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.

Composite materials are finding increasing application, for example in commercial aircraft. Traditionally fiber angles are restricted to 0 • , ±45 • and 90 •. The current work exploits the possibility of using multiple 'non-conventional' laminates where either fiber steering ('variable stiffness'), ply drops ('variable thickness'), or a combination of both is used. This leads to varying mechanical properties which means the load is being redistributed, increasing the overall buckling load. A flat panel of 400 × 600 mm loaded in uni-axial compression is optimized in the current work. As a benchmark a conventional laminate is used. The non-conventional laminates are 15% lighter to emphasize the possible weight savings. Only using variable stiffness or variable thickness is experimentally shown to not be sufficient to match the buckling load of the benchmark panel. However, using a combination of both, a 10% increase in the buckling load was found for a panel that is 15% lighter. This highlights the potential of non-conventional laminates.