Large area corrosion detection in complex aircraft components using lamb wave tomography

An ultrasonic guided wave computed tomography (CT) technique has been developed to monitor corrosion in complex aircraft components. The technique has shown excellent corrosion detection sensitivity when applied to large aluminum structures. The resulting CT images are capable of determining damage size, location, and severity. The technique has also demonstrated the ability to detect and discriminate between multiple damaged regions in localized areas. An overview of the technology is as follows: A practical sparse guided wave sensor array is strategically positioned and embedded on the structure. Reference guided wave data is acquired by transmitting and receiving guided waves with every possible sensor combination in the array. Guided wave data is reacquired at predetermined time intervals. CT images are constructed using different guided wave features of the reference data in comparison to the reacquired data. Damage location, area, and severity are accurately mapped in the CT image. The technology is applicable to a wide variety of composite materials and all metallic structures. The sparse array can be of any geometry. Novel sensors have been developed for activating and receiving the guided waves. The sensors are light-weight, small in size, and uniquely packaged for robustness. The sensors can be installed individually or in prepackaged strips. Several CT algorithms have been developed that take advantage of different guided wave features for image construction. Selection of the proper CT algorithm has shown the ability to increase damage detection probability and decrease false defect calls. Customized software has been developed to allow fast and simple data acquisition and image construction and analysis. The software allows the user to define the geometry of the array, perform diagnostics to assure that the sensors are working properly, and also to recall previous data and CT images. A light-weight portable data acquisition (DAQ) system has been developed, using customized hardware, to allow easy field inspection. The DAQ hardware can be carried in a shoulder strap case and controlled via a tablet PC.