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Effect of Melt Quality & Melt Flow on Defects in Gravity Casting of AS5U3G Aluminum Alloy
, M.Sc. Thesis Sharif University of Technology ; Varahram, Naser (Supervisor)
Abstract
AS5U3G and AS7U3G are two prevalent types of alloy which are used in producing cylinder head. In this research AS5U3G alloy is studied. Gravity casting is one of the method of producing this part. Produced porosities in cylinder head casting process, cause leakage in this part. In order to solve this problem, some actions have been taken that we can divide them into quality operations improvement of melt and making changes in casts. The sampling is done in four levels to evaluate the gas porosity and shrinkage. In these levels, pressure and degassing duration and strontium's modifying in a fixed temperature have been evaluated. Based on reports by comparing density of relative samples, it...
Thermo-mechanical behaviours of light alloys in comparison to high temperature isothermal behaviours
, Article Materials at High Temperatures ; Vol. 31, issue. 1 , 2014 , pp. 12-17 ; ISSN: 09603409 ; Farrahi, G. H ; Winter, G ; Eichlseder, W ; Sharif University of Technology
Abstract
In this article, out-of-phase thermo-mechanical fatigue (TMF) behaviours of light alloys were investigated in comparison to their high temperature low cycle fatigue (LCF) behaviours. For this objective, strain based fatigue tests were performed on the A356 aluminium alloy and on the AZ91 magnesium alloy. Besides, TMF tests were carried out, where both strain and temperature changed. The fatigue lifetime comparison demonstrated that the TMF lifetime was less than that one under LCF loadings at elevated temperatures for both light alloys. The reason was due to severe conditions in TMF tests in comparison to LCF tests. The temperature varied in TMF test but it was constant under LCF loadings....
Failure analysis of a cracked gasoline engine cylinder head
, Article Journal of Failure Analysis and Prevention ; Volume 12, Issue 3 , 2012 , Pages 286-294 ; 15477029 (ISSN) ; Mafi, A ; Roozban, M ; Moghaddam, F ; Sharif University of Technology
2012
Abstract
This article presents a failure analysis on a gasoline engine cylinder head made of aluminum alloy, which has been used in passenger cars. During an endurance test, a crack initiated from the interior wall of a hole in the center of the cylinder head and then propagated through the thickness of the cylinder head. The metallurgical examinations are conducted in the crack origin zone. The results show that there are many casting pores due to poor quality of casting in the failed cylinder head which has certainly played a crucial role in initiating the crack. Finite element analysis of the cylinder head is performed to identify the stress components. Modeling of a bolt for the hole shows that...
Experimental fatigue lifetime of coated and uncoated aluminum alloy under isothermal and thermo-mechanical loadings
, Article Ceramics International ; Volume 39, Issue 8 , December , 2013 , Pages 9099-9107 ; 02728842 (ISSN) ; Farrahi, G. H ; Winter, G ; Eichlseder, W ; Sharif University of Technology
2013
Abstract
This paper presents the fatigue lifetime of an aluminum-silicon-magnesium alloy, widely used in diesel engine cylinder heads, both with and without a thermal barrier coating (TBC) system. The coating system in this study consists of two layers including a 150 μm thick metallic bond coat and a zirconium oxide top coat 350 μm thick. These coating layers were applied on the substrate of A356.0 alloy by air plasma thermal spraying. The isothermal fatigue tests were conducted in low cycle fatigue (LCF) regime at various temperatures. Out-of-phase thermo-mechanical fatigue (OP-TMF) tests were also performed at different maximum temperatures and constraint factors. Experimental results demonstrate...
Thermal Analysis of Tiba Engine Cylinder Head
, M.Sc. Thesis Sharif University of Technology ; Afshin, Hossein (Supervisor) ; Hosseini, Vahid (Supervisor)
Abstract
These days, the heat transfer phenomena is an important issue in internal combustion engines design because of direct effects on the performance, efficiency and emission of engine. One of the main parts is cylinder head which contacts with hot gases in combustion chamber and expose high heat flux. In this thesis, cylinder head of Tiba engine modeled by three dimensional and transient thermal analysis. In this modeling in order to consideration the effect of fluid flow, different domain of cylinder head (water jacket, intake/exhaust ports) has been simulated and appended to the model. Also combustion phenomena modeled separately, and then the heat transfer coefficient in the surface of...
Effects of preheating temperature and cooling rate on two-step residual stress in thermal barrier coatings considering real roughness and porosity effect
, Article Ceramics International ; Vol. 40, Issue. 10 , December , 2014 , pp. 15925-15940 ; ISSN: 02728842 ; Farrahi, G. H ; Azadi, M ; Ghodrati, M ; Sharif University of Technology
Abstract
In this research, a finite element model was developed in order to simulate the two-step residual stress distribution of a thermal barrier coating system, considered to be used in diesel engine cylinder head, with a real roughness and real porosity. Two steps including the bond coat and the top coat deposition processes were taken into account. The real geometry of coating layers, including the roughness and the porosity, was also considered based on a scanning electron microscopy image. Then, effects of the convective heat transfer coefficient and initial substrate and substrate/bond coat preheating temperatures on the residual stress were studied. Obtained results illustrate that the...
Numerical simulations of cyclic behaviors in light alloys under isothermal and thermo-mechanical fatigue loadings
, Article Materials and Design ; Vol. 56 , April , 2014 , pp. 245-253 ; ISSN: 02641275 ; Shamloo, A ; Felfeli, M ; Azadi, M ; Sharif University of Technology
Abstract
In this article, numerical simulations of cyclic behaviors in light alloys are conducted under isothermal and thermo-mechanical fatigue loadings. For this purpose, an aluminum alloy (A356) which is widely used in cylinder heads and a magnesium alloy (AZ91) which can be applicable in cylinder heads are considered to study their stress-strain hysteresis loops. Two plasticity approaches including the Chaboche's hardening model and the Nagode's spring-slider model are applied to simulate cyclic behaviors. To validate obtained results, strain-controlled fatigue tests are performed under low cycle and thermo-mechanical fatigue loadings. Numerical results demonstrate a good agreement with...
Comparison between isothermal and non-isothermal fatigue behavior in a cast aluminum-silicon-magnesium alloy
, Article Strength of Materials ; Volume 47, Issue 6 , November , 2015 , Pages 840-848 ; 00392316 (ISSN) ; Winter, G ; Farrahi, G. H ; Sharif University of Technology
Springer New York LLC
2015
Abstract
In the present study, the out-of-phase thermomechanical fatigue (OP-TMF) behavior of a cast aluminum-silicon-magnesium alloy, the A356.0 alloy which has been widely used in diesel engine cylinder heads, is compared to room-temperature and high-temperature low cycle fatigue (RT-, HT-LCF) behaviors. For this purpose, strain/temperature-controlled isothermal and non-isothermal fatigue tests were performed based on realistic loading conditions in cylinder heads. Fatigue tests results showed that the plastic strain increased during cycles under constant mechanical strain amplitude, while the specimen failed. Under LCF loadings, the cyclic hardening occurred at low temperatures for the A356.0...
Investigation of the relationship between engine valve leakage and acoustic emission measured on the cylinder head ignoring combustion effects
, Article Proceedings of the Institution of Mechanical Engineers, Part E: Journal of Process Mechanical Engineering ; Volume 230, Issue 1 , 2016 , Pages 3-9 ; 09544089 (ISSN) ; Mehdigholi, H ; Behzad, M ; Sharif University of Technology
SAGE Publications Ltd
Abstract
Finding leakage in valves is important to troubleshoot performance of internal combustion engines. Leakage can lead to a reduction in engine power and an increase in emissions. The main objective of the present study is to investigate relationship between valve leakage and the acoustic emission generated from the steady flow in the cylinder head of the internal combustion engine. The test rig is the cylinder head for a spark-ignited engine. The test rig simulates the valve leakage due to valve clearance. The valve clearance fault was artificially simulated by a very small lift in valve. The acoustic emission method was used to measure acoustic emission signals generated by valve flow....
Numerical simulation of thermal barrier coating system under thermo-mechanical loadings
, Article Proceedings of the World Congress on Engineering 2011, WCE 2011, 6 July 2011 through 8 July 2011 ; Volume 3 , July , 2011 , Pages 1959-1964 ; 9789881925152 (ISBN) ; Azadi, M ; Farrahi, G. H ; Sharif University of Technology
2011
Abstract
In the present paper, numerical simulation of thermal barrier coating system under thermo-mechanical loadings is performed, using the finite element method in ABAQUS software. The base material is Aluminum-silicon alloy, A356.0 which is widely used in automotive components such as diesel engine cylinder heads. Thermal barrier coatings (TBCs) are applied to combustion chamber in order to reduce fuel consumption and pollutions and also improve fatigue life of components. The roughness effect of coating layers on stress distribution of test specimens is investigated. Semi-ellipsoid roughness of the interfaces between substrate/bond coat and bond coat/top coat are simulated to get the stress...