Evaluation of Laminate composite Distortion by an Integrated Numerical-Experimental approach.
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The ELADINE project has developed a software tool that can predict the unwanted shape distortion and uneven shrinkage that frequently occurs during the manufacturing of composite structures.
Lightweight composite materials are ideal for use in aircraft structures — however, composites are prone to distortion during manufacture. This misshaping, referred to as ‘spring-in’, causes internal stresses in the final product, which shortens its service life and leads to an inferior fit between components when installed into the aircraft. These distortions are mainly due to the varying cooling rates of different materials (carbon fibres and bonding resin) as they combine and solidify during the curing (processing) stage.
Once the ELADINE tool has anticipated the extent of shrinkage that would likely occur it preemptively redefines the tool dimensions so that the final produced composite component, once cured, shrinks and stabilises into the intended shape and correct dimensions, in readiness for installation into the aircraft.
ELADINE was one of the projects supporting the Clean Sky 2 OPTICOMS (Optimised Composite Structures for Small Aircraft) project which aimed to reduce recurring costs of low-volume production in composite manufacturing.
The project followed two parallel development streams: an experimental set of activities dedicated to manufacturing, process monitoring, evaluation of coupons (small test samples to check the behaviour of materials) and production of a small-scale demonstration rig (to test the ELADINE process prior to its use at full scale). Secondly, a numerical (software) simulation tool development stream, starting with small coupons and progressing to a full-size seven-metre wing-box (the structure that connects the wings to the aircraft’s fuselage).
To ensure accuracy in the development of the tool, the experimental programme mirrored the numerical tool development steps. Process monitoring and data collection was performed using FBG (Fiber Bragg Gratings) sensors, a type of optical fibre-based sensor that measured residual stress, combined with specialised sensors (called dielectric sensors) that monitored the pace of the curing process. Together, these sensors detected vitally important variations in the progress of the curing of the resin and composite material. This was in order to ensure that the produced component solidified and stabilised in line with the intended dimensions, thereby guaranteeing a good fit once installed in the aircraft.