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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5. Conclusions In this work, the influence of AM defects on the Specific Energy Absorption (SEA) of a lattice structure is investigated through numerical simulations in LS-Dyna environment. Two typologies of defects are considered: i. diameter variation; ii. lack-of-fusion The numerical model is firstly validated on the experimental results of a testing campaign of lattice specimens performed in a previous work. Two collapse modes were identified, i.e, a progressive crushing, where each layer of unit-cells of the specimen progressively collapses, resulting in a force-displacement curve characterized by peaks and valleys, and a foam-like failure, where the whole specimen yields when crushed. The numerical model proved capable to capture both the collapsing modes and a very good agreement between the numerical and the experimental force displacement curves is obtained. The influence of the defects is investigated through the validated FE model. Defects are randomly distributed in the unit-cell, which is then replicated to construct the specimen. Different defect populations are considered, i.e., defectivity ratios of 5%, 12%, 25% and 50%, corresponding to 2, 4, 9 and 18 defective beams in the unit-cell, respectively. For each percentage, three simulations are performed in order to average the effect of the location of the defects within the structure. Results show that both defects significantly affect the SEA of the structure, with the lack-of-fusion defects being more detrimental for the crushing performance. The analysis also shows that the location of the defects influences the SEA, with increasing data scatter in the middle range of defectivity where the pristine beams are no longer able to compensate the presence of the defects and the defects are yet not prevalent. In conclusion, curves of variation of the SEA with the defectivity can be adopted both in the design stage of the lattice structure for energy absorbers and in the quality control stage. Validation of the defect modelling is required and represents a future development of this work. References 1. A.A. Zadpoor Mechanical performance of additively manufactured meta-biomaterialsActa Biomater. (2018). 2. X.Z. Zhang, et al. Selective electron beam manufactured Ti-6Al-4V lattice structures for orthopedic implant applications: Current status and outstanding challengesCurr. Opinion Solid State Mater. Sci., 22 (3) (2018), pp. 75-99. 3. Tobias Maconachie, Martin Leary, Bill Lozanovski, Xuezhe Zhang, Ma Qian, Omar Faruque, Milan Brandt, SLM lattice structures: Properties, performance, applications and challenges, Materials & Design, Volume 183. 4. Zuhal Ozdemir, Everth Hernandez-Nava, Andrew Tyas, James A. Warren, Stephen D. Fay, Russell Goodall, Iain Todd, Harm Askes, Energy absorption in lattice structures in dynamics: Experiments, International Journal of Impact Engineering, Volume 89, 2016, Pages 49-61. 5. Boursier Niutta, C.; Ciardiello, R.; Tridello, A. Experimental and Numerical Investigation of a Lattice Structure for Energy Absorption: Application to the Design of an Automotive Crash Absorber. Polymers (Basel). 2022 , 14 , 1116 – 1137, doi:https://doi.org/10.3390/polym14061116. 6. LSTC, LS- DYNA Keyword User’s Manual Volume I, 2021. 7. Calignano F., Lorusso M., Roppolo I., Minetola P. Investigation of the mechanical properties of a carbon fiber reinforced nylon filament for 3D printing. Machines, 2020, 8 (3), 52. 8. Sanaei, N.; Fatemi, A. Defects in additive manufactured metals and their effect on fatigue performance: A state of-the-art review. Prog. Mater. Sci. 2021, 117 , 100724.