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Functional Design of a Coating System for the Telescope Mirrors, A Recognition to Telescope of Iranian National Observatory
, M.Sc. Thesis Sharif University of Technology ; Moshfegh, Alireza (Supervisor) ; Khosroshahi, Habib (Co-Advisor)
Abstract
Functional design of coating system for the primary mirror of the Iranian National Observatory (INO) is done. This telescope has a 3.4 m primary mirror in diameter, made of Zerodur from Schott. Although similar coating systems are in use since years ago, this is the first attempt to design a system for such a large surface case in Iran. Systematic approach led us first to clarify and identifying the design requirements. Lower limit of 80% for reflectance on all wavelength range from 325-1000 nm, thickness of 100 nm with un-uniformity of 5 nm, adhesion enough to pass the selotape test and surface roughness of less than 8 nm. Study of the available methods for coating and selection of the best...
Thermo-mechanical stress analysis of thermal barrier coating system considering thickness and roughness effects
, Article Surface and Coatings Technology ; Vol. 243 , 2014 , pp. 91-99 ; ISSN: 02578972 ; Azadi, M ; Farrahi, G. H ; Sharif University of Technology
Abstract
Cast aluminium-silicon alloy, A356.0, is widely used in automotive and aerospace industries because of its outstanding mechanical, physical, and casting properties. Thermal barrier coatings can be applied to combustion chamber to reduce fuel consumption and pollutions and also improve fatigue life of components. The purpose of the present work is to simulate stress distribution of A356.0 under thermo-mechanical cyclic loadings, using a two-layer elastic-visco-plastic model of ABAQUS. The results of stress-strain hysteresis loop are validated by an out of phase thermo-mechanical fatigue test. Different thicknesses from 300 to 800. μm of top coat and also roughness of the interfaces are...
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...
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...
Damage prediction for un-coated and coated aluminum alloys under thermal and mechanical fatigue loadings based on a modified plastic strain energy approach
, Article Materials and Design ; Volume 66, Issue PB , 2015 , Pages 587-595 ; 02613069 (ISSN) ; Farrahi, G. H ; Winter, G ; Huter, P ; Eichlseder, W ; Sharif University of Technology
Abstract
In this article, a novel energy-based lifetime prediction model has been presented for uncoated and coated aluminum alloys, subjected to thermal and mechanical fatigue loadings. For this objective, isothermal and thermo-mechanical fatigue tests were performed on the A356.0 alloy, with and without thermal barrier coating systems. This model, which was based on the plastic strain energy, had three correction factors including temperature, strain and mean stress effects. The predicted lifetime showed a proper agreement with experimental data. By the present model, higher accuracy was obtained in comparison to other existed approaches. Besides, the present model had lower number of material...
Anticorrosion properties of smart coating based on polyaniline nanoparticles/epoxy-ester system
, Article Progress in Organic Coatings ; Volume 75, Issue 4 , 2012 , Pages 502-508 ; 03009440 (ISSN) ; Shojaei, A ; Shariatpanahi, H ; Neshati, J ; Sharif University of Technology
2012
Abstract
In this study, the anticorrosive effect of dodecylbenzenesulfonicacid-doped polyaniline nanoparticles [n-PANI (DBSA)] as a conductive polymer was investigated using electrochemical impedance spectroscopy (EIS) and X-ray photoelectron spectroscopy (XPS) techniques. Initially, the n-PANI (DBSA) were successfully synthesized via inverse microemulsion polymerization leading to the spherical nanoparticles with an average diameter less than 30 nm. Two coating systems including 1 wt% n-PANI(DBSA) blended epoxy ester (n-PANI(DBSA)/EPE) and neat epoxy ester (EPE) were coated on the carbon steal substrate. The anticorrosion performance of the prepared coatings was studied using EIS measurement in 3.5%...
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...
Corrosion resistance evaluation of rebars with various primers and coatings in concrete modified with different additives
, Article Construction and Building Materials ; Volume 262 , 2020 ; Jahandari, S ; Rasekh, H ; Shariati, M ; Afshar, A ; Shokrgozar, A ; Sharif University of Technology
Elsevier Ltd
2020
Abstract
Corrosion of steel rebars in concrete can reduce the durability of concrete structures in coastal environments. The corrosion rate of these concrete structures can be reduced by using suitable concrete additives and coating on rebars. This paper investigates the corrosion resistance of steel rebars by the addition of pozzolanic materials including fly ash, silica fume, polypropylene fibers, and industrial 2-dimethylaminoethanol (FerroGard 901) inhibitors to the concrete mixture. Three different types of rebars including mild steel rebar st37, and two stainless steel reinforcements, AISI 304 and AISI 316, were used. Various types of primer and coating including alkyd based primer, hot-dip...