Failure of Alumina Scales on NiAl under graded scale loading

Abstract
The fracture‐mechanical behaviour of alumina scales on NiAl has been investigated under a graded scale loading produced by four‐point bending and spherical indentation. Typical crack and spallation patterns of oxide scales on the side face of bending bars and near spherical indents are presented. The development of crack patterns in the scale is analysed theoretically and the possibility of deriving the oxide fracture toughness and tensile strength from the patterns for known graded scale loading is discussed. The analysis has been complemented by stress measurements in the scale by means of optical fluorescence spectroscopy employing the piezo‐spectroscopic effect.

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