Carbon Fiber Reinforced Polymer (CFRP) is increasingly critical in industry due to its low density, high corrosion resistance, and superior fatigue performance, making the detection of defects essential to prevent catastrophic failures. Traditional Non-destructive Testing methods assess damage by analyzing linear properties such as sound velocity, scattering, dispersion, reflectivity, and attenuation rate. However, these traditional linear indices often fail to resolve micro-cracks due to wavelength limitations. In response to this challenge, the present study introduces a fully non-contact ultrasonic imaging system based on multiple enhanced damage indices. In this system, a six-axis robotic arm controls an air-coupled ultrasonic sensor to acquire wavefield signals around the fatigue crack in a non-contact manner. Ultrasonic signals from various sampling points are pre-processed, and enhanced indices are extracted for ultrasonic imaging. This improvement is particularly evident in the depiction of the crack’s outline and the identification of severely damaged areas. Quantitative comparison between the enhanced and linear indices reveals a substantial improvement in detection accuracy, with the proposed method reducing imaging artifacts around the crack outline by 73.3% in ROI 1 and 94.7% in ROI 2 .
Yu et al. (Mon,) studied this question.