PEER REVIEW
20
th
Australian International Aerospace Congress, 27-28 November 2023, Melbourne
Distributed Fibre Optic Sensing and Adhesion Strategies
for Strain Evaluation of an Aircraft Structure
Gerard Natividad
1
, Suzana Turk
1
, Kelly Tsoi
1
and Daniel Bitton
1
1
Defence Science and Technology Group, 506 Lorimer Street, Fishermans Bend, Victoria, 3207, Australia
Abstract
This paper reports on work demonstrating the repeatability and accuracy of a high-density strain
measurement capability based on distributed fibre optic sensors (FOSs). Four FOS bonding
strategies were experimentally validated on a large aircraft structure subjected to full scale
fatigue testing under representative flight loading. Sensors were surface mounted using three
different aerospace grade adhesives and an adhesive mesh tape. The strain measurements
obtained under the different bonding methods were comparable, with key strain distribution
features consistent. The FOS measurements were also compared at multiple locations to single
point strain measurements from electrical resistance foil strain gauges, with good correlation
demonstrated.
Keywords: fibre optic sensing, distributed strain measurement, fatigue testing, structural health
monitoring
Introduction
Distributed fibre optic strain sensing based on draw tower grating (DTG) technology [1] can
deliver high-density strain measurements. Fibre optic sensors (FOSs) are immune to
electromagnetic interference, resistant to corrosion, have a high tensile fatigue failure strain and
a small spatial footprint. These attributes make FOSs highly suitable for application in structural
testing and for structural health monitoring (SHM). However, prior to implementation on
operational aerospace platforms, further full-scale demonstration on geometrically complex
aircraft structures is required to develop confidence in the method. Although it has been shown
that FOSs are capable of withstanding high strain fatigue testing for extended periods on test
coupons [2], there is uncertainty around the long-term reliability, repeatability, and accuracy of
FOS strain measurement under combat aircraft loading conditions.
Additionally, most demonstrations of distributed sensing technologies based on Rayleigh and
Brillion scattering and quasi-distributed fibre Bragg gratings (FBGs) have been limited to flat
uniform structures such as aircraft wing surfaces [3-6]. In these studies FOSs were installed
using foil strain gauge (FSG) bonding adhesives, which are susceptible to degradation by the
effects of time, elevated temperature and moisture absorption. Another study evaluated
packaged and direct surface-bonded discrete FBGs under axial load in environmental chambers
to simulate in-flight environmental conditions [7]. Evaluation of fibre packaging and bonding
using discrete FBGs limits the ability to characterise the influence of the packaging and
adhesive material on strain distribution. Furthermore, the discrete FBG tests were carried-out
on test coupons rather than geometrically complex structures where the fibre installation path
is usually complicated and may need to traverse obstructions and sharp bends.
This paper compares strain measurements from distributed FOSs, installed using four adhesive
packaging strategies, to FSG strain measurements on a geometrically complex aircraft
component undergoing full-scale fatigue testing. Three aerospace grade adhesives were
