Innovative methods, based on thermodynamics theory, will be developed to establish a unified approach in quantifying the damage state of thermal barrier coatings (TBC) under high temperature service conditions. After surveying existing material damage models, a mechanistic model which describes rate- and temperature-dependent deformation behavior of TBC with material damage will be proposed. Specifically, effects of creep (or viscoelasticity) and time dependent changes in various contributing factors, such as stress relaxation, due to microcrack growth, and oxidation at the bond coat/top coat interface, on the overall stress-strain behavior of TBC, will be considered. Two dominant damage parameters, one associated with the microcrack initiation and propagation and the other with formation and growth of oxide, will be employed in the damage constitutive anisotropic elastic/creep law. Numerical algorithms associated with the proposed life prediction model will then be developed. Finally, the proposed TBC life prediction model ~r;will be validated against existing experimental results.Commercial Applications:The proposed research will establish a unified life prediction methodology for TBC coated components, thereby, eliminating the 7 purely empirical life prediction techniques funded by previous NASA research programs. In addition, the methodology can be used to tailor the material properties of the TBC materials, so that more thermal resistant TBC processes can be developed more quickly.
