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

Yuantian Huang; Joseph A Turner; Yongfeng Song; Peijun Ni; Xiongbing Li

doi:10.1016/j.ultras.2019.05.010

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

Ultrasonics. 2019 Sep:98:20-27. doi: 10.1016/j.ultras.2019.05.010. Epub 2019 May 28.

Authors

Yuantian Huang¹, Joseph A Turner², Yongfeng Song¹, Peijun Ni³, Xiongbing Li⁴

Affiliations

¹ School of Traffic and Transportation Engineering, Central South University, Changsha 410075, China.
² Mechanical and Materials Engineering, University of Nebraska-Lincoln, Lincoln, NE 68588, USA.
³ Inner Mongolia Metallic Materials Research Institute, Ningbo 315103, China.
⁴ 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: lixb_ex@163.com.

PMID: 31170544
DOI: 10.1016/j.ultras.2019.05.010

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.