Computational modelling of delamination

Delamination in composite structures is best modelled at a mesoscopic level. In this approach, the plies are modelled as continua, which can either be assumed to behave linearly elastically or to degrade according to a damage law. Delamination in the interfaces between them is modelled using a discrete relation between interface tractions and relative displacements. Key in this type of modelling is the presence of a work of separation or fracture energy, which governs the growth of the delamination. This cohesive-surface approach has traditionally been implemented numerically using special interface elements which connect the continuum elements that are used to model the plies. Exploiting the partition-of-unity property of finite element shape functions to model the interface separation process offers some advantages, since interfaces can be inserted at the onset of delamination and not a priori, as in the conventional approach. As a consequence, elastic compliance of the interface prior to onset of delamination, spurious traction oscillations ahead of the delamination front and spurious wave reflections because of the presence of a high stiffness value are avoided. Moreover, unlike the conventional approach, unstructured meshes can be employed.