NDTnet 1998 Aug, Vol.3 No.8

Full-Text - Abstract

This research is part of an investigation into the potential of embedded optical fibre sensors for gradual damage detection in composite structures. One of the first steps in the development of such a sensor always has to be an investigation into the influence of the embedded optical fibres on the mechanical properties of the resulting structures. The material under investigation was a quasi-isotropic [0,45,-45,90]_s CFRP laminate with optical fibres embedded in the different interfaces at right angles to the loading direction. A preliminary investigation (1) has shown that the fatigue properties of this laminate are considerably degraded when optical fibres are embedded in the 0/45 and the -45/90-interfaces.

This paper will focus on the use of different NDT-techniques to determine which damage phenomena are responsible for the observed degradation. To this extent interrupted fatigue tests were carried out on composite specimens with optical fibres embedded in the different interfaces. The tests were interrupted at 100, 1000, 10000, 25000, 50000, 100000, 250000, 500000 and 1000000 cycles, if specimen fracture did not occur before one of these levels was reached. All tests were monitored using both stiffness degradation and the acoustic emission technique. During each interruption all specimens were examined using microfocus radiography which allowed to quantify the damage state at different moments during the fatigue tests.

Combining all results will reveal which damage phenomena (matrix cracking, delamination, fibre failure,...) are responsible for the observed degradation in fatigue properties. Moreover an analysis of the acoustic emission results in terms of traditional parameters like amplitude and duration combined with the radiographic images should give more insight into the nature of the acoustic emission signals caused by the different damage phenomena.

1. M. Surgeon, Al Wevers; Static and dynamic testing of a quasi-isotropic composite with embedded optical fibres, submitted to Composites Part A

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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