Elastic Buckling Analysis of Curvilinear Stiffened Cylindrical Shells under Axial Load

Nowadays, fuselage structure mostly uses straight stiffeners, called longerons. Their manufacturing simplicity results in both time saving and cost reduction. However, new manufacturing systems such as the Friction Stir Welding(FSW), 3D printing or Electron Beam Free Form Fabrication have widened the possibilities for fuselage fabrication and thus design. Complex shapes stiffeners are now conceivable. This work proposes an approach to simultaneously improve the buckling resistance and decrease the weight of a cylindrical shell by using straight and curvilinear stiffeners. Several parameters are involved in designing the stiffeners such as the shape of the stiffeners, the distance between the stiffeners but also the height and thickness of the stiffeners. Parameters for the shell itself such as the shell thickness and the curvature of the shell are also considered. Furthermore, addition of circular cutouts simulating windows in an aircraft fuselage is also undertaken in the computational studies to investigate their influence on the buckling behavior of the shell. Simulations with the finite element software ABAQUS reveal different buckling behavior with the evolution of the cross section of the stiffener. Moreover, a drop in the critical buckling load is noticed for a particular radius of the hole for the highest curvature of the shell. Finally, optimization studies reveal that curvilinear stiffeners can increase the critical load by 7.3% compared to similar straight stiffener configuration for the same weight. The optimal design depends on the curvature of the shell. It depends also on the spacing between the stiffeners and the shape of the stiffeners Having much more parameters, curvilinear stiffeners brings many more possibilities but also more complexity as all those parameters are dependent on each other.