Stiffened Variable Angle Tow Skins Broderick Coburn, Paul Weaver, Zhangming Wu www.bris.ac.uk/composites 2/7 Stiffened Skins • Lightweight buckling solution. – Thin skin with stiff (in-plane and flexural) regions. • Failure modes: – Local buckling, global buckling, material strength, skin-stiffener debond… • Local buckling: – Factors: skin D-matrix, load distribution, stiffener spacing, EA of stiffeners. Airbus A350 XWB stiffened wing skin (Image courtesy of Airbus). • Global buckling: – Factors: stiffener EI, length, spacing. Global buckling Local buckling Broderick Coburn Stiffened Variable Angle Tow Skins 3/7 Stiffened VAT Skins • VAT laminates: ss [U = 0] U3 = Δx 3 – High tailorability. o T1 = 0 – Load redistribution. – Increased buckling loads compared ss o to straight fibre (up to 80% in T0 = ±45 x some cases) (Comp.A. Gurdal 2008). – Enhanced buckling performance. y ss [U = 0] • Representative section of 3 stiffened panel. Local buckling • Poisson’s ratio mismatch – |νxy,skin - νxy,stiff| < 0.2 – Limiting for straight fibre case. – VAT skin has varying Poisson’s ratio allowing higher percentage of 0o in stiffener. Global buckling Broderick Coburn Stiffened Variable Angle Tow Skins 4/7 Analytical Method • Rayleigh-Ritz energy minimisation. Prebuckling: RR on total complementary energy -> In-plane stress distribution • Buckling shape functions: y x Nx Buckling: RR on total potential energy -> Buckling loads and mode shape Transverse shear λlocal γ , local mode w, local mode xz Transverse shear γyz, local mode LP: Legendre polynomial λglobal w, global mode Broderick Coburn Stiffened Variable Angle Tow Skins 5/7 Preliminary Results • High load cases: Nx > 3.5 kN/mm. • Shear important. • FEA comparison • Stiffener eccentricity requires – Local mode in good agreement (<5%). further characterisation. – Global mode with eccentric stiffener (5-20%). End shortening example Local Global Skin: 10mm, o o <0 |45 > FEA Nx = 3.69 kN/mm FEA Nx = 4.23 kN/mm Stiff: 8mm, [(±45) 0 ] 2, 6 S Analytical Nx = 3.63 kN/mm Analytical Nx = 4.77 kN/mm 60mm height Broderick Coburn Stiffened Variable Angle Tow Skins 6/7 Future Work • Extend and improve model: • Explore novel configurations – Stiffener eccentricity. – Include skin thickness variation. • Perform optimisation – Include stiffener foot. – Analytical model and FEA. – Extend to omega stiffeners. • Manufacture and test a demonstrator stiffened VAT skin. Integrated stiffened VAT skin Blade stiffened VAT skin Fibre paths Broderick Coburn Stiffened Variable Angle Tow Skins 7/7 Thank You Questions? Broderick Coburn Stiffened Variable Angle Tow Skins .