Simulation of the effect of sub- micron interface roughness on the stress distribution in functionally graded thermal barrier coatings (FG- TBC)

 In this research, a numerical modeling was utilized to calculate the stresses caused during thermal cycling in a functionally graded thermal barrier coating (FG - TBC). The temperature – dependent material response of this protective material was taken into account and the effects of thermal cycle and interface morphology of the ceramic / metallic layer in functionally graded coating system was investigated. Sinusoidal mode of asperity with specific wavelength and amplitude was considered to model the two dimensional geometry of interface profile between layers. A finite element model (FEM) was used to model the effect of thermal loading imposing on the thermo- mechanical response and stress distribution of FG- TBC. In this regard, different observable facts are taken into account in the model such as: non- homogenous temperature distribution, periodic boundary condition and convective heat transfer.  These phenomena depict the most real- world situation in numerical simulation of multi- layer coating during cooling and thermal cycling, specifically near the ceramic/metal interface. In addition, regions which are potent to crack initiation and propagation at the system and the subsequent delamination places of the TBCs system were predicted.