Advanced Materials Research Vols. 488-489

Abstract: The increase of population in developed cities has improved the requirement for new advanced transportation method such as urban railway system. Therefore, the needs of developing advanced technology in the tunnelling construction for the use of underground railway system are necessary. Underground railways are one of the most accepted systems used for transporting a large amount of people in highly populated cities, which its development requires a set of advanced science such as in the tunnelling construction process. One of the significant failure may occur in tunnels is ceiling collapse. This failure is a major concern during construction to avoid hazardous for workers. In the past few decades, the combination of sprayed concrete and steel meshes (shotcrete) are utilised as temporary support for tunnels during the construction process. This was a time consuming procedure and for a team of workers, they face plenty of obstacles from safety concern to limited working space area when mounting some heavy panel inside the tunnels. To overcome these problems, an experimental test was carried out using Hard Density Polyethylene (HDPE) which is approximately has the same stiffness to shotcrete but 50% less of the weight of the structure. A rectangular beam sample of was manufactured as a precast panel and experimentally tested under three-point bending load as in the real conditions. Maximum deflection and total reaction force of the panels was recorded. The nonlinear mechanical behaviour of the specimen is analysed based on the bending stiffness. Considering the hyper-elastic behaviour of HDPE, the overall response of the sample had shown a good acceptable strength 14.3% higher than the desired strength which can approve the right material selection. In addition, discussion was given on total stiffness and reduced stiffness because of nonlinear behaviour of the HDPE. The value of strain is measured at the bottom surface of the HDPE beam along the length and width the sample for further discussion. This type of polymer can be assumed as large strain material and it is showing a large deformation under three-point bending condition which can help to inform workers about the safety of the whole structure.

Abstract: This study examines the deformation response of CFRP composites with preexisting delamination crack under Mode I loading. A DCB specimen is used in a series of Mode I interlaminar tests, each having a different initial delamination crack length. The 48-ply composite laminate has a symmetric ply sequence with 0/0 fiber orientation at the mid-plane. Apparent toughness is indicated by the composite specimen with a starter film insert, likely due to the presence of a neat pocket of resin at the front of the starter crack. The compliance of pre-delamination cracked specimens increases faster beyond the normalized delamination length, a/L of 0.68 due to effects of severe deflection of the longer DCB specimen arm. The critical energy release rate, G_IC = 0.5 N/mm is determined based on pre-cracked DCB specimens. Fractographic analysis revealed a smooth fracture plane that indicates interface delamination as the primary failure mode.

Abstract: Insitu polymerization of aniline was carried out in the presence of stannous oxide (SnO) to synthesize Polyaniline (PAni)/SnO composites by chemical oxidation method. The surface morphology of the composites were studied by scanning electron microscopy (SEM).The electromagnetic interference (EMI) shielding properties of the composites were investigated for different wt % of SnO (10,20,30,40 and 50 wt%) in PAni. The EMI measurements were carried out in the frequency range from 8.2 to 12.4 GHz (X-band), which is relevant for practical applications. EMI shielding effectiveness (EMI SE), microwave absorption and reflection, the influence of SnO concentration in PAni on EMI SE of the composites are reported. The composites exhibit EMI SE value of -18 to -23 dB. The absorption dominated EMI SE of these composites indicates the potential applications of these materials for microwave attenuation in the X-band.

Abstract: In this paper, the polypropylene (PP)nanocomposites containing 1, 3 and 5 wt % of nanoclay particles are prepared via direct melt mixing in the presence of maleic anhydride grafted PP (PP-g-MA) as compatibilizing agent. PP-g-MA is known to facilitate the dispersion of clay particles in a nonpolar PP matrix and to increase the adhesion between PP and the clay particles.The effect of different nanoclay contents on the PP composites are investigated for tensile characterization at both room temperature(RT) and cryogenic temperature (CT).The results showed that the cryogenic tensile strength, Young’s modulus, percentage of displacement at break and the energy absorptionat cryogenic temperature are all enhanced ascompared to the neat PP by the addition of clay at appropriate contents

Abstract: In this paper, Polypropylene (PP) nanocomposites are prepared by melt mixing in a twin-screw extruder by injection molding. The role of compatibilizing agent is performed by maleic anhydride grafted polypropylene (PP-g-MA) between nanoclay and PP. The effect of nanoclay particles (1, 3, 5 wt %) on the PP composites is investigated for tensile test at high temperature for the first time. Mechanical behaviors of PP/clay nanocomposites at both room temperature (RT) and high temperature (HT) are investigated in terms of tensile properties. Addition of nanoclay showed a significant enhancement in stiffness of PP/clay nanocomposites. Nearly 36% and 157% increase in the tensile modulus at both RT and HT are observed, respectively. But, the increase in tensile strength is almost negligible.

Abstract: The coupled TiO₂/WO₃ nanocomposites were synthesized by hydrothermal method by using hydrogen titanate and ammonium metatungstate hydrate as the precursors of TiO₂ and WO₃, respectively. The effects of hydrothermal conditions to prepare hydrogen titanate powders were studied. It was found that the hydrothermal condition at 130 °C for 24h shown the best result. The TiO₂/WO₃ nanocomposites were carried out as a function of varied molar ratio of TiO₂/WO₃ for 1:1, 3:1 and 1:3. The coupled TiO₂/WO₃ nanocomposites are characterized by transmission electron microscopy, UV-vis absorption spectra by UV–VIS spectrometer and photocatalytic activity by degradation of MB solution under visible light. The results show that the absorption spectra of the coupled TiO₂/WO₃ nanocomposites can be seen in visible light region which higher than pure TiO₂ (from hydrothermal method) and P25-Degussa.

Abstract: No-wait flow shop scheduling is a type of manufacturing scheduling which finds applications in advanced manufacturing systems and falls under the category of NP-hard combinatorial optimization problem. Heuristic methods are found to be the most suitable ones for obtaining solutions to these problems. We propose a heuristic method based on Vogel’s Approximation Method for developing the solution for the objective of minimizing total flow time in no-wait flow shop. The computational results are compared with the results of the well known existing heuristics in no-wait flow shop for minimizing the total flow time criterion. The results reveal that the proposed method significantly outperforms the existing heuristics, with comparable computational time. Statistical tests are used to validate the performance of the proposed method.

Abstract: Polymer blend of chitosan and poly(ethylene oxide) (PEO) electrolytes were prepared by employing solution cast method. Ammonium nitrate (NH₄NO₃) was added to the blend to supply the charge carriers for ionic conduction. The impedance of the electrolytes was measured by electrical impedance spectroscopy (EIS) over the frequency range of 50 Hz to 1 MHz. The permittivity ɛr and electric modulus Mr of the complex were analyzed. Dispersion at low frequencies caused by space charge effect from the electrodes was observed. The modulus plots indicated that the dispersion deviated from the Debye behaviour. The relaxation time, τ decreased to 1.64 × 10^-7 s as the NH₄NO₃ content was increased up to 40 wt.%.

Abstract: This work investigated the thermal stability of nano-silica thermal insulating composites, which consisted of fumed silica, fibers and opacifiers. The volume shrinkage was introduced as an evaluation index to characterize thermal stability of the composites at different temperatures. The effects of serving temperature, serving time, particle size of fumed silica and mass ratio of SiC were discussed. The results indicated nano-silica thermal insulating composites have excellent thermal stability under the temperature of 800°C. The volume shrinkage was correlated positively with serving time. High specific surface area of fumed silica could bring good thermal insulating performance, but at the same time caused high volume shrinkage when applied at high temperatures. SiC as an opacifier has little influence on volume shrinkage, but too much amount may yet increase solid heat transfer and lead to the drop of thermal insulating properties.

Abstract: Hydroxyapatite (HA) ceramics were prepared from the bone ash which is mostly used as animal feeds or raw materials. Dissolving behaviors of the HA in buffered water were investigated and compared with commercial HA for further use as biomaterials. HA ceramics were prepared by soaking the bone ash in 0.1 M of NaOH solution at 80°C for 4 h. The ash was calcined at 800°C for 1 h to completely remove organics, and then sintered at 1200°C for 1 h under moisture protection. The bone ash derived-HA consists of mostly HA and small amounts of α-tricalcium phosphate, calcium oxide phosphate, magnesium oxide and calcium oxide. After polishing the HA ceramics, they were immersed in buffered water at 37°C for 3 and 7 days. We previously found that grain boundaries of synthetic HA were intensively dissolved in buffered water. On the other hand, the bone ash derived-HA shows high stability in liquid environment with immersion time compared with commercial HA.