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Effect Analysis of Arrangement, Sequence and Plate Thickness of Spot Welding on Residual Stress and Fatigue Life of The Joint
, M.Sc. Thesis Sharif University of Technology ; Farrahi, Gholamhosein (Supervisor)
Abstract
There are about 5,000 spot welds in the car body. Simulation of this number of spot welds to optimize the body of the car is practically impossible. In researches done in order to model and optimize the spot weld, standard spot weld sample with a nugget have been always used. Electrical current in spot welding process turns to heat according to the Ohm ratio, and causes the melting of the pieces and bonding. So amount of the electrical resistance, especially at the contact surface of the two pieces, is very important.In order to investigate the residual stresses induced in the connection of a three-sheet spot weld sample and its effect on fatigue life, first, a spot weld sample with...
A Survey in Inflation and Roots of Axionic Inflationary Models
,
M.Sc. Thesis
Sharif University of Technology
;
Abolhasani, Ali Akbar
(Supervisor)
Abstract
Inflation first introduced for solving the puzzles of the standard model of cosmology. Soon it became clear that this paradigm can provide a natural way for production of Initial conditions for the birth of large-scale structures: cosmological perturbations. But inflationary models are usually phenomenological models. They are constructed to solve the problems of the standard model of cosmology and explain the properties of cosmological fluctuations. Where do they come from? A property of a big family of inflationary models is the flatness of their potential. What would may be the cause of this flatness? . . .. In this thesis our purpose is searching about one probable field theoretic root...
Experimental Study of Venturi-Enhanced Solar Evaporative Desalination System
, M.Sc. Thesis Sharif University of Technology ; Shafii, Mohammad Behshad (Supervisor)
Abstract
The scarcity of freshwater resources in many communities worldwide is a pressing challenge that requires immediate attention. One of the most promising solutions to address this issue is the conversion of seawater into freshwater using solar energy to power desalination processes. The efficiency of this process can be further enhanced by reducing energy consumption through the lowering of the vapor saturation temperature of saline water.To this end, the present study investigates the use of evacuated tube collector technology for water heating and a vacuum system to lower the evaporation temperature of saline water. Specifically, the system employs a water cycle with a venturi to facilitate...
A geographical question answering system
, Article 3rd International Conference on Web Information Systems and Technologies, Webist 2007, Barcelona, 3 March 2007 through 6 March 2007 ; Volume WIA , 2007 , Pages 308-314 ; Ghasemzadeh, H ; Sheykh Esmaili, K ; Minaei Bidgoli, B ; Sharif University of Technology
2007
Abstract
Question Answering systems are one of the hot topics in context of information retrieval. In this paper, we develop an open-domain Question Answering system for spatial queries. We use Google for gathering raw data from the Web and then in a few iterations density of potential answers will be increased, finally based on a couple of evaluators the best answers are selected to be returned to user. Our proposed algorithm uses fuzzy methods to be more precise. Some experiments have been designed in order to evaluate the performance of our algorithm and results are totally promising. We will describe that how this algorithm can be applied to other type of questions as well
Analysis of resistance spot welding process parameters effect on the weld quality of three-steel sheets used in automotive industry: Experimental and finite element simulation
, Article International Journal of Engineering, Transactions A: Basics ; Volume 33, Issue 1 , 2020 , Pages 148-157 ; Reza Kashyzadeh, K ; Minaei, M ; Sharifpour, A ; Riazi, S ; Sharif University of Technology
Materials and Energy Research Center
2020
Abstract
In the present research, the effects of spot-welding process parameters on the nugget diameter and electrode penetration depth of spot-welded joints were investigated. To achieve this, a spot-welded joint of three-thin sheet low carbon steels (same thicknesses of 0.8 mm) was simulated as an electerical-thermal-mechanical coupling of 3D finite element model. After validating the finite element simulation presented in this study by comparison with the experimental results for the spot diameter, various cases of spot welds were analyzed based on the design on experiment (i.e., Taguchi method). Six variables including electrode force, electric current, and quadrilateral times (squeeze, up-slope,...
Detection of inappropriate working conditions for the timing belt in internal-combustion engines using vibration signals and data mining
, Article Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering ; Volume 231, Issue 3 , 2017 , Pages 418-432 ; 09544070 (ISSN) ; Banakar, A ; Ghobadian, B ; Agha Mirsalim, M ; Minaei, S ; Jafari, S. M ; Sharif University of Technology
SAGE Publications Ltd
2017
Abstract
Abnormal operating conditions for the timing belt can lead to cracks, fatigue, sudden rupture and damage to engines. In this study, an intelligent system was developed to detect and classify high-load operating conditions and high-temperature operating conditions for timing belts. To achieve this, vibration signals in normal operating conditions, high-load operating conditions and high-temperature operating conditions were collected. Time-domain signals were transformed to the frequency domain and the time-frequency domain using the fast Fourier transform method and the wavelet transform method respectively. In the data-mining stage, 25 statistical features were extracted from different...
Numerical study of shunting effect in three-steel sheets resistance spot welding
, Article International Journal of Engineering, Transactions B: Applications ; Volume 35, Issue 2 , 2022 , Pages 406-416 ; 1728144X (ISSN) ; Farrahi, G. H ; Minaei, M ; Masajedi, R ; Gholamnia, M ; Shademani, M ; Sharif University of Technology
Materials and Energy Research Center
2022
Abstract
The main purpose of the present research is to investigate the shunting phenomenon in a three-sheet RSW joint usingfinite element simulation. To this end, a three-sheet resistance spot weldingjoint was simulatedas an electrical-thermal-mechanical couplingproblem.Tovalidate the presentedsimulation, the finite element results were compared with the experimental results, including nugget size and geometric shapein theresistance spot weldingjoint.Afterwards, the multi-spot welds of three-sheet low carbon steels with the same thicknesses were analyzed considering the sequential distance of 45 mm. Various techniques, includingnewspot-welddiametermeasurement, electrical current density, electrical...
Fatigue life analysis in the residual stress field due to resistance spot welding process considering different sheet thicknesses and dissimilar electrode geometries
, Article Proceedings of the Institution of Mechanical Engineers, Part L: Journal of Materials: Design and Applications ; Volume 237, Issue 1 , 2023 , Pages 33-51 ; 14644207 (ISSN) ; Farrahi, G ; Ahmadi, A ; Minaei, M ; Ostad Rahimi, M ; Barforoushan, S ; Sharif University of Technology
SAGE Publications Ltd
2023
Abstract
A typical vehicle body contains many 3-sheet spot-welded connections with different sheet thicknesses. In addition, the use of dissimilar electrode geometries is extremely common in the automotive industry. These two factors lead to an asymmetric spot weld with asymmetric residual stress distribution and heat-affected zone. This asymmetry has considerable effects on the fatigue behavior of these joints. Although many previous studies were dedicated to the analysis of spot welds, consideration of different electrode geometries and fatigue analysis of 3-sheet spot-welded joints are absent in the literature. To this end, in the present paper, the resistance spot weld process of three-sheet low...