Design and mechanical characterisation of lattice structures for additive manufacturing

Along two decades, wide research has been carried out within the 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 condition. However, tensile characterization is rarely addressed because of the difficulties related to the definition of a suitable design. The present study aims to expand the knowledge about these structures produced with metallic powders, evaluating their tensile behaviour. Two different customised lattices structures are designed. The specimen is designed according to the BS EN ISO 6892 ¿ 1 standard and using a graded geometry from full solid bulk to the lattice within the strain gauge length. Specific samples are designed and produced using both electron beam (EB-PBF) and laser powder bed fusion (L-PBF) technology and the different materials Ti6Al4V and AlSi10Mg, respectively. Moreover, the L-PBF structures are printed with two different building orientations and four different internal struts angulation, to evaluate the influence of defects such as porosity and dross formation. Finally, to perform a more complete characterization, four batches of specimens intended for compression have been produced with two different scanning technique of EB-PBF, using the same lattice designs adopted for tensile tests. The main mechanical properties are compared with the Ashby and Gibson¿s model. The experiments show that L-PBF-manufactured samples were subjected to a stress concentration near the transition area that cannot be removed, even when stress relief is performed. As a results, these specimens have almost no plastic deformation. Instead, EB-PBF-manufactured tensile samples meet the expectations, providing a localised failure within the gauge length and showing also interesting mechanical properties. The experimental data obtained are used to implement a simulation model created with Ansys Mechanical APDL.