INDENTATION OF SANDWICHES USING A LAYERWISE MODEL WITH FIXED DEGREES OF FREEDOM

A zig - zag plate model with variable kinematics and fixed degrees of freedom recently developed by the authors is applied to study indentation of sandwiches with honeycomb/foam core, with the aim of reducing the computational burden. This model, which a priori fulfils the stresses a nd displacements continuity requirements, has a hierarchic representation of displacements, but just five degrees of freedom. The core crushing behaviour is determined apart once at a time in order to account for the variable elastic properties of the core during the structural analysis. Specifically, shell elements with elastic - plastic isotropic material are adopted to discretize the cellular structure and the faces, instead solid elements with nonlinear material behaviour are chosen to model foams. Once t he properties of core are determined, the analysis is quickly carried out in closed form by the zig - zag model. As customarily, the onset of damage is determined using stress based criteria, while its growth is accurately and efficiently described using a m esoscale model. In this way, the degraded properties of the failed regions are evaluated with a physically based model, instead of guessing suited multiplication factors. The numerical results of simulations are shown to be in good agreement with experimen ts taken fro m the literature .