Synthetic aperture focusing of ultrasonic inspection data to enhance the probability of detection of defects in strongly attenuating materials

Ultrasonic inspection is applied in many industrial fields, where one of the main tasks with respect to quantitative nondestructive evaluation is the determination of location, shape, size and orientation of defects. In this study, the determination of the size of flaws in strongly attenuating materials and the determination of the probability of detection (POD) from ultrasonic data is considered. Exemplarily, Duplex stainless steels are addressed whose ferritic-austenitic mixed microstructure causes a considerable attenuation of the ultrasonic waves. Therefore, the synthetic aperture focusing technique (SAFT) has been applied which leads to a reduction of the microstructural noise signals and thus to an improvement of defect detection. Based on the ultrasonic rf-data acquired on a test block with model defects an a^ versus a-approach has been performed to determine the POD for the inspected Duplex specimen according to MIL-HDBK-1823. It is shown that SAFT-processing of the ultrasonic data leads to a clear-cut improvement of defect detectability.