PSI - Issue 41

Fabio Distefano et al. / Procedia Structural Integrity 41 (2022) 470–485 Author name / Structural Integrity Procedia 00 (2019) 000–000

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which are defined by the dimensions and connectivity of their constituent strut elements, that are connected at specific nodes. Additive Manufacturing (AM) techniques allow the fabrication of complex lattice structures with geometry that is unachievable by traditional manufacturing methods (Maconachie et al., 2019). Many lattice structures made of different unit cells have been studied over the years. Microlattice structures with strut-based unit cells derived from the observation of the nature, for instance: BCC, FCC, octet-truss, diamond, gyroid have been studied by carrying out experimental tests and finite element (FE) analysis (Al-Saedi et al., 2018; Yu et al., 2019). Other research analysed these structure for application in the biomechanical field (du Plessis et al., 2018; Wang et al., 2019). In other works, the mechanical response and the deformation mechanism process at different strains were investigated by means of quasi-static compression tests and FE analysis for microlattice structures (Zheng et al., 2021) and single unit cells (Wei et al., 2022). Recently, focus shifted towards cellular structures with mathematically defined architectures such as triply periodic minimal surface (TPMS) based topologies (Bobbert et al., 2017; Kadkhodapour et al., 2014). Some researches compared the structural performance of strut-based and TPMS structures (Al-Ketan et al., 2018; Refai et al., 2020), showing that TPMS structures present superior mechanical properties than strut-based structures. Other works investigated the effect of cell shape and size on the mechanical response of lattice structures (Li et al., 2014; Yang et al., 2020; Zhao et al., 2016). Unit cell lattice structures have been used and studied by means of FEA for application in the biomechanical field for the manufacture of devices with both porous and bulk structures in the treatment of bone diseases in hip (Harrysson et al., 2008), mandible (Gao et al., 2019) and in the vertebral column (Epasto et al., 2019a). The aim of the research is the mechanical and morphological characterization of BCC-derived unit cells made of Ti6Al4V ELI alloy and produced via electron beam melting (EBM) technology for applications in biomechanical devices used for the treatment of bone diseases. Such structures are: the G7 strut-based unit cell and the IWP sheet based TPMS unit cell. Compressive tests were carried out to evaluate the mechanical properties of the G7 unit cell. The morphological features, the microstructure and the fracture surfaces were observed with a scanning electron microscope (SEM) to analyse the failure modes of the structures. Different levels of relative density were evaluated during experimental tests; thus, the results were used to plot the Gibson-Ashby diagrams in order to find the correlation between mechanical properties and relative density of the structure. A FE model of a single unit cell was developed to evaluate the compressive behaviour of the G7 and IWP cells and to evaluate the effects off cells size and shape on the mechanical performance of the structures. 2. Materials and Methods 2.1. Unit cells analysed Two classes of unit cells have been investigated: the first one is a strut-based cell, the second is a TPMS cell. The selected unit cells were the G7 strut-based and the IWP sheet-based TPMS structures (Fig. 1).

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Fig. 1 (a) G7 unit cell (b) IWP unit cell