Advanced Materials Research Vols. 47-50

Abstract: Due to environmental reasons and their acceptable mechanical properties, natural fiber based polymer composites have been increasingly used in various applications, e.g. housing materials, automotive parts. However, their low thermal resistance and fire behavior limit the use of these materials. In this work, magnesium hydroxide (Mg(OH)2), as a flame retardant, was incorporated into sisal/polypropylene composites. Ratio of sisal fiber to Mg(OH)2 in each composite sample was varied. Maleic anhydride grafted polypropylene (MAPP) was also used to improve the interface of polypropylene and fillers. Flammability and thermal behavior of the composites were examined using a horizontal burning test and thermo gravimetric analyzer, respectively. Morphology and mechanical properties of the composites were also investigated.

Abstract: Impact event monitoring and source location in some critical structures. The current work evaluated the feasibility and limitation of using fiber Bragg gratings (FBGs) for this purpose. Impact testing carried out on a cold rolled aluminum plate showed that impact event monitoring with the FBGs is feasible with the current intensity modulation interrogation method. Source location is successful at part of the impact location but not at the others. This phenomenon is caused by the complex wave propagation pattern on the plate so that differently oriented FBGs receive the signal from the same impact at different time.

Abstract: This study succeeds to replicate a micro-feature by ultrasonic nanoimprint. The conjunction effect of the pressure and the ultrasonic vibration enables flowing of plastic into a more precise micro-feature of the metal mold. The longitudinal wave generated by an ultrasonic system of the frequency 35KMz and output power 900W. The micro-feature of the Ni mold insert used in the experiment is a groove shape. The groove’s width is 49 µm and its depth is 25 µm. The PMMA, PC and PP are chosen with the replication materials. This study also discusses the replication properties of plastic film by different processing parameters (delay pressure, fusion pressure, embossing pressure, delay time, fusion time and embossing time).

Abstract: In this article, we report the fabrication of novel poly(L-lactide) (PLLA) nanocomposites based on PLLA and magnesium-aluminium layered double hydroxides (MgAl-LDH) which were mixed the polylactide with carboxyl end group (PLA-COOH) in acetone . Both the X-ray diffraction data and transmission electron microscopy images of the PLLA/LDH nanocomposites indicate that most of the LDH layers were disorderly exfoliated into the PLLA matrix. The thermal degradation behaviors of PLLA and its nanocomposites were studied using thermal gravimetric analysis (TGA) under nitrogen atmosphere at heating rates from 5 to 40 °C/min. The TGA profiles of the PLLA/LDH nanocomposites show less thermal stability than that of neat PLLA due to the presence of Mg and Al which has a drastic influence on thermal stability of PLLA. The activation energy of PLLA, 1 wt% and 3 wt% PLLA/LDH nanocomposites were 158, 140 and 130 kJ/mol, respectively.

Abstract: In this work, an application of wide-gap updoed-Al0.22Ga0.78As bulk to perform the field-plate gate (FP-gate) on Al0.22Ga0.78As/In16Ga84As/Al0.22Ga0.78As DH-HEMTs was investigated. The simulated FPG-devices with a bulk thickness of 1200 Å, exhibit an excellent dispersing property to the electric field peak under gate electrode near to drain side, hence, the breakdown characteristics were effectively improved. Measured gate-diode performance of FPG-device presents a higher breakdown voltage (VBR) of -25.5 V than devices with single recess (SRG-device). Enhancement of device breakdown is contributive to microwave power performances. At 2.4 GHz load-pull measurement of studied devices which were biased at class AB operation, the saturated output power (POUT), power gain (GP) and power-added efficiency (PAE) were 13.06 dBm (202 mW/mm), 12.8 db and 47.3% for FPG-device. These measured results of SRG-device were 10.3 dBm(107 mW/mm), 13.2 db and 38.5%, According to the simulated results, FPG-devices structuring with a bulk layer exhibit excellent performance for high breakdown and microwave power operation.

Abstract: Features of penetration into copper barrier and in the barrier made of iron alloys are viewed. At creation of "channel" elements initiation is viewed. Regulation of superdeep penetration due to preliminary refrigeration strikers and barrier up to-1960С is shown. Expenses of energy for superdeep penetration are reduced ≈ 180 times.

Abstract: In this research, vetiver grass was used as a filler in polypropylene (PP) composite. Chemical treatment was done to modify fiber surface. Natural rubber (NR) and EPDM rubber at various contents were used as an impact modifier of the composites. The composites were prepared by using an injection molding. By adding NR or EPDM to PP composites, a significant increase in the impact strength and elongation at break was observed in PP composite with rubber content more than 20% by weight. However, the tensile strength and Young’s modulus of the composites decrease with increasing rubber contents. Nevertheless, the tensile strength and Young’s modulus of the composites with NR or EPDM are still higher than those of PP up to 10% and 20% rubber contents, respectively. Comparisons between NR and EPDM rubber on the mechanical properties of the composites were elucidated.

Abstract: An impact monitoring system using an array of fibre Bragg grating (FBG) sensors has been established on a wind turbine blade. The effect of the locations and detection capability of the FBG have been investigated. The possibility to identify the location of an impact is also discussed. This preliminary work may shed some light on how to establish an optimal monitoring system with a minimum number of sensors while achieving the acceptable sensitivity and coverage. With such a system, the corresponding strain history and occurrence of local damage can be monitored, thus helping to narrow down the scope of more detailed examination during an overhaul and enabling the integrity of a wind turbine blade to be more reliably assessed and monitored.

Abstract: Cellulose nano whiskers (CNW) are recently known for their tremendous applicability in development of eco-friendly material for various applications. Present attempt was aimed to extract the nano crystals of cellulose from grass of Korea and fabricate the composites with poly (lactic acid) in presence of compatibilizer after modification. Functional group variation, thermal behavior, surface morphology, and crystallinity were monitored by FT-IR, TGA, SEM, and XRD respectively. The water sensitivity measurements were also carried out for study of moisture resistance of composites. It was found that CNW have lower thermal stability than alkali treated long fiber whereas the crystalline nature of composites decreased significantly. The effect of modification of whiskers on the mechanical properties was also discussed in which increase in modulus was observed.

Abstract: This study demonstrates the replication property and surface roughness for metal micro-mold that combines the replica molding (REM) and electroforming techniques. The micro-mold firstly uses the silicon wafer to fabricate the master mold by UV-LIGA method, and then uses the sputtering method to sputter the Ni element as the seed layer on the surface of master mold. The electroforming method manufactures the Ni mold insert from the master mold with seed layer. Finally, this study uses the PDMS material to replicate the micro-feature from the Ni mold insert by replica molding. This study indicates the replication property and surface roughness of different micro-feature shapes and sizes (concave and convex) for Ni mold insert and molded PDMS.