Finite element modelling of tbc failure mechanisms byusing extended finite element method and cohesive zonemethod

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Tezin Türü: Yüksek Lisans

Tezin Yürütüldüğü Kurum: Orta Doğu Teknik Üniversitesi, Fen Bilimleri Enstitüsü, Türkiye

Tezin Onay Tarihi: 2019

Tezin Dili: İngilizce

Öğrenci: SAFA MESUT BOSTANCI

Danışman: Ercan Gürses

Özet:

Thermal Barrier Coatings have been widely used in modern turbine engines to protect the nickel based metal substrate from the high temperature service conditions, 1600-1800 K. In this study, failure mechanisms of typical Air Plasma Sprayed Thermal Barrier Coatings (TBC) used in after-burner structures composed of three major layers: Inconel 718 substrate, NiCrAlY based metallic bond coat (BC) and Yttria Stabilized Zirconia (YSZ) based ceramic top coat (TC) are investigated. Investigation of the cracking mechanism of TBC in terms of design and performance is very important because the behavior of TBCs on ductile metallic substrates is brittle. To this end, four-point bending experiments reported in [1] are analyzed by using the Extended Finite Element Method (XFEM) and the Cohesive Zone Method (CZM). All the analyses are conducted with the commercial finite element software ABAQUS. Three different models with varying TC and BC thicknesses are studied. It is observed that multiple vertical cracks are initiated in the TC. Cracks initiate at the top of YSZ and propagate through the whole TC until they reach the interface between the TC and the BC. Then, delaminations at the interface between the TC and the BC start. It is observed that the average spacing of cracks in TC increases with the increasing thickness of the TC and the delamination becomes prominent with the increasing TC thickness. Numerical results are found to be consistent with the experimental results.