Design and mechanical characterization of lightweight polymeric structures for additive manufacturing production

Along two decades, wide research has been carried out within characterisation of the mechanical properties of cellular or lattice structures made by additive manufacturing. Being one of the most complex geometries, lattice structures have been extensively studied in compression conditions. However, tensile characterization is rarely addressed because of the difficulties related to the definition of a suitable design for. The present study aims to expand the knowledge about these structures produced with polymeric powders, evaluating their tensile behaviour. Two different face and body centred lattice topologies with different strut diameters are investigated. The specimen is designed integrating the UNI EN ISO 527 – 1 standard guidelines with a lattice-suited graded geometry pattern optimization of the load introduction portion from the full solid bulk clamping extremities to the central lattice within the strain gauge length. Specific samples are designed and manufactured via selective laser sintering technology (SLS) with Nylon PA12 powder along two different building orientations evaluating the anisotropic and the defects correlated influences on the exhibited mechanical performances. Finally, to perform a deeper characterization of the examined topologies, three batches of compression specimens have been produced using the same unit cell geometrical parameters adopted for tensile tests. The manufactured designed specimens were tested under tensile loads exhibiting proper failure locations within the gauge length and mechanically characterized via homogenized stress and strain calculations. Furthermore, a bulk specimen batch have been printed in the same job of the lattice samples along the horizontal and vertical orientation to calibrate the material model later employed in the finite elements analysis (FEA) of the hybrid structures in question via ANSYS Mechanical APDL. The performed numerical simulations described accurately the mechanical response of the horizontal specimens with higher strut diameters, while overestimating consistently the performance of both thinner and vertically oriented lattice structures in inverse proportion to the thickness of the struts, thus suggesting future investigations on process related material properties changes and poor dimensional accuracy when considering thin features.