PSI - Issue 53

Costanzo Bellini et al. / Procedia Structural Integrity 53 (2024) 227–235 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

229

3

lighter than expected, denoting a thinning of the trusses and skins induced by the process. In order to reduce the detected incongruity between numerical and experimental results, the diameter of the trusses and the thickness of the skins were reduced by the amount required so that the weight of the virtual model matched the experimentally measured weight. However, the abovementioned strategy allowed a reduction of the gap, but further refinement of the model and greater accuracy of the results can be achieved by incorporating the local mechanical properties of the material. In fact, in the previous model, mechanical properties obtained from tests on massive parts were taken into account, whereas lattice structures consist of thin elements. Therefore, in the present work, sandwich structures with lattice cores have been produced, and local mechanical characteristics have been investigated and implemented in the numerical model to reduce the left gap. 2. Materials and methods In order to minimize the design work, the analysis of lattice structures from a quantitative perspective necessitates the creation of particular approaches. Such interactive modelling of structures is very time-consuming and difficult. As a result, a simpler model was created, based on shell and beam elements, and it was employed in the current work to examine the mechanical behaviour of octet-truss cells. In the following, the utilized numerical model is briefly described, together with information on the specimens created using the EBM method, the outcomes of the experimental tests, and an assessment of the local mechanical properties. The octet-truss cell served as the basis for the lattice design. This cell is made up of an octahedron with 12 struts, which is encircled by a cube made of another 12 struts. Each node is created by the convergence of 12 struts when the entire structure is made up of this type of cell only (Dong et al. (2015)). The optimal combination of cell geometrical parameters required to enable the effective unfused powder removal following the EBM manufacturing stage was determined to be a strut nominal diameter of 1 mm and a cell side of 6 mm. The Ti6Al4V alloy, the most popular titanium alloy in the aerospace and aeronautics area, was employed to make the titanium powder used in the current research work. This powder, which can be seen in Fig. 1, had spherical particles, an apparent density of 2570 kg/m 3 , and a flow rate of 25 s/50 g. A lattice core with a width of 30 mm, a thickness of 9 mm, and a length of 270 mm formed the investigated lattice structures. Because the side of a cell was 6 mm, one cell and a half in the thickness direction was used to achieve the required thickness of 9 mm, while five cells were taken into account for the width direction. Skins with a 0.6 mm thickness covered the lattice core. In Fig. 2, an example of the manufactured specimens is shown.

Fig. 1. The titanium alloy powder used as raw material for 3D printing.