Applied Mechanics and Materials Vols. 110-116

Abstract: This paper deals with forced vibration behavior of adhesively bonded single-lap joint theoretically and experimentally. The finite element analysis (FEA) software was used to predict the natural frequencies and frequency response functions (FRFs) of the joint. The dynamic test software and the data acquisition hardware were used in experimental measurement of the dynamic response of the joint. It is shown that the natural frequencies of the joint from experiment are lower than those predicted using finite element analysis. It is also found that the measued FRFs are close to the predicted FRFs for the first two modes of vibration of the joint. Above the second mode of vibration, there is considerable discrepancy between the measured and predicted FRFs.

Abstract: Welding is one of the most significant causes of residual stresses and typically produces large tensile stresses whose maximum value can be approximately equal to the yield strength of the materials being joined. These large tensile stresses are often responsible for premature component failure. Metallurgical welding joints are extensively used in the fabrication industry, including ships, offshore structures, steel bridge, and pressure vessels. In this study, residual stresses in welded specimens of AL–6061 were evaluated by using ACOUSTIC EMISSION method which is one of the nondestructive tests. In this work, AE signals formed during the tensile test of welded specimens were investigated. The results show that AE signals in specimens which have large amount of residual stress were detected in less load.

Abstract: In this paper, a new mathematical programming model is developed to address common issues relating to single-stage CONstant-Work-In-Process based production lines. A Ge-netic Algorithm (GA) approach is then proposed to directly solve the model in order to simultaneously determines the optimal job sequence and WIP level. Unlike many existing approaches, which are based on deterministic search algorithms such as nonlinear programming and mixed integer programming, our proposed method does not rely on a linearized or simplified model of the system. results from a comprehensive numerical example indicate computational efficiency and validation of our method.

Abstract: In this paper, electroosmotic phenomena in power law fluids are investigated. This assumption is applicable in many cases such as blood. Flow channels assumed to be in nanoscale. Navier-Stokes, Poisson-Boltzmann and electrochemical equilibrium equations govern these phenomena. It is notable that, these governing equations should be modified according to fluid complexity. Electroosmotic phenomena occur in the presence of electric double layer (EDL). Potential in the edge of the inner layer (stern layer) is called zeta potential. In this paper, according to follow the applicability of the subject, zeta potential is assumed to be so small, that makes the Poisson-Boltzmann equation linear and be able to solve analytically. Method employed for analytical solution is based on developed Bessel differential equation. This paper aims to investigate the fluid properties, zeta potential and Debye-Huckel parameter effect on the viscosity, electroosmotic mobility and velocity field in the nanotube. These expected achievements help us to study the properties of blood and some other non-Newtonian fluids more precisely.

Abstract: Mechanochemical synthesis of two or more different precursors is a simple method to prepare metallic alloys, polymer and ceramic composite materials. This mechanical reaction based synthesis also has been employed to produce hydroxyapatite (HA) powder for bone implant application. In this present study, we employed mechanochemical method to synthesize hydroxyapatite nanopowder from dry mixture of calcium hydroxide (Ca (OH)₂) and di-ammonium hydrogen phosphate [(NH₄)₂HPO₄] powders. The effect of mechanochemical process on powder properties was investigated. Three rotation speeds of 170 rpm (M1), 270 rpm (M2) and 370 rpm (M3) were chose with 15 hours milling time respectively. The milling time at 370 rpm (M3) was extended to 30 hours (T1) and 60 hours (T2). Characterization of nanopowders were accomplished by Fourier transform infrared (FTIR), X-ray diffraction (XRD), nanosizer analysis, field emission scanning electron microscope (FESEM) and transmission electron microscope (TEM). Rotation speed and milling time affected the obtained powders with nanocrystallite HA structure. The narrow peaks appeared with the incremental of crystallite size (9 – 21 nm) and crystallinity (21-59%) when the rotation speed was increased to 370 rpm (M3). However, particle size distribution (322-192 nm) was decreased with the rotation speed. Morphological evaluation indicated that the average particle size of resultant powder which consists of agglomerate crystals and irregular shapes reached about 17 - 36 nm. The as synthesized nanopowder showed that 370 rpm at 15 hours of milling is the suitable parameter to be applied for hydroxyapatite nanopowder synthesis in mechanochemical method.

Abstract: This paper discusses the dependence of microstructure and mechanical properties of sintered biphasic calcium phosphate (BCP) on sintering temperature and compacting pressure of BCP dense bodies. BCP nanopowders were prepared via hydrothermal method using eggshell as the calcium source, followed by compaction into circular disc shape at various pressure and sintered pressureless in air at various sintering temperatures. X-ray diffraction analysis of nanopowders revealed the existences of hydroxyapatite (HA) as the main phase, with β-tricalcium phosphate (β-TCP) and calcium pyrophosphate (CPP) as the second phases. Morphological evaluation by scanning electron microscopy showed BCP exhibited uniform microstructure at low temperature and coalescence of pores and exaggerated grain growth at increasing temperature. Mechanical strength tests shown by compression strength and Vickers’ hardness test revealed an increase of strength with increasing temperature of up to 1100°C, after which it dropped. Mechanical strength also proved to be better with higher compacting pressure.

Abstract: How nanoparticle concentration affects on thermal and hydrodynamic parameters of a nanofluid (water+Al₂O₃) is numerically investigated in a horizontal tube while these parameters are impressed by buoyancy force under constant heat flux and mass flow rate. Comparisons with previously published experimental and numerical works on mixed convection in horizontal tubes show good agreements between the results. Results which are obtained using the two – phase mixture model indicate that adding the nanoparticles causes changes in the properties of nanofluid and finally increases the temperature of the flow. Whereas, dimensionless pressure drop along the tube length could increase with the nanoparticle concentration.

Abstract: Fully developed laminar mixed convection of a nanofluid (water/Al₂O₃) in a horizontal curved tube is numerically investigated. Three-dimensional elliptic governing equations have been solved to show how nanoparticle concentration affects on thermal and hydrodynamic parameters while these parameters are impressed by centrifugal and buoyancy forces under constant mass flow rate and heat flux. Comparisons with previously published experimental works on horizontal curved tubes show good agreements between the results. Results which are obtained using the two – phase mixture model indicate that adding the nanoparticles causes changes in the properties of nanofluid and finally increases the temperature of the flow. Furthermore, increasing nanoparticles volume fraction at first augments the heat transfer coefficient of nanofluid and then, for higher concentration of particles, decreases this thermal parameter of nanofluid.

Abstract: In this paper, Poisson-Boltzmann equation and Navier-Stokes equation will be solved by Homotopy Perturbation method (HPM). Working fluid in this paper is assumed to be non-Newtonian which follows power law model. Zeta potential that is used for the potential in near wall area of a tube will be small enough in order to use some simplifications. In this paper, Poisson-Boltzmann equation for a 30 nm diameter nanotube with large zeta potential has been solved by Homotopy Perturbation Method (HPM). According to the literature, results have been compared with numerical solutions and consistency of the results has been considered. Results show that HPM can approach to this problem reliably.

Abstract: Anofluids are suspensions of metallic or nonmetallic nanopowders in base liquid and can be employed to increase heat transfer rate in various applications. In this work turbulent flow forced convection heat transfer of Al₂O₃-water nanofluid inside an annular tube with variable wall temperature was investigated experimentally. The Nusselt number of nanofluid was obtained for various Reynolds numbers and nanoparticle concentrations at atmospheric pressure. The addition of nanoparticles in water enhances heat transfer coefficient and the enhancement increases with increase in the nanoparticle concentration and flow rate. Experimental results emphasize the enhancement of heat transfer due to nanoparticles presence in the fluid.