Slenderness-dependent imperfection sensitivity and defect tolerance of steel-CFRP hybrid pressure cylinders: a design by analysis approach

This study examines the slenderness-dependent buckling and defect tolerance of steel-CFRP hybrid cylinders for high-performance containment applications. Using Geometrically and Materially Nonlinear Analysis with Imperfections (GMNIA), the research assesses moderately thin (R/t = 100) and ultra-thin (R/t = 600) shells under axial compression and localized impact damage. Findings demonstrate a behavioral shift dictated by slenderness. For yield-dominated moderately thin shells, a CFRP-skinned sandwich maximizes global bending resistance. In contrast, ultra-thin shells require a steel-skinned sandwich to absorb sharp curvatures and prevent plastic hinging. Furthermore, utilizing highly axial-biased layups (±75°) in the internal CFRP core effectively routes longitudinal stresses around geometric flaws. This macro-mechanical stress routing makes ultra-thin hybrids exceptionally defect-tolerant, preserving 93.5% structural capacity at severe defect depths (a/t = 1.0). Finally, comparing these numerical models to ASME Code Case 2286-2 highlights the extreme conservatism of legacy isotropic standards, underscoring the necessity of a 'Design by Analysis' structural design approach.