Laser ultrasonic anomalous wave propagation imaging method with adjacent wave subtraction: Application to actual damages in composite wing

Laser ultrasonic wave propagation imaging methods have great potential for integrated structural health management and non-destructive evaluation. However, application of these techniques to complex structures in the field is difficult because they give rise to complicated wave propagation patterns. We developed an anomalous wave propagation imaging method with adjacent wave subtraction using laser ultrasonic scanning to solve this problem. The proposed method is suitable for non-destructive evaluation of complex structures because it highlights the propagation of anomalous waves related to structural discontinuities, and suppresses complex incident waves without the need of pre-stored reference data. In this study, the method was applied to a real composite wing subjected to bending and impact tests. The method enhanced the visibility of the anomalous waves related to damages such as stringer tip debonding, skin-spar debonding, and invisible impact damage. Based on these anomalous waves, variable time window amplitude mapping was performed to show the damage location, size, and shape resemble to the actual damage. Comparisons showed that the methods performed better than the ultrasonic A-scan in terms of damage detection and sizing accuracy. The presence of structural elements such as spars, stringers, ribs, and surface-mounted PZT elements did not adversely affect the inspection. The proposed wing test setup with a built-in ultrasonic propagation imaging system for automatic NDE could be easily expanded throughout a hanger for maintenance inspection.