Dynamic analysis of full-ceramic bearing-rotor system under thermally induced loosening in aerospace applications

Full ceramic bearings have excellent characteristics such as high temperature resistance and high speed, which can meet the requirements of aerospace engines and other precision machinery in a wide temperature range. Nonetheless, a challenge arises due to the disparate thermal expansion coefficients between full-ceramic bearings and steel housings. This incongruence results in a gradual loss of control over the seat hole by the outer ring as temperatures elevate. The loosening of ceramic bearings is a crucial factor causing misalignment of rotary centers, exacerbating rotor system vibration with rising temperature. In this study, a full-ceramic bearing-rotor system's dynamic model under thermally induced loosening is presented. The dynamics characteristics of the shaft end output - time domain, frequency domain, and axis trajectory are analyzed. The proposed model undergoes validation through the application of the mean square loss function, the value remains below 2. Through a comprehensive analysis, both theoretically and experimentally, it has been established that frequencies 2fr, 3fr, and 8fr serve as suitable references for discerning thermally induced loosening faults within full-ceramic bearing rotor systems. Recommendations include opting for a tighter fit or increasing heat-conducting rings in aero-engines, underscoring the importance of meticulous engineering in aerospace design and performance enhancement.