Analytical and numerical investigations of the crack behavior in thermal barrier coatings under the trip thermal load

Abstract

Increasing the temperature of the combustion products in power plant turbines is one of the easiest way to enhance the efficiency and decrease the fuel costs. Therefore, using thermal barrier coating (TBC) to protect the load carrying components in the hot gas path is inevitable. In this manuscript, the damage caused by trip shutdown in power plants as an emergency thermal shock is investigated based on analytical and finite element (FE) analysis for in-plane stress condition. The used geometry is a thin disk under axisymmetric condition. The results show that as a consequence of a fast and inhomogeneous temperature loss, a thermal strain of more than 1.1% occurs in the TBC top layer. Similar behavior is observed in the stress and thus the stress intensity factor of a preexisting surface crack because it approaches the critical value of the ceramic top layer. This condition has a significant effect on the length and growth rate of the crack in comparison with heating and constant temperature period as the crack length is about one- third of the ceramic layer thickness at the end of a single cycle. In addition, the analytical and the finite element calculation results match together and the determined crack behavior is compatible with the other researcher's output.