Bolt tightness monitoring using multiple reconstructed narrowband Lamb waves combined with piezoelectric ultrasonic transducer

Abstract

Abstract Narrowband tone burst excitation with a carefully selected frequency is generally utilized to generate Lamb waves for mode purity, dispersion diminution and signal interpretability. Narrowband excitation exhibits saturation phenomenon and even non-monotonic trends with the development of bolt looseness. In this research, a piezoelectric ultrasonic transducer with high signal-to-noise ratio is designed and fabricated for bolt tightness monitoring. The chirp signal is utilized to drive the actuator to generate broadband Lamb waves in the connected plate, and a transfer function-based signal reconstruction algorithm is innovatively proposed to extract narrowband tone burst responses with different center frequencies from the broadband chirp response for bolt tightness monitoring. The leaked wave energy-based bolt tightness indexes (TIs) are calculated based on the extracted multiple tone burst responses and a feature-level data fusion strategy is proposed to combine the TIs for exploiting the merits of different-frequency inspecting waves for different bolt tightness conditions. The fused TI not only presents a monotonic tendency with the increasing of bolt tightness, but also tackles the low sensitivity of narrowband Lamb waves for embryo bolt looseness. The proposed method contributes a novel and stable scheme for bolt tightness monitoring and opens a new perspective for damage evaluation of structures.