Efficient monitoring and inspection of plate-like structures with ultrasonic guided waves

Periodic nondestructive inspections of critical structural components are typically both expensive and time-consuming, contributing to high maintenance costs and undesirable downtime. Permanently mounted transducers that both generate and received guided waves are an alternative approach whereby plate-like structures are frequently monitored for changes. The sparse guided wave array (SGWA) is a configuration whereby simple, piezoelectric disks are spatially distributed on the structure. Such an array is efficient in that a relatively large area can be monitored with a small number of transducers. The performance of SGWA imaging algorithms is evaluated for a variety of damage scenarios, and the in situ transducers are then used as sources of guided waves for follow-up inspection of limited areas via wavefield imaging. Fatigue cracks in metallic plates and impact damage in composite plates are considered as well as several types of simulated damage. Fatigue cracks are highly directional scatterers, whereas impact damage exhibits complex scattering that is not always point-like; both situations affect imaging performance. Regardless of the imaging method, the results can be used to define a region of interest for follow-up inspection. Wavefield scans of this region are performed using multiple transducers as sources, and data are analyzed to verify detection of a scatterer and then to better locate and characterize it. Results demonstrate the advantages of the two guided wave methods and also illustrate potential issues with using simulated damage for performance assessment.