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Effect of microthread design of dental implants on stress and strain patterns: A three-dimensional finite element analysis
, Article Biomedizinische Technik ; Volume 58, Issue 5 , September , 2013 , Pages 457-467 ; 00135585 (ISSN) ; Raoofi, S ; Kadkhodazadeh, M ; Movahhedi, M. R ; Khademi, M ; Sharif University of Technology
Walter de Gruyter and Co
2013
Abstract
The aim of this study was to use finite element analysis (FEA) to assess the influence of microthread design at the implant neck on stress distribution in the surrounding bone. A commercially available implant with 3.5 mm diameter and 10.5 mm length was selected and used as a model. For the purpose of designing the microthread implant model, microthreads were added to the implant neck in a computerized model. A force measuring 100 N was then applied to the entire surface of the abutment in the vertical direction. The results showed that in both models, stress was mainly concentrated at the cortical bone adjacent to the neck of the implant. Maximum stress values in the cortical bone...
Using a vibration absorber to suppress chatter vibration in turning process with a worn tool
, Article Proceedings of the ASME International Design Engineering Technical Conferences and Computers and Information in Engineering Conference 2009, DETC2009, 30 August 2009 through 2 September 2009 ; Volume 1, Issue PART B , August-September , 2010 , Pages 1335-1341 ; 9780791848982 (ISBN) ; Bakhtiari Nejad, F ; Movahhedi, M. R ; Sharif University of Technology
2010
Abstract
Dynamic vibration absorbers are used as semi-active controllers to reduce the undesirable vibrations in many applications such as electrical transmission lines, helicopters, gas turbines, engines, bridges and etc. One type of these absorbers is tunable vibration absorber (TVA). In this paper, regenerative chatter in an orthogonal turning process is suppressed using a (TVA). It is shown that TVA can modify the frequency response function of the cutting tool so as to improve cutting stability in turning process. In addition, tool wear is an important factor which works as a positive damping and helps the chatter suppression beside exertion of the TVA. Finally, using the SIMULINK Toolbox of...
Using a vibration absorber to suppress chatter vibration in turning process with a worn tool
, Article Proceedings of the ASME Design Engineering Technical Conference, 30 August 2009 through 2 September 2009, San Diego, CA ; Volume 1, Issue PARTS A AND B , 2009 , Pages 1335-1341 ; 9780791848982 (ISBN) ; Bakhtiari Nejad, F ; Movahhedi, M. R ; Sharif University of Technology
2009
Abstract
Dynamic vibration absorbers are used as semi-active controllers to reduce the undesirable vibrations in many applications such as electrical transmission lines, helicopters, gas turbines, engines, bridges and etc. One type of these absorbers is tunable vibration absorber (TVA). In this paper, regenerative chatter in an orthogonal turning process is suppressed using a (TVA). It is shown that TVA can modify the frequency response function of the cutting tool so as to improve cutting stability in turning process. In addition, tool wear is an important factor which works as a positive damping and helps the chatter suppression beside exertion of the TVA. Finally, using the SIMULINK Toolbox of...
A tunable vibration absorber design to suppress chatter in boring manufacturing process
, Article ASME International Mechanical Engineering Congress and Exposition, IMECE 2007, Seattle, WA, 11 November 2007 through 15 November 2007 ; Volume 9 PART C , 2008 , Pages 1943-1950 ; 0791843033 (ISBN); 9780791843031 (ISBN) ; Bakhtiari Nejad, F ; Movahhedi, M. R ; Sharif University of Technology
2008
Abstract
Dynamic vibration absorbers are used to reduce the undesirable vibrations in many applications such as electrical transmission lines, helicopters, gas turbines, engines, bridges and etc. One type of these absorbers is tunable vibration absorber (TVA) which can act as a semi-active controller. In this paper, by applying a (TVA), chatter vibration is suppressed during boring process in which boring bar is modeled as a cantilever Euler-Bernoulli beam. The optimum specifications of absorber such as spring stiffness, absorber mass and its position can be determined by developing an algorithm based upon mode summation method. Finally, using the SIMULINK Toolbox of MATLAB, the analog simulated...
A novel approach to radio direction finding and detecting the number of sources simultaneously: DMSAE algorithm
, Article Conference Proceedings- 34th European Microwave Conference, London, 12 October 2004 through 14 October 2004 ; Volume 2 , 2004 , Pages 745-748 ; 1580539920 (ISBN) ; Tadaion, A. A ; Aref, M. R ; Sharif University of Technology
2004
Abstract
In smart antenna systems, The localization and direction of desired source(s) must be known. In this paper, we introduce a method called "DMSAE" (Direction finding of Multiple Sources by Alternating Eliminations) to find the radio directions of signals impinging on an arbitrary antenna array and the number of the signals. This method which is based on the Minimum Variance Distortionless Response (MVDR) algorithm, can not only detect the direction and the number of sources, simultaneously, but also has better resolution ability compared to the other conventional direction finding algorithms. This method can also detect very weak sources when other powerful sources exist in the environment. In...
Sintering characterizations of Ag-nano film on silicon substrate
, Article Advanced Materials Research ; Volume 829 , 2014 , Pages 342-346 ; ISSN: 10226680 ; ISBN: 9783037859070 ; Akbari, J ; Movahhedi, M. R ; Alemohammad, H ; Sharif University of Technology
2014
Abstract
Nowadays, thin films have many applications in every field. So, in order to improve the performance of thin film devices, it is necessary to characterize their mechanical as well as electrical properties. In this research work we focus on the development of a model for the analysis of the mechanical and electrical properties of silver nanoparticles deposited on silicon substrates. The model consists of inter-particle diffusion modeling and finite element analysis. In this study, through the simulation of the sintering process, it is shown that how the geometry, density, and electrical resistance of the thin film layer are changed with sintering conditions. The model is also used to...
Adaptive control of regenerative chatter in turning process with tool wear effect
, Article ASME International Mechanical Engineering Congress and Exposition, Proceedings ; Volume 10, Issue PART B , 2010 , Pages 1023-1030 ; 9780791843833 (ISBN) ; Moradi, H ; Vossoughi, G. R ; Alasty, A ; Movahhedi, M. R
2010
Abstract
Chatter suppression is of great importance for achieving high precision and surface quality in machining processes. A single degree of freedom model of orthogonal turning process is used to set up the nonlinear delay differential equation of motion. Tool wear effect is considered as the contact force between the workpiece and tool flank surfaces. Uncertainties in parameters of dynamic model and machining conditions are included in the model. An adaptive control strategy is applied for chatter suppression in cutting process. The force provided by a piezoactuator is the control input of the system. Results of stability analysis and adaptive control for two distinct cases of sharp and worn...
Qualitative Comparative Analysis of Policies for Fuel Subsidies Reforming in Selected Countries: Recommendations for Iran
, M.Sc. Thesis Sharif University of Technology ; Maleki, Abbas (Supervisor)
Abstract
Energy subsidies are one of the most challenging issues for many countries in the world, specially oil and gas exporting countries. Iran is one of the countries that has lost more than ten percent of its GDP due to energy subsidies in recent years. In this thesis, we are going to analyze experiences of different countries and try to provide policy makers with generalizations about this problem so they can implement reform policies more successfully. We have used Qualitative Comparative Analysis (QCA) methodology. This method can provide modest generalizations by using systematic cross-case comparison between a small number of cases. Details of this method and reasons behind choosing it are...
Experimental Study and Simulation of Ultrasonic Vibration Effect on Powder Spreading in Selective Laser Sintering Process
, M.Sc. Thesis Sharif University of Technology ; Movahhedi, Mohamadreza (Supervisor)
Abstract
Selective laser sintering is an additive manufacturing technique based on fusion of powder bed, wherein after spreading a powder layer, a focused laser beam directs onto selected points of powder bed to fuse powder particles together. This process is repeated layer by layer until the final part is created. Although utilization of blade as a conventional powder spreading (CPS) mechanism has a good compression ability, the fixed contact line between blade and powder bed surface results in improper powder flowability and increasing shear forces applied on underneath layer. In this study, in order to obtain the basis for conducting practical experiments, discrete element simulation of powder...
Investigation on Pulsed TIG Lap Welding of Al-5052 Sheet to Al-1050 Clad St-12 Sheet
, M.Sc. Thesis Sharif University of Technology ; Movahhedi, Mojtaba (Supervisor)
Abstract
In this study, Al-5052 aluminium alloy sheet was lap joined to aluminium clad steel sheet using pulsed gas tungsten arc welding and Al-Si filler metal. Effect of heat-input, thickness of clad layer and frequency were investigated on the formation of intermetallic reaction layer, microstructure of the weld seam and shear strength of the joints are explored. Stress analysis in weld is also used in order to justify the fracture location in the welds the microstructure and shear-tensile strength of the welds (joining with A1-1050 clad layer with two thickness of 350 μm and 1000 μm). Before welding, aluminum clad steel sheets were produced by roll bonding and 450 °C annealing temperature and 90...
Design and Prototyping of an Ultra High Speed Air Micro Spindle
,
M.Sc. Thesis
Sharif University of Technology
;
Movahhedi, Mohammad Reza
(Supervisor)
Abstract
Today, the need for high-speed machine tools, in areas such as defense, medical and electronic for producing parts with millimeter dimensions, and with features smaller than the millimeter, increased. To meet this need, the machine tool can be used with smaller dimensions and with high speed. These machines are able to produce these parts with high production rates.The project aims to improve technical design and construction of a micro spindle to achieve sustained speed about one hundred thousand RPM. In this project, the first step in understanding the fundamentals of the theory and the system components, and the whole operation was performed. The design is based on studies carried out in...
Aerodynamic Performance Improvement of Megawatt Wind Turbine Rotor Using Plasma Actuator
, M.Sc. Thesis Sharif University of Technology ; Ebrahimi, Abbas (Supervisor)
Abstract
For validation of simulation, plasma actuator was modelled on a flat plate in quiescent flow, which is result in low-speed jet near the wall. The results were compared with similar model and were showed good agreement with them. After that, blade was modelled in three-dimensional manner with MRF technique and periodic method and the results were validated in clean situation (absence of plasma). In the following, turbine was analysed with a code, which was written in MATLAB software based on BEM method and the results were compared with present CFD simulation. Then, plasma actuator was used in chordwise in parts of the blade to improve wind turbine performance. Also it was used in spanwise...
The Effect of Different SLS Parameters on the Density of Polymer-Metal Parts
, M.Sc. Thesis Sharif University of Technology ; Movahhedi, Mohammad Reza (Supervisor)
Abstract
Selective Laser Sintering (SLS) is one of the powder-based Additive Manufacturing (AM) technology in which parts built by CO2 laser. In this research work, Titanium-PMMA-Stearic Acid powders are mixed together to produce parts by Indirect Metal Laser Sintering (IMLS) method. The optimum process parameters such as energy density, Percentage composition of Titanium-PMMA and Scan Sintering are obtained by adopting the Taguchi method for getting the maximum density and minimum porosity. Experiments are planned by Taguchi’s Mix-L8 orthogonal array. According to the results obtained from this study, the percentage of combination Ti-PMMA and Energy density, respectively, are a major parameters that...
FEM Simulation and Investigation of Thickness Change Effect on Direct 3D Printed Clear Aligner Behaviour
, M.Sc. Thesis Sharif University of Technology ; Movahhedi, Mohammad Reza (Supervisor)
Abstract
Orthodontics, a dental specialty focused on tooth alignment, has been practiced for centuries for both therapeutic and aesthetic reasons. Traditional orthodontic treatment involves the use of brackets and wires, a method that has been widely adopted since the 1970s. However, since the early 21st century, the use of clear, polymer-based orthodontic aligners has emerged as an alternative approach for tooth straightening. Clear aligners are typically fabricated using a thermoforming process, where a sheet of polymer is heated and vacuum-formed over a 3D-printed model of the patient's teeth. A more recent approach involves the direct 3D printing of aligners based on digital scans of the teeth,...
Adaptive control of regenerative chatter in turning process with tool wear effect
, Article ASME International Mechanical Engineering Congress and Exposition, Proceedings ; Vol. 10, Issue PART B , 2010 , pp. 1023-1030 ; ISBN: 9780791843833 ; Moradi, H ; Vossoughi, G. R ; Alasty, A ; Movahhedi, M. R ; Sharif University of Technology
2010
Abstract
Chatter suppression is of great importance for achieving high precision and surface quality in machining processes. A single degree of freedom model of orthogonal turning process is used to set up the nonlinear delay differential equation of motion. Tool wear effect is considered as the contact force between the workpiece and tool flank surfaces. Uncertainties in parameters of dynamic model and machining conditions are included in the model. An adaptive control strategy is applied for chatter suppression in cutting process. The force provided by a piezoactuator is the control input of the system. Results of stability analysis and adaptive control for two distinct cases of sharp and worn...
Investigation of Microstructure and Fracture Behavior of Similar and Dissimilar Dual Phase Steels and Martensitic Steel Spot Resistance Welding
, M.Sc. Thesis Sharif University of Technology ; Pouranvari, Majid (Supervisor) ; Movahhedi, Mojtaba (Supervisor)
Abstract
The new generation of advanced high-strength steels use in the automotive industry cause resistance spot welding study and their failure characteristics during static and dynamic loading are important. In this study, the relationship among microstructure, failure mode and mechanical properties are investigate during similar and dissimilar DP980 and MS1400 jointing advanced high-strength steels resistance spot welding. To search for micro and macro structural changes, the optical microscope, stereographic microscope and scanning electron microscope were used. Micro-hardness test, tensile shear test and Cross tension test to evaluate the mechanical properties were conducted. As well as...
Investigation of Mechanical Properties and Microstructure of Al/Fe3O4 Nano Composite Produced by Friction Stir Processing
, M.Sc. Thesis Sharif University of Technology ; Kokabi, Amir Hossein (Supervisor) ; Movahhedi, Mojtaba (Supervisor)
Abstract
Friction Stir Processing (FSP) was used to fabricate Al1050/Fe3O4 nanocomposite in three different weight percent (2.5%, 4% and 5.3%). The effects of rotational speed (1200-1600 rpm), traverse speed (5-15 cm/min) and the number of FSP passes (1, 2, 3 and 6 passes) on microstructure and mechanical properties were investigated. In order to study microstructure evolution, optical and field emission scanning electron microscopes were used. Micro hardness, longitudinal and transverse tensile and wear test were carried out to investigate mechanical properties of the obtained composites. Results showed that increase of the rotational speed and decrease of the traverse speed in 1 pass processed...
Prediction of Machining Chatter Based on 2 Dimensional FE Dynamic Modeling of Chip Formation
, M.Sc. Thesis Sharif University of Technology ; Movahhedi, Mohammad Reza (Supervisor)
Abstract
In machining processes, chip formation is one of the most important methods to obtain the final shape of a work-piece. Improving the machining processes leads to the increase in the material removal rate (MRR) and reduction of high economical costs. Vibration is an undesirable phenomenon in machining processes because it results in reduction of material removal rate (MRR), poor surface finish and increased tool wear. Among various types of vibration, self-excited vibration or chatter is the most important one. It is obvious from previous investigations that for prediction of machine tools vibration, many simplifications were assumed while the linear and non-linear effects are not considered...
Hip Joint Preforms Designing Steps With Inverse Finite Element Method
, M.Sc. Thesis Sharif University of Technology ; Movahhedi, Mohammad Reza (Supervisor) ; Akbari, Javad (Co-Advisor)
Abstract
Forging process is recognized as the high speed method, economical and with ability to produce high strength parts between metal forming processes. Preform design is the most important step in forging process. In the past this work was done based on experiences. In the complex parts because of error in design there was probability of diverse dies, so that method needed to spent so many times and costs. However recently with progress in computer programming we don’t need to produce diverse dies but spend many times. In this field many investigations are done to dispose designers skills, so forging preform design based on inverse finite elements method is denoted for this gold. In this thesis...
Experimental and Simulation Study of Barite Settlement Phenomenon under Static and Dynamic Condition
, M.Sc. Thesis Sharif University of Technology ; Shad, Saeed (Supervisor) ; Hosseini Mokhtari, Zahra (Co-Advisor)
Abstract
In petroleum related drilling, Barite particles settling and Barite sag as major problems in drilling wells can potentially impose significant operational issues. In this study, a computational fluid dynamics (CFD) and experimental investigation of Barite settlement in annular space were conducted in both static and dynamic conditions. The Euler-Euler approach was used to model the multiphase flow of solid Barite particles and drilling fluid. In this approach, the momentum lost between phases has been taken into account by means of particle-particle and particle-fluid exchange coefficients. The governing equations were numerically solved using finite volume method by CFD software package...