Investigation on buckling resistance of the stringer-panel structure with variable stiff laminate

Improving the elastic stability of composite materials is essential for aerospace structural components. Most research on variable-stiffness laminates (VSLs), enabled by automated fiber placement (AFP), has focused on flat, unstiffened plates with simplified boundary conditions, and few studies have applied VSLs to stiffened panels representative of aircraft fuselage or wing structures. This study investigates the buckling behavior of an experimentally validated stringer-stiffened panel by implementing VSLs exclusively in the two plies adjacent to the mid-plane of its 22-ply symmetric skin. This approach tailors the in-plane stiffness while preserving the bending stiffness and the baseline stacking sequence. Linear eigenvalue buckling analyses showed that the varying the fiber angle increased the first buckling load by 12.5% relative to the straight-fiber design, and modifying the fiber-path formulation to a third-order polynomial increased the improvement to 18.2% without any mass penalty. This improvement results from the redistribution of compressive load from the critical central skin bay toward the stringers. These findings show that localized stiffness tailoring of selected plies provides a practical route to AFP-based design of lightweight, high-performance, stiffened aerospace structures.