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Rail Defect Imaging by Improved Ultrasonic Synthetic Aperture Focus Techniques

This paper presents a prototype system for the ultrasonic imaging of defects in rails that uses an improved version of the synthetic aperture focus technique (SAFT). A rail flaw imaging system is needed to quantitatively assess the size and the shape of a defect in a manner that goes beyond the operator’s judgment. Improvements in rail maintenance practice on several levels can be expected if the rail defect verification step is truly quantitative. The SAFT was chosen over a traditional phased array imaging system due to the reduced hardware complexity, improved focus, and speed. The system being developed implements various steps to further improve the performance of the SAFT including: (a) compounding various wave propagation modes to reduce artifacts and increase array gain; (b) including a wedge in the beamforming algorithm for optimum detection of transverse defects; (c) utilizing the parallel processing structure of the graphical processing unit (GPU) architecture for increased imaging rates; and (d) stitching together 2D slices to reconstruct 3D volumetric images. Results are shown on rail sections with simulated and natural transverse defects borrowed from the Federal Railroad Administration (FRA) Rail Defect Library. While the focus of the current research is on manual handheld flaw imaging, several of the proposed algorithmic steps can be useful for in-motion rail inspections.

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