Scientia Iranica
Volume:24 Issue: 6, Nove-Dec 2017

Nanostructured copper-doped fluorapatite (Cux.Ca(10-x).(PO4)6.F2) having crystallite sizes of 19, 29 and 34 nm at x = 0.9, 0.4 and 0.0, respectively, was synthesized by planetary ball milling of CaO, P2O5, CaF2 and CuO powders. Specifications of the products were determined by Fourier transform infrared spectroscopy, field emission scanning electron microscopy, transmission electron microscopy and X-ray diffraction analysis. In-vitro studies and Mossman's Tetrazole Test (MTT) assays were also conducted by incubating Cux.Ca(10-x).(PO4)6.F2 powder into Kokubo’s simulated body fluid (SBF) and against BT-20 cell, respectively, to determine bioactivity and biocompatibility of the material. Antibacterial effects toward Staphylococcus aureus was assessed by the disc diffusion test method. Measurements showed that the rate of formation of fluorapatite was lowered by Cu content. Besides, in vitro experiments showed the same SBF interacted apatite precipitation for all samples. In contrast, MTT assays revealed different behavior for pure fluorapatite and apatite with x=0.9 Cu against BT-20 cell after 24 h of incubation. This highlights increase of fluorapatite cytotoxicity when Cu ion is present in the apatite structure. Copper-doped fluorapatite was, however, desirably antibacterial. This stemmed from copper ions interactions with the bacterial metabolism which resulted in enzymes neutralization and copper-doped fluorapatite antibacterial behavior

This paper presents an alternative boom design for mobile cranes and a method to produce it for minimizing the energy consumption during its production. The main change in the production of the crane booms is the shape of the booms. Normally two symmetric boom parts are manufactured and then these parts are welded by two welding processes, in the proposed design, firstly only one part is manufactured and bended. Therefore one welding will be sufficient and more energy-friendly process is achieved. With the proposed shape, the corner joints are eliminated while forming the boom shape without any need to produce them beforehand. Single welding process is applied to minimize the energy consumption during the manufacturing of the boom, so the welding quality becomes more important. In order to satisfy the welding quality, a welding manipulator is designed and manufactured. By using this welding manipulator used in a closed area and applied filter devices, the harmful gases were not released on the operator and the environment. Finally the energy and time required during the plasma cutting process of boom parts are decreased about 41%, and the energy consumption during the welding process is decreased about 53% compared to the traditional methods.

Cutting tool wear in machining processes reduces the product surface quality, affects on the dimensional and geometrical tolerances and causes tool breakage during the metal cutting. Therefore, online tool wear monitoring is needed to prevent reduction in machining quality.An artificial neural network (ANN) model was developed in this study to predict and simulate the tool flank wear. To reach to this aim, an experiment array was provided using of full factorial method and the tests were conducted on a CNC lathe machine tool. Vibration amplitude of the cutting tool and cutting forces were considered as criterion variables in monitoring the tool flank wear. For designing the model, the cutting parameters, cutting forces and vibration amplitude were defined as model input and tool flank wear was selected as output. The model was also introduced as a simulation block diagram to be used as a useful model in online and automated manufacturing systems. The estimated and measured results were then compared with each other. Based on the comparison results, maximum squared error values are under and the R2 is 1 which it means that the designed model can predict the results with a high and reliable accuracy.

Surface texturing is one of the economic solution of modification die if compared with tool change and hot works. In extrusion die design, it has become increasingly common to add dimple for maintaining lubricant flow along the metal forming process. For that reason, this research was done by embedded a dimples on a taper die sliding contact surface to explore its effectiveness on a finished product of cold extrusion process. Beside, an alternative lubricant from palm oil was also tested and mineral oil was used for comparison purpose. As a result, dimpled taper die may help to decrease the extrusion load of cold extrusion process, so as resulting finer surface roughness of extruded product. Palm oil based lubricant also presents similar results with mineral oil which means that, palm oil has a potential to be considered as new metal forming lubricant in a future.

In this paper, we model the dynamics of microbeams under the effects of electrostatic force, mechanical shock, squeeze film damping (SQFD) and fringing field. A Galerkin-based reduced-order model is used to convert the partial differential equation of motion (PDE) to an ordinary differential equation (ODE). Furthermore, the system dynamics is studied using the developed nonlinear finite element code. Two different simpler models are validated by the results in the literature which are in good compatibility. It is shown that the effect of squeeze film damping can dominate mechanical shock significantly. The response of microbeam to electrostatic actuation is also delayed when damping is included. The simultaneous and sole effects of electrostatic actuation, mechanical shock, squeeze film damping and fringing field are investigated in this study for the first time.

The axisymmetric flow of a nanoparticles-saturated-fluid with existence of thermic radiation over a stretched sheet is investigated. The effects of zero (passive control) as well as nonzero fluxes (active control) of nanoparticles on the plate towards distributions of temperature and volumetric fraction of nanoparticles are investigated together comparatively. Through the supposition of boundary layer, the Navier-Stokes equations are simplified hence converted into non-dimensional form by similarity transformation. A shooting technique is engaged to deal with the emerging nonlinear system of ordinary differential equations numerically in MATLAB software. Several distributions of velocity, thermal energy and volumetric fraction of nanoparticles under zero/nonzero normal flux are graphically demonstrated. The impact of the parameters towards the reduced coefficient of skin friction, and are investigated too. The presence of thermic radiation under consideration of both zero and nonzero normal fluxes have significant effects on the intensification of the flow heat transfer. Thermophoresis enhances the heat conductivity performance in the case of zero fluxes of nanoparticles.

The enhanced strength, fatigue life and corrosion resistance properties of Ti-alloys have attracted many industries for its utilization in various components exposed to extreme operating conditions. The machining of these alloys using conventional machining techniques is one of the main challenges in its wide application in many components and there is an obvious demand to analyse the materials response of these alloys in machining processes by developing simulation based models. The materials behaviour used in simulation of machining processes are usually determined by means of split-Hopkinson-pressure-bar (SHPB) setup.
A 3D thermo-mechanically coupled finite-element (FE) model of SHPB is developed in the current work to analyse materials response of the β-Ti-15333 at selected temperature, strain rate and strain. The obtained materials response of the tested alloys is used in 3D thermo-mechanically coupled FE model of ultrasonically-assisted turning and conventional turning at various tested cutting conditions. The developed FE model was used for parametric analysis of β-Ti-15333 machining and the obtained FE results were in good agreement with experimental results.

Vortex breakdown in compressible flows over a 60-degrees sweep delta wing with a sharp leading edge undergoing pitching oscillations is computationally studied. Emphasis in this study is on possible supersonic vortex breakdown for pitching motion of a delta wing, as well as aerodynamic characteristics behavior during a cycle. Unstructured grid, turbulence model and dual-time implicit time integration are used. Accurate simulations are performed for various Mach number and mean angles of attack to cover different flow structures and phenomena associated with them. Variations of flow structure around the wing and hysteresis loops associated with lift coefficient and vortex breakdown location during a pitching cycle are investigated. The trends with Mach number, mean angle of attack, amplitude of pitching and pitching frequency are illustrated.

The use of ferrofluids as shapeable external appendage to a submerged body and as a mean of vortex flow induction is studied in this paper. Ansys-CFX numerical results are validated against analytical problems and used to analyze the ferrofluid free surface shape affected by gravity, different magnets and different densities of the surrounding non-magnetic fluids. It is demonstrated that the height, width, and curvature of ferrofluid can be controlled by magnet size and strength. It is also observed that ferrofluid mass loss may occur due to gravity which should be addressed in designing a fluid appendage. Subsequently, vortex production inside the ferrofluid is investigated via a shear flow on the magnet. It is shown that ferrofluid can contain complex vortices while being shaped by the magnetic field, gravity, and the vortices. It is also observed that vortices inside the ferrofluid affect the flow of the surrounding fluid. Additionally, the effects of surface tension and viscosity are briefly analyzed to roughly show the importance of these parameters for further works. Overall, it is concluded that using ferrofluids as appendages for shaping and controlling fluid flow around submerged bodies seem to be practical and needs further attention.

This paper presents a family of computational schemes for the solution of the Bagley-Torvik equation. The schemes are based on the reformulation of the original problem into a system of fractional differential equations of order 1/2. Then, suitable exponential integrators are devised to solve the resulting system accurately. The attainable order of convergence of exponential integrators for solving the fractional problem is studied. Theoretical ndings are validated by means of some numerical examples. The advantages of the proposed method are illustrated by comparing several of the existing methods

In this paper, the influence of the outer diameter of multi-walled carbon nanotubes (MWCNTs) on the fracture behavior of epoxy adhesives was investigated experimentally and numerically. MWCNTs with three different outer diameters of less than 8, 20-30 and 50-80 nm were used to toughen the epoxy adhesive. Double Cantilever Beam specimens were tested to determine the fracture energy. The results indicated that improvement in the adhesive fracture resistance by introducing MWCNTs was considerably dependent on the outer diameter of MWCNTs. Toughening the epoxy adhesive by incorporating MWCNTs with 8 nm diameter improved the adhesive fracture energy three times higher compared to the MWCNTs with larger diameters. The SEM fractography of the fracture surfaces was also utilized to assess the governing fracture mechanisms occurred in the toughened epoxy adhesives. Moreover, a cohesive zone model was used for numerical investigation of the effect of the MWCNT diameter on the damage behavior of epoxy adhesives.

This paper presents a thermal fluid–structure interaction (FSI) study of printed circuit boards (PCBs) during wave soldering. The influences of PCB thickness on displacement, stress and temperature distribution are the foci of the study. Five PCB thicknesses (i.e., 0.6, 1.0, 1.6, 2.4, and 3.1 mm) are considered. The paper focuses on a simple PCB with a single hole and constructed in a three-dimensional model. The thermal FSI of the PCB is solved by fluid (FLUENT) and structure (ABAQUS) solvers that are connected using the mesh-based parallel code coupling interface method. Molten solder advancement is tracked using volume-of-fluid technique in the thermal fluid analysis. ABAQUS solves PCB displacement, von Mises stress, and temperature distributions when high solder temperature is experienced during wave soldering. The correlations of PCB thickness to displacement, von Mises stress, temperature distribution, and molten solder filling time are studied. Results reveal that an increase in PCB thickness yields a linear correlation to solder filling time. Temperature distribution, von Mises stress, and displacement of PCB exhibit polynomial behavior to PCB thickness. A laboratory-scale two-way wave-soldering machine is also used to measure PCB temperature during wave soldering. The predicted temperature of PCB is substantiated by the experimental results.

This paper aims at introducing a proportion-preserving composite ob-jective function for multi-objective optimization, namely, PPCOF, and validating its eciency through demonstrating its applicability to opti- mization of the kinetostatic performance of planar parallel mechanisms. It exempts the user from both specifying preference factors and conduct- ing decision-making. It consists of two terms. The rst one adds the normalized objective functions up, where the extrema are resulted from single-objective optimization. To making the composite objective func- tion steer the variations of the objective functions while preserving ra- tional proportions between them, as the main contribution of the paper, it is sought that the normalized objective functions take closely similar values, to which end, they are juxtaposed inside a vector, which is then scaled such that its Euclidean norm-2 is equal to that of the vector of all ones with the same dimensions, and then the second term is constructed as the addition of penalty factors standing for the absolute value of the di erence between each element of the foregoing vector from 1. Based on the experimental results, with a considerably smaller computational cost, the PPCOF obtains an optimal solution that is not dominated by any point from a set of Pareto-optimal solutions o ered by NSGA-II.