| Thermal barrier coatings is usally a kind of ceramic materials, which with verylow thermal conductivity and excellent high temperature oxidation resistance, whichis deposited on the surface of high temperature resistant metal or superalloy.Thermal barrier coatings can reduce the work temperature of the protected superalloy substrate and reduce the thermal shock effectively. Furthermore, it canalleviate the cooling air and significantly improve the thermal efficiency of themachine. So thermal barrier coatings has been used in the fields of the hotsection ofearonaoutic and astronaoutics, chemistry and chemical engineering, metallurgyindustry and energy industry. Because of the complexity of thermal barrier coatingswhich are covered on the surface of turbine blade system, their structures and theseverity of operating conditions make the stress evolution and life prediction of thesystem in service process is a key and difficult issue. So the main aim of this thesisis to simulate and predict the stress field evolution and the key factors in TBCScovered turbine blade system during thermal cycles, to explore thermal barriercoating life prediction theory and experiment method. The main contents and theonnovations of this thesis are listed as follows,First, this paper based on Fourier law of heat transfer and the finite elementmethod, got the steady temperature distribution and heat insulation effects of thefour hot flat model of the system under different TBC surface temperature. The resultsshow that the TBC layer bear the main temperature gradient, the temperature gradientin TGO BC Substrate is small. This paper simulated the influence of coatingthickness on the temperature distribution, found that the TBC is thicker, thetemperature of the substrate in service process is lower, the heat insulation of the TBCis better. But the TBC thickness increased to a certain degree, the increase ofinsulation effect with the increase of the TBC thickness is very limited. This paperexamined the influence of the porosity on heat transfer coefficient of TBC, found thatthe porosity have a major influence on heat transfer coefficient of TBC. The porosityis higher, the heat transfer coefficient of TBC is smaller, the heat insulation of theTBC is better. The paper also fit the equation between equivalent heat transfercoefficient and the porosity.Secondly, this paper simulated initial residual stress field of the TBC system. When the thermal barrier coating system with flat plate sturcture cooling frompreparation temperature to room temperature, there are uneven residual stress in them,the preparation temperature is higher, initial residual stress in the system is bigger.Residual compression stress in TGO especially large. This layer exist stresssingularity which is one of the main reasons cause thermal barrier coating failure.Through the simulation found that the residual stress in TBC, TGO appear the trend toreduce along with the increase of ceramic powder coating thickness; the thickness ofthe TGO produce in the fabrication process is not obviously affect the stressdistribution in TBC and TGO. In the presence of a temperature gradient conditions tocooling, the change of initial residual stress distribution and ideology in the systemclosely related to the preparation temperature.Third, this paper puts forward a kind of finite element modeling methodapplicable to thermal barrier coating turbine blade system, which can be effective inestablishing the system for finite element analysis model, based on finite elementsoftware and3D modeling software; This paper also puts forward two kinds ofthermal barrier coating turbine blade stress evolution and dangerous area forecastmethod, which can reduce the pre-treatment cost and artificial processing error rateand improve the accuracy of the prediction results; This paper also creates a largenumber of support software with thermal barrier coating of the finite elementanalysis under thermal cycle conditions, which not only make the turbine bladesthermal barrier coating in the large number of thermal cycle work under thecondition of the finite element analysis quick and easy to realize.Fourth, in this paper, the thermal barrier coating turbine blade system in theprocess of stress fields are simulated, so we can obtain some relative results such asthe system in the process of thermal cycle about each layer of the3d temperaturefield, the displacement field and the evolution of stress and strain, and we canascertain the distribution of the danger area in the ceramic layer based on the firststrength theory, which is predicted the most likely happened first damage area. Thispaper also work to simulate the influence of working temperature to thermal barriercoating turbine blade system stress distribution and evolution, and discusses thethermal barrier coating the life of turbine blade system. Finally, we also investigatethe thermal barrier coating of turbine blade system. Through compared the results ofthe finite element with the experimental results, such as the actual measured thesystem of the temperature field, the strain field and the failure of the position, which further verified the finite element simulation of the accuracy of the results.In general, the thesis is based on the finite element experimental method. In theessay, we simulate the critical physical quantities of the thermal barrier coatings inthe service process, provide important reference for the designing of turbine bladesand the optimization of fabricating parameters of the thermal barrier coatings, andalso expand the application scope of the finite element method. |
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