Applied Mechanics and Materials Vol. 736

Abstract: Aluminum-Copper-Lithium alloys are of strategic important [1] in lightweight aerospace structures due to their high specific modulus and specific strength and are under consideration for one of the potential choices for Korea Space Launch Vehicle structure. However, this is one of the most complicated alloys due to the precipitation of a large number of second phase particles. In this study, the precipitation kinetics of an Al-4.3%Cu-1.2%Li alloy was studied by differential scanning calorimetry (DSC) technique since precipitation plays an important role for hardening of this alloy. Several models including Kissinger’s, Starink’s and Chaturvedi’s were used to obtain the activation energy and precipitation kinetics.

Abstract: In order to study the differences in load-carrying capacity of surface-textured soft materials and stiff materials, a theoretical hydrodynamic model considering elastic deformation is developed for numerical simulation analysis. Minimum oil film thickness at a certain load is computed as an index to evaluate the load-carrying capacity of textured sliding surfaces made of soft materials and stiff materials. The results show that the elastic modulus affects greatly on the load-carrying capacity. In the case of the surface texture with a dimple aspect of 0.05, textured soft materials has a higher load-carrying capacity than that of the stiff materials. In the case of the surface texture with a dimple aspect of 0.01 and only under high loads, textured stiff materials provides a better load-carrying capacity than that of the soft materials.

Abstract: Had been synthesized different composites from recycled polypropylene (rPP) using Pineapple leave Fiber (PaF), commercial Bentonite (comBen) and zinc borate (ZB). In the optimum formula with ratio rPP/PaF/comBen was 65/15/20 (w/w) and 5 % ZB of different composites are measured their flame retardancy, tensile strength (TS) and biodegradability. This new rPP/PaF/comBen/ZB composites materials have heat combustion (Hg), tensile strength (TS) and biodegradability better than the starting materials. The Hg of rPP/PaF/comBen/ZB decreased to 28%. The TS of rPP/PaF/comBen/ZB according to ASTM D 638 arised to 83%. The biodegradability of rPP/PaF/comBen/ZB in burial test arised to 15.7%.

Abstract: This study was carried out to investigate the effects of grain size on mechanical properties in Cu-Sn foil with a thickness of 30 um. The grain size was varied from approximately 7 um to 50 um using heat treatment at 773 K for 2 h to 24 h in a vacuum atmosphere. Tensile test was carried out at room temperature with strain rate of 1mm/min. Typical yield drop phenomenon was observed. Mechanical properties were found to be strongly affected by microstructural features including grain size. The yield strength and tensile strength gradually decreased with increasing the grain size. The strain to fracture also decreased by grain growth. These results could be explained by not only the grain size dependence of yield strength but also the ratio of thickness to grain size dependence of yield strength.

Abstract: In this work, a comparative study of the microstructure and mechanical properties of Al-8Fe based bulk alloys fabricated by three different rapid solidification methods and subsequent hot extrusion was carried out. Spray forming, gas atomization, and melt spinning methods were used as techniques for rapid solidification having various cooling rates. Equiaxed grains containing Al-Fe, Al-Fe-(Mo, V), and Al-Zr phase particles were characterized. The yield strength of the melt spun and extruded specimen was estimated to approximately 800 MPa at room temperature, a value which is roughly 1.5 times higher than that obtained for the atomized and extruded specimen and roughly 2.5 times higher than for the spray formed and extruded specimen. The higher strength of the melt spun and extruded specimen originated from a finer microstructure compared to the atomized and extruded specimen and the spray formed and extruded specimen.

Abstract: In this paper, we consider the deformation of multilayer bars in torsion and tension. Thus, in the analyzed strength calculations rod having a rectangular cross section of the composite material. Namely, the choice of the structure of the material, satisfy the specifications of the rod in terms of stress-strain state in a torsion-bending coherence taking into account features of the composite materials. On the example with a layered core, being under the influence of centrifugal forces shows the effect of shifts between the layers on the redistribution of normal and shear stresses in layers. Depending on the magnitude of the anisotropy coefficient of the material used, normal and shear stresses in the outer layers is increased by 2-5 times. Comparison of these values ​​with limit stress for these layers allows you to select how the reinforcement of these layers. Collection of data about the influence of the stiffness of the individual layers by an angle promotion rod and durability allow the optimal folding of the reinforcing layers and the type of reinforcement and matrix.

Abstract: Palm oil and methanol do not form a single phase mixture in transesterification process in stirred tank due to a poor surface contact between them; hence give a relatively slow mixing process of the mixing. Introduction of new baffles in the stirred tank with a fractal pattern due to the fractal shape can give a high turbulent level when a fluid flow through the fractal pattern is the new idea in optimizing the using of the fractal pattern in engineering especially in mixing industries. Hence, in the present study, a new concept of baffles with a fractal design was proposed to enhance a palm oil-methanol mixing in stirred tank. In order to achieve the objective, the simulation of palm oil-methanol mixing was carried out by using ANSYS Fluent software. The simulation was carrying out primarily in the stirred tank equipped with the fractal baffles and the levels of mixing were observed at 60, 120, 180 and 240 seconds after the beginning of introduction of methanol in the stirred tank. An effectiveness of the fractal baffles will be evaluated by determining the Coefficient of Variation (COV). The simulation results also were compared in term of homogeneity level of palm oil-methanol mixing to the normal baffles in order to determine the significant effect of the fractal baffles. Based on the simulation results, the value of COV for the mixing process in the stirred tank equipped with fractal baffles at the selected time interval are 0.066, 0.0436, 0.0326 and 0.0226 respectively. Since the values of COV between 0.01 and 0.05 are a reasonable target for many industry applications, the results for new approach of stirred tank with fractal baffles represent completely homogeneous mixing for the palm oil-methanol simulated in this study. Definitely this new approach of fractal baffles gave better results because of lower number of COV compared to the stirred tank with normal baffles.

Abstract: This paper presents the results of a analysis of rough thermo-elastohydrodynamic lubrication (TEHL) of line contact with non-Newtonian lubricant blended with Al₂O₃ nanoparticles and MoS2 microparticles. The simultaneous systems of time independent modified Reynolds equation, elasticity equation, load carrying with micro particle equation and energy equation were solved numerically using multigrid multilevel with full approximation technique. In this study, the effect of Al₂O₃ nanoparticle and MoS₂ microparticle additives and surface roughness were implemented to obtain film thickness, film pressure, film temperature, friction coefficient and load carrying with microparticle in the contact region. The simulation results showed that the maximum film temperature and friction coefficient increase slightly but the minimum film thickness decreases slightly with an increase in Al₂O₃ nanoparticle concentration due to thermal enhancement of nanofluid. For increasing of microparticle concentration, the minimum film thickness and friction coefficient decrease because the increasing of friction heating of MoS₂ microparticle.

Abstract: The SnO₂ doping can increase the nonlinear coefficients of ZnO varistors, the highest α value is achieved at the 0.75 wt% doping level samples sintered at 1150^oC. The improved I-V nonlinearity may be attributed to the donor behavior of Sn⁴⁺ ions. The SnO₂ doping can enhance the ZnO grain growth that lower the breakdown field of doped samples.