Size optimization of composite stiffened panels under axial compression

Abstract Composite stiffened panels are widely used in aerospace structures, where buckling under axial compression often governs structural design. This study presents a sizing optimization investigation of three representative composite stiffened panel configurations, namely hat-type, J-type and T-type stiffeners, aiming to enhance buckling resistance without increasing structural mass. A fully parameterized finite element model is established in Abaqus to perform linear eigenvalue buckling analysis and is validated through axial compression experiments, with discrepancies within 5%. For the hat-type stiffener, the web height, top width and web inclination angle are optimized; for the J-type stiffener, the web height, cap width and foot width are optimized; and for the T-type stiffener, the web height and foot width are optimized. Under a cross-sectional area constraint of ±2%, the optimization leads to a reduction in web height for all 3 configurations, a reduction in hat top width and J-type cap width, and an increase in the hat web inclination angle as well as the foot width of the J- and T-type stiffeners, thereby redistributing sectional dimensions to improve buckling resistance. A gradient-based NLPQLP optimization algorithm implemented in Isight is employed to maximize the first linear buckling eigenvalue. Within the linear eigenvalue buckling framework, the first eigenvalue (and the corresponding eigenvalue-based critical load) increases by 19.65%, 37.9% and 23.4% for the hat-, J- and T-type stiffened panels, respectively. These improvements indicate comparative sizing trends under the adopted idealized buckling metric and should not be directly interpreted as increases in ultimate load capacity. Comparative analysis highlights the distinct geometric sensitivities associated with different stiffener configurations.