Energy Barrier Topology and Disturbance Sensitivity in Imperfect Open-Section Thin Shells

This study investigates the influence of imperfections on the buckling response of an open-section thin-shell structure. A probing methodology is employed to quantify imperfection sensitivity and disturbance sensitivity through the buckling energy barrier and characterize the underlying stability landscape. The results reveal that the natural buckle width, defined by the localized postbuckling deformation of the perfect shell, acts as a critical length scale governing disturbance sensitivity. A transition in behavior is observed when the imperfection width becomes comparable to this intrinsic deformation scale. Imperfections wider than this length scale alter the postbuckling response and modify the buckling energy barrier, whereas narrower imperfections lead to a different response. This demonstrates that beyond modulating the buckling energy barrier, certain imperfections can also suppress the formation of postbuckling equilibria and increase the minimum buckling load. The results further show that the orientation of the imperfection (outward versus inward) plays an important role in determining the resulting stability landscape. Probing across the shell length reveals that outward imperfections shorten the disturbance-sensitive region, leading to more spatially deterministic buckle initiation, whereas inward imperfections broaden this region and produce a more spatially chaotic buckling initiation. These findings identify the natural buckle width as a governing parameter for disturbance sensitivity and characterize how localized imperfections reshape the stability landscape of open-section thin-shell structures.