The postbuckling performance of sandwich and composite shells with in-plane shear nonlinearity and unsymmetric layers

We have used the natural approach to construct a curved triangular shell element NATCOP for analysis of sandwich and composite shells in previous work (see J. Zhu, Application of natural approach to nonlinear analysis of composite and sandwich composite plates and shells, Comput. Methods Appl. Mech. Engrg. 120 (1995) 355-388). The sandwich and composite shells can be either symmetric or unsymmetric and the in-plane shear relation can be linear or nonlinear. In this paper, element NATCOP is used to analyse the postbuckling behaviors of some typical sandwich and composite plates and shells, in order to show the influence of the in-plane shear nonlinearity and unsymmetric layers on the buckling and postbuckling of the multilayered shells. The analysis results show that only slight influence has the nonlinearity of the in-plane shear on the buckling and post-buckling for the thin composite plates and shells, while for the thick and medium thick composite plates and shells with certain layup, the influence of the nonlinear in-plane shear relation is significant. The influence of asymmetry on the buckling and postbuckling of sandwich and composite shells is complicated and depends on the layup, the number of layers and the thickness.