Dynamics of kink band formation in columnar thermal barrier oxides

The dynamics of kink band formation in columnar yttria-stabilized zirconia (YSZ) have been investigated via dynamic finite element modeling. A microstructure-based constitutive law models each column as a low-porosity solid and the intercolumnar zones as a high-porosity elastic-plastic foam. In the simulations, a rigid particle impacts a YSZ coating at fixed velocity. At the lowest velocities, kink bands develop having the characteristic location, orientation, and width established in previous quasi-static assessments. However, with increasing impact velocity and/or decreasing YSZ yield strength, kink bands are observed to form at increasingly shallower declinations. Thus a yield-strength-dependent velocity threshold exists, above which kink bands become non-penetrating. Kink band suppression is attributed to inertial stabilization of the columns against buckling. Further interrogation reveals that, for a given particle and YSZ yield strength, there exists a critical coating thickness above which kink-band-induced spallation cannot occur, regardless of impact velocity.