On the opening of a class of fatigue cracks due to thermo-mechanical fatigue testing of thermal barrier coatings |
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| Authors: | M.T. Hernandez D. Cojocaru M. Bartsch A.M. Karlsson |
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| Affiliation: | 1. Department of Mechanical Engineering, University of Delaware, Newark, DE 19716-3140, USA;2. German Aerospace Center (DLR), D-51147 Cologne, Germany;1. Korea Institute of Nuclear Safety, Daejeon, Republic of Korea;2. Department of Mechanical Engineering, Korea University, Seoul, Republic of Korea;3. The University of Manchester, Manchester M13 9PL, UK;4. Department of Mechanical Engineering, Imperial College, London SW7 2BX, UK;1. Icahn School of Medicine at Mount Sinai, United States;2. Celiac Center, Beth Israel Deaconess Medical Center, United States;3. Celiac Disease Center, Department of Medicine, Columbia University Medical Center, United States;4. Department of Epidemiology, Mailman School of Public Health, Columbia University Medical Center, United States;1. State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, China;2. University of Chinese Academy of Sciences, Beijing 100049, China;3. The State Key Laboratory of Tribology, Tsinghua University, Beijing 100084, China;1. School of Materials Science and Engineering, Shandong University, Jinan 250061, China;2. School of Materials Science and Engineering, Shandong Jianzhu University, Jinan 250101, China |
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| Abstract: | The evolution of fatigue cracks observed in thermal barrier coatings (TBCs) subjected to an accelerated test scheme is investigated via numerical simulations. The TBC system consists of a NiCoCrAlY bond coat and partially yttria stabilized zirconia top coat with a thermally grown oxide (TGO) between these two coatings. The cracks of interest evolve in the bond coat parallel and near the interface with the TGO during thermo-mechanical fatigue testing. In their final stage, the cracks lead to partial spallation of the TBC. This study focuses on why the cracks open to their characteristic shape. To this end, finite element simulations are utilized. The crack surface separation is monitored for a range of material properties and oxidation rates. The simulations show that the inelastic response of the bond coat and the oxidation rate of the TGO govern the crack surface separation. Most interestingly, permanent separation of the crack surfaces is caused by a structural ratcheting in the vicinity of the crack. |
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