13th International Conference on Fracture June 16–21, 2013, Beijing, China -8- The influence of variational crack locations, length and direction on the development of stress and the instability amplitude is discussed. The main results from the calculations suggest: (1) The crack within TC would promote the TGO displacement instability significantly, especially the crack close to the instability site. (2) The tensile part of the out-of-plane stress, which is responsible for the delamination, mainly concentrates on the zone near the instability site and it can be promoted by the crack existing within TC. However, the compressed part of in-plane stress, which is responsible for the buckling, is restrained by this crack. (3) The crack length and direction are two key factors affecting the displacement instability, especially the crack length. As the increase of the crack length, the amplitude of displacement instability increases significantly, which results in a serious interface distortion. The effect of crack direction mainly focuses on the downward displacement instability. The crack in the direction perpendicular to the flat interface is the optimal choice for prevent the large instability. Acknowledgements The work is supported by the National Natural Science Foundation of China (11021202 and 11172227) and National 973 Program (2013CB035701). References [1] Padture, N.P., M. Gell, and E.H. Jordan, Materials science - Thermal barrier coatings for gas-turbine engine apptications. Science, 296(2002) 280-284. [2] Karlsson, A.M., J.W. Hutchinson, and A.G. Evans, A fundamental model of cyclic instabilities in thermal barrier systems. Journal of the Mechanics and Physics of Solids, 50(2002) 1565-1589. [3] Evans, A.G., et al., Mechanisms controlling the durability of thermal barrier coatings. Progress in Materials Science, 46(2001) 505-553. [4] Evans, A.G., M.Y. He, and J.W. Hutchinson, Mechanics-based scaling laws for the durability of thermal barrier coatings. Progress in Materials Science, 46(2001) 249-271. [5] Mumm, D.R., A.G. Evans, and I.T. Spitsberg, Characterization of a cyclic displacement instability for a thermally grown oxide in a thermal barrier system. Acta Materialia, 49(2001) 2329-2340. [6] Karlsson, A.M., C.G. Levi, and A.G. Evans, A model study of displacement instabilities during cyclic oxidation. Acta Materialia, 50(2002) 1263-1273. [7] Ambrico, J.M., M.R. Begley, and E.H. Jordan, Stress and shape evolution of irregularities in oxide films on elastic-plastic substrates due to thermal cycling and film growth. Acta Materialia, 49(2001) 1577-1588. [8] He, M.Y., A.G. Evans, and J.W. Hutchinson, The ratcheting of compressed thermally grown thin films on ductile substrates. Acta Materialia, 48(2000) 2593-2601. [9] Karlsson, A.M. and A.G. Evans, A numerical model for the cyclic instability of thermally grown oxides in thermal barrier systems. Acta Materialia, 49(2001) 1793-1804. [10] Karlsson, A.M., J.W. Hutchinson, and A.G. Evans, The displacement of the thermally grown oxide in thermal barrier systems upon temperature cycling. Materials Science and Engineering A, 351(2003) 244-257. [11] Karlsson, A.M., J.W. Hutchinson, and A.G. Evans, A fundamental model of cyclic instabilities in thermal barrier systems. Journal of the Mechanics and Physics of Solids, 50(2002) 1565-1589. [12] He, M.Y., A.G. Evans, and J.W. Hutchinson, The ratcheting of compressed thermally grown thin films on ductile substrates. Acta Materialia, 48(2000) 2593-2601. [13] Karlsson, A.M. and G. Evans, A numerical model for the cyclic instability of thermally grown oxides in thermal barrier systems. Acta Materialia, 49(2001) 1793-1804.
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