Theoretical and experimental harmonic analysis of cracked blade vibration.

Blade cracks pose deadly threats to aviation safety and have caused serious aviation accidents in recent years. In order to diagnose blade cracks at the early stage, the harmonic vibration of cracked blade was analyzed theoretically and experimentally. Firstly, a recursive form solution was deduced for the complex the nonlinear dynamic equation of blade vibration, revealing the close relationship between harmonic component power and crack parameters. Furthermore, the upper bound of the adjacent harmonic component power ratio was obtained by theoretical derivations. The results show that the harmonic power decreases as the harmonic component order increases, and the degree of attenuation is decided by the crack parameters. Therefore, a crack detection approach was proposed according to the power ratio of harmonic components. The advantage of this method is that the blades do not need to be in a resonant state and can process vibration data at all rotational frequencies. This improves data utilization and diagnostic robustness. The recommended method was validated by the simulation analysis of stainless-steel and titanium blades. Finally, a test bench for blade vibration was set up whose highlight was the use of optical sensors for non-contact measurements of blade vibration. The results of both simulation and testbed experiment were much consistent with the theoretical inference. • Although a closed-form solution to the nonlinear kinetic equation of blade vibration is theoretically not available, we obtain a solution in a recursive form. • Further, the energy attenuation function of adjacent harmonic components is defined, and it is theoretically derived that there is an upper bound of the energy attenuation function. Moreover, the upper bound of the energy attenuation function is determined by the harmonic order, crack location, and crack depth. • The results of simulation and test bench experiments are consistent with theoretical inferences. [ABSTRACT FROM AUTHOR]