Journal of the Mechanics and Physics of Solids
Cyclic morphological instabilities in the thermally grown oxide (TGO) represent a source of failure in some thermal barrier systems. Observations and simulations have indicated that several factors interact to cause these instabilities to propagate: (i) thermal cycling; (ii) thermal expansion misfit; (iii) oxidation strain; (iv) yielding in the TGO and the bond coat; and (v) initial geometric imperfections. This study explores a fundamental understanding of the propagation phenomenon by devising a spherically symmetric model that can be solved analytically. The applicability of this model is addressed through comparison with simulations conducted for representative geometric imperfections and by analogy with the elastic/plastic indentation of a half space. Finite element analysis is used to confirm and extend the model. The analysis identifies the dependencies of the instability on the thermo-mechanical properties of the system. The crucial role of the in-plane growth strain is substantiated, as well as the requirement for bond coat yielding. It is demonstrated that yielding of the TGO is essential and is, in fact, the phenomenon that differentiates between cyclic and isothermal responses.
Karlsson, A. M., Hutchinson, J. W., and Evans, A. G., 2002, "A Fundamental Model of Cyclic Instabilities in Thermal Barrier Systems," Journal of the Mechanics and Physics of Solids, 50(8) pp. 1565-1589.
NOTICE: this is the author’s version of a work that was accepted for publication in Journal of the Mechanics and Physics of Solids. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Journal of the Mechanics and Physics of Solids, 50, 8, August 2002; 10.1016/S0022-5096(02)00003-0