NDTnet 1998 Aug, Vol.3 No.8

Full-Text - Abstract

Inspection of layered structures using pulse-echo ultrasound is a classical NDT method used in the aerospace industry. Detection of disbands between different layers is possible due to the change of reflection coefficient resulting in variations of amplitude and phase of the respective echos. In some practical applications where the ultrasonic coupling is not reliable and/or the damping in the upper layer is variable, the phase information is more reliable for the detection than the amplitude of the echo.

In this paper we present a method suitable for automatic detection of disbands based ontimefrequency representation of the ultrasonic signals acquired during the inspection of layered structures. The time-frequency representation serves as a preprocessing method enabling extraction of features used for the detection. The features are amplitude invariant and robust against changes of the inspection parameters, such as, ultrasonic coupling and acoustic impedance of the layer under the disbond area. The features extracted from the time-frequency representation are fed to a multilayer perceptron neural network performing the detection.

The performance of the detector has been verified using practical ultrasonic measurements performed on a multilayered aerospace structure covered with rubber. It is shown that in this case the detector is capable of detecting very small (10 x 10 mm) artificially introduced disbands for two different types of structures, aluminum plate and honeycomb structure lined with gum.

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:

Publication Contact:
7th ECNDT, Park Alle 345, DK-2605 Broendby, Denmark, Fax: +45 46 26 70 11, Email: 101373.3414@compuserve.com