Integrating monitoring and inspection with attached ultrasonic transducers

Ultrasonic methods are widely applied for nondestructive evaluation of structural components during both the manufacturing process and subsequent field inspections. The field inspections often require expensive teardown in order to access the back surfaces of critical components. Active ultrasonic methods are also a subject of ongoing research for structural health monitoring whereby transducers are permanently attached to a structure and signals are monitored to detect changes caused by structural damage. This paper presents a methodology for effectively combining ultrasonic monitoring and inspection. During the monitoring phase, detection and localization of possible damage is demonstrated on several specimens using attached transducers. This detection phase is followed by demonstration of a new inspection method referred to as Acoustic Wavefield Imaging (AWI) which utilizes the attached transducers as sources and a single externally scanned air-coupled transducer as a receiver. The acoustic wavefield images are useful for both checking the viability of the attached transducers and quantifying the extent of damage. The AWI method approaches the sensitivity of conventional through transmission ultrasonic methods but does not require access to both sides of structural components. Thus, it is very well suited for rapid field inspection of structural assemblies.