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failure-analysis
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Total 152 records
Vulnerability Assessment of Existing RCMRF Structures Subjected to Near Field Earthquakes
, M.Sc. Thesis Sharif University of Technology ; 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...
Micromechanic Failure Analysis of Carbon/Phenolic Composite Conic Structures under Thermal Loading
, M.Sc. Thesis Sharif University of Technology ; Hosseini Kordkheili, Ali (Supervisor)
Abstract
In this study, through explaining a micromechanical model of progressive damage, failure in a composite conical structure under mechanical and thermal loads with 36 layers of carbon/phenolic material have been studied. To this end, first, mechanical behaviors of composite layers in micro and macro scale and their properties via fiber and matrix characterizations are discussed. In the following, selection of a proper RVE along with different types of boundary conditions on RVE are discussed. Then stress reinforcement coefficients in order to convert the mechanical and thermal stresses from macro to micro scale for carbon / phenolic material are extracted through defining appropriate RVE for...
Use of the Bayesian Approach in Failure Analysis and Life Prediction of Coil Springs of a Suspension System
, M.Sc. Thesis Sharif University of Technology ; Adib Nazari, Saeed (Supervisor) ; Karimzadeh, Ardavan (Supervisor)
Abstract
In this thesis, bayesian network has been used in analyzing the failure of a structural component. The design life of a structural component of a system can be limited or unlimited depending on the working conditions considered by the designers. However, usually during the operation of an industrial system or device, a structural component of it fails prematurely, in other words, its actual life is less than the design life. In this case, the failure must be analyzed to find the causes and factors. The method of work is such that first, according to the problem and the type of failure, the required analyzes and studies are considered. Then, a number of samples of the components, whose...
Failure Analysis in Conical Structures Made by Tape Winding Method under Cold and Hot Thermal Load
, M.Sc. Thesis Sharif University of Technology ; 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...
A Progressive Multiscale Model to Predict the Fatigue life of Laminated Composite Reinforced with Nanoparticles
, Ph.D. Dissertation Sharif University of Technology ; Hoseini Kordkhili, Ali (Supervisor)
Abstract
The increasing growth of composite materials in various industries and the use of these materials in the production of the main structures, recognized study and simulation of accurate behavior of these materials at different scales. On the other hand, the appearance of Nano-scale materials with amazing physical and mechanical properties and the use of these nanoparticles as reinforcement in the structure of polymer composites, further highlights the importance of simulating the behavior of polymer nanoparticles at different scales. One of the issues that is considered in various industries, especially in the airspace industry, is the phenomenon of fatigue. The complexity of the fatigue...
Analysis of Degradation for Laminated Notched Plate in Micromechanics by “Strain Energy Release Rate” Method and Illustrations the Results in Ansys
, M.Sc. Thesis Sharif University of Technology ; Hosseini Kordkheili, Ali (Supervisor)
Abstract
By developing composites, difficulties of modeling of degradation of properties as stiffness is most considered. The recent advances in the modeling of degradations in stratified composites have led to improved models on all scales. Macro scales methods are good to estimate fracture but not to estimate the failure in micro scale (as microcrack) and moreover, they need many experimental data. Therefore by considering a stratified structure which contains fiber, matrix and intermediate area, mesoscale modeling method is most suitable. In this research Micromechanical Progressive Algorithm (MPA) is used. The method employed is Micromechanic Method of Fracture (MMF). In this work by developing a...
Optimum Mechanical Joint Design for a Composite Laminate to a Metal Part
, M.Sc. Thesis Sharif University of Technology ; 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...
A Micromechanical Progressive Damage Algorithm for Prediction of Failure in Composite Laminates
, M.Sc. Thesis Sharif University of Technology ; 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,...
Progressive Flexural Fatigue Failure Analysis of Composites Through Layer Failure Determination
, Ph.D. Dissertation Sharif University of Technology ; Adibnazari, Saeed (Supervisor)
Abstract
Non-uniform damage growth of the composites under flexural fatigue loading condition makes it difficult to predict the fatigue behavior. In this thesis, A new modeling procedure is developed to introduce a progressive damage model. By using this model, it will be possible to define layer failure through its damage growth and layers constituents’ properties. On the other hand, an efficient micromechanics model must be utilized to relate the external loading to the constituents’ properties. Indeed the micromechanics model must be capable of including both constituent's properties and also fiber/matrix interface efficiency. For representing a complete description of the constituents’ properties...
Failure Tolerance of Epidemic Spreading in Complex Network
, M.Sc. Thesis Sharif University of Technology ; Jalili, Mahdi (Supervisor)
Abstract
Complex networks serve as generic models for many social, technological and biological systems that have been shown to share a number of common structural properties such as power-law degree distribution and small-worldness. These networks determine interactions and influence the spread of diseases, behaviours and ideas. Epidemics and failures like new behaviours ideas and innovations can spread throughout a network and prevent it from doing its functionalities. In this work, we investigate error and attack tolerance of epidemic spreading in complex networks. The main content of this thesis is arranged in three sections as follows: Firstly, the effect of random and systematic failures is...
Application of Composite FRP Decks in Building Structures
, M.Sc. Thesis Sharif University of Technology ; Mofid, Masood (Supervisor)
Abstract
This study is devoted to the analysis and design of a recently proposed steel-FRP deck system. A methodology is being proposed to analysis the elastic behavior of the proposed deck. In this method the deck is modeled as an equivalent orthotropic plate which is constrained by rotational springs along its edges. An analytical model of the proposed deck is derived by using Rayleigh-Ritz method where the primary Rayleigh-Ritz shape functions are generated from orthonormal polynomials by using Gram-Schmidt procedure. The results of the proposed methodology show good agreement with finite element analysis results. In order to test the applicability of the proposed deck as buildings flooring...
Failure Analysis of Torsion bar and Improvement of Manufacturing Processes
, M.Sc. Thesis Sharif University of Technology ; Farrahi, Gholamhossein (Supervisor)
Abstract
In order to improve the fatigue performance of torsion bar, induction surface hardening is performed. The aim of the present study is failure analysis of torsion bar and improvement of manufacturing process. Induction hardening was simulated using finite element method. As a result temperature history and residual stresses were obtained. Temperature and residual stress distributions are affected by the component geometry, the material behavior and the induction treatment parameters. Based on the residual stress distribution and the external fatigue loads, cracks can nucleate from the surface or below the hardened layer. Therefore, it is very important to determine the residual stress...
Reliability Estimation in the Presence of Censored Data A Case Study in an Automotive Part Manufacturing System
, M.Sc. Thesis Sharif University of Technology ; 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...
Improvment of Plant Availabilty Through Failure Prioritization Approach
, M.Sc. Thesis Sharif University of Technology ; Ghodrati, Behzad (Supervisor)
Abstract
In order to survive in the competitive market, companies should increase the availability of plants. In order to increase the availability of a system, the occurrence of failures should be decreased. It is not possible to eliminate all of failures simultaneously. It means, it is not cost effective and logical to concentrate on elimination of all failures. In Addition, the cause of some failures might not be eliminated. So, the occurrence of those failures should be postponed to the later time as much as possible. Therefore, the critical failure modes should be identified to be concentrated for further analysis. Ultimately; the root causes of these failures should be explored and if it is...
Computerized Maintenance Management System for Cement Plants (CMMS)
, M.Sc. Thesis Sharif University of Technology ; 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...
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 ; 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...
Performance-based seismic assessment of steel frames using endurance time analysis
, Article Engineering Structures ; Vol. 69 , 2014 , Pages 216-234 ; ISSN: 01410296 ; Sattar, S ; Estekanchi, H. E ; Sharif University of Technology
Abstract
The current performance-based seismic assessment procedure can be computationally intensive as it requires a large number of time history analyses (THA) each requiring time intensive post-processing of results. This study proposes the endurance time analysis (ETA) method as an alternative method to THA and incremental dynamic analysis (IDA). ETA is a time history based dynamic pushover procedure that applies a set of gradually intensifying acceleration functions to the structure and monitors the performance of the building accordingly. In this paper, the application of ETA in the seismic assessment of multistory steel concentrically braced frames is compared with THA and IDA methods....
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 ; 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...
Simulation of blood oxygenation in capillary membrane oxygenators using modified sulfite solution
, Article Biophysical Chemistry ; Vol. 195, issue , Dec , 2014 , p. 8-15 ; Amoabediny, G ; Rasouli, A ; Ramedani, A ; Poorkhalil, A ; Kashefi, A ; Mottaghy, K ; Sharif University of Technology
Abstract
Blood oxygenation is the main performance characteristic of capillary membrane oxygenators (CMOs). Handling of natural blood in in vitro investigations of CMOs is quite complex and time-consuming. Since the conventional blood analog fluids (e.g. water/glycerol) lack a substance with an affinity to capture oxygen comparable to hemoglobin's affinity, in this study a novel approach using modified sulfite solution is proposed to address this challenge. The solution comprises sodium sulfite as a component, simulating the role of hemoglobin in blood oxygenation. This approach is validated by OTR (oxygen transfer rate) measured using native porcine blood, in two types of commercially available...
Failure analysis: Sulfide stress corrosion cracking and hydrogen-induced cracking of A216-WCC wellhead flow control valve body
, Article Journal of Failure Analysis and Prevention ; Vol. 14, issue. 3 , 2014 , p. 376-383 ; Kokabi A.H ; Mostowfi J ; Sharif University of Technology
Abstract
The wellhead flow control valve bodies which are the focal point of this failure case study were installed in some of the upstream facilities of Khangiran's sour gas wells. These valve bodies have been operating satisfactorily for 3 years in wet H2S environment before some pits and cracks were detected in all of them during the periodical technical inspections. One failed valve body was investigated by chemical and microstructural analytical techniques to find out the failure cause and provide preventive measures. The valve body alloy was A216-WCC cast carbon steel. During investigation many cracks were observed on the inner surface of the valve body grown from the surface pits. The results...