Operating safety monitoring of aero-engine rotor blades is critical to engine reliability. Rotor blades generally exhibit broadband multi-modal vibration characteristics. Conventional vibration measurement methods using blade tip timing (BTT) system fail to meet monitoring requirements for wide-range and high-frequency vibration. In this study, a velocity-based full-field strain sensing method of aero-engine rotor blades using BTT is proposed. This study has three novelties. First, blade tip velocity calculation is proposed based on BTT measurements. The advantage of the BTT velocity calculation is the prominent characterization of wide and high frequency vibration information. Second, an L_1/2-norm sparse regularization method is innovatively developed to identify multi-modal vibrating velocity parameters, which enables a wide frequency band and accurate amplitude identification. Third, a velocity-to-strain transforming method is creatively proposed to sense the blade strain distribution in whole rotor spinning. This study enables real-time vibrating strain monitoring of operating rotor blades. Experimental simulation is employed to validate the developed approach. The errors in frequency identification of the multi-modal vibration are all within 0.15% and the strain sensing errors are all within 6%. The sensing results illustrate the accuracy and robustness of the proposed method. This study is promising for monitoring the rotor blades across all stages of an aero-engine in a non-contact and real-time way.

Aero-engine rotor blades, Vibration monitoring, Blade tip timing, Velocity calculation, Strain sensing