Advanced Materials Research Vols. 383-390

Abstract: Tungsten carbide - Cobalt (WC-Co) reinforced metal matrix composites are most commonly used as tool and die materials. The machining of WC- Co metal matrix composites is usually done by wire electric discharge machining. However during WEDM of WC-Co samples possibility of defects and electrolyzation is high. Also coating of Cu-Zn tool electrode on machined surface and void space takes place, thereby affecting material integrity. Analyzing the microstructures can remarkably reveal the identification, location, extent and criticality of the defects. In this study WC-Co metal matrix composite was wire electric discharge machined with two critical parameters, pulse on time and delay time. The machined samples were analyzed using micrographs, scanning electron microscope, EDAX and the results tabulated. It was found, that lower pulse-on time and medium pulse-off time leads to less rapid quenching and subsequent improvement in surface finish, less craters, voids. This prevents potential sites for defect and weakening of material by filling with cu-zinc particles for unbounded tungsten particle.

Abstract: Testing material specimen on impact using high speed puncture machine can be used to observe the ability of material to withstand under a certain impact speed by looking at the energy required to tear the material. Other detail parameters such as stress, strain and tearing development on impact cannot be seen or measured. This paper presents a finite element method approach to see the strain history and the tearing sequence that cannot be obtained during impact puncture testing of plastic material (Polyethylene Terephthalate / PET). Simulations in different speed; 10 m/s (36 km/h) and 20 m/s (72 km/h) are performed employing a dynamic-explicit Impact finite element program suite. The simulations are able to capture the tearing process, to see the strain histories of tearing region and to predict the tearing pattern. The tearing pattern simulation results are verified by comparing with that from experiment.

Abstract: Characterization of feedstocks for powder injection molding of SiC_p-reinforced aluminium composite, as potential use for automotive and light-weight applications, has been studied in this research. Al-4.5 wt.% Cu powder, SiC_p and polymeric binder were pre-mixed and compounded using a twin screw extruder at 170oC prior to powder injection molding at 170 oC. Effects of varied solid loadings at 52, 55 and 58% on green properties of the feedstocks have been investigated. Experimental results showed that compounding followed by powder injection molding allowed uniform distribution of SiC_p surrounding the aluminium powder. It was found that higher solid loading improved bulk density while hardness values were observed to be similar. Molded specimens of 55% solid loading provided the optimum bend strength and strain at failure. Moreover, it was observed that the opposing abrasive property with angular shape of SiC_p resulted in SiC_p scratching effect, leading to irregular surface of aluminium powder after injection molding. This consequence and molding porosity were expected to be responsible for relatively low density of the molded specimens, giving the difficulty in molding at higher solid loading.

Abstract: A front bumper of a car is attached to the main vehicle structure by using hollow metals. This paper investigates various cross section profiles that can be used as bumper attachments. Several cross section profiles with the same circumscribe are firstly selected, i.e. round, square, triangular and hexagonal shape cross sections. Each model is then numerically impacted in an axial mode as if it is crashed into a rigid wall with an impacting velocity of 10 m/s or equivalent to 36 m/s. A dynamic-explicit open source software Impact is employed to do the simulation. The displacement results are monitored in the first 1:8ms then compared to the models that can absorb better showing the less displaced in certain examination nodes. The results shows that the triangle cross section performs better compared to other cross sections.

Abstract: The transmittance, absorbance, and reflectance of PMMA/TiO2 composites, in different weight percentage of TiO2, prepared by a solution cast technique are investigated. The Optical transmission and UV-VIS absorption spectra have been recorded in the wavelength range 200nm-800nm for different compositions of TiO2 doped PMMA polyfilms. The absorption coefficient, optical (Direct/Indirect) energy gap, Refractive index, Optical Dielectric constant, Constant B, ratio of carrier concentration to the effective mass have been evaluated. The effects of doping percentage of TiO2 on these parameters have been discussed and behaviors of all parameters are investigated.

Abstract: Polymer composite of polyvinyl alcohol (PVA), Aluminum Iodide have been prepared by solution cast method for different doping concentrations. The absorption of pure and doped films have been investigated in the visible and ultraviolent wavelength regions. It was found that the optical absorption is due to direct and indirect transitions, and the optical energy gaps values shifted to lower energies on Aluminum Iodide doping concentration for all transitions, while the band edge width of the tail localized states increase with increasing Aluminum Iodide concentration. The band gap of all films shows to be decrease after thermal treatment. The optical constants refractive index n, extinction coefficient k, the complex dielectric constant have been also calculated. The dielectric constant increased in the composite samples as compared with the pure PVA sample prepared by the same method.

Abstract: The structural and optical properties of virgin and gamma rays irradiation on aromatic polymers (PET, PES and Kapton) at various doses varying from 16 to 300kGy. The optical and Structural studies have been observed by using UV-VIS Spectroscopy and Powder X- Ray Diffration techniques. The diffraction pattern of virgin samples shows that polymers are semi crystalline in nature. But due to irradiation, the overall crystalline peak intensity and crystallite size is found to be increased with increasing dose. The UV-Visible absorption spectra show the existence of the maximum absorption, their shifting and broadening as a result of gamma irradiation has been discussed. Finally the value of direct and indirect band gap in virgin and gamma irradiated on aromatic polymers has been decreased.

Abstract: It’s necessary to research and analyze the correctness of internal stress measurement, in order to effectively deal with the measurement problem of stress field and rightly describe the distribution character of stress in aluminum alloy thick plate. Firstly, the total uncertainty of stress calculation in layer removal method (LRM) is determined by experimental error and model error, and less than ±10MPa, in which the accuracy of experiment is high. Secondly, in the integral calculation of LRM, a modified function is proposed by the multi-methods of simulation and experiment, and can compensate the deviation resulted from unpredictable error for experimental conditions. Then the multi-methods achieve the value of X-ray surface stress, simulation calculation and experimental results to consistent, the correctness of experimental calculation is enhanced. The research presents that the LRM can exactly describe distribution of internal stress in thick plate under special experiment conditions.

Abstract: 25% Zinc doped Cadmium Telluride thin films were prepared using Stacked Elemental Layer method. The structural studies were conducted by the X-Ray technique and the results were compared with standard data which confirmed the presence of mixed phases (CdTe, ZnTe and CdZnTe) in the stack annealed at 425°C. Transmittance spectra depicted the effect of Zn on the optical properties of CdTe thin film. The calculated band gaps from the transmittance spectra were lie between 1.42 and 1.51eV. Scanning Electron Microscope images elucidated the influence of Zn on surface morphology and the grain growth for CdTe thin films.

Abstract: In this work, ZnO nanorod has been grown by hydrothermal solution method. The samples were prepared by two stages. The first stage was seeding process where the ZnO nanoparticles are spin-casted onto ITO coated glasses and the second stage was hydrothermal process. The morphology of nanorods were investigated by using scanning electron microscope (SEM) and different of length and diameter of nanorods with different growth durations have been observed. The differences of diameters and aspect ratio of nanorods have affected the optical and electrical properties of the ZnO-coated thin film with dye due to its surface area and morphologies of growth rod. Aspect ratio of ZnO nanorods increases by increasing the reaction time (growth time). From the band gap energy study, the thin film with the longest ZnO nanorods growth time has the lowest band gap energy (3.55 eV). The higher aspect ratio of the nanorod affected the conductivity, by increasing the conductivity when combined with N3 dye.