Methodology to predict mechanical properties of PA-12 lattice structures manufactured by powder bed fusion

Abstract

Topology optimization for weight reduction of additive manufacturing parts is commonly achieved throughout the creation of lattice structures, typically generated with beams of small size cross-section. In order to carry out accurate simulations of these lattice structures, knowing the mechanical behavior of pillars is required. In this paper, a methodology for determining the mechanical properties of small size pillars printed in PA-12 material, using polymer powder bed fusion (PBF) and in particular the Selective Laser Sintering (SLS) technology, is presented. The effect of defects originated during the manufacturing process on the macroscopic mechanical properties is studied and the mechanisms which influence these properties are analyzed. A methodology for the determination of these properties is proposed, based on a successive correction of the printed nominal diameters according to two approaches; one due to the outer skin of unmelted material and the other due to internal melting defects. Once the material properties are determined, as a function of the cross-section of the lattice pillars, the numerical simulation of lattice-type structures has been carried out and the degree of adjustment of the proposed methodology has been experimentally verified, obtaining good results. This validation provides a reliable method for the simulation of the macroscopic behavior of lattice-type structures with reduced sizes, taking into account the intrinsic defects generated during the printing process.