In-situ detection and assessment of low velocity impact-induced damage in composite materials using developed fibre optic sensor technology

Abstract

For the first time cumulative impacts on woven carbon fibre-reinforced composites incorporating fibre Bragg grating sensors are studied.  The effect of embedded optical fibres on the post-impact mechanical performance of the host composite is explored.

Embedded Bragg gratings in unidirectional composites together with a novel interrogation system are capable of detecting impact events of very low incident impact velocities/energies.  The optical sensors produce reading were other conventional sensors fail and are capable of assessing the impact by producing a measurement of the residual strains present in the composite.  The signal feature extraction and identification of damage modes based on impact data from the Bragg gratings is investigated by applying the wavelet transforms.  The method proved to be promising for future application in impact signals from fibre optic sensors.  A further development of the interrogation system holds the key to a complete and successful implementation of Bragg grating sensors to various composite materials applications.  With an increase in its sampling frequency the interrogation system could provide the sensors with feature extraction, damage mode identification and damage mode localisation capabilities. The work concludes that embedded fibre Bragg grating sensors are suitable for low velocity impact detection and assessment in CFRP, unidirectional and woven, and they display high survivability even when subjected to cumulative impact loading.

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