Delamination growth analysis in laminated structures with continuum-based 3D-shell elements and a viscoplastic softening model

In this paper we consider the simulation of delaminations in composite structures. For this purpose we discuss two aspects of a numerical treatment. The first one is the formulation of an accurate 3D-shell element to describe the global as well as the local behaviour in laminates in a proper way. Here a refined eight-node brick element is presented. The modifications of the element are based on assumed natural strain - and enhanced assumed strain methods. This element is used in the second part of the paper to describe delamination within an interface element with a small but non-vanishing thickness. Thus, strains, stresses and the delamination criterion are calculated in a standard manner from the displacement field and the material law. We introduce - based on an extension of the delamination criterion of Hashin (J. Appl. Mech. 47 (1980) 329-334) - an inelastic material model with softening. Here, the critical energy-release rate G(o) is the crucial parameter to describe the damage behaviour. Furthermore, a viscoplastic regularization with strain rates according to an approach of Duvaut and Lions is used to prevent negative stiffness parameters in the consistent tangent operators. Numerical calculations show the successful application of the 3D-shell element and the delamination concept. (C) 2000 Elsevier Science S.A. All rights reserved.