Analytical and Finite Element Investigations of Trip Effect on Thermal Stress and Strain and Crack Growth in TBCs

Increasing the temperature of combustion products of turbines in power plants for increasing efficiency and decreasing fuel costs resulted in using thermal barrier coating (TBC) to protect hot gas path components of the turbo engines. TBCs consist of a ceramic top coat, an intermediate thermally grown oxide layer, and a metallic bond coat. In this paper, the damage caused by thermal shock during trip shut down in power plants is investigated based on analytical and finite element calculations in plain stress condition. The used geometry is a thin disk under an axisymmetry condition. The results show a sudden jump in thermal strain and stress in the ceramic top layer of TBC due to fast and inhomogeneous temperature loss. The fact that leads to similar behavior in stress intensity factor of a preexisting surface crack as it approaches critical value of ceramic top coat. This condition has a significant effect on length and growth rate of the crack in comparison with heating and constant temperature period. In addition, analytical calculation and finite element results match together and obtained crack behavior is compatible with other researcher's output.