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 stru ctures. For this purpose we discuss two aspects of a numerical treatment. T he 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. He re a refined eight-node brick element is presented. The modifications of th e 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 thi ckness. Thus, strains, stresses and the delamination criterion are calculat ed in a standard manner from the displacement field and the material law. W e introduce - based on an extension of the delamination criterion of Hashin (J. Appl. Mech. 47 (1980) 329-334) - an inelastic material model with soft ening. Here, the critical energy-release rate G(o) is the crucial parameter to describe the damage behaviour. Furthermore, a viscoplastic regularizati on with strain rates according to an approach of Duvaut and Lions is used t o prevent negative stiffness parameters in the consistent tangent operators . Numerical calculations show the successful application of the 3D-shell el ement and the delamination concept. (C) 2000 Elsevier Science S.A. All righ ts reserved.