Ultrasonic Full-Matrix Imaging of Defects in Curved-Shape Components Based on Frequency-Domain Elastic Reverse Time Migration

Abstract

Ultrasonic phased array has been widely used for detection and characterization of defects inside components. However, it remains challenging to inspect the the curved-shape components with high accuracy. In this paper, frequency-domain elastic reverse time migration (FD-ERTM) is proposed to realize high precision imaging of the defects in the curved-shape components. The elastic wave equation is discretized in the frequency domain, where the source and received wavefields of all excitations are reconstructed simultaneously at each frequency. The Holmholtz-decomposition imaging condition is implemented to the wavefields to retrieve the defects with high precision. Simulation and experiments have demonstrated the advantages of the proposed method in terms of imaging accuracy and resolution. Compared with the total focusing method, the imaging accuracy improves 2-36 times due to the full coverage of waveforms and precise modelling of the mode conversions. In addition, the time cost of the proposed method is reduced to 1/14 of that of the conventional ERTM for lower requirement on the computational complexity and memory. Therefore, the proposed method has great potential in defect detection for curved-shape components.

Keywords: Full matrix imaging, curved-shaped component, frequency-domain elastic reverse time migration, phased array, ultrasonics