Numerical simulation of damage and inelastic deformation of porous thermal barrier coatings system under high-temperature fatigue loading condition

Abstract

In this study, a finite element (FE) analysis code installing an inelastic constitutive model and crack growth algorithm for thermal barrier coatings (TBCs) developed by Arai et al. was applied to TBCs and porous TBCs (P-TBCs) to evaluate stress, damage and crack initiation and propagation behavior under cycling loading at high temperatures of 673 K and 973 K. The results showed that (i) number of cycles until the crack tip reaching the interface between top coat and bond coat in P-TBC was longer than that in TBC. In other words, the fatigue crack growth rate of P-TBC was slower than that of TBC. (ii) Comparison of the cross-sectional observation results with the finite element analysis showed that the crack initiation location and the crack propagation path in FE analysis results were in good agreement with the observation results. The reason for slow fatigue crack growth rate observed in the P-TBC was as follow: the crack becomes stationary by reaching the wall of open pore. After that, the fresh crack initiates at the edge of open pore by subjecting to more cyclic loading. Consequently, the crack propagates as sewing between pores with cyclic loading which leads to the slow crack growth rate. (iii) Comparison of the surface crack initiation life between test results and the FE analytical results shows that the prediction results by finite element analysis agreed well with the observed results.

Keywords

• gas turbine
• thermal barrier coatings
• finite element analysis
• porosity
• high-temperature fatigue
• fatigue crack
• crack initiation life