Abstract
The results of Lamb wave identification for the aerospace structures could be easily affected by the nonlinear-dispersion characteristics. In this paper, dispersion compensation of Lamb waves is of particular concern. Compared with the similar research works on the traditional signal domain transform methods, this study is based on signal construction from the viewpoint of nonlinear wavenumber linearization. Two compensation methods of linearly-dispersive signal construction (LDSC) and non-dispersive signal construction (NDSC) are proposed. Furthermore, to improve the compensation effect, the influence of the signal construction process on the other crucial signal properties, including the signal waveform and amplitude spectrum, is considered during the investigation. The linear-dispersion and non-dispersion effects are firstly analyzed. Then, after the basic signal construction principle is explored, the numerical realization of LDSC and NDSC is discussed, in which the signal waveform and amplitude spectrum preservation is especially regarded. Subsequently, associated with the delay-and-sum algorithm, LDSC or NDSC is employed for high spatial resolution damage imaging, so that the adjacent multi-damage or quantitative imaging capacity of Lamb waves can be strengthened. To verify the proposed signal construction and damage imaging methods, the experimental and numerical validation is finally arranged on the aluminum plates.
Highlights
To determine the integrity and reduce the life-cycle costs of critical aerospace structures, the concept of structural health monitoring (SHM) is increasingly acknowledged
To verify the proposed signal construction and high spatial resolution imaging methods, an experiment is arranged on a 1000 mm × 1000 mm × 1.5 mm 2024 aluminum plate, which is largely used in aerospace structures
As the dispersion influence is efficiently removed in the linearly-dispersive signal construction (LDSC)-processed results, both the single damage and the dual neighboring ones can be visibly and accurately recognized as bright focalized spots in Figures 16b1 and 13b2, showing the outstanding spatial resolution and SNR of the proposed LDSC-based damage imaging method
Summary
To determine the integrity and reduce the life-cycle costs of critical aerospace structures, the concept of structural health monitoring (SHM) is increasingly acknowledged. SHM can permit the real-time and in-situ damage identification via distributed network sensors permanently mounted on or embedded into the structures [1,2,3,4,5]. As a kind of guided ultrasonic waves in thin-wall structures, Lamb waves can travel over large distances with high sensitivity to both the surface and internal defects. The suitability of Lamb waves for SHM of plate-like aerospace structures has been well demonstrated. Besides the classic ellipse or triangulation damage location, Lamb wave imaging of phased array [6,7], reverse-time migration [8], tomography [9], time reversal [10,11,12] or delay-and-sum [13,14], is frequently proposed and performed for metallic or composite structures.
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