Shear band formation in columnar thermal barrier oxides

Columnar thermal barrier oxides either impressed or impacted by projectiles at high temperature develop kink bands. The bands emanate from sub-surface sites adjacent to the contact zone and extend diagonally toward the substrate. At the boundaries, the columns are cracked, indicating that the material has been weakened, and rendering them preferred sites for material removal upon subsequent impact. In some cases, the bands reach the interface with the thermally grown oxide and initiate a delamination crack. The experimental challenges in characterizing the bands and in relating their occurrence to constituent properties and microstructure are extreme. To address this limitation, the present article explores methods for numerical simulation of the bands. By modeling the material within the columns as a minimally porous Gurson solid and treating the inter-columnar material as a low density foam, it will be demonstrated that bands can be simulated consistent with those observed experimentally. (c) 2005 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.