Experimental investigation on detection of coating debonds in thermal barrier coatings using vibrothermography with a piezoceramic actuator

Abstract

Coating debond, caused by thermal stress, is inevitable during the service of thermal barrier coatings (TBCs) in gas turbine engines. This study investigated detection of coating debonds in TBCs structures using a vibrothermography method. First, the mechanism of detecting coating debond with the vibrothermography was theoretically studied. Then, a finite element model of a TBC structure with an interfacial debond was established and accordingly the eigenfrequency of the local defect resonance was estimated. Second, the vibrothermography tests were conducted on a thermally-spraying coating specimen with artificial debonds. The local heat of the debond defect was generated using a low-power piezoceramic actuator with a selected excitation frequency according to the numerical estimation. Finally, thermal images were captured by an infrared camera and analyzed by thermal signal reconstruction (TSR), principle component analysis (PCA), and fast Fourier transform (FFT). The results indicate that the first principle component of PCA provides the highest temperature contrast and signal-to-noise ratio (SNR). The debond with a diameter of 2 mm and coating thickness of 0.5 mm can be detected with excellent image quality. Also, the debonding area and relative error were quantitatively estimated. The experimental results demonstrate that vibrothermography can provide a fast, reliable, and effective evaluation on detection of debonds in TBCs structures.