PSI - Issue 38

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Benaouda Abdellaoui et al / Structural Integrity Procedia 00 (2021) 000 – 000

Benaouda Abdellaoui et al. / Procedia Structural Integrity 38 (2022) 116–131 © 2021 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of the scientific committee of the Fatigue Design 2021 Organizers Keywords: Fatigue; additive manufacturing; materials; structures; innovation; mechanical developments

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1. Introduction Additive manufacturing by selective laser melting consists of aggregating, by in an enclosure under neutral gas, the particles of a powder bed using a laser beam. This one sweeps the surface and melts the powder on a given section. Once the layer is solidified, the construction platform is lowered to be able to spread a new layer of powder of predetermined thickness. The laser again scans the surface of the powder to create an additional section superimposed on the previous layer. The powder is not completely self-supporting, the construction of building supports is necessary for certain parts with cantilevered areas. The manufacturing parameters and the completions have a great influence on the fatigue performance of these materials as well as on their mechanical properties. The products from the selective laser melting have a very particular microstructure and contain multiple defects such as pores or a lack of fusion. Their irregular shapes have a negative effect on fatigue performance. Differences in durability can be found on two materials with the same chemical composition but from different manufacturing methods. Higher surface roughness is one of the reasons for the low fatigue performance of selective laser melting materials compared to conventional machining. A machining resumption would reduce surface roughness to avoid high stress concentrations. This treatment may also improve fatigue performance by creating residual compressive stresses and eliminate some of the defects present in the underlay. The stacking direction of the layers has a strong influence on static and dynamic mechanical properties. Some studies have shown that the fatigue resistance of selective laser melting materials improve by manufacturing them in the horizontal direction [1]. Because of the longer time intervals between layers, horizontal samples have longer cooling times and better solidification. In the case of a part containing many defects, a specific heat treatment can be beneficial to improve the performance of fatigue. The Hot Isostatic Pressing treatment (HIP) will close the pores which can significantly increase the maximum elongation of a part [2]. These defects, associated with the selective laser melting manufacturing method, are of three types: voids, pores, and projection particles. The rate of internal porosity depends mainly on the parameters related to the volume energy density (laser power, scanning velocity and laser beam diameter) but also on the temperature of the tray, the size of the powder grains, the scanning pattern, etc. To summarize, the additive manufacturing as a rule is a metallurgical science that is today in full swing. Dozens of scientific articles and theses are also in progress to optimize the mechanical performance of parts from these manufacturing methods. Because of the long list of factors influencing fatigue life, every aspect of the fatigue life in the design cycle should be considered. To do this, we have completely redesigned in additive manufacturing, optimized and qualified a mechanical part corresponding to a pivot used in cable winding machines with significant inertial forces (see in Fig. 1 (a)). The pivot in Fig. 1 (a) is driven by the gray part (lyre) which is rotated at high-speed (700 rpm). The assembly made up of the pivot part and the pulleys (in green) are subjected to inertial forces generated by this rotation. The cabling machine must operate 24 hours a day, with 15 stops per start-up per day. The pivot of Fig. 1 (b) is a topological optimization in additive manufacturing of the part presented in Fig. 1 (a). The volume of the red part in Fig. 1 (a) has been reduced significantly by 30% while keeping the associated inertial forces. In this paper, we present some of the results of the study on this mechanical part.