SHM system for bonding line monitoring of composite wing box skin-spar cap during manufacturing

  • Ciminello, Monica (CIRA)
  • Concilio, Antonio (CIRA)
  • Mercurio, Umberto (CIRA)
  • Apuleo, Gianvito (Piaggio Aerospace)

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The CFRP wing box section under investigation is a stringerless wing box (OPTICOMS research project) and consists of a two parts an upper portion, made of co-cured spars and a top skin panel and a bottom portion made of a cured skin panel. Subsequently the two portions are joined with a secondary bonding obtaining the final wing box. During that final assembly step, distributed fiber optics were embedded between the spar caps and the bottom skin panel. The embedded FO consists of six distributed fibres running within the bonding layer for 1 m along the span direction. An irregular damage map was defined simulating manufacturing bonding defects, where faults were different for width and length, to check SHM system capabilities in individuating such flaws under typical curing loads. The SHM system was tested on manufactured item, after bonding process, by exploring info contained within the “residual strains” data log. It is a matter of fact that the structural system would have experienced some thermal and even unwanted pre-stress solicitations after having being cured. Residual strains are intended as the strains that are present in (or recorded by) the fibres after the manufacture (1), handling (2), delivery (3), and installation (4) processes. Results obtained by post processing data for each fiber optic, are reported. The cumulative damage index with the eligible sensors are provided as outcomes. Based on the available data (unloaded structure), the algorithm appeared to be sensible at hundreds of microstrain signals. Concerning faults detection, sensor density seems a key, to be further investigated Errors in damage extension estimation confirmed to be in the region around 15%.