PSI - Issue 42

Jakub Šedek et al. / Procedia Structural Integrity 42 (2022) 398–403 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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1. Introduction Panels incline to buckling behaviour when loaded in compression, especially if being designed with reinforcement by stringers. Skin buckling is commonly present in light-weight structures like airframes since the strength is beyond the buckling load. Using composite materials in a structure allows more effective methods of manufacturing than riveting or bolting, but it also brings some disadvantages. Fibre reinforced thermoplastic polymers allow manufacturing by co-consolidation with joins of sub-parts realized by a filler as introduced in van Ingen at al. (2019). Such structure profits from the rivet-free design, but also is prone to skin-stringer debonding under buckling and the strength of the panel is reduced as shown in Kassapoglou (2010). The buckling, post-buckling, and strength behaviour of pristine (defect-free) and cracked panels were investigated in this work. The focus was given not only to load response, but also to buckling shape and the mode of failure.

Nomenclature CFRTP Carbon Fibre Reinforced Thermoplastic Polymer CZM Cohesive Zone Modell DIC Digital Image Correlation E Young’s modulus G shear modulus G c fracture toughness H height of the panel PbP Ply-by-Ply PEKK Poly-Ether-Ketone-Ketone W width of the panel ν Poisson’s ratio σ F strength τ F shear strength

2. Panels description Panels were manufactured by molding and co-consolidating of flat sub-parts made of laminates from carbon fibre reinforced thermoplastic polymer PEKK (Poly-Ether-Ketone-Ketone). The skin was supported by 5 stringers that were composed of the web and the cap. The laminate was made by consolidation of unidirectional laminae of 0.14 mm thick. The skin consisted of 18 plies, the stringer web contained 18 and the cap 20 plies. In addition, two glass/PEKK layers were placed on the outer side under stringers. The stacking sequence is introduced in Table 1. The scheme of the panel with the description of individual sub-parts is shown in Fig. 1. Panel dimensions were 545 mm x 690 mm (H x W).

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Fig. 1: a) Scheme of the panel, b) Composition from sub-parts