Static and Fatigue Testing for evaluating Damage Tolerance performance of an Out Of Autoclave – Liquid Resin Infused Carbon-Epoxy Curved Stiffened Panel

  • Fanteria, Daniele (University of Pisa)
  • Boni, Luisa (University of Pisa)
  • Romano, Fulvio (Italian Aerospace Research Centre)

In session: - Fatigue

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In the quest for replacing traditional, pre-preg based, technologies to manufacture composite structures for aeronautical applications, the vacuum assisted infusion of dry carbon preforms with Liquid Resin (LRI) and an oven, that is Out-of-Autoclave (OoA), curing process have recently received great attention and have demonstrated increasingly good performances . Within the Regional Aircraft IADP of H2020 program Clean Sky 2, design approaches and manufacturing procedures have been developed to produce a representative primary structure of a regional aircraft manufactured by means of LRI-OoA process applied to a carbon fibre dry preform. The selected structure is a composite curved panel, reinforced by inverted “T” stringers, that is representative of the upper wing panel located at the tip of the outer wing box of the Regional Aircraft taken as a reference within the research program. The present work is focused on the testing of the curved panel. Tests are aimed at demonstrating the damage tolerance characteristics typically required by primary structures that must be certified in compliance to civil airworthiness regulations. The panel is tested in compression after inflicting impacts with energies able to produce a Barely Visible Damage (BVID) associated to a delamination/disbonding of a significant portion of a stringer. Detailed FE analyses have been developed to define the test set-up and to select the location of strain gauges (SG) to monitor deformation of potentially buckling critical areas. Special care has been devoted to place SG in the skin-stringer delamination area so that any possible growth of the delamination can be detected during testing. The testing procedure comprises an initial fatigue phase, during which several blocks of constant amplitude cycles are applied. Between each block of fatigue cycles, a strain survey is carried out to verify the status of the delaminated/damaged zones. Upon completing the fatigue phase, the BVID damaged panel is statically loaded to verify its ultimate load capability, then, it is loaded up to failure while recording the evolution of strains with load. Data recorded during tests are used as a term of comparison for the numerical predictions made by means of FE models of varying complexity.