NDTnet 1998 Aug, Vol.3 No.8

Abstract

Introduction
Nondestructive testing techniques for welded joints usually include visual, radiographic, magnetic particle, liquid penetrant and ultrasonic testing methods. Of interest in this paper is the radiographic testing (RT) technique.
Our work is a part of an ongoing research project for the development of an automated weld inspection system. This paper presents an invariant pattern recognition method, applied to radiographic images of welded joints for the extraction of feature vectors of the weld defects and their classification so that they will be recognized automatically by the inspection system.

Invariant Pattern Recognition
The general invariant pattern recognition problem is to construct a system which takes as input an element f of V (set of possible patterns) and computes a value s(f), with the intention that s(f)=c(f) for all f V • c(f) is the desired classification off, invariant under the action of all transformations (translations, rotations, scalings, etc.).

Digital Hartley Transform and Experimental Results


Table 1. Two Hartley feature vectors of a defect.
	Rotation (20°)	Rot. (20 °) + Scaling (50%)
H[2]	0.254127	0.260218
H[3]	0.111315	0.114237
H[4]	0.061237	0.062647
H[5]	0.042525	0.044109
H[6]	0.028964	0.031119
H[7]	0.021795	0.023398
H[8]	10.016215	0.016770

We present in Table 1 the results of theapplication of the DFIT on an edge image of a radiographic film containing a lack of penetration as a defect. The two transformationwe present in this abstract are the rotation and the rotation with a scaling Theobtained results are very satisfactory and we can see clearly the invariance of the feature vectors under the transformations.

Conclusion
An invariant pattern recognition method, based on the Hartley transform, applied toradiographic images is presented. The results show that this method is capable to describe anyweld flaw into a small feature vector, allowing its recognition by the inspection system.

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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