# Additive Manufacturing in Industry
###### Abstract  
The advent of additive manufacturing (AM) processes applied to the fabrication of structural components has created the need for design methodologies and structural optimization approaches that take into account the specific characteristics of the fabrication process. While AM processes give unprecedented geometrical design freedom, which can result in significant reductions in the components' weight (e.g., through part count reduction), on the other hand, they have implications for the fatigue and fracture strength, because of residual stresses and microstructural features. This is due to stress concentration effects, anisotropy, distortions and defects whose effects still need investigation. This Special Issue aims at gathering together research investigating the different features of AM processes with relevance for their structural behavior, particularly, but not exclusively, from the viewpoints of fatigue, fracture and crash behavior. Although the focus of this Special Issue is on AM, articles dealing with other manufacturing processes with related analogies can also be included, in order to establish differences and possible similarities. additive manufacturing (AM); functionally graded (FG); directed energy deposition (DED); laser powder bed fusion (LPBF); cold metal transfer (CMT); wire arc additive manufacturing (WAAM); defects; fatigue; fracture; crash +
Footnote †: 2021: 11, 840. The performances of an AM automotive component were assessed numerically in [5], with respect to the delivered crashworthiness and compared with those of the traditional component. In particular, a frontal impact sled test was simulated, and the damages to the occupant's legs were assessed, with specific reference to the dashboard's glove box. The key aim was therefore to reduce weight and costs of the newly proposed AM component, guaranteeing at the same time a safe design for passengers. The materials analyzed were polyamide and polypropylene, both reinforced with 5% basalt. The tests were simulated according to Euro New Car Assessment Program (NCAP), and the main biomechanical parameters required by the Euro NCAP were estimated for both the current and the additive production of the component. In [6], a porous functionally graded (FG) rotor-bearing system was simulated numerically via the finite element method (FEM). Stiffness, mass and gyroscopic matrices were derived for porous and non-porous FG shafts. The considered materials were FG, whose inner core was a stainless steel, whereas the outer layer was made of a ZrO2 ceramic. It was found that the power law index, volume fraction of porosity and thermal gradient provided a significant influence on the natural and whirl frequencies of the FG rotor-bearing system, thus providing several guidelines for their subsequent designing process. FG materials were also studied in [7], with reference to a thick-walled cylindrical tube subjected to different combinations of loading conditions, such as internal pressure, thermal gradients and/or bending. The main aim was to derive the elastic-plastic responses of the component so as to give guidance to designers working with FG materials. In [8], laser powder bed fusion (LPBF) technology was used to manufacture SS316L specimens. The impact of production-induced porosity on fatigue strength of 316L was investigated, and the fatigue strength compared with that of the base material and with that of a novel ferritic steel, named HiperFer, this latter promising an increased fatigue strength. Directed energy deposition (DED) technology was considered in [9]. The aim was to determine how platform preheating and a sealed deposition environment, with respect to the exclusive use of an Ar flow as a protective mean, impacted on the final quality of Ti-6 Al-4V samples built via DED. Information about the final quality of specimens was derived based on the environment in the chamber during manufacturing, with the end purpose of evaluating the possible up-scaling of this AM technology.