Advanced Materials Research Vol. 845

Abstract: Al-Si alloys are the most common aluminium cast products owing to their high resistance to hot cracking and excellence fluidity during the molten state. They play important roles in aerospace, automobile and structural industries where high strength to weigh ratio, superior heat conductivity and good corrosion resistance applications are necessary. Alloying elements such as copper, magnesium, zinc and nickel are added into the Al-Si alloys for further strength enhancement. However, impurities such as iron are often present in Al-Si alloys, forming brittle intermetallic phases and hence reducing the mechanical strength of the alloys. In this paper, previous studies on the effects of alloying elements on physical and mechanical characteristics of Al-Si alloys will be accounted. Moreover, a comprehensive review on the Al-Si alloy casting methods will also be included.

Abstract: In this investigation, the mechanical behavior of sandwich hollow cylinders under internal pressure is carried out numerically. Functionally Graded (FG) foam core sandwich hollow cylinders are fabricated by employing filament winding technique with [±55] carbon fiber/epoxy as skins with the FG foam core made using centrifugal casting technique of polyurethane foam with epoxy resin. A finite element (FE) model is developed employing a FE commercial code to determine the stresses and deformations. Numerical analysis is performed to find the effect of one particular functional grading on the deformation and stresses. The results are compared with similar tubes using uniform PU foam core. The results show that grading the foam core affects the displacements and stresses in a significant way. The FG foam sandwich core tube possesses a lower displacement magnitude and higher maximum stresses taking into account the mass of the two types of pipes and rigidity compared to uniform PU foam core under internal pressure of 10 MPa.

Abstract: A laminated beam containing an initial delamination subjected to thermal gradient is analyzed on the basis of classical beam theory. The axial forces are induced in the parts of the constituent beams above and below the delamination. For the case where crack faces are open, a nonlinear equation for determining the in-plane forces is derived by modeling the delaminated part as two lapped beams hinged at both ends, and by imposing the compatibility condition of the deformations of the two beams. Numerical solutions are obtained for some model beams. It is shown that the relative displacement at the center of the delamination increases gradually with the increase very rapidly, i.e., local delamination buckling occurs. Energy release rate is small for temperature gradient below the critical value, but it takes a large value when the temperature gradient is increased beyond the critical value.

Abstract: Cross-linked polyethylene is widely used as electrical insulation because of its excellent electrical properties such as low dielectric constant, low dielectric loss and also due to its excellent chemical resistance and mechanical flexibility. Nevertheless, the most important reason for failure of high voltage equipment is due to its insulation failure. The electrical properties of an insulator are affected by the presence of cavities within the insulating material, in particular with regard to the electric field and potential distributions. In this paper, the electric field and potential distributions in high voltage cables containing single and multiple cavities are studied. Three different insulating media, namely PE, XLPE, and PVC was modeled. COMSOL software which utilises the finite element method (FEM) was used to carry out the simulation. An 11kV underground cable was modeled in 3D for better observation and analyses of the generated voltage and field distributions. The results show that the electric field is affected by the presence of cavities in the insulation. Furthermore, the field strength and uniformity are also affected by whether cavities are radially or axially aligned, as well as the type of the insulating solid. The effect of insulator type due the presence of cavities was seen most prevalent in PVC followed by PE and then XLPE.

Abstract: Nickel enables nucleation and growth of well oriented diamond crystals from the small lattice mismatch between nickel and diamond. However, its solubility for carbon causes carbon loss during diamond deposition and, consequently, results in poor nucleation density. In this study, carburizing of Ni/WC-Co specimens in high temperature furnace with inert gas atmosphere was adopted to provide nickel with sufficient carbon prior to diamond deposition. This process was carried out using charcoal powder as source of carbon at different treatment temperatures (750°C and 850°C) and durations (20min and 60min). Effect of the process in altering the nickel layer composition was characterized by microscopy, element analysis, and phase identification techniques. Results show that carburization leads to formation of metallic phases, such as nickel carbide and nickel cobalt, which are considered beneficial for diamond nucleation and growth.

Abstract: This paper proposes a new iterative method to achieve an optimally fitting plate for pre-operative planning purposes. The proposed method involves integration of four commercially available software tools, Matlab, Rapidform2006, SolidWorks and ANSYS, each performing specific tasks to obtain a plate shape that fits optimally for an individual tibia and is mechanically safe. A typical challenge when crossing multiple platforms is to ensure correct data transfer. We present an example of the implementation of the proposed method to demonstrate successful data transfer between the four platforms and the feasibility of the method.

Abstract: Analysis of structural and mechanical properties of cubic zirconia was conducted using a simulation code (GULP) that is based on the concept of energy minimization. Some mechanical properties of zirconia were computed such as elastic constant tensors, shear modulus, bulk modulus, Youngs modulus and others along the lattice planes. The stiffness constants obtained (C₁₁, C₂₂ and C₃₃) were equal, implying that zirconia is flexible in all directions of the lattice plane. The predicted bulk modulus was 285 GPa with the shear modulus ranging between 78 and 105 GPa. The Youngs modulus of 577 GPa indicates higher ductile behavior as confirmed by the compressibility of 0.0035. The Poissons ratio with values ranging from 0.16 to 0.31 may indicate high anisotropy. Other acoustic features related to mechanical properties of zirconia such as velocity wave ratio, stress matrix dielectric constants and others were also analyzed. All estimations obtained show good agreement to recent measured properties of zirconia.

Abstract: Transition metal chalcogenide molybdenum ditelluride (MoTe₂) thin films have been electrosynthesized cathodically on indium tin oxide-coated (ITO) conducting glass substrates from ammonaical solution of H₂MoO₄ and TeO₂. The electrode potential was varied while the bath temperature was maintained at 40±1 oC and deposition time of 30 minutes. Highly textured MoTe₂ films with polycrystalline nature are observed by X-ray diffraction analysis. Compositional analysis by EDX gives their stoichiometric relationships. Scanning electron microscope (SEM) was used to study surface morphology and shows that the films are smooth, uniform and useful for device fabrication. The optical absorption spectra showed that the material has an indirect band-gap value of 1.91-2.04 eV with different electrode potential. Besides, the film exhibited p-type semiconductor behavior. Keywords: Molybdenum ditelluride; Thin films; Electrodepositon; Solar cell;

Abstract: This paper deals with the mechanical properties in conventional heat treatment of Al (6061)-B₄C-Graphite. Aluminium Metal Matrix Composites (MMC) is fabricated through two step stir casting method. The composites were fabricated with various volume percentage levels as Aluminium reinforced with (5, 10 &15%) Boron Carbide and (5,10 & 15%) of Graphite. Fabricated composites were subjected to conventional heat treatment for enhancing the mechanical properties. Influences of Graphite reinforcement on mechanical properties of Aluminum-Boron carbide composites were analyzed. The microstructure studies were also carried out. It is observed that increasing the graphite content within the aluminum matrix results in significant decrease in ductility, hardness, ultimate tensile strength. The addition of boron carbide conversely increased the hardness of the composites.

Abstract: In this changing global scenario, modification, transplantation, and replacement can be the eternal solution for most of the problems in the medical field. Hence replacement technique finds a very prominent place in medicine as a remedy having closely tied up with biomechanics. One of the most important joints in the human body is the hip joint, the big and complex joint. Many researches were conducted and many are in progress, but most of these works use simplified models with either 2D or 3D approaches. The hip joint is formed by four components like femoral head cortical bone, stem, and neck. In this system we can find orthotropic and isotropic materials working together. The main objective of this research is to develop a three dimensional surface and solid finite element model of the hip joint to predict stresses in its individual components. This model is a geometric non-linear model, which helps us understand its structural mechanical behavior, seeming to suggest with advanced research in the future new hip joint prosthesis, as well as to prove the prosthesis joint interaction before being implanted in the patient. This research explains a complete human hip joint model without cartilaginous tissue, using ANSYS 10.0 Multiphysics Analysis for nine different postures in hip joint using three different materials (CoCr, Ti6Al4V, and UHMWPE) to calculate fatigue life. The result obtained from the analysis of surface model and solid model serve to help in predicting the life cycle, surface characteristics, shear stress in XY plane, stress concentration and areas that are prone to failure. Von Mises stress on the surface of our model facilitates us to equip and design an optimized prosthesis device having unique materials composition , with a highly bio-compatible and durable alloy at a low cost could be produced. In this way, a first important step towards the structural characterization of human hip joint has been developed.