PSI - Issue 68

Ivan Senegaglia et al. / Procedia Structural Integrity 68 (2025) 610–618

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Ivan Senegaglia at al. / Structural Integrity Procedia 00 (2025) 000–000

(2017)). In particular, understanding their behavior under repeated loading is crucial for evaluating the performances after accumulated damage. Lattice-powered designing allows the elastic and plastic response of components control by tuning the cells’ geometry and repetition scheme, permitting us to create a component that can withstand significant deformation while preserving a macroscopic elastic behavior, (Ozdemir et al., (2016)). It can be successfully exploited for the production of lightweight shock absorbers for automotive applications, (Boursier Niutta et al., (2022)). Furthermore, TPMS lattices have found a promising application to produce heat exchangers that can be subjected to significant mechanical loads, (Saha et al., (2013)). Understanding the deformation of the structure due to impacts is fundamental for assessing the components’ functionality preservation. The static and fatigue properties of TPMS lattice structures have been recently deeply evaluated in the scientific literature, (Dallago et al., (2021); Murchio et al., (2021); Refai et al., (2020); Yan et al., (2021)), but the effects of the structure deformation on its mechanical properties are critical for the design of an energy absorber that employs these geometries. This study investigates the stiffness properties in lattice structures subjected to cyclical loading after pre-straining to various levels of plastic deformation. TPMS gyroid lattice-filled specimens were subjected to controlled steps of compressive pre-straining, inducing plastic deformations. Subsequently, the specimens underwent cyclic loading unloading tests to characterize their elastic response. Stress-strain curves were monitored to determine the apparent elastic modulus at each cycle. Finally, two surrogate Finite Element (FE) models, employing a single cell geometry with different boundary conditions, were implemented to approximate the mechanical behavior of the whole specimen while reducing the requirements in terms of computational resources.

Nomenclature DOF

Degree of freedom Apparent elastic modulus Material Young modulus

E*

E

FE Finite Element L-PBF Laser Power Bed Fusion LVDT Linear Variable Differential Transformer PBC Periodic Boundary Conditions RVE Representative Volume Element TPMS Triply Periodic Minimal Surface

2. Materials and methods 2.1. Specimen design and manufacturing The specimen used for testing consisted of a lattice region designed as a 3D array of 5x5x5 gyroid unit cells, shown in Figure 1. The lattice cell has an edge length (l c ) and nominal density (ρ) reported in Table 1. A full-dense base was implemented in the design to ensure proper alignment and centering within the testing machine, reducing misalignment errors during the compression tests. Table 1 and Figure 1 summarize the key dimensions of the specimen. The specimens were printed using an L-PBF process in Inconel 718, using a Renishaw RenAM 500S Flex machine installed in the "Metal Additive Manufacturing" laboratory of the University of Pisa. A standard Inconel 718 powder for L-PBF applications was employed, having a powder size distribution comprised between 15μm and 53μm (D10 D90). The specimens were printed in the vertical direction (y), namely with the cylindric base parallel to the machine build plate, and were oriented at 45° to the recoater blade, to minimize the risk of surface roughness inhomogeneities. A layer thickness of 60μm was adopted and a process parameter set aimed to ensure a full-dense material was employed (Beghini et al., (2024); Macoretta et al., (2023)). All the specimens were tested in the as-built condition.