NDTnet 1998 Aug, Vol.3 No.8

Abstract

Introduction
The possibility to acquire some information allowing to characterize defects has necessitated the development of techniques more evolved than classical methods used in ultrasonic technique. These methods use signal processing algorithms in order to enhance signal to noise ratio (1). The aim of this work is to develop some mathematical tools based on signal processing allowing a better detection, exact sizing of defects and discrimination between cracks and another spherical defects. These tools are put in a B-Scan, C-Scan, D-Scan, T-Scan software.

Signal processing algorithms


• We apply Hilbert transform to detect the envelope of high frequency time signals. this technique seems to be optimal for the location of echo signals using the filtering RC in classical techniques (Fig. 1).

• We develop detection and location techniques of superposed defects that can induce in error the expert controllers in the interpretation of control results. We show in Fig. 2 that Cepstre of energy or Spectral density can allow to increase detection or resolution possibilities. Thus, we analyse the problem of the superposed echo separation and wepresent results of application of these techniques.

• We use Intercorrelation functions to determine the resemblance of echoes coming from edges of cracks and echoes of a small spherical defect. Thus, we establish a mathematical tool allowing an automatic discrimination between cracks ands pherical defects.

  Finally, all these tools are put in a software of ultrasonic imagery allowing the control of welded joints, research of corrosion, thickness measure, control of coatings...

  Fig. 1. Two superposed echoes and its envelops

  
  

  Fig.2. Spectral density and Energy Cepstrurn

  Reference
  1. PARADISE (L), Development of methods and a device of signal processing adapted toNDT by ultrasonic waves, Thesis of Doctor Engineer, 17VP Grenoble, 1983.

Abstract Source:
Book of Abstracts, 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN: 87-986898-0-00

Full-Text Source:
Proceedings of the 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN:

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