Experimental characterization and finite element validation of orthotropic 3D-printed polymeric parts

Abstract

Components fabricated via Fused Filament Fabrication (FFF) have an anisotropic response, which is further complicated by an intra-part and a part-to-part variation of their mechanical properties. In addition, the mechanical characterization and analysis process has not been standardized yet, making it difficult to assess the structural behavior and verify the compliance of a part with the performance criteria in service. This paper intends to fill this gap for specific printing process parameters. First, it speculates that a linear infill with a 100% infill could help to reduce the anisotropy of the parts to a mild orthotropy. Thin components have provided a quick and preliminary confirmation of the approach. After an initial test setup design, which was required to standardize the method, the in-plane behavior was studied. Classical dog-bone specimens returned unsatisfactory results when coupled with the internal structures. As a result, the paper takes inspiration from the test methods for Uni-Directional Composites (UDCs). It uses sets of Design of Experiments (DoEs) to determine the optimal shape of the tabs. This method managed to quantify the factors of the 3 × 3 reduced elastic coefficients matrix. Finally, the paper presents a set of three-point bending, simple bending, and bending–torsion tests on samples featuring different laminations. 2D FE models tuned with the experimental properties simulated them, following the Classical Lamination Theory (CLT) approach. For consistency, a shear penalization was introduced for the out-of-plane shear. The FE models delivered an excellent mechanical response prediction; this result appears to validate the approach and the method and endorses 2D FEM and CLT as reliable tools to analyze linear infill FFF parts.