A software tool for lifetime prediction of thermal barrier coating systems
Résumé
Thermal barrier coatings (TBCs) are widely used to extend the lifetime of key components within gas turbines, and so the ability to predict the lifetime of TBCs is a high priority for gas turbine users. A complete model of TBC failure requires characterisation of the coating system, identification of the main failure mechanisms, quantitative description of stress evolution in the key areas within the coating system and robust failure criteria for each failure mechanism. Thus lifetime prediction invariably requires a massive effort both in terms of determining the appropriate input parameters for the model and in computing the solution. In order to reduce the need for extensive calculation, a software tool has been developed that interpolates the key stresses for each failure mechanism from a matrix of previously calculated values. The matrix of values is generated using a recently developed finite element (FE) model of TBC lifetime of an IN738/MCrAlY/EB-PVD YSZ system. The stress distribution predicted by this model is dependent on exposure time and temperature as well as the morphology of the bond coat/ceramic interface and requires FE calculation for each specific set of conditions. The software tool interpolates the FE results with respect to time, temperature and a geometric parameter to predict key stresses that drive failure, and coating system lifetime. This paper describes the principles behind the development of the algorithms implemented in the software tool. Validation of the approach is in progress through comparison of predictions with non-destructive measurements on the coating system.