Issue 35

T. Sadowski et alii, Frattura ed Integrità Strutturale, 35 (2016) 492-499; DOI: 10.3221/IGF-ESIS.35.55 492 Cracks path growth in turbine blades with TBC under thermo – mechanical cyclic loadings T. Sadowski, P. Golewski Lublin University of Technology, Nadbystrzycka 40, 20-618 Lublin A BSTRACT . Blades of combustion turbines are extremely loaded turbojet elements, which transmit operative energy onto a rotor. Experiences of many years indicate, that cracks initiation and propagation in the blades during the operation time can cause destruction not only of the engine, but sometimes an airplane. In high temperature one of the most often occuring interactions in the turbine engine are time variable force fields, caused by non-stationary flowing of an exhaust gas and aerodynamical interaction of the engine elements. The extremal thermo-mechanical loadings initiate gradual degradation process of the blades as a result of fatigue and material creep. More often Thermal Barrier Coatings (TBCs) are applied on the turbine blade surface to provide protection not only against the high temperature but also against aggressive environment. The paper presents the advantages of applying of the TBC layers for increase of the cracks resistance to gradual degradation of the turbine blades. The level of save values of thermo-mechanical loading was estimated. Analysis of critical values of loading leading to crack initiation, further growth and the final blade fragmentation was performed. The most efforted places of the turbine blades were selected and crack paths due to thermo-mechanical cyclic loading were determined. K EYWORDS . Turbine blade; Thermal barrier coating; Finite element method. I NTRODUCTION he process of thermo - mechanical fatigue [1-3] takes place in structural elements, working in conditions of cyclic temperature changes and under variable mechanical loadings. This mainly concerns for example: rotors of turbines, turbine blades, heat exchangers, pieces of nuclear reactors, heads, valves and pistons of combustion engines. The observation of thermal fatigue process in construction is usually very complex. It results mainly from the interaction between many factors influencing the fatigue process, and also from the fact that the visual assessment of degradation stage is possible only in the final stage. In high temperature, one of the most often occurring interactions in the turbine engine are the time variable force fields, caused by non-stationary flowing of an exhaust gas and aerodynamic interaction of engine elements. They cause degradation of the blades as a result of fatigue and material creep. Moreover, unfavorable influence of the high temperature on durability of the blades results from intensification of corrosion and erosion processes [4], which change internal structure of the turbine material and gradual degradation of its strength. T