Buckling and Vibration Characterization and Optimization of Composite Panels with NURBS-Configured 3D-Printed Stiffeners

Stiffeners are structural components widely used in thin-walled structures to significantly improve structural rigidity while only providing minor increases in weight compared to an equivalent unstiffened panel. Traditional manufacturing techniques often limit stiffener designs to straight and prismatic profiles. This research seeks to overcome these limitations by employing additive manufacturing techniques to enable stiffeners to have free-form layouts. In this work, a methodology was developed to design, analyze, and optimize stiffened panels consisting of stiffeners with varying curvatures along their lengths, and to understand the buckling and vibration responses of these structures. Stiffened panels were subject to free or simply supported boundary conditions. For the buckling cases, various edge loads were combined to investigate buckling responses. Stiffener geometries were created using Non-Uniform Rational B-Splines (NURBS) and analyzed using finite element analysis. A particle swarm optimization algorithm was developed to optimize stiffener layouts by varying stiffener control point locations. A unique aspect of this work is the incorporation of a local boundary parameter to allow stiffeners to shift along the perimeter of the plate. By including this parameter, stiffeners have freedom to vary between longitudinal, transverse, and hybrid orientations throughout the optimization procedure. The results from this work show that stiffened panels consisting of free-form stiffeners can improve the buckling strength-to-weight ratio by more than 50% when compared to stiffened panels with straight stiffeners. Free-form stiffeners were also found to significantly increase the fundamental natural frequency of stiffened panels and provide more flexibility for mode-tuning.