Low-power ultrasonic-induced thermography for visualization of debonding defects in CFRP-reinforced steel tubular members

Debonding defects are inescapable during the fabrication and service of CFRP-reinforced steel tubular members. This paper investigates the visualization of debonding defects in CFRP-reinforced steel tubular members using the low-power ultrasonic-induced thermography (LUIT) technique through experimental studies. First, the LUIT inspection process and the heat generation mechanism at defect locations are introduced. Next, a novel infrared image processing framework, which integrates gravitational force and lateral inhibition networks (GF&LIN) with conventional infrared image sequence processing techniques, is proposed to enhance defect visualization. The LUIT experimental setup is then established, and tests are conducted on CFRP-reinforced steel tubular specimens. By analyzing infrared images and temperature data, the effectiveness of the LUIT detection technique is verified. Additionally, a modified transducer with an arc-shaped bottom is introduced, and experimental results confirm its suitability for defect detection in CFRP-reinforced steel tubular members. Finally, experimental data containing weak defect features are processed using the proposed infrared image processing framework and traditional methods. The results demonstrate that the proposed framework achieves the highest contrast-to-noise ratio (CNR) across various detection configurations, surpassing conventional methods in enhancing defect visualization. Overall, experimental findings confirm that the LUIT technique offers a fast and efficient method for detecting debonding defects in CFRP-reinforced steel tubular members.