Ultrasonic structural health monitoring: Strategies, issues and progress

Several different strategies are being considered for ultrasonic structural health monitoring systems using a variety of approaches. Guided wave techniques for interrogating large plate-like structures have probably generated the most interest; these methods have the potential of monitoring large areas with a low sensor density while remaining sensitive to defects. The acousto-ultrasonic nondestructive evaluation method has motivated the use of long-time, reverberating waves which “fill” a structure and hence monitor large areas. Local methods based upon several different wave modes have been considered for monitoring known “hot spots” such as fastener holes and critical bonds. Presented here are examples of these three strategies where the purpose is to both show progress which has been made and illustrate key issues, mainly in the context of aerospace applications. The progress and problems thus far show both the promise of ultrasonic structural health monitoring and the significant challenges in moving from the laboratory to deployed systems.