PSI - Issue 68

Antti Järvenpää et al. / Procedia Structural Integrity 68 (2025) 619–625 Antti Järvenpääa et al. / Structural Integrity Procedia 00 (2025) 000–000

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1. Introduction Additive manufacturing (AM) has brought new possibilities to create functional structures with enhanced performance, e.g., for heat exchangers, orthopedic implants, and general weight reduction. Lattice structures, characterized by their interconnected network of struts, are one of these interesting solutions. Laser powder bed fusion (LPBF) has been recognized as the current key technology for fabricating internal architectures with extremely small strut sizes even below 200 µm, as shown by Soro et al. 2022 and Barba et al. 2019. Based on their micro-architecture, lattice structures may exhibit either periodic or non-periodic characteristics, with the latter also referred to as stochastic (Yu et al. 2022 and McGregor et al. 2021). Triply periodic minimal surfaces (TPMS) are intriguing structures that arise from the principles of differential geometry in engineering contexts. These surfaces are characterized by periodicity in three independent spatial directions and possess minimal surface area properties as described by Bobbert et al. 2017. The minimal area property indicates that the surface configuration locally minimizes its area, rendering them stable forms in specific physical systems. These mathematically grounded concepts are particularly attractive due to their remarkable topological, mechanical, and mass transport characteristics, making them highly relevant for various engineering applications, including materials science and fluid dynamics. This study is based on an orthopedic implant development by Instituto Tecnológico de Costa Rica and the University of Oulu, where the consortium has been able to decrease the stress-shielding effect and maximize the cell growth properties of the metallic implant materials, as shown by Araya et al. in 2024 in few publications. The study has shown the superior performance of the developed gyroid structures in biomedical applications, but much larger potential is seen in other sectors of industry. Since the literature is mainly focusing on medical applications, most of the mechanical data is available from compression tests. In this study, we will highlight the tension properties of the developed lattice structures and make a literature comparison to analyze the performance in general. 2. Experimental methods 2.1. Design parameters Two distinct open-cell lattice configurations were selected for the study: a gyroid and a Voronoi Volume Lattice. These configurations represent two of the primary classifications of lattice structures, with the former being shaped by mathematical surfaces and the latter consisting of elements resembling struts or beams. A gyroid structure with walls was based on the Triply Periodic Minimal Surface (TPMS). The structure is governed by equation (1), where “a” determines the size of the unit cell, while “t” influences its porosity. The Voronoi Volume Lattice is characterized by its stochastic arrangement formed through random points within space. Five relative densities of 0.1, 0.2, 0.3, 0.4, and 0.5 were considered in both structures to study the effect of density and design features on the static properties. Strut thicknesses were varied in the range from 200 µm to 300 µm. The ten different models are detailed in Fig. 1. ( , , ) !"#$%& = , ' ) ( - ' ) ( + , ' ) ( - , ' ) ( - + , ' ) ( - , ' ) ( - = t (1)

Fig. 1. Studied models showing both the walled TPMS gyroid and Stochastic Voronoi lattices with relative densities of 0.1, 0.2, 0.3, 0.4, and 0.5.