Crack detection in riveted lap joints using fiber laser acoustic emission sensors

Fiber laser ultrasonic sensors are demonstrated to be capable of measuring acoustic emission generated by cracks in aluminum panels. A single laser sensor is integrated into a riveted lap joint, which is subject to accelerated fatigue. Acoustic emission generated by crack formation in the panel in addition to other acoustic events due to fretting within the joint are clearly resolved by the laser sensor. Localization of an acoustic emission event is demonstrated with a multiplexed array of three laser sensors. This manuscript also calculates the fundamental limit to displacement resolution of the fiber laser sensor and presents measurements of the directional response to Lamb waves. The high measurement resolution and multiplexing capability of the fiber laser ultrasonic sensor makes it an ideal candidate for structural health monitoring applications. (C) 2017 Optical Society of America