A new stiffened shell element for geometrically nonlinear analysis of composite laminates

A new stiffened shell element combining shallow beam and shallow shell elements is developed for geometrically nonlinear analysis of stiffened composite laminates under mechanical loading. The formulation of this element is based on the principle of virtual displacements in conjunction with the co-rotational form of the total Lagrangian description of motion. In the finite element formulation, both the shell and the beam (stiffener) elements account for transverse shear deformations and material anisotropy. The cross section of the stiffener (beam) can be arbitrary in geometry and lamination. In order to combine the stiffener with the shell element, constraint conditions are applied to the displacement and rotation fields of the stiffener. These constraint conditions ensure that the cross section of the stiffener remains co-planar with the shell section after deformation. The resulting expressions for the displacement and rotation fields of the stiffener involve only the nodal unknowns of the shell element, thus reducing the total number of degrees-of-freedom. Also, the discretization of the entire stiffened shell structure becomes more flexible. The robustness of the stiffened shell element has been proven by comparison against other shell elements considered previously.