Damage monitoring of SiC/SiC turbine blisk under overspeed rotation testing using X-ray computed tomography and natural frequency

In this paper, the SiC/SiC turbine blisk was fabricated and tested to rupture under overspeed rotation. Under the overspeed rotation testing, the natural frequency of 24 blades and disk were tested using the force hammer−sound pressure sensor method, and the internal defects and damages inside the SiC/SiC turbine blisk were observed and analyzed under the computed tomography and digital imaging system. After overspeed rotation rupture, the fracture surface of the blisk was observed under the scanning electronic microscope, and a large number of fibers’ pullout was observed. Relationships between the rotation speed, internal damage evolution, and the natural frequency degradation in the blisk were established. After 98,000 R.P.M. rotating speed experiment, the natural frequencies of the blade and the disk decreased obviously. The frequency of more than half of blades decreased by 1.5−2.0%, with 13 blades in total; 17% of blades decreased by 1.0−1.5%, with 4 blades in total. The natural frequency of the disk also decreased with the increase of the rotating speed, and the natural frequency of the first three order decreased from 1.0 to 1.5%.