Investigation of Reinforcement Around the Lightening Hole in Composite Plates Under Tension and Shear Loads

Different methods can be applied to strengthen the weakened structure in perforated composite plates. A comparison of the four reinforcement models around the hole (ring, daisy, square and ellipse) under pure tension, pure shear, and combined (both tensile and shear loads) loadings was presented using Tsai-Wu failure criteria and calculations by finite element method (FEM). Before FEM analysis, tensile tests were performed with 12 tensile- and 6 shear-test specimens made of woven carbon fiber epoxy prepreg. During the tests of shear-test specimens, the strain distribution was obtained using the digital image correlation (DIC) method. Finite element verification was performed with both the applied force-deformation curve determined in the tensile test and the strain distribution obtained by the DIC technique. It was observed that four different reinforcement models, which have 38% volume of the created lightening hole, provide at least by 30% strength improvement to the unreinforced structure under tensile and shear loadings. Under combined loadings, according to the tensile/shear load ratio, the reinforcement types provide improvements at different rates.