Vibration Characteristics of a Shaft–Disk–Cracked-Blade Coupling System Under Multisource Excitation

Aeroengine blades operating in harsh environments are susceptible to cracking, significantly reducing their lifespan and compromising the safety of the aeroengine. This study investigates the vibration characteristics of a shaft–disk–cracked-blade coupling system under multisource excitation using a hybrid modeling approach that combines the finite element method and the assumed modes method. The validity of the proposed model is confirmed through comparisons with the finite element model and existing literature on natural frequencies and vibration responses. A systematic analysis is conducted on the influence of multisource excitation, such as gravity load, unbalanced load, and aerodynamic load, on the vibration characteristics of the coupling system. The impact of different crack parameters on blade tip bending and shaft torsion is also investigated. Results show that for healthy blades, gravity load induces blade bending vibrations at the rotational frequency, while unbalanced load leads to static deformation. In the cracked system, equilibrium positions of blade tip bending displacements offset, and aerodynamic loads cause nonlinear vibrations due to the breathing behavior of the blade crack. Blade crack also induces additional torsional vibrations in the shaft. Furthermore, the amplitude ratios of blade bending and shaft torsion related to the constant component, rotational frequency component, and aerodynamic excitation frequency component are effective indicators for evaluating breathing cracks. This study provides a theoretical basis for diagnosing blade crack faults and improving the reliability of aeroengine operation.