PSI - Issue 34

Federico Uriati et al. / Procedia Structural Integrity 34 (2021) 184–190 Author name / Structural Integrity Procedia 00 (2021) 000–000

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near-net-shape components characterized by complex geometry. Parts with geometrical characteristics driven by optimized lightweight trade-offs would be readily produced by L-PBF and when combined to adequate strength are of great interest for sectors such as automotive and aerospace. In parallel with the evolution of the AM technology, the finite element-based software provides simulation and optimization tools that allow full exploitation of 3D printing potential. Different optimization methods have been developed and proved useful for the resolution of specific problems in relation with the Design for Additive Manufacturing (DfAM) rules, (Thompson et al. 2016). Here the authors will focus on a topology optimization (TO) application. TO has been originally introduced from Bendsøe, (Bendsøe 1989, 1995) and it is now available in commercial software for AM technology exploitation. TO addresses the engineering task of optimizing material use in a design space in the presence of given boundary conditions and given loads. Available computational tools efficiently provide optimized and intricate part geometries. However, the subsequent part fabrication and experimental validation is still a challenging task when the L-PBF technology of metal alloys is concerned. Structural integrity assessment of metal AM components requires an integrated know-how of the fatigue behavior of L-PBF metals under the combined effect of stress gradients, residual stresses, surface condition and process-induced internal defects (Molaei e Fatemi 2018). When using AM on existing parts, the biggest challenge is to identify promising candidates. The search for these parts is much more difficult than setting up a new part from scratch, as the business case must cover all change costs, including changes to manufacturing drawings, component lists, possible fastener adjustments, quality checks, maintenance, and repair guidelines, etc. A valuable example for the aerospace section is proposed by (Klippstein et al. s.d.). Nonetheless, here the part identification process is simplified, and it is referred to the automotive sector. The main aims of this contribution are i) the presentation and discussion of an integrated design workflow of a metal AM part (i.e., from geometrical topological optimization to AM process simulation before production), ii) the actual part fabrication in an industrial-grade L-PBF system using the AlSi10Mg alloy powder and iii) structural qualification by fatigue testing of actual parts under realistic working conditions. Knowledge of the link between technology-dependent factors and the fatigue strength was determined with a specific test methodology using miniature specimens (Nicoletto 2017). 2. Component identification and redesign The component identified for the present study is the lower suspension arm of a car shown in Fig. 1a. It develops a key structural function as it is connected to the chassis, to the wheel upright and the shock absorber. The suspension arm was selected because it is subjected to dynamic loading and therefore it requires a fatigue integrity assessment at the design stage and subsequent experimental verification. A scaled version of the component (i.e., 18mm x 43mm x 180 mm) was studied to contain costs, to facilitate L-PBF fabrication of multiple parts in one job exploiting the chamber dimensions of the AM system and to easily fit into a testing system available in the lab. Joint configuration was also modified replacing the spherical joint of the original version with a cylindrical coupling to accurate control the boundary condition during testing.

a) b) Figure 1. (a) car suspension assembly; (b) defeatured lower suspension arm with “Design space” (orange) and “Non design spaces” (grey)