Analysis of crack nets development in thermal barrier coatings

After a relatively short time in service, components with thermal barrier coatings (TBCs) protection typically develop a system of cracks that propagate from the coated surface toward the interface. Usually these cracks propagate across the thickness of the protective coating and branch along the interface between the coating and the bank metal. The presence of these crack nets is a concern for the durability of the components with TBCs. In the study of thin TBCs by Rubinstein and Tang (Int J Solids Struct 42: 5831-5847, 2005), it was found that in a number of cases, these components may still serve for a long time because of crack growth resistance development for cracks growing along the interface, which was found to be the most stable crack path under thermal loading conditions. One of the aims of this study is to determine whether similar fracture resistance is typical for thick TBC coatings as well. The emphases of the analysis presented here are on cases when the coating thickness is comparable to the thickness of the bank material, and on the effect of heat conduction changes due to branching of the developing cracks in a direction parallel to or along the interface. These items were not addressed in sufficient detail in the previous investigations.