Strengthening of a curved composite beam by introducing a flat portion

This paper deals with the effect of the introduction of a central flat zone on the mechanical strength of quasi-isotropic curved composite beams. Composite fittings, a particular kind of curved composite beams, are often used in the aeronautical industry as junction parts. In most cases, and in order to connect parallel or orthogonal panels, they present a C-, T- or L-shaped geometry. Subjected to complex loadings, including bending, they have to face out-of-plane tension in their curved region. This phenomenon, known as unfolding, can lead to unstable delaminations and to a global failure of the assembly. In this study, a central flat zone is introduced in the curved region of a L-shaped laminated composite curved beam. Experimental results demonstrate the strengthening effect of this architecture, with a rise in the mechanical strength of around 15%. A finite element model, based on continuum mechanics and cohesive zones model, is developed. After dealing with the difficulties met with cohesive zones model and mesh size dependency, the proposed model presents results in agreement with experimental observations. It enables the understanding of the differences between the failure scenario of the original and modified curved composite specimens.