Mechanics of damage initiation and growth in a TBC/superalloy system

Creep analysis was used to estimate stresses in different layers especially in bond coat and the thermally grown oxide (TGO) layer to determine the ro le of creep on damage initiation in the TBC system, Microcracks were observ ed to initiate near the bond coat/TGO interface after only a few thermal cy cles, The origin of these microcracks can be attributed to the buildup of t hermal stresses that may magnify due to asperity of the TGO layer and the b ond coat, The TGO/bond coat interface was modeled as a rough periodic surfa ce, Finite element calculations were conducted to determine the magnitude o f stresses at the bond coat/oxide interface (modeled as a sine wave), It wa s found that large normal interface stresses arise at the peaks. while larg e shear stresses arise at the mean line of the rough interface, These resid ual stresses can exceed the interfacial tensile or shear strength of TGO. E ffect of oxide layer growth between bond coat and Thermal barrier coating ( TBC) was modeled as volume increase and subsequently as an induced pressure across the interface inside the crack, Mixed-mode fracture analysis of a t hin circular delamination in an axisymmetric multi-layer circular plate was developed to assess growth, (C) 2001 Elsevier Science Ltd, All rights rese rved.