This paper presents a continuum-based sheardeformable ®nite element formulation for geometrically nonlinear analysis of thick layered composite shells. The proposed variational formulation is based on an assumed strain method. From a kinematical viewpoint displacements and rotations are assumed ®nite while strains are in®nitesimal. The model is then cast in a co-rotational framework which is derived consistently from the updated Lagrangian method. Close relationship between the co-rotational procedure and the underlying updated Lagrangian procedure is presented to highlight the ef®ciency of the method for application to composite shell analysis. Numerical examples are presented to demonstrate the accuracy and the range of applicability of the proposed formulation. IntroductionLaminated structures made of advanced ®lamentary composite materials continue to be of great interest for engineering applications. Their high strength to weight ratio and the¯exibility to tailor make various components with strength far exceeding that of the parent constituent materials are their main attributes. These engineered materials are generally orthotropic in nature and quite often show very unique response even under simple loading conditions and geometric con®gurations. For a detailed account on nonlinear response of composite materials and structures see, e.g., Brank et al.

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A continuum based layerwise shear-deformable nite element formulation is presented for elasto-plastic analysis of layered composites shells. The proposed formulation is cast in a corotational con guration for nite deformation analysis. The elasto-plastic constitutive equations that are based on rate-independent deviatoric plasticity are also written in the corotational kinematic framework. Issues of covariance and spatial invariance are addressed, and an appropriate stress updating strategy is proposed. Numerical examples are presented to demonstrate the range of applicability of the proposed framework for bending-dominated response of elasto-plastic layered composite shells.