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Total 127 records

    Microstructural evaluation and fracture mechanisms of failed IN-738LC gas turbine blades

    , Article Case Studies in Engineering Failure Analysis ; Volume 1, Issue 2 , April , 2013 , Pages 85-94 ; 22132902 (ISSN) Attarian, M ; Khoshmanesh, R ; Nategh, S ; Davami, P ; Sharif University of Technology
    2013

    A failure analysis study on the fractured connecting bolts of a filter press

    , Article Case Studies in Engineering Failure Analysis ; Volume 4 , 2015 , Pages 26-38 ; 22132902 (ISSN) Molaei, S ; Alizadeh, R ; Attarian, M ; Jaferian, Y ; Sharif University of Technology
    Elsevier Ltd  2015
    Abstract
    The purpose of this study was to investigate the main causes of the co-fracture of sixteen connecting bolts of a filter press cylinder-piston system. Stress state of the bolts during the service conditions has been analyzed and the failure reasons were determined from the fractography analysis and gathered information. According to the obtained results, it was concluded that the bolts had failed by the fatigue mechanism. It seems that insufficient torque was used during assembly  

    Failure analysis of a first stage gas turbine blade

    , Article Engineering Failure Analysis ; 2010 ; 13506307 (ISSN) Kazempour Liacy, H ; Abouali, S ; Akbari Garakani, M

    Failure analysis of a repaired gas turbine nozzle

    , Article Engineering Failure Analysis ; 13506307 (ISSN) Kazempour Liacy, H ; Abouali, S ; Akbari Garakani, M ; Sharif University of Technology

    A Micromechanical Progressive Damage Algorithm for Prediction of Failure in Composite Laminates

    , M.Sc. Thesis Sharif University of Technology Rajaeenezhad, Iman (Author) ; Hosseini Kordkheili, Ali (Supervisor)
    Abstract
    Macro models which are used to predict failure of composite structures in most cases predict ¬reasonable results; however, they are not able to consider micro level parameters such as micro cracks. Furthermore, these failure macro models need various empirical data. Considering micromechanical construction of composites; including fiber, matrix and their interfaces, using micromechanical models for predicting failures in these phases is more appropriate. The aim of this study is to represent a micro-mechanical algorithm in order to predict progressive failures of fiber-reinforced composites. The failure model which is used in this study is a micromechanical modeling of failure (MMF) model,... 

    Failure analysis of automatic coupler SA-3 in railway carriages

    , Article Engineering Failure Analysis ; Volume 14, Issue 5 , 2007 , Pages 903-912 ; 13506307 (ISSN) Mousavi zadeh Noughabi, S. M ; Dehghani, K ; Pouranvari, M ; Sharif University of Technology
    2007
    Abstract
    In the present work, failure analysis of an automatic coupler in railway carriages which failed in service and caused derailment, was carried out. An evaluation of the failed coupler was undertaken to assess its integrity, including visual examination, photo documentation, fractography, chemical analysis, hardness measurement, tensile and charpy impact testing and microstructural characterization. Results show that some casting defects (e.g. mis-run, cold lap, hot crack and inclusion) resulted in poor mechanical properties. Mis-runs were also responsible for fatigue crack nucleation from two different locations. Beach marks can be observed on the fracture surface. According to the results of... 

    A new scheme on recovery from failure in NICE overlay protocol

    , Article 1st International Conference on Scalable Information Systems, InfoScale '06, Hong Kong, 30 May 2006 through 1 June 2006 ; Volume 152 , 2006 ; 1595934286 (ISBN); 9781595934284 (ISBN) Abdolhosseini Moghadam, A. R ; Barghi, S ; Rabiee, H. R ; Ghanbari, M ; Sharif University of Technology
    2006
    Abstract
    Overlay networks have been an active area of research for the past few years. The control overhead and the recovery from failure are the two important issues in the topology aware embedded overlay networks. In this research, we have introduced an enhanced version of the NICE protocol, called resilient NICE (R-NICE) that reduces the control overhead significantly. Furthermore, by saving the join path for an end host, the time and overhead of rejoining for isolated nodes have also been reduced. This will cause the clusters and consequently the overall network to become more stable and the effect of a node failure become localized. Our experimental results have confirmed the superior... 

    Aseptic loosening of femoral components - A review of current and future trends in materials used

    , Article Materials and Design ; Volume 42 , 2012 , Pages 459-470 ; 02641275 (ISSN) Bahraminasab, M ; Sahari, B. B ; Edwards, K. L ; Farahmand, F ; Arumugam, M ; Hong, T. S ; Sharif University of Technology
    2012
    Abstract
    The variety of new biomaterials and different surface treatments being applied to existing materials all intended for total knee replacement (TKR) are self-evident of the demand for longer lasting knee prostheses. Aseptic loosening is one of the main reasons for the revision of TKR components including the femoral component, which has more challenging problems because of the different causes of failure. This paper therefore, focuses on aseptic loosening of femoral components and materials options available. Several current and promising new metallic, ceramic and polymeric biomaterials are discussed to highlight their advantages and their shortcomings. It is concluded that current materials... 

    The effect of routing-update time on network's performability

    , Article 2007 IEEE/ACS International Conference on Computer Systems and Applications, AICCSA 2007, Amman, 13 May 2007 through 16 May 2007 ; 2007 , Pages 655-658 ; 1424410312 (ISBN); 9781424410316 (ISBN) Shaad Zolpirani, M ; Bidmeshki, M. M ; Miremadi, S. G ; Sharif University of Technology
    2007
    Abstract
    By occurring failures in computer networks, routing protocols are triggered to update routing and forwarding tables. Because of invalid tables during update-time, transient loop may occur and packet-drop rate and end-to-end delay increase which means that the quality of service decreases. This paper studies the effect of routing-tables update-time on networks' performability, i.e. the ability of network to deliver services at predefined level. A sample network is studied and the simulation results show that faster updates of routing table, improve network's performability in the presence of failures. Since it may not worth or even be practical to accelerate all routers in the network, this... 

    Vulnerability Assessment of Existing RCMRF Structures Subjected to Near Field Earthquakes

    , M.Sc. Thesis Sharif University of Technology Seyedi Rezvani, Mohammad Hosein (Author) ; Rahimzadeh Rofooei, Fayyaz (Supervisor)
    Abstract
    The objective of this study is to evaluate the seismic vulnerability of the existing buildings subjected to the near field earthquakes. The main applications of this research are loss estimation and performance evaluation of the existing buildings. That could provide a better solution and particularly more useful information to the owners, investors, and insurers about the expected performance of buildings under earthquake excitations. A number of 2, 5 and 8 story reinforced concrete buildings, designed according to the old Iranian seismic provisions of ISIRI-519 and ACI 318-83 codes for the ordinary moment resisting frames, are considered. By the use of a number of near field earthquake... 

    Computerized Maintenance Management System for Cement Plants (CMMS)

    , M.Sc. Thesis Sharif University of Technology Marvasti, Ehsan; Pourhosseinali, Mohammad (Author) ; Aditya, Parida (Supervisor)
    Abstract
    This project is providing appropriate software which could manage maintenance activities in a plant. All sections of the software have been designed in a way that can ease the management of maintenance activities. There are about 100 forms in the software that have been designed according to the forms which are being used in some Iranian cement plants and other maintenance software and also what we recognized important to be added or designed. One of the most important aspect of this software is the analytical section of the software where the user can get analytical reports from the software and based on the reports judge about the status of the plant and make new decisions in order to... 

    Optimum Mechanical Joint Design for a Composite Laminate to a Metal Part

    , M.Sc. Thesis Sharif University of Technology Nasrollahi Fekejvar, Majid (Author) ; Kouchakzadeh, Mohammad Ali (Supervisor)
    Abstract
    In this investigation, the behavior of pin loaded composite plates is studied numerically. A failure prediction model is used to predict the ultimate strength considering three different mechanisms of failure: bearing, shearout and net tension. The model consists of two major parts: stress analysis and failure analysis. The main difference between this investigation and others is considering more realistic assumptions in modeling of the problem. As an example, we consider nonlinear behavior in the shear stress/ shear strain relationship of each unidirectional ply and use this model in optimization problem to reach maximum strength. The results are compared with experimental results available... 

    Failure Analysis in Conical Structures Made by Tape Winding Method under Cold and Hot Thermal Load

    , M.Sc. Thesis Sharif University of Technology Karimian, Mehdi (Author) ; Hosseini Kordkheili, Ali (Supervisor) ; Parviz, Hadi (Co-Supervisor)
    Abstract
    The aim of this study is numerical simulation of progerasive failure in conical structures that manufactured by tape-winding proceses in various temperatures. For this purpose, flat laminates by tape-winding proceses firstly manufactured using carbon/phenolic prepreg tape. Then tensile, compression, shear and thermal expansion coefficient specimens are cut from these laminates. Tensile and compression test are done on these specemens in fiber and matrix directions in temperature range 23-200℃ and stress-strain and stress-time curves are achavied. Using these curves tensile elastic modulus in fiber and matrix directions and Poisson's ratio are obtained in room temperature. Also tensile and... 

    Reliability Estimation in the Presence of Censored Data A Case Study in an Automotive Part Manufacturing System

    , M.Sc. Thesis Sharif University of Technology Seyed Esfahani, Zahra (Author) ; Eshraghniaye Jahromi, Abdolhamid (Supervisor)
    Abstract
    In this study a brief definition of the basic concepts of the reliability and censoring data is given as well as the literature review of the censored data and introduction to concept of robust. In order to find suitable distribution by considering censored data, the goodness of fit test, Chi-squared test, and Anderson-Darling approaches are used. Moreover to estimate Parameter of the reliability distribution, Maximum Likelihood estimation (MLE) is given. A case study in an automotive part manufacturing system is presented and the distributions of reliability parameters of several critical components (i.e. reliability, hazard rate, etc.) have been estimated. Considering all data, and... 

    Impacts of fault diagnosis schemes on distribution system reliability

    , Article IEEE Transactions on Smart Grid ; Vol. 3, issue. 2 , 2012 , p. 720-727 ; ISSN: 19493053 Kazemi, S ; Lehtonen, M ; Fotuhi-Firuzabad, M ; Sharif University of Technology
    Abstract
    Design and development of fault diagnosis schemes (FDS) for electric power distribution systems are major steps in realizing the self-healing function of a smart distribution grid. The application of the FDS in the electric power distribution systems is mainly aimed at precise detecting and locating of the deteriorated components, thereby enhancing the quality and reliability of the electric power delivered to the customers. The impacts of two types of the FDS on distribution system reliability are compared and presented in this paper. The first type is a representative of the FDS which diagnoses the deteriorated components after their failing. However, the second type is a representative of... 

    Circuit-breaker automated failure tracking based on coil current signature

    , Article IEEE Transactions on Power Delivery ; Vol. 29, issue. 1 , February , 2014 , pp. 283-290 ; ISSN: 08858977 Razi-Kazemi, A. A ; Vakilian, M ; Niayesh, K ; Lehtonen, M ; Sharif University of Technology
    Abstract
    The online condition assessment of circuit breakers (CBs) has been increasingly requested by power utilities in recent years. Trip and close coil current (CC) signature is an effective and noninvasive parameter in CB online condition monitoring. This paper gives an insight into the impacts of the various failures on the coil current waveform, as well as on the CB operation time. The failures and their causes are categorized based on the outcome of these investigations. Finally, a new algorithm using trip/close CC is proposed to detect the mode and cause of CB incipient failures. In this study, the CC patterns are acquired by measurements carried out on (healthy and faulty) CBs of 72.5-kV and... 

    A risk-based decision making approach to determine fireproofing requirements against jet fires

    , Article Journal of Loss Prevention in the Process Industries ; Volume 26, Issue 4 , 2013 , Pages 771-781 ; 09504230 (ISSN) Badri, N ; Rad, A ; Kareshki, H ; Abdolhamidzadeh, B ; Parvizsedghy, R ; Rashtchian, D ; Sharif University of Technology
    2013
    Abstract
    API Publication 2218 is one of the most referred practices for fireproofing of onshore structural supports. Despite the extensive citation, it solely considers the effects of pool fire and rarely addresses jet fire outcomes. This absence of an explicit approach is common among all the other major references. Therefore, the basic objective of this paper is to introduce a new approach for determination of the necessity for fireproofing of structural supports against jet fires. For this purpose, the flame geometry and duration of jet fires are simulated for different leak sizes in identified fire potential sources. Then, following a worst-case analysis, those structures that may be impinged by... 

    Impacts of fault diagnosis schemes on distribution system reliability

    , Article IEEE Transactions on Smart Grid ; Volume 3, Issue 2 , February , 2012 , Pages 720-727 ; 19493053 (ISSN) Kazemi, S ; Lehtonen, M ; Fotuhi Firuzabad, M ; Sharif University of Technology
    2012
    Abstract
    Design and development of fault diagnosis schemes (FDS) for electric power distribution systems are major steps in realizing the self-healing function of a smart distribution grid. The application of the FDS in the electric power distribution systems is mainly aimed at precise detecting and locating of the deteriorated components, thereby enhancing the quality and reliability of the electric power delivered to the customers. The impacts of two types of the FDS on distribution system reliability are compared and presented in this paper. The first type is a representative of the FDS which diagnoses the deteriorated components after their failing. However, the second type is a representative of... 

    Failure analysis of superheater tube

    , Article Engineering Failure Analysis ; Volume 48 , February , 2015 , Pages 94-104 ; 13506307 (ISSN) Movahedi Rad, A ; Plasseyed, S. S ; Attarian, M ; Sharif University of Technology
    Elsevier Ltd  2015
    Abstract
    The failure analysis of a ruptured superheater tube after 20. years service in the oil-fueled boiler, as the typical problems in power plants, was investigated. A thin-lipped rupture at failed region was observed in superheater tube. By measuring the tube's wall thicknesses far from failed region, non-uniformity was seen. The suggested main root cause of failure was fireside corrosion of the tube during the service. Because of low grade of used fuel, sodium, sulfur, and vanadium elements were observed at the outer surface, which caused continuously scale formation and reduction of wall thickness, by metal consumption. In addition, it seems that it has been worsened by occurrence of long-term... 

    Investigating power outage effects on reliability of solid-state drives

    , Article Proceedings of the 2018 Design, Automation and Test in Europe Conference and Exhibition ; Volume 2018-January , 2018 , Pages 207-212 ; 9783981926316 (ISBN) Ahmadian, S ; Taheri, F ; Lotfi, M ; Karimi, M ; Asadi, H ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2018
    Abstract
    Solid-State Drives (SSDs) are recently employed in enterprise servers and high-end storage systems in order to enhance performance of storage subsystem. Although employing high speed SSDs in the storage subsystems can significantly improve system performance, it comes with significant reliability threat for write operations upon power failures. In this paper, we present a comprehensive analysis investigating the impact of workload dependent parameters on the reliability of SSDs under power failure for variety of SSDs (from top manufacturers). To this end, we first develop a platform to perform two important features required for study: A) a realistic fault injection into the SSD in the...