Double superposition shear deformation theory for buckling analysis of layered composite circular closed cylindrical shells in underwater environments

Abstract

Despite considerable research on the underwater buckling of laminated composite circular closed cylindrical (CCCC) shells, most approaches are based on equivalent single-layer (ESL) theories. These theories fail to fully satisfy the interlayer continuity of transverse shear stresses or the traction-free conditions on the shell surfaces. Additionally, existing nonlinear formulations neglect the complete contributions of in-plane displacements, strains, and the deepness term (1 + z/R). This research introduces an efficient quasi-3D finite element (FE) model to analyze the buckling behavior of laminated CCCC shells in underwater environments. A newly developed double superposition-based shear deformation theory (SDT), incorporating seven field variables, is adopted for estimating the displacement fields of the submerged CCCC shell. In contrast to most of reported shell formulations, the deepness term (1 + z/R) is incorporated in the present formulation. In addition to out-of-plane rotations, the contribution of in-plane displacements and strains are also considered in the nonlinear equations. Transverse shear stresses satisfy interlayer continuity and vanish on the inner and outer shell surfaces. The hydrostatic pressure applied on the composite shell's surface is treated as a follower live load, and its resulting extra stiffness is explicitly included in the FE formulation. The presented FE formulation bypasses shear correction factors and retains computational efficiency with a small number of degrees of freedom (DOFs). For model validation, various buckling tests are performed and the results are compared against the available shell theories and 3D FE solutions. The comparative results demonstrate the efficiency and accuracy of the proposed FE formulation for stability analysis of laminated CCCC shells under hydrostatic pressure.