Damage Identification for Isotropic Structures Using Lamb Wave Based on a Reference-Free Location Imaging Method

A Lamb wave-based reference-free damage localization imaging algorithm is proposed for online determination of the imperceptible defects due to harsh service environments, complex alternating, and impact loads in the plain isotropic structures (mainly aluminum alloys), which are crucial components of aircraft skin, bogies, and underframes of high-speed train, so as to overcome the deficiencies of the majority of localization imaging methods that rely on reference data in a healthy state. The analyses were implemented by configuring specific transducer arrays to pick alternate reference signals from the existing transmitter–receiver paths. A chirp excitation approach was introduced to choose the actuation frequency of ultrasonic Lamb wave more concisely and effectively. Simulations and experiments were conducted to recognize and pinpoint the defects in four damage scenarios in aluminum alloy plates with 12 surface-mounted piezoelectric transducers, and the damage area identified by the proposed methodology was compatible with the genuine position. The results between simulations and experiments are likewise essentially consistent, demonstrating that the proposed algorithm is able to identify and localize damage in plain isotropic structures without the requirement of healthy reference signals.