the negative values of Δ G and Δ H showed that the adsorption process of C n TAB onto the GO was spontaneous and exothermic.

Achieving remarkable mechanical properties for very low levels of reinforcement, nanocomposites are nowadays a new class of materials with high potential. Thanks to the stiffening aspect of the interface region between the matrix and the inclusions, nanocomposites often exhibit improved mechanical and physical properties compared to the conventional composites reinforced with micron-sized particles. This paper presents a strategy based on the introduction of an equivalent inclusion phase that allows managing the ellipsoidal morphology of inhomogeneous inclusion nanophase in the determination of estimates for the homogenized elastic moduli. Application to clay-polymer nanocomposites is presented in the framework of the dilute scheme. The latter gives theoretical estimates in good agreement with experimental results reported in the literature.

This study focuses on the fabrication of aluminum treated with nanocomposites made of aluminum and NbB 2 and ZrB 2 nanoparticles. These nanoparticles were obtained by fragmentation in a ball mill and then mechanically alloyed with pure aluminum powder to form Al/NbB 2 and Al/ZrB 2 nanocomposite pellets, which were then sintered at 260°C for half an hour to improve the metal/borides interface. The sintered nanocomposites were incorporated into molten pure aluminum to produce 1-mm-diameter wires after cold forming. The wire specimens were mechanically characterized and their electrical resistivity was measured. Our results demonstrated the feasibility of improving the mechanical properties of aluminum wires with the addition of nanocomposites without significantly affecting their electrical conductivity.

The Ce-substituted bismuth titanate (Bi 4 Ti 3 O 12 ) ferroelectric thin films were prepared on Pt/Ti/SiO 2 /Si substrates by sol-gel method and annealed at 700°C. The Bi-layered perovskite (with Ce substitution for Bi) single phase films were obtained and the thickness was 500 nm. At 12 V amplitude and 1000 Hz frequency, ferroelectric tests results showed a hysteresis loop with remnant polarization (2Pr) and coercive field values (2Ec) of 9.86 μC/cm 2 and 208 kV/cm, respectively. The structure and lattice parameters were analyzed by X-ray diffraction (XRD). The results showed that by increasing Ce substitution the ratio of a/c, the ferroelectric properties, increased when the Ce-substitution of 0.6, a and c values were 5.40734 Å and 5.3559 Å, respectively. The a-axis highly oriented structure may have influenced the remnant polarization and coercive field values of the films obtained.

In order to understand the effect of additive Al 2 O 3 powders on the film corrosion resistance and the microstructure of the micro-arc oxide (MAO) ceramic film of magnesium alloy, AZ91D die cast magnesium alloy was oxidized with a special micro-arc apparatus. Morphological characteristics and phase constituent of ceramic coatings were analyzed by scanning electron microscope (SEM) and X-ray diffraction (XRD). And the aluminum (Al) element of before and after the Al 2 O 3 accession were analyzed by energy-dispersive X-ray (EDX). The results showed that after adding Al 2 O 3 powders, pores on ceramic coatings decreased, the loose layer became more compact, the new phase of Al 2 O 3 appeared, and the Al element of the ceramic membrane increased. Ultrasonic waves promoted the content of Al 2 O 3 in the layer. Electrochemical corrosion experiments in 3.5% NaCl solution showed that the corrosion resistance of ceramic coatings after adding Al 2 O 3 powders was improved greatly.

This experimental study deals with the flexural behaviors of composite single-lap adhesive joints after impact tests. Increasing impact energies are applied at the center of the composite plates having three different overlap lengths. It is shown that the overlap lengths and impact energy levels affect considerably the impact responses of the composite single-lap joints. It is also shown that the bending stiffness of the composite increases with increasing overlap length. For this reason, after the impact tests, how these effects influence the flexural behaviors of the impacted composite lap joints was also investigated. The flexural loads of the impacted and non-impacted composite single-lap joints were determined and compared with each other. It is shown that the residual flexural loads after impact increase with increasing overlap lengths but decrease with increasing impact energy.

Diffusion bonding of dissimilar metals QSn4-3 and GH34 by using a QSn6.5-0.1 interlayer has been conducted in this study. The purpose of the study is to investigate the interface microstructure and strength of the joints, and to demonstrate the feasibility of using another high Sn content tin bronze interlayer to fabricate a typical microstructure joint. Microstructure examinations show that a penetration structure is formed by using a QSn6.5-0.1 interlayer, and its feature is apparent. Also, prolonging the holding time is conducive to the forming of the penetration structure. Shear testing results show that the penetration structure formed in a diffusion bonded joint of QSn4-3 and GH34 enhances the joint strength to almost the same as the QSn4-3 base metal. The mechanism forming the penetration structure is as follows: Sn atoms diffuse faster than Cu atoms into GH34 causing more Sn atoms to aggregate at the GH34 grain boundary. When the bonding temperature reaches 950°C for a short time, the aggregated Cu alloys having higher content of Sn than 5.3wt.% will melt, and penetrate and disrupt some grains from GH34 base metal.

The damage behavior of the potting materials around a pinhole, being used in the mechanical joints of sandwich composites, is investigated experimentally. The sandwich composite panels used in the tests were manufactured by the vacuum-assisted resin infusion technique. Each of the top and bottom face sheets of the panels consisted of two woven E-glass/epoxy layers. As the core material, PVC foam (AIREX ® C70.55) was used. The potting material consists of an epoxy resin and hardener system mixed with short E-glass fibers (4 wt%). The diameter of the potting material D and the edge distance to the center of pinhole E were considered as the two main varied dimensions. They were chosen as D = 10, 12, 15, and 18 mm and E = 15, 20, and 25 mm. The damage mechanisms of the potting material and sandwich sections are presented by using load-displacement variations and images of the damaged samples, subjected to in-plane pin loading.

In this paper, the low velocity impact characteristics of honeycomb sandwich panels with varying cell sizes such as the maximum load absorbed, absorbed energy and failure modes were investigated. Low-velocity impact tests were carried out at different energy levels using an instrumented drop-weight apparatus as per ASTM D3029-95. Honeycomb core sandwich composite panels were made with glass fabric/epoxy honeycomb core with different cell sizes i.e., 8, 12, 16 and 20 mm using the vacuum bag molding technique. Tests were conducted at impact energies that ranged ranging from 7 to 50 J. The energy absorption mechanism and the damage process are analysed with parameters derived from the load-time and energy-time curves. It is observed that at low energy levels, the core buckles while it gets crushed at higher levels. This buckling of the core is due to damage to the epoxy resin that allows the glass fiber to bend freely, and core crushing is due to the breakage of the glass fiber reinforcement within the core. It is inferred that for a given core height, as the cell size increases, the peak load at which cracking occurs in the face sheet decreases drastically. This is attributed to the fact that a core with a smaller cell size has fewer load paths to distribute the absorbed energy. It is evident from the post impact damage analysis that three types of failure modes occur viz., crack initiation, cracking of the face sheet along with debonding, and the crushing of cells. The common damage pattern observed on the front facing has a square shape which is the same as the shape of the indentor.

This research investigates the application of calender extrusion as a novel technique in the production of cement fiberboards. The technique is successfully used in the production of non-structural building elements. The properties of the produced composites are discussed in this paper, particularly with regards the polyvinyl alcohol (PVA) fiber used in the study. The research involves an experiment to examine the mechanical properties and microstructure of the composites, and the results indicate that calender extrusion is a promising method for the production of thin and wide cement composites. These products can be shaped into various three-dimensional forms in the green state after processing. Based on the results, the mechanical properties of cement-bonded fiberboards vary with processing direction due to the alignment of fibers. Fiber content is the most significant factor with regards the tensile and flexural properties of fiber-reinforced cementitious products processed with calender extrusion. Moreover, processed composites have adequate screw head pull-through and freeze-thaw resistance.

This study aims to prepare optimal feedstock for fabrication of Al/SiC nanocomposites by the low-pressure injection molding technique. For this purpose, micron-sized aluminum and nanosized SiC powders were mixed with different amounts of the binder consisting of 89 wt% paraffin wax, 9 wt% bees wax, and 2 wt% stearic acid. Rheometry analyses as well as the Weir model were utilized to determine the optimal feedstock with the desired rheological properties and high homogeneity. Considering powder to binder ratios, shear sensitivity, flow activation energy, and homogeneity within the rheometry analyses, the feedstock of 78 wt% powder loading is selected as the optimal sample for injection molding. Investigation of optimal feedstock by the scanning electron microscopy technique also verified the high homogeneity of this feedstock. In addition, it was observed that all of the feedstocks had thixotrop behavior.

In this paper, composite specimens were fabricated from a glass fiber chopped strand mat and unsaturated polyester resin using the hand lay-up method. To evaluate the effects of open holes on the mechanical properties, different factors, including the volume fraction of glass fiber and material thickness were investigated. Both the unnotched strength of smooth specimens and the notched strength of specimens with holes, increased as volume fraction increased, but the trends were different. For notched specimens with closer volume fractions, increased thickness or width-to-depth ratio led to a lower resistance on the open hole. In investigating the fracture behaviors of notched specimens, two different fracture areas were distinguished: parallel areas and fan-shaped areas. The length of each parallel area was measured. To evaluate the material properties, characteristic distance was calculated using linear elastic methods in finite element software (MSC-Marc, MSC Software Corporation, Tokyo, Japan). The results revealed that characteristic distance has a good correspondence with parallel area length.

In this study, the influence of hybridization on natural frequency and damping properties of laminated composite plates consisting of various combinations of fibers and boundary conditions are examined. Carbon (C), Kevlar ® (K), and S-glass fibers are used as reinforcement with epoxy resin for hybridization. Experiments are conducted on hybrid composites under the combinations of clamped, free, and simply supported boundary conditions. Natural frequency analyses of hybrid composites are performed using finite element analysis software ANSYS. Vibration test results obtained from experimental and numerical studies are compared with each other. Results show that hybridizations with three different fibers and their substitutions in the layers have strongly effected the damping and vibration characteristics of composite plates.

The wear behavior of Al/SiC composites prepared by stir casting technique is investigated to find out the effects of the weight percentage of SiC, load, and the number of strokes on a shaper machine. Metal matrix composite (MMC) pins are prepared with different weight percentages of SiC (10%, 15%, and 20%). The tests are carried out with different load conditions (25, 50 and 75 N) and different number of strokes (420,780 and 1605 strokes). Wear surfaces of tested samples are examined in scanning electron microscope (SEM). Hardness and impact tests are also carried out on the MMC samples. The experimental results show that the hardness of composites increases with an increase in SiC particle, and the impact strength decreases with increase in SiC content. The volume loss of MMC specimens are less than that of the matrix alloy. Moreover, the temperature rise near the contact surface of the MMC specimens increases with increase in wt% of SiC, load, and number of strokes. The coefficient of friction decreases with increase in load and the number of strokes.

High-plasticity clayey subgrade, which is unsuitable for road construction, may sometimes occur along highway routes. In such cases, engineers need to change the route of a highway project, resulting in an increase in road length and project costs. In this study, waste pumice was examined for stabilization of high-plasticity clayey subgrade, which is inappropriate for road construction. For this purpose, the physical and index properties of clay and pumice were determined. Then, the pumice was mixed with high plasticity clay at different ratios by weight. By performing standard Proctor compaction tests on the mixtures, the effects of adding pumice on compaction were also studied. Unconfined compression tests and California bearing ratio (CBR) tests were performed on all pumice-clay mixtures, and the test results and the CBR ratios were compared for each sample, respectively. The results showed that pumice stabilization improved the mechanical properties and reduced the swelling potential of high plasticity clayey subgrade.