PSI - Issue 47

G. Morettini et al. / Procedia Structural Integrity 47 (2023) 296–309 Author name / Structural Integrity Procedia 00 (2019) 000–000

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1. Introduction The scientific research of the last century, in the field of materials engineering and production technologies, has always been at the service of the industrial needs of creating components with increasingly complex geometries. Among the techniques that have proven to effectively respond to the need to optimize the design of components, in numerous sectors of industrial production, the so-called "additive manufacturing" (AM) technologies have recently been included. These have made it possible to abandon the traditional manufacturing principle, centered on the removal of material, by introducing an additive logic that makes it possible to produce components that cannot be made in any other way (Gonzalez-Gutierrez at al. (2018)) Ultimately, the 3D printing of metal, polymer, ceramic, and composite parts, thanks to the continuous progress of those branches of engineering and science that deal with the discovery and design of new materials, is changing how some key components in the industrial field are designed, produced and tested. If on the one hand, however, the creation through AM of metal components capable of withstanding operational loads is advancing in many fields (Morettini at al. (2019)) (among all, the example of additive manufacturing for aerospace components is valid (Nyamekye at al. (2023))) this is still not this happened for plastic materials such as PLA, the use of which has not yet gone into the production of components with structural responsibility. Yet, if that were to happen, a great many industries would benefit from it. First of all, the automotive sector (Landi at al. (2021)) with its vast production of plastic gear wheels. This change of approach in the manufacturing industry has made it possible on the one hand to face new challenges in the design field, on the other, however, it feels the need to study the mechanical behavior of materials according to the specific technological parameters that distinguish the manufacturing process additive. This first prompted the scientific community to discuss the effect of single variations of the printing parameters on the mechanical properties of the material such as the effect of the Raster Angle on the stiffness properties studied by S. Sheth (Sheth at al. (2017)), Z. Abdullah (Abdullah at al. (2018)), and S. Es-Said (Es-Said at al. (2000)) analyzed respectively the effects of layer thickness and layer orientation on the tensile strength, M.F. Alfonse (Alfonse at al. (2016)) and D. Corapi (Corapi at al. (2019)) have instead studied the effect of the build part orientation on mechanical properties of the material, T. D. McLouth (McLouth at al. (2017)) has characterized the impact of the raster pattern on fracture toughness. Recently, however, to push technology and materials towards an introduction into the industrial world, various authors have begun to provide optimal parametric settings which, depending on the applications, help the designer manufacture the components. Among these, we find the work of J. Chacon (Chacon (2017)), that of L. Safai (Safai (2019)) and others (Mohamed et al. (2015), Sood et al. (2010), Ezeh et al. (2018), Morettini at al. (2022). Only thanks to this last activity will additive production (especially with regard to thermoplastic materials) be able to insert itself decisively alongside ordinary production, making up in a malleable way for situations of necessity in the event of breakage of links in the production line, with significant company savings. Once the optimal parameter sets have been identified, the next step is to see how these materials/components behave with ordinary structural requirements. It is precise with this goal that this study activity is developed. The object is primarily aimed at the characterization of the behavior mechanics of notched specimens produced using the Deposition Modeling (FDM) technique by PLA Filaments. The study will take care of deepening how, the choice of particular geometries attributable to notch can significantly alter the mechanical behavior of the material; but more importantly, to identify what analytical and simulation tools a designer can use to predict correctly the behavior of notched AM components. Some authors have already started dealing with this topic (Ahmed at al. (2017), Susmel at all. (2019)), Seibert et al. (2020) applied the Average Strain Energy Density (ASED) criterion successfully in AM PLA material using an alternative approach to evaluate the control volume. Given the current relevance of the problem, starting from simple static cases, there is an urgent need to find which predictive procedures can be used to predict the failure of the components designed with this new technology. As for other technologies in the AM products, the presence of notches can in fact lead to a brittle failure of the component even when the same is generally characterized by a ductile behavior. This problem has one fundamental importance since brittle failure can occur at stresses much lower than that of yielding.