NDTnet 1998 Aug, Vol.3 No.8

Abstract

The non destructive evaluation of weld depth penetration on structure is a sharp problem in the industrial area. A laser ultrasounds system, coupled to a interferometric detection constitutes a powerful tool especially in order to control pieces of complex geometry with restricted access.
The main purpose of this paper is to present this technics to detect and to localize a lack of weld penetration, taking into account the shape, the time of flight and the echodynamic curve of the reflected waves. We use a Q-switched Nd:YAG Laser ( = 1,06 gm; t = 25 ns) and a heterodyne interferometer in the bandwidth (20 kHz - 30 MHz) in an echographic mode.
According to the accuracy of the Bscan ultrasonic views, the control configuration (pump laser and interferometer located at the same place or shifted) and the acquisition parameters (average, spatial and time sampling) are discussed.
The experiments are performed on 2.5 mm. thick cylindrical specimens. They contain artificial and real defects with calibrated heights. One of the difficulties is the low incident energy chosen to avoid any material damage (thermoelastic regime). Results obtained on such defects are compared to classical non destructive testing by immersion transducers. The sensitivity and spatial resolution are analyzed.

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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