Abstract:
A portable and compact demodulation system was constructed and calibrated. It was
found that the best performance could be achieved using the peak detection algorithm
written in a LabView™ program. A resolution of 0.96±0.07pe was achieved over a
range of 30,000ps.
This system was used to characterise IFBG sensors. Firstly the temperature effects on
the strain response of a number of IFBGs written into a number of differing fibre types
was investigated. A model was derived to gauge if the observed changes were
consistent with the accepted theory of Bragg gratings. It was found that the strain
response changed on average by 0.21 ^.O Sfm ps'1 °C 1. The obtained results were in
agreement with the predicted result simulated using the model. Secondly, a spliced pair
IFBG configuration was examined to assess its effectiveness as a temperature
independent strain sensor. From the results that were obtained it was concluded that this
sensor configuration can usefully measure applied temperature and strain, though errors
in the solution matrix led to significant errors in the final measurements.
For the process monitoring application both IFBGs and dielectric sensors were
embedded in the same carbon fibre epoxy composite. These were used together during
the curing process to make in-situ measurements of internal strain and conductivity. The
results obtained demonstrate that it is possible to monitor the strain levels in the optical
fibre resulting from the onset of liquification, gelation, and vitrification within the
surrounding resin matrix.
For the impact detection application IFBGs were embedded in epoxy resin carbon fibre
composite coupons, and these coupons were then subjected to impact events. In
addition, a force transducer and resistive foil strain gauges were used to make parallel
measurements of strain. Comparisons of the data obtained are provided. The IFBGs
successfully survived the impacts and recorded strain transients that characterise typical
fracture events.
