Optimization of bulk/lattice interface in hybrid structures fabricated by Additive Manufacturing

Optimization of interfaces in hybrid structures fabricated by additive manufacturing. The search for more resistant materials with a lower specific weight has favoured the introduction of lattice structures in the components obtained through Additive Manufacturing. Lattice structures, i.e. those structures obtained by repeating an elementary cell until a portion of the part is completely filled, have both stiffness and resistance much lower than that of a solid; therefore they are made in areas with low stress, leaving a portion of solid sufficient to guarantee the desired resistance to the piece itself. From this derives the need to develop hybrid components, consisting of full zones with structural function (bulk) and lattice zones that allow to lighten the component where it is less loaded, reducing the consumption of material, the production time and the weight of the component. The study of this design has highlighted the possibility of stress peaks occurring at the transition point from bulk to lattice due to abrupt variation of the component section. This thesis starts from this consideration and aims to realize the design of a gradual transition from bulk to lattice to mitigate the effect of intensification of stresses and then verify it through FEM (Finite Element Method) analysis and experimental tests. Due to the complexity of lattice structures, the design and FEM structural analysis of components of this type are complicated. In particular, one factor that creates many difficulties is the computational cost of the analysis itself. This is due to the length of time needed to calculate the mesh (discretization) of the component and to the difficulty of calculating 3D FEM analysis: a high number of nodes leads to the inversion of a very large stiffness matrix. To overcome these problems, the homogenization technique is used, which allows to evaluate the behavior of the elementary lattice cell and to replace it with a single computational element having as properties those of an equivalent homogeneous material. Finally, a previously designed real component, containing lattice structures, is modified to accommodate the bulk-to-lattice transition realized and is manufactured using the Metal Powder Bed Fusion technique.