Article Periodicals » Materials Evaluation » Article
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.


Anon, F., 1990, “Rail-Flaw Detection. A Science that Works,” Railway Track and Structures, Vol. 86, No. 5, pp. 30–32.

Cannon, D.F., K.‐O. Edel, S.L. Grassie, and K. Sawley, 2003, “Rail Defects: An Overview,” Fatigue & Fracture of Engineering Materials & Structures, Vol. 26, No. 10, pp. 865–886.

Flaherty, J.J., K.R. Erikson, and V.M. Lund, 1967, “Synthetic Aperture Ultrasonic Imaging Systems,” US Patent 3,548,642.

Frazier, C.H., and W.D. O’Brien, 1998, “Synthetic Aperture Techniques with a Virtual Source Element,” IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, Vol. 45, No. 1, pp. 196–207.

Garcia, G., and J. Zhang, 2006, “Application of Ultrasonic Phased Arrays for Rail Flaw Inspection,” Report DOT/FRA/ORD-06, July, US Department of Transportation, Washington, DC.

Hall, J.S., and J.E. Michaels, 2010, “Minimum Variance Ultrasonic Imaging Applied to an In Situ Sparse Guided Wave Array,” IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, Vol. 57, No. 10, pp. 2311–2323.

Jeong, D.Y., 2003, “Correlations between Rail Defect Growth Data and Engineering Analyses, Part I: Laboratory Tests,” UIC/WEC Joint Research Project on Rail Defect Management, US Department of Transportation, Washington, DC.

Lanza di Scalea, F., 2007, “Ultrasonic Testing Applications in the Railroad Industry,” Chapter 15, Part 2: Special Applications of Ultrasonic Testing, in Nondestructive Testing Handbook, 3rd edition, Vol. 7: Ultrasonic Testing, American Society for Nondestructive Testing, Columbus, OH, pp. 535–540.

Lanza di Scalea, F., S. Sternini, and T.V. Nguyen, 2017, “Ultrasonic Imaging in Solids Using Wave Mode Beamforming,” IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, Vol. 64, No. 3, pp. 602–616.

Martin-Arguedas, C.J., D. Romero-Laorden, O. Martinez-Graullera, M. Perez-Lopez, and L. Gomez-Ullate, 2012, “An Ultrasonic Imaging System Based on a New SAFT Approach and a GPU Beamformer,” IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, Vol. 59, No. 7, pp. 1402–1412.

Pagano, D.A., 1979, “Two-Wheel Ultrasonic Rail Testing System and Method,” US Patent 4,174,636, issued November 20.

Schmerr, L.W. Jr., 2016, “An Ultrasonic System,” in Fundamentals of Ultrasonic Nondestructive Evaluation, Springer International Publishing, New York, NY, pp. 1–13.

Sternini, S., A.Y. Liang, and F. Lanza di Scalea, 2018, “Ultrasonic Synthetic Aperture Imaging with Interposed Transducer-Medium Coupling Path,” Structural Health Monitoring,

Sternini, S., A. Quattrocchi, R. Montanini, A. Pau, and F. Lanza di Scalea, 2017, “A Match Coefficient Approach for Damage Imaging in Structural Components by Ultrasonic Synthetic Aperture Focus,” Procedia Engineering, Vol. 199, pp. 1544–1549.

Witte, M., and A. Poudel, 2016, “High-Speed Rail Flaw Detection Using Phased-Array Ultrasonics,” Technology Digest TD-16-030, Transportation Technology Center, Pueblo, CO.

Usage Shares
Total Views
42 Page Views
Total Shares
0 Tweets
0 PDF Downloads
0 Facebook Shares
Total Usage