NDTnet 1998 Aug, Vol.3 No.8

Abstract

At the Institute fuer Theoretische Nachrichtentechnik und Informationsverarbeitung at the University of Hannover investigations were carried out in cooperation with the Institute of Nuclear Engineering and Nondestructive Testing concerning 3D analysis of internal defects using stereoradioscopy based on camera modelling.

In this paper a method to determine 3D position and volume of internal defects using only two different X-ray images recorded from arbitrary directions will be described. In contrast to other stereoradioscopy systems we don't need precise control over sample movements to determine the 3D position of the defects. Based on camera modelling a simple calibration pattern is used to calculate the position and orientation of sample and X-ray source relative to the image detector in 3D space and to reduce the distortion inherent in the image intensifier tube. This calibration enables to calculate the three dimensional positions of the defects from two defect projections without further informations concerning sample movements.

The volume of defects is calculated using intensity evaluation. Considering the polychromatic radiation of our microfocus X-ray tube a gauge function depending on tube voltage and sample material is used to determine material thickness. To determine defect thickness material thickness in defect areas is estimated from surrounding material thickness. Defect thickness is calculated as the difference between estimated and measured material thickness in defect areas. To obtain defect volumes defect thickness is integrated within the defect areas considering the previously calculated 3D defect positions.

The system performance was determined using a test sample with different types of known internal defects. The system achieves an accuracy of 0.5 mm calculating the 3D position using a sample rotated only 10° between the views and an accuracy of 0.3 mm using 25° rotation. During calibration the distortion inherent in the image intensifier tube is reduced from a maximum of 3.8 mm to 0.1 mm (less than 0. 5 pixel). The defect volumes are calculated with an overall accuracy of 10 %.Additional results will be presented using the system to analyze casting defects.

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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