Detection of debonding in stiffened composite panels by acoustic nonlinear response of broadband ultrasonic guided waves

Abstract

Debonding defects in the bonding layers of stiffened composite panels pose significant safety risks. However, they are challenging to detect due to their deep location and complex geometry, where conventional linear ultrasonic methods often fail. This study presents a broadband nonlinear ultrasonic guided wave approach for accurate debonding imaging. Chirp guided wave mixing (CGWM) is employed to excite broadband signals and effectively eliminate time-consuming signal processing. Defects are detected by analyzing three types of nonlinear components: second-harmonic generation (SHG), sum-frequency harmonic (SFH), and difference-frequency harmonic (DFH) responses. Results demonstrate that while linear ultrasonic detection struggles with deep debonding, all nonlinear ultrasonic components enable successful defect identification and imaging. Crucially, SFH and DFH allow efficient frequency-domain filtering, significantly reducing computational time compared to time-frequency domain processing required for SHG. Furthermore, the CGWM technique enhances nonlinear source behavior at defects while minimizing spurious nonlinearities from instruments.