akbar sajadi; F. Javanroodi; M. Borhani
Volume 5, Issue 2 , March 2012
Abstract
Fabrication of ultrafine grained materials by imposing severe plastic deformation for improvement of mechanical and physical properties of metals has been the focus of many researches over the past few years. In this process, a sheet is subjected to repetitive shear deformation conditions by utilizing ...
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Fabrication of ultrafine grained materials by imposing severe plastic deformation for improvement of mechanical and physical properties of metals has been the focus of many researches over the past few years. In this process, a sheet is subjected to repetitive shear deformation conditions by utilizing asymmetrically grooved and flat dies through alternate pressing. In this study, a 2mm thick commercial pure aluminum sheet was subjected to repetitive pressing up to four passes. Mechanical properties including, hardness and tensity were obtained. Results show that, although increasing the number of passes causes higher strength magnitude, the strength’s slope decreases. After validation of finite element modeling, strain distribution and uniformity behavior of the grooved plate were investigated using plain strain and plain stress conditions. Results show that strain in the surface and near the teeth of the die is lower than other areas.
A. Amirimighadam; M. Maarefdoust
Volume 5, Issue 2 , March 2012
Abstract
Conjugated polymer actuators can be employed to achieve micro and nano scale precision, and have a wide range of applications including biomimetic robots, and biomedical devices. In comparison to robotic joints, they do not have friction or backlash, but on the other hand, they have complicated electro-chemo-mechanical ...
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Conjugated polymer actuators can be employed to achieve micro and nano scale precision, and have a wide range of applications including biomimetic robots, and biomedical devices. In comparison to robotic joints, they do not have friction or backlash, but on the other hand, they have complicated electro-chemo-mechanical dynamics which makes modelling and control of the actuator really difficult. Besides the positive characteristics of these actuators, they have some disadvantages such as creep, hysteresis, highly uncertain and time-varying dynamics. This paper consists of two major parts. In the first part the Takagi–Sugeno (T–S) Fuzzy model is used to represent the uncertain dynamic of the actuator, and the resulted Fuzzy model will be validated using experimental data. In the second part a proportional-derivative fuzzy controller is designed to control the highly uncertain dynamic of conjugated polymer actuator. In order to optimize the performance of fuzzy controller, Genetic Algorithm (GA) is used for tuning the output membership functions. The obtained results show that the designed controller can achieve good performance despite the existence of uncertain actuator dynamics and also it has a better performance than conventional PID controller.
Ehsan Ahmadi; Rasool Mokhtari Homami; Sadegh Rahmati
Volume 5, Issue 2 , March 2012
Abstract
Abstract: The lifetime of a cutting tool is an important and determinant parameter for evaluating its performance. The amount of tool abrasion affects seriously dimensions and surface quality of the working piece so that one of the main factors to determine the lifetime of a tool is the level of its ...
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Abstract: The lifetime of a cutting tool is an important and determinant parameter for evaluating its performance. The amount of tool abrasion affects seriously dimensions and surface quality of the working piece so that one of the main factors to determine the lifetime of a tool is the level of its wearing. For this purpose, an abrasion standard is defined for each particular tool above which the tool is not applicable any more. In the current paper, studies are concentrated on the machining of PH-hardened Austenitic-ferritic (Duplex) stainless steel (330HRC) to analyze the effect of tool wear on the lifetime of the ceramic cutting tool with Alumina base (aluminum oxide). Abrasion tool parameters like Flank wear, Crater wear, and Notch wear have been considered. To develop the mathematical models for the parameters considered in tool wear, the experimental results are applied in multi regression analysis (MRA) and the results obtained by these models are considered and analyzed by the analysis of variance (ANOVA).
Navid Bozorgan
Volume 5, Issue 2 , March 2012
Abstract
Abstract: In this study, Al2O3/EG and TiO2/EG nanofluids as coolants have been used in the double-tube heat exchanger. The hot solvent inlet heat exchanger must be cooled down with a specified amount. We can use nanofluids as coolants in the heat exchanger for optimization of the heat transfer area. ...
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Abstract: In this study, Al2O3/EG and TiO2/EG nanofluids as coolants have been used in the double-tube heat exchanger. The hot solvent inlet heat exchanger must be cooled down with a specified amount. We can use nanofluids as coolants in the heat exchanger for optimization of the heat transfer area. Therefore, the efficacy of nanofluids as coolants is verified. Furthermore, flow rate of coolant is optimized by using the Al2O3/EG and TiO2/EG nanofluids in the heat exchanger. Thus with decreasing the heat transfer area and flow rate of the coolant, we can reduce the costs such as pumping power, fouling costs, etc in a double-tube heat exchanger. The heat transfer relations between hot solvent and nanofluids as coolants in the heat exchanger have been investigated. The results showed that the overall heat transfer coefficient was high, when the probability of collision between nanoparticles and the wall of the heat exchanger was increased under higher concentration. Consequently, we calculated the heat transfer coefficient, overall heat transfer coefficient, friction factor, pressure drop and pumping power for Al2O3/EG and TiO2/EG nanofluids used as coolants in a double-tube heat exchanger.
M. Vahdati; A.R. Vahdati
Volume 5, Issue 2 , March 2012
Abstract
Recently, incremental sheet metal forming (ISMF) process as one of the new methods in rapid prototyping collection has been considered by researchers. This process is based on a defined path in CNC controller and applies a spherical-head tool that supplies the required pressure for sheet metal forming. ...
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Recently, incremental sheet metal forming (ISMF) process as one of the new methods in rapid prototyping collection has been considered by researchers. This process is based on a defined path in CNC controller and applies a spherical-head tool that supplies the required pressure for sheet metal forming. Despite affirmation of process ability in forming symmetric geometries, some of its aspects such as: high cost in die design and its manufacturing, high cost in using NC machine tools and time consuming forming processare its constraints. Hereupon, a new method for incremental sheet metal forming on turning machine has been presented. This process uses a spherical-head tool in tool-holder turret, forming sheet metal in symmetric geometries in shortest possible time without requiring a die. With a view to increasing sheet formability, two types of forming strategies were designed and implemented. Finally, the best forming strategy based on final forming depth and effective strain calculations is introduced.
Mohammad Taghi Ghorbani
Volume 5, Issue 2 , March 2012
Abstract
Abstract: A time domain semi-analytical solution to study thermoelastic creep behavior of functionally graded rotating axisymmetric disks with variable thickness is presented. The rate type governing differential equations for the considered structure are derived and analytically solved. To solve ...
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Abstract: A time domain semi-analytical solution to study thermoelastic creep behavior of functionally graded rotating axisymmetric disks with variable thickness is presented. The rate type governing differential equations for the considered structure are derived and analytically solved. To solve these equations, the disk is divided into some virtual sub-domains. General solution of equilibrium equations in each sub-domain can be obtained by imposing the continuity conditions at the interface of the adjacent sub-domains together with global conditions. Finally, solution in terms of rate of stress and strain is obtained. The advantage of present work, is to avoid simplifications and restrictions, which are normally associated with other creep solution techniques in the literature. Results for the stress and strain rates presented due to centrifugal force and thermal loadings for different boundary conditions. Results obtained are verified with those available in the literature for easier cases.
Mohsen Dashti Ardakani; Seyd Mohammad Mehdi MizanAdl
Volume 5, Issue 2 , March 2012
Abstract
Abstract: In this paper, a new population-based search called the Bees Algorithm (BA) is presented to estimate the time-dependent heat transfer coefficient and the corresponding heat flux at the boundaries of a two-dimensional body subjected to transient heat conduction, using the temperature measurements ...
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Abstract: In this paper, a new population-based search called the Bees Algorithm (BA) is presented to estimate the time-dependent heat transfer coefficient and the corresponding heat flux at the boundaries of a two-dimensional body subjected to transient heat conduction, using the temperature measurements at discrete nodal locations on the boundaries, where heat flux is specified as the boundary condition. In the forward problem, a two dimensional transient heat conduction problem subjected to heat flux boundary conditions is solved for temperature distribution at the boundaries using the boundary elements method. In the inverse problem the heat transfer coefficient (h) at the boundaries where thermal conditions are over specified is estimated by minimizing an objective function which is defined as the sum of the squared differences between the measured and computed temperatures at the nodal locations on the boundary. The Bees algorithm which is a new global evolutionary optimization method is used to investigate the inverse problem. The average value of the heat transfer coefficient at the boundaries is assumed over each time interval from initial time until the final steady-state time. The optimum parameters of Bees algorithm are found and used to estimate the heat transfer coefficient as a function of time. The effect of temperature measurement errors on the identification process is also investigated.
reza azarafza; SAEED MOHAMMAD Hoseni; MOHAMMAD FARROKHI
Volume 5, Issue 2 , March 2012
Abstract
Sliding mode control (SMC) is a powerful approach to solve the tracking problem for dynamical systems with uncertainties. However, the traditional SMCs introduce actuator chattering phenomenon which performs a desirable behavior in many physical systems such as servo control and robotic systems, ...
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Sliding mode control (SMC) is a powerful approach to solve the tracking problem for dynamical systems with uncertainties. However, the traditional SMCs introduce actuator chattering phenomenon which performs a desirable behavior in many physical systems such as servo control and robotic systems, particularly, when the zero steady state error is required. Many methods have been proposed to eliminate the chattering from SMCs which use a finite DC gain controller. Although these methods provide a free chattering control but they deals with only the steady state error and are not able to reject input disturbances. This paper presents a fuzzy combined control (FCC) using appropriate PID and SMCs which presents infinite DC gain. The proposed FCC is a free chattering control which guarantees a zero steady state error and rejects the disturbances. The stability of the closed loop system with the proposed FCC is also proved using Lyapunov stability theorem. The proposed FCC is applied to a two degree of freedom robot manipulator to illustrate effectiveness of the proposed scheme.
Mina Alafzadeh; Shahram Talebi
Volume 5, Issue 2 , March 2012
Abstract
Abstract: Since the field of micro electromechanical systems (MEMS) continues to grow, the flow in micro devices have become an area that receives a significant attention. The microscopic flows are usually characterized by the Knudsen number (Kn). When the characteristic size of the particle decreases ...
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Abstract: Since the field of micro electromechanical systems (MEMS) continues to grow, the flow in micro devices have become an area that receives a significant attention. The microscopic flows are usually characterized by the Knudsen number (Kn). When the characteristic size of the particle decreases down to a value comparable to the mean free path of the molecules, the continuum assumption fails and the Navier-Stokes equations with no-slip boundary conditions cannot be applied, so the numerical method which is not based on continuity of the flow is needed. Recently the lattice Boltzmann method (LBM) has received considerable attention by fluid dynamic researches. The LBM is based on the lattice Boltzmann equation with Bhatnagar-Groos-Krook (BGK) collision approximation. In this paper the incompressible laminar flow in a 2D micro semi-circular cavity with lid driven is simulated by LBM. It should be mentioned that the flow in semi-circular cavity in macro scale has been simulated too and the obtained results were found to be in good agreement with those given from the finite volume method. In the present work, the computational results showed that the slip could have influence on the center of vortex and moved it in horizontal and vertical direction in semi-circular cavity. Computing the friction coefficient on the lid driven presented that the friction coefficient was increased as Kn was increased. The slip could affect on the maximum velocity in cavity too and decreased it.