Asymmetric double cantilever beam testing for interfacial fracture toughness in TBCs based on X-ray imaging: A stiffness evolution study

Interfacial failure is an overriding concern affecting the service reliability of thermal-barrier coatings (TBCs). To address this, an Indentation-loaded asymmetric double cantilever beam (IL-ADCB) method based on X-ray imaging was developed and used to conduct tests on two types of pre-notched specimens. The grayscale distribution curves near the interface were obtained from the digital radiography (DR) images, and the cracks could be identified based on changes in grayscale. The relationship between the mechanical response including the load-displacement, stiffness-displacement, and stiffness evolution rate-time curves, and the crack evolution behavior was established. It is found that the interfacial fracture tends to occur in the specimen with the central plane of pre-notch located in the substrate, and mixed mode tends to occur in the specimen with the central plane of pre-notch loacted in the ceramic layer. The point where the interfacial crack appears corresponds to the maximum stiffness value. The influence of pre-notch position and fracture parameter on the fracture mode was studied in detail by finite element analysis (FEA). This study provides guidance for the application of the IL-ADCB method in the characterization of interfacial fracture toughness for TBCs.