Buckling performance of elliptical and tori-spherical heads with multi-mode geometric imperfections and variable wall thickness

This study investigates the nonlinear buckling behavior of ellipsoidal and torispherical pressure vessel heads subjected to internal pressure, employing advanced finite element analysis to evaluate structural stability under realistic loading conditions. A key novelty of the work lies in the comprehensive, parametric investigation of both global and local geometric imperfections, including eigenmode-affine shapes, localized dimples, and circular cutouts. These imperfections are systematically varied in terms of type, amplitude, location, and distribution across multiple geometries. The simulations utilize geometrically nonlinear analysis with the arc-length (Riks) method, enabling accurate tracking of the post-buckling response and capturing sudden instability phenomena. A particular emphasis is placed on the sensitivity of buckling strength to imperfection characteristics. The results demonstrate that local dimples significantly reduce the buckling capacity, especially when positioned near the apex of the head. In contrast, imperfections located in less critical zones exert a more moderate influence. Additionally, the introduction of variable wall thickness, strategically increasing local thickness in high-stress regions, proves to be an effective design strategy for enhancing buckling resistance without excessive weight penalties. The study also reveals distinct imperfection sensitivity trends between ellipsoidal and torispherical heads, highlighting the importance of geometry-specific optimization. These findings provide valuable insights for the improved design, fabrication, and inspection of thin-walled pressure components in critical engineering applications.