Production process monitoring and post-production strain measurement on a full-size carbon-fibre composite aircraft tail cone assembly using embedded optical fibre sensors

Abstract

Multiplexed optical fibre sensors were embedded into a carbon-fibre-reinforced-preform during the industrial production of a full-sized, one-piece tail cone assembly for a regional jet aircraft. Optical fibre Fresnel sensors monitored both the infusion of the resin, via measurement of the refractive index-dependent attenuation in the reflected light signal, and the degree of cure of the resin, via measurement of the chemical cure reaction-dependent change in refractive index. The resin cure was also monitored by optical fibre Bragg gratings (FBGs) fabricated in high linearly birefringent optical fibre, which measured through-thickness strain development, while FBGs in standard single mode optical fibre measured longitudinal strain development. The magnitudes and profiles of the transverse and longitudinal strains developed during the curing process were consistent across different locations on the tail cone. Typical transverse and longitudinal strains, related to cure reaction-induced shrinkage, were −1500 ± 17 μϵ and −500 ± 5 μϵ, respectively. Post-production, the same embedded FBG sensors were used subsequently to monitor structural strains when the tail cone was subjected to vacuum pressure loading. The longitudinal strains measured using the embedded FBG sensors were generally in good agreement with the longitudinal strains measured by the surface-bonded resistance foil strain gauge (RFSG) sensors, both qualitatively and quantitatively. The in-plane transverse and circumferential strains, oriented collinearly, were measured by the embedded FBGs and appropriately oriented surface-bonded RFSG sensors, respectively, and were, qualitatively, in good agreement.

An Overview of the Measurement of Permeability of Composite Reinforcements

“…Yu et al [ 77 ], instead, used FBG sensors in their hybrid piezoelectric-fiber sensor network described in Section 3.3.2 to monitor resin flow front in the thickness direction through the shift of Bragg wavelength caused by contact between resin and sensors. Chehura et al [ 96 ] applied embedded fiber optics to monitor the filling stage and the cure cycle of a carbon fiber-reinforced tail cone, as the refractive index of resin is also sensitive to density variation [ 98 ].…”

“… ( a ) Sensing principle of fiber optics based on Fresnel law (adapted from Chehura et al [ 96 ]), ( b ) a sketch of the Fiber Bragg Grating structure, and ( c ) an example of embedded fiber optics application for flow front monitoring. …”

Fibre-optic measurement of strain and shape on a helicopter rotor blade during a ground run: 1. Measurement of strain

“…These features can allow their use as surface mounted sensors on aerodynamic surfaces, as has been shown for fixed wing applications [2,3]. In addition, optical fibres can be embedded within fibre reinforced composite structures and components during fabrication [4].…”

Temperature compensated strain sensor in fused silica by femtosecond laser inscription

“…The applications can range from monitoring machine movement to determining whether a process step is completed, during for example curing of composites. 9,10 Currently, one of the most common, established technologies to measure strain are strain gauges. They come in different sizes and can be used in countless applications.…”