Affiliations: State Key Laboratory of Mechanics and Control of Mechanical Structures, Nanjing University of Aeronautics {&} Astronautics, Nanjing, China
Correspondence:
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Corresponding author: Jinhao Qiu, State Key Laboratory of Mechanics and Control of Mechanical Structures, Nanjing University of Aeronautics & Astronautics, Nanjing, China. Tel.: +86 25 84891123; E-mail:qiu@nuaa.edu.cn
Abstract: A spatially distributed array of piezoelectric sensors is
widely used in structural health monitoring (SHM) for active ultrasonic
methods. Owing to many advantages of delay-and-sum algorithm such as
intuition, low computation cost and accurate imaging result, it is very
suitable for damage localization. However, due to the dispersion effect of
Lamb waves, the wave packet becomes wide and distorted as it propagates in
the structure which will have a negative effect in the spatial resolution of
the damage imaging. This paper presents an active imaging method using
warped frequency transform (WFT) to improve the spatial resolution of the
imaging result. In WFT, the warped frequency range is limited in narrowband
and the central frequency is fixed to keep the wave packet undistorted.
Then, the dispersion effect can be compensated and the velocity of the wave
packet is converted into phase velocity which is much lower than group
velocity. Due to the compensated wave packet and low wave velocity, the
spatial resolution of the delay-and-sum algorithm is improved. Both single
damage and dual adjacent damages are detected in the experiments. The
comparisons between delay-and-sum algorithm with and without WFT are made to
demonstrate the proposed method.
Keywords: Lamb wave, damage localization, warped frequency transform, active structural health monitoring
