NDTnet 1998 Aug, Vol.3 No.8

Full-Text - Abstract

Alternating loads on multi-layered rivet-joint aluminum-alloy structures cause fatigue-cracks, which are influenced in their origin and shape by various interfering effects. Thus a prediction of the time of origin and the shape of the cracks is not possible and the reliability in operation can only be assured by repeated inspections. For reducing the inspection costs, sensitive and reliable non-destructive testing methods are required. The eddy current testing offers good opportunities so solve this tasks and is widely used in this field. However the sensitivity of eddy current testing systems depends ondepth and volume of the cracks and the reliability is reduced by the strong influences of the rivets. As generally known the use of multifrequent eddy current systems basically increases the amount of information, which is necessary for a success-fur separation of different influences. The CS-pulsededdy current method allows the excitation of the whole relevant frequency range within one pulse,instead of time consuming serial excitations of monofrequent signals . This technique furthermore provides a controlled generation of amplitude and phase within the frequency range, which supports the adaptation of the transmitting CS-pulse due to specific testing requirements. Adapting thetransmitting CS-pulse during a calibration process before the testing, can replace time consuming signal processing afterwards and reduces the evaluation of the CS-pulse to storing the maximal amplitude. The CS-technique combines a fast testing with a good suppression of interference effects, as already before presented for testing corrosion in joint aluminum-alloy structures .

This article presents CS-pulsed eddy-current measurements on various rivet-joint aluminum-alloystructures of aircrafts and demonstrates the opportunities of this technique for a sensitive crack-detection along with a successful suppression of the disturbing interference resulting from the rivets. A further development of the CS-pulsed eddy-current technique generates rotating eddy-current fields by using specific multi-transmission sensors and series of amplitude modulated CS-pulses. This technique provides an additional indication of orientations and therefore supports abetter description of cracks. The presented basic research results will explain the function and the opportunities of this new development.

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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