A three-dimensional solid element model for finite rotation of composite shells

An eighteen-node solid element has been developed to model the behavior of isotropic as well as laminated composite shell structures undergoing finite rotation under static loading. The present three-dimensional solid element formulation is simpler than the degenerate solid shell element formulation. The element formulation utilizes independently assumed strain in addition to assumed displacement. Four sets of assumed strain fields are introduced to stabilize the finite element model while alleviating locking. A modified stress-strain relation is introduced to incorporate thin shell behavior by decoulping normal strain from other strain components. The strain and the determinant of Jacobian matrix are assumed to be linear in the thickness direction. This linear assumption allows analytic integration in the thickness direction regardless of ply layups in laminated composite shell structures. Numerical results demonstrate the validity and the accuracy of the present formulation. The present solid element model allows large incremental rotation in the Newton-Raphson iteration because it does not include trigonometric functions in the formulation. Therefore, it is more advantageous than other existing finite element models for the analysis of buckling and postbuckling problem. Even though numerical tests are concentrated on thin shell structures, the present finite element model can handle thick shell structures.