Heterogeneous ultrasonic time-of-flight distribution in multidirectional CFRP corner and its implementation into total focusing method imaging

Abstract

A precise time-of-flight (TOF) of phased array ultrasonic is crucial to the high-quality total focusing method (TFM) imaging in the corner of multidirectional carbon fiber reinforced plastics, but quite challenging owing to the complex material and geometric factors. With a comprehensive consideration of the curved shape, laminated structure, and elastic anisotropy, we propose a high-fidelity finite element model of the corner based on the stiffness matrix analysis. A strategy in virtue of the maximum energy of A-scan signals, is further implemented to determine the TOF and compared with the exiting minimum time method. The resulted heterogeneous TOF distributions are input into TFM imaging, respectively. Results show that of an isotropic approximation presents a larger positioning error and a higher noise level of defects. In contrast, the anisotropic algorithms, especially for the maximum energy method, obviously improve the defect echo amplitude and suppress the sub-surface noise, demonstrating a superior performance in CFRP characterization.