Advanced Materials Research Vol. 445

Abstract: This paper focuses on the mechanical properties of Titanium Carbide (TiC) particulate reinforced aluminium-silicon alloy matrix composite subjected to mould vibration during solidification. In this experimental study, mould vibration is applied to TiC particulate reinforced LM6 alloy matrix composites with a wide range of frequencies. TiC particulate reinforced LM6 alloy matrix composites are fabricated by adding different particulate weight fraction of TiC in the matrix by carbon dioxide molding process. Mechanical properties such as tensile strength, hardness, are determined and microstructural features are analyzed through SEM. Besides, fracture surface analysis has been performed to characterize the morphological aspects of the test samples after tensile testing. Preliminary works show that the mechanical properties have been improved with 10.2Hz frequency when compared with the gravity sand-castings without vibration.

Abstract: Highly [00 textured KSr₂Nb₅O₁₅ (KSN) ceramic fibers were fabricated by a combination of novel alginate gelation method and templated grain growth using acicular KSr₂Nb₅O₁₅ template particles. Fibers were drawn from alginate based slurries without or with 25 and 100wt% KSN template particles. A texture fraction of 0.90 was obtained in the case of 25 wt% and a single crystal like texture was obtained in the case of 100wt%. Piezocomposites with 1-3 connectivity were prepared from the KSN fibers and their electrical and electromechanical properties were investigated. Dielectric constant of 140, piezoelectric charge coefficient of 45 pC/N, remnant polarization of 16.6 μC/cm² and electric field induced strain of up to 0.035% were obtained from piezocomposites with textured fibers.

Abstract: Previous work has shown the importance of the mechanical behaviour of coatings and thin materals, where the elastic properties vary in depth. Such coatings and materials are investigated under the broad subject of Functionally Graded Materials (FGMs). There has been also a vast interest in the general coupled field analysis of thermopiezomagnetic materials under which smart piezoelectric and magnetostrictive materials can be studied. The smart materials are often bonded as thin films on host structures for the purpose of sensing and/or actuation. This work aims to combine these two important areas of thermopiezoelectro-magnetism and FGMs. The thermopiezoelectro-magnetic materials are modeled using the finite element method assuming variations in material properties similar to FGMs. The resulting equations of modeling are then applied to an example problem in smart material sensing/actuation.

Abstract: In this study, %7 Li modified and 0.67 % copper oxide added potassium sodium niobate (KNN) ceramics were investigated. Copper oxide was used as a sintering aid. The ceramics were prepared with conventional solid state calcination technique. All samples were crystallized in pure perovskite phase with no additional peak. The density of the samples increased with copper addition and lithium modification. The Curie temperature of KNN ceramics was found to shift to lower temperatures by CuO addition. The Curie temperature was measured as 414°C and 504°C for copper oxide added and lithium modified KNN samples, respectively. The maximum strain of copper oxide added sample was 0.12%, whereas Li modified KL ceramics yielded up to 0.10 %.

Abstract: Perovskites have gained attraction as electrode and interconnect materials for Solid Oxide Fuel Cells (SOFCs) due to their catalytic, ionic and electrical conductivities, chemical and thermal stabilities at higher temperatures. The operation and efficiency of SOFC depends mainly on the electrodes. Each electrode, anode and cathode, has demanding materials selection criteria. State of the art nickel-yittria stabilized zirconia cermet anodes are unable to work efficiently with hydrocarbon fuels and at intermediate operating temperature range (600-800°C). Hence, there is an increasing demand for the development of alternate anode materials to improve the fuel flexibility and efficiency of SOFCs. Perovskite based materials have oxygen ion vacancies depending on composition, temperature, and surrounding crystalline environment that impart mixed ionic and electronic conductivities to them. Since perovskite can accommodate all the elements in the periodic table they can offer excellent catalytic properties. The report is about the present status of perovskites based anode materials for SOFC application.

Abstract: Sliding wear behaviour of Mg alloy AM60 reinforced with Al₂O₃ fibers and particles, i.e, AM60-9% (Al₂O₃)_f and AM60-(9% (Al₂O₃)_f + 4% (Al₂O₃)_p) have been studied by performing boundary lubricated pin on disk tests against AISI 52100 steel counterface under low loads (1.0-5.0 N). The results showed that the material loss from Mg composites tested under 1.0 N and 2.0 N loads was negligible. Under 5.0 N load and after 1.0×10⁵ sliding cycles, AM60-9% (Al₂O₃)_f showed increased volumetric loss whereas under the same conditions AM60-(9% (Al₂O₃)_f + 4% (Al₂O₃)_p) continued to protect the Mg-matrix from damage by the counterface as Al₂O₃ fibre+particle height remained exposed over the Mg matrix by 1.8 μm and acted as load bearing elements. Transfer of Fe particles to the worn surface of Mg composites resulting from extensive counterface damage due to abrasion by hard Al₂O₃ fibres and particles was also detected.

Abstract: The effects of clay loading and the extent of sonication time on water uptake in epoxy-organoclay based nanocomposites have been investigated as a function of exposure time in 3.5% NaCl at room temperature. Three clay loadings (2%, 4%, and 5wt.%) were dispersed in the epoxy resin by 10 and 60 minute sonication. The weight gains in the neat epoxy and the nanocomposites with 2 wt.% and 4 wt.% clay loadings showed a common asymptotic saturation value of 0.72 wt.% after 1000 hours of exposure. The saturation value was independent of sonication time. Nanocomposite with 5% clay loading and 60 minutes sonication exhibited a unique behavior and did not show saturation after 1000 hours of exposure. Scanning electron microscopy of tensile fractured nanocomposite specimens revealed the presence of organoclay aggregates, the size and number of which increased with an increase in clay loading. The Glass transition temperatures (T_g) for the nanocomposites decreased by approximately 20-25C° after 1000 hours of exposure in 3.5% NaCl solution.

Abstract: This paper presents manufacturing and testing of a 1/3-scaled demonstrator of a full-scale thin-shell reflector. The demonstrator reflector is an offset reflector with a diameter of 2 m, and a focal length of 1.6 m, and an offset distance of 0.1 m. The reflector structure is a simple monolithic structure, and consists of a reflector surface and a skirt. The skirt is an integral part of the reflector and used to stiffen the reflector. The demonstrator is made of plain-woven carbon/epoxy by vacuum assisted resin infusion process. It is aimed that the manufactured reflector has a low manufacturing cost, a high precision surface, and demonstrates capability of folding and deploying.

Abstract: There has been a vast interest in the general coupled field analysis of thermopiezoelectro-magnetic materials under which smart piezoelectric, thermopiezoelectric and magnetostrictive materials can be studied. The smart materials are often bonded as thin films on host structures for the purpose of sensing and/or actuation. It is well-known that the placement of sensors and actuators is important in order to obtain the appropriate sensor input and to provide the adequate actuation power. This study aims at modeling the important phenomenon of thermopiezoelectro-magnetism suitable for beam and/or plate type-host structures. The thermopiezoelectro-magnetic materials are modeled using the finite element method and the resulting equations are used for decision making on the best placement of the smart actuators on various host structures.

Abstract: This paper describes the preparation and thermal conductivity characterization of solid glass micro-spheres (SGMs) filled polymer composites. SGMs of different sizes are embedded in epoxy resin to develop composites by hand layup technique. A numerical simulation of the heat-transfer within the composites is made by using finite element method (FEM). Three-dimensional spheres-in-cube lattice array models are constructed to simulate the microstructure of composite materials for various SGM content ranging from 0 to about 27 vol % and the effective thermal conductivities (K_eff) of the composites are estimated. K_eff values are also calculated using some of the existing theoretical models. Finally, guarded heat flow meter test method is used to measure the conductivity of these composites. The simulations are compared with K_eff values obtained from experiments and it is found that the FEM simulations are fairly close to the measured K_eff. This study shows that the incorporation of SGMs results in reduction of conductivity of epoxy resin and thereby improves its thermal insulation capability. Further, the size and content of SGMs influence the extent of reduction of K_eff. Keywords: Composites; Glass Microspheres; FEM; Thermal Conductivity; Simulation