On the Collapse of Delaminated Composite Shells Under External Pressure

Abstract

The collapse of cylindrical shells under external fluid pressure is generally controlled by elastic buckling, material failure or a combination thereof. Composites like other laminated materials suffer from layer separation or delamination, which may affect the stiffness and stability of the structural component. Deep delaminations, near cylinder mid surface, are expected to reduce the effective flexural stiffness of the shell wall and lead to possible premature collapse. This problem is treated numerically and studied parametrically. A Fourier series-based 2-D shell finite element is formulated for delaminated composite long cylinders. The compatibility of deformation at the delamination tip is maintained by means of Lagrange multipliers. Contact between the separated layers is taken into account through a penalty formulation. A parametric study is conducted to assess the influence of delamination length, depth, and orientation on the reduction in collapse pressure of imperfect cylindrical shells.