Modeling of an auxetic lattice structure fabricated through Additive Manufacturing

Additive Manufacturing (AM) is a cutting-edge technology that allows the fabrication of mechanical parts characterized by very complex geometries providing also good mechanical properties to the final product. However, when the component to be produced is small-sized and high-detailed AM still presents some limitations. In particular, lattice structures produced by AM show dimensional inaccuracies respect to the designed CAD model, so the component is compromised also from a structural point of view. Thus, there is a substantial discrepancy between the mechanical properties of the designed lattice structure and the fabricated one. In an accurate design process this difference cannot be neglected: this paper explores which are the most common defects introduced by AM and how they affect mechanical behavior. Furthermore, this work aims to create a simulation model able of including the fabrication imperfections in order to have a prediction of mechanical properties of the component closer to reality. Since these fabrication defects strongly depend on the design feature of every single strut, the simulation model has been developed through a script in Matlab which in turn generates a parametric code to be run in ANSYS APDL. This study also proposes a "Design of Experiments" to detect correlations between geometrical and mechanical properties of lattices. Thanks to this approach it has been designed an auxetic lattice thought to substitute a honeycomb in a typical sandwich structure. Lastly, the discrepancy between the mechanical properties of the designed structure and those predicted for a fabricated one has been highlighted. So, to close this structural gap, an optimization of the structure has been proposed.