thermal conductivity. When the maximum normal stresses for
various thicknesses are compared with the strength of all materials,
the values are lower than that.
TBCs have a limited life because of crack nucleation and propagation
in a direction parallel to the ceramic-bond coat interface.
Another important thermal stress is the shear stress which leads to
the coating delamination. The maximum thermal shear stress distribution
versus coating thickness at the bond coat and substrate
surface is plotted in Fig. 13. The maximum value of the shear stress
is observed on the bond coat surface and its value is 138.4 MPa for
0.2 mm coating thickness. When the coating thickness increases
gradually, the maximum shear stress diminishes as a non-linear
behavior. The character of the curve is convex. As regards the
substrate surface, maximum normal stress is 74.1 MPa for 0.2 mm
coating thickness. When the coating thickness increases rhythmically,
the maximum shear stress of the substrate surface decreases
almost linearly. The maximum shear stress is inversely proportional
to the coating thickness.