NDTnet 1998 Aug, Vol.3 No.8

Full-Text - Abstract

Aerospace structures are characterised by the use of high specific strength materials which are exposed to extreme variations of temperature and load. As these structures deserve also special attention in terms of safety and reliability, there is a persistent challenge to develop methods allowing for nondestructive inspection to monitor the integrity of structures.
This paper describes a method allowing for remote inspection of areas of several m² within typically 4 minutes where no surface preparation is required. The method is based on optical generation of thermal waves by absorption of intensity modulated optical radiation. The resulting phase of the thermal waves is analysed in the whole field of view of a thermography camera working in the long wavelength band (8 - 12 µm). The basic setup is shown in Fig. 1. The phase fields obtained using this "lockin thermography" (which is phase sensitive modulation thermography responding only to sinusoidal temperature changes of a given modulation frequency) display near-surface structures and imperfections to a depth which amounts to about 5 mm in GFRP and CFRP materials. Examples will be shown for various kinds of aerospace structural components thereby indicating the potential of this fast and large area inspection method.

References
1. Busse, G., Mu, D., Karpen, W., J. Appl. Phys. 1992, 71, 8: 3962-3965.
2. Mu, D., Busse, G., Materialprüfung 1994, 36: 393-399

Fig.1 Experimental arrangement for lockin-thermography

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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