Quantitative characterization of disbonds in multilayered bonded composites using laser ultrasonic guided waves

A quantitative method for evaluating the sizes of defects has been proposed to be applied to laser ultrasonic guided waves testing multilayered bonded composites. The finite element model was built for studying on laser-generated ultrasonic waves in a bonded composite. A laser ultrasonic inspection system using lasers for generation and detection of ultrasonic waves was established to be utilized to conduct a series of experiments for verifying the simulation results. The lowest guided wave modes generated by a pulsed laser were used to characterize a bonded joint. The interaction of laser ultrasonic guided waves with disbonds was investigated to determine a reasonable source-receiver distance to reach a compromise between detection accuracy and efficiency. The -8 dB method has been proposed to measure the sizes of disbonds based on the scanning laser source technique, and the relative errors between the measurement sizes and the actual sizes are not more than 8%. The C-scan results based on laser ultrasonic guided waves jointed with the proposed quantitative method not only facilitate the visualization of disbonds, but also provide precise information on the bonded quality, which has great potential for online inspection of adhesively bonded composites.