Vibration analysis of composite sandwich spherical-cylindrical joined shells with interface compatibility and layerwise kinematics

Abstract

Abstract

The vibration characteristics of composite sandwich spherical-cylindrical joined shells are jointly governed by geometric differences between the shell segments, sandwich interlayer deformation, and structural connection conditions. When the relative core shear constraint is weak or transverse shear deformation becomes pronounced, an equivalent single-layer description may not retain the layer-specific in-plane motions required for stable branchwise prediction. This study develops an interface-compatible Jacobi-Ritz semi-analytical model based on layerwise theory with first-order shear deformation theory (LWT-FSDT). Separate displacement fields are assigned to the top face sheet, core, and bottom face sheet, and the perfectly bonded interface conditions analytically reduce the initial 15 layer variables to nine independent variables while retaining layer-specific rotations. The spherical and cylindrical segments are described in a unified curvilinear framework, and layerwise penalty springs represent numerical sub-segment connections, the spherical-cylindrical joint, and end restraints. The formulation is assessed through convergence studies, published benchmarks, three-dimensional finite element validation, and comparison with an equivalent-single-layer first-order shear deformation theory (ESL-FSDT) model. For core moduli from 10 MPa to 10 GPa and thickness-to-radius ratios from 0.01 to 0.10, the mean and maximum absolute relative differences between the layerwise model and the finite element results over 320 matched frequency points are 0.174% and 0.889%, respectively, and the layerwise model is closer to the finite element results at 281 points. The core modulus alone does not define a universal soft-core condition. ESL-FSDT remains effective for some branches with low or moderate circumferential wave numbers in thin shells with a low-modulus core, whereas LWT-FSDT provides more stable branchwise accuracy across the examined range. The effects of boundary conditions, length-to-radius ratio, thickness-to-radius ratio, core modulus, and ply angle are further examined.