Damage Detection in Composites by Noncontact Laser Ultrasonic

This study proposes an instantaneous damage localization technique for composite structures using noncontact laser ultrasonics. First, a velocity profile of the target composite structure is obtained by measuring wave velocities on paths with various directions. Second, laser ultrasonic responses from two excitation-sensing pairs, called inspection pairs, are obtained. Then possible damage locations are estimated through time-of-flight triangulation of damage reflected waves. Once possible damage locations are estimated, ultrasonic response collection is repeated near the estimated locations for precise damage localization. The proposed technique has following advantages over existing technique: (1) It does not require any sensor installation; (2) Wave velocity profile, which has been mandatory information for time-of-flight triangulation, can be easily experimentally constructed; and (3) It can localize damage with a high precision with its scanning capability. The feasibility of the proposed technique is examined by localizing a delamination in a real 10 kW wind turbine blade.