Enhanced ultrasonic detection of near-surface flaws using transverse-wave backscatter.

Affiliation

School of Traffic and Transportation Engineering, Central South University, Changsha 410075, China; Key Laboratory of Traffic Safety on Track (Central South University), Ministry of Education, Changsha 410075, China. Electronic address: [Email]

Abstract

Diffuse ultrasonic backscatter measurements have been shown to enhance the detection capability of sub-wavelength flaws when combined with extreme value statistics. However, for a normal-incidence immersion measurement, a "dead zone" created by the ring-down of the front-wall echo will hide near-surface flaws. In this article, a pulse-echo transverse wave backscatter measurement is used to detect near-surface flaws under high gain. The approach is validated using a magnesium specimen with side-drilled holes. The confidence bounds of the grain noise from this specimen are given by a transverse-to-transverse scattering model, which takes the grain size distribution and the hexagonal crystal symmetry into account. The upper bound is then treated as a time-dependent threshold for the C-scan. Experiments show that the developed method has good performance for detecting sub-wavelength, near-surface flaws, and can suppress both missed detections and false positives.

Keywords

Extreme value statistics,Grain size distribution,Sub-wavelength near-surface flaws,Time-dependent threshold,Transverse-to-transverse (T-T) scattering,Ultrasonic testing,

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