Defect detection using ultrasonic arrays: The multi-mode total focusing method

• Published in: NDT & E international : independent nondestructive testing and evaluation Vol. 43; no. 2; pp. 123 - 133
• Main Authors: Zhang, Jie, Drinkwater, Bruce W., Wilcox, Paul D., Hunter, Alan J.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.03.2010; Elsevier
• Subjects: Arrays; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Focusing; Fundamental areas of phenomenology (including applications); Imaging; Inclusions; Inspection; Materials science; Materials testing; Mathematical models; Non-destructive testing; Physics; Position (location); Scattering coefficient matrix; Solid mechanics; Structural and continuum mechanics; Ultrasonic arrays; Vibration, mechanical wave, dynamic stability (aeroelasticity, vibration control...); Ultrasonic arrays; Scattering coefficient matrix; Non-destructive testing; Measurement; Wave conversion; Far field; Longitudinal wave; Elastic wave; Welded joint; Reflection mode; Ultrasonic control; Focusing; Metrology; Hybrid model; S wave; Localization; Non destructive test; Mode conversion; Ray theory; Defect detection
• ISSN: 0963-8695; 1879-1174
• DOI: 10.1016/j.ndteint.2009.10.001

Ultrasonic arrays allow a given scatterer to be illuminated from a wide range of angles and hence are capable of extracting significant information about the scatterer. In this paper a general imaging methodology, termed multi-mode total focusing method, is proposed in which any combination of modes and reflections can be used to produce an image of the test structure. Like the total focusing method, this approach is implemented by post-processing the full matrix of array data to achieve a synthetic focus at every pixel in the image. A hybrid model is used to predict the array data and demonstrate the performance of the multi-mode imaging concept. This hybrid model combines far field scattering coefficient matrices with a ray-based wave propagation model. This allows the inclusion of longitudinal waves, shear waves and wave mode conversions. It is shown that, with prior knowledge of likely scatterer location and orientation, the mode combination and array location can be optimised to maximise the performance of array inspections. A practically relevant weld inspection application is then described and its optimisation is discussed.