Volumetric Imaging Using 2D Phased Arrays

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)

Abstract

Phased arrays are commonly employed in the ultrasonic non-destructive testing of industrial components. Their use allows the full-matrix capture (FMC) acquisition technique to be used; this contains all possible information of an inspection for a specific array location, and therefore allows a number of imaging algorithms to be applied in post-processing. One such algorithm, termed the total focusing method (TFM), produces fully focused images of inspection regions and outperforms conventional imaging techniques.

Having access to three-dimensional (3D) volumetric knowledge of a specimen's interior is imperative for accurate inspections, as it enables any defects present to be accurately characterised so their severity can be evaluated. The type of array used also has an impact on the resulting TFM images. As two-dimensional (2D) phased arrays have the ability to focus in multiple directions, more information regarding a defect is able to be obtained from a single array location when compared to a linear one-dimensional (1D) array. Furthermore, the use of a 2D array can speed up inspections and reduce data size, as volumetric inspections with a linear array requires multiple data sets to be captured as the array is scanned over a given area. This thesis aims to demonstrate the benefits of using a 2D array over a linear array when obtaining accurate volumetric knowledge of defects.

A 2D array is also used to investigate 3D volumetric imaging of defects within a complex-shaped specimen, which is a current challenge in industry. This is achieved by extracting an estimate of the surface profile using a novel TFM image-based method. The extracted surface is then used to produce another 3D TFM image of the interior of the specimen to enable defect detection and characterisation to be investigated. Scanned array inspections using a 2D array are also explored to investigate the 3D characterisation of machined defects within a large specimen.

The response of a defect varies with inspection setup, which can result in one region of the specimen being viewed well from one array position and poorly from another. This effect is investigated by generating a 3D ultrasonic model of the predicted defect response and using it to improve the detection of defects within simple and complex specimens.
Date of Award21 Jan 2021
Original languageEnglish
Awarding Institution
  • The University of Bristol
SupervisorPaul D Wilcox (Supervisor) & Rob Malkin (Supervisor)

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