An indentation-based method for characterization of non-uniform triaxial residual stress in curved thermal barrier coating

In this paper, a modified Knoop indentation method is developed for the evaluation of triaxial residual stress (RS) in thermal barrier coating (TBC) on curved substrate. The triaxial RS component can be determined by comparing the peak load differences. The conversion factors between the indentation peak load difference and the RS are calibrated via finite element analysis. The deflection angle is introduced to correct the deviation between the long diagonal of the Knoop indenter and the principal stress direction. The distributions of the axial, hoop, and radial RS in the curved TBC are discussed. The maximum RS of the TBC on curved substrate is located near the interface. The RS in the TBC sprayed on substrates with different curvature radii was investigated. The accuracy of the Knoop indentation results is verified by X-ray diffraction (XRD). Compared with XRD, the test error of the Knoop indentation method is less than 7%.