PSI - Issue 39

Riccardo Caivano et al. / Procedia Structural Integrity 39 (2022) 81–88 Author name / Structural Integ ity Procedia 00 (2019) 000–000

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Fig. 1. Original component geometry and boundary conditions. With the aim of designing the component in the fatigue regime, the nominal load conditions are required. Therefore, according to [35] the nominal load conditions can be calculated dividing the maximum ones by a factor equal to 1.5. Table 1 reports the maximum and the nominal conditions which the brackets undergo during its life.

Table 1. Applied loads in worst and nominal conditions. Load Worst condition Nominal condition

[ ] [ ] 12 [ ] 1121 747 9 [ ] -6861 -4574 9 [ ] 21830 14553 9 [ ] 1372 915 10432 6955 8

As already mentioned, the re-design material is supposed to be Ti6Al4V processed by EBM technology. The material data about EBM Ti6Al4V are reported in Table 2 and it is directly obtained by the material data sheet provided by Arcam company [36]. Additionally, in Table 2, the data related to the defect distribution, needed for the TO problem setup, are reported. The data are extrapolated from the defect population found in [37] of Arcam EBM Ti6Al4V samples, with suggested process parameters, machined and without post-process heat treatment. This experiment setup can be assumed to be fairly close to that for possible production of the analysed component. If very different process parameters or post-production treatments, such as the hot isostatic pressure (HIP), were employed, a novel defect analysis would be necessary to estimate the LEVD parameters as indicated by [32]. The optimisation in Hypermesh is carried out using the nominal set of loads reported in Table 1 since the bracket must be verified structurally in the fatigue regime. This condition is verified during the optimisation imposing a constraint over the maximum first principal stress ̄ , , according to Eq.(4). This value is equal to 450 MPa for the defect population data reported in Table 2. For more, another constraint is imposed over the maximum allowable final mass, as prescribed by Leonardo Spa. Since the original bracket weight is 160 g, the maximum allowable mass results to be 156 g. This constraint is equivalent and substitutes the volume fraction constraint imposed in the TopFat procedure [33]. Last, a limit over the von Mises equivalent stress equal to the Yield stress is imposed to verify the quasi-static safety. The objective of the optimisation is compliance minimisation, i.e. global stiffness maximisation.