Baseline-free defects localization in CFRP laminates by acoustic nonlinear response of broadband guided waves

This study proposes a novel strategy for localization of defect-induced acoustic nonlinear response by means of circular laser measurements of ultrasonic guided waves. Two long-duration chirp signals are applied to actuate two broadband guided wave bursts. The measurements capture out-of-plane velocity along two circular paths. A post-processing algorithm is developed to estimate wave directions relative to the scanning circles through signal symmetry and correlation matrix analysis. A wave source map is then constructed based on these estimated directions to reveal the wave source. Initial validation experiments successfully demonstrated precise localization of an ultrasonic guided wave source (PZT actuator) in an undamaged specimen. The methodology was further applied to impact damage localization in a woven CFRP laminate through integration with nonlinear ultrasonic guided waves. The method successfully utilized nonlinear harmonics to localize the defect-induced acoustic nonlinear response, confirming its capability for accurate impact damage identification. This research presents a baseline-free approach for impact damage localization in quasi-isotropic composites, particularly advantageous for materials with unknown properties.