A fundamental model of cyclic instabilities in thermal barrier systems. (English) Zbl 1116.74345

Karlsson, A. M.; Hutchinson, J. W.; Evans, A. G.

J. Mech. Phys. Solids 50, No. 8, 1565-1589 (2002).

Summary: 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.

MSC:

74F05	Thermal effects in solid mechanics
74C05	Small-strain, rate-independent theories of plasticity (including rigid-plastic and elasto-plastic materials)
74M15	Contact in solid mechanics
74S05	Finite element methods applied to problems in solid mechanics

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