Instantaneous damage identification and localization through sparse laser ultrasonic scanning

Abstract

This study proposes an instantaneous damage identification and localization technique through sparse laser ultrasonic scanning. First, an inspection path is selected from an intended inspection region of a target structure. Then, ultrasonic waves are generated at one endpoint A of the path with a pulse laser and the corresponding ultrasonic responses are obtained at the other endpoint B with a laser Doppler vibrometer (LDV). Second, ultrasonic waves generated at point B are measured at point A reciprocally. Once two reciprocal ultrasonic signals are obtained, a damage index (DI) representing the violation of the linear reciprocity on the path is computed by comparing the reciprocal signals. DI will increase when the path passes through damage as this generates nonlinearity to the path. Third, the aforementioned steps are repeated for all predetermined inspection paths within the inspection region by scanning both pulse laser and LDV. Finally, the paths associated with high DI values are identified as damage regions. The effectiveness of the proposed sparse scanning technique is validated using an aluminium plate with a fatigue crack and a composite plate with an impact induced delamination.