PSI - Issue 42

C. Boursier Niutta et al. / Procedia Structural Integrity 42 (2022) 1449–1457 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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FDM Fused Deposition Modeling FE Finite Element SEA Specific Energy Absorption

1. Introduction Thanks to the recent advancements in 3D printing technologies, lattice structures are increasingly used in several industrial sectors. Lattice structures are three-dimensional structures that are composed of repeated unit-cells [1-3]. The mechanical response of a lattice structure is affected not only by the geometrical configuration of the unit-cell, but also by its density and its size. Therefore, different material properties can be obtained by designing the spatial configuration of the cell. The topological definition of the unit-cell then allows to obtain an engineered response to a specific structural problem, which is probably the most outstanding potentiality of these structures [4]. In a previous work [5], the authors have investigated the energy absorption capability of the lattice structure shown in Fig. 1, produced by Fused Deposition Modeling (FDM) of a carbon nylon filament.

Fig. 1. Lattice structure geometry [5].

In particular, the effect of the diameter, d , and of the length, l , of the beams on the absorbed energy in quasi-static crushing test has been addressed. The experimental campaign has also allowed the validation of a Finite Element (FE) model of the lattice structure. In this work, the numerical model is exploited to investigate the influence of defects in the unit-cells on the energy absorption capability of the structure. In particular, t wo typologies of defects, typical of AM components, are considered: i) the variation of the diameter of the beam with respect to the nominal value, which is a geometrical defect; ii) the presence of lack-of-fusion portions of material within the beams, which is a process-related defect. The defects are randomly disposed in the unit cell and different defect populations are simulated through transient nonlinear FE analyses in LS-Dyna environment. Results show that both beam diameter variations and lack-of-fusion portions affect the absorbed energy although with different severities. Further, by randomly distributing the defects within the unit-cell, it is shown that the crushing performance is affected by their location. The work is organized as follows: firstly, the experimental campaign addressed in [5] is briefly recalled together with the main results. The FE model is then described and the modelling of the diameter variation defect and of the lack-of-fusion defect is detailed. Thereafter, the comparison of numerical and experimental results [5] is shown. Finally, the results of the influence of the AM defects on the energy absorption capability of the structure are discussed and conclusions are drawn. 2. Experimental campaign on the lattice structure The experimental campaign conducted in [5] investigated the influence of the beam diameter d and size of the unit cell l on the specific energy absorption (SEA) capability of the structure. In addition, the effect of the number of cells n was investigated.