PSI - Issue 39

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

Table 2. Values of material, defect population and fatigue modelling parameters. Parameter Value EBM Ti6Al4V Young modulus [ ] [36] = 119 EBM Ti6Al4V Poisson ratio [36] = 0.3 EBM Ti6Al4V density [ 3 ⁄ ] [36] = 4.42 ∙ 10 −3 EBM Ti6Al4V Yield limit 02 [ ] [35] 02 = 866 EBM Ti6Al4V Vickers hardness [35] = 350 Superficial defect location parameters 1 [32] 1 = 1.41 LEVD location parameter √ [ ] [36] √ = 60.78 LEVD scale location parameter √ [ ] [36] √ = 10.15 Reference volume 0 [ 3 ] [32] 0 = 0.01 Maximum admissible mass [ ] = 156 Final structure volume, = ⁄ [ 3 ] = 35294

Fig. 2 shows the division in non-design domain (NDD) in red and design domain (DD) in grey of the bracket for the TO process. As it can noticed, both the bushings, Clevis and 9gLug, are set as NDD to ensure the connectivity with the pins. Similarly, an offset circular zone is set around the holes to guarantee the rivets hold. The DD is set equal to the remaining part of the bracket where the lightening features from the traditional manufacturing are removed. In particular, the full thickness of the rib is included and handles around the fixed holes are removed. No other additions of material can be done to the design domain due to the necessity of guaranteeing the assembly of the final part with other components.

Fig. 2. Design domain and No design domain definition. The geometry in Fig. 2 is used for the optimisation and it discretised in 449444 first-order R-tetra elements. The connection between the NDD and the DD is ensured using contact elements. The convergence parameter is set equal to 0.005 while no maximum number of iterations is imposed. The filtering radius is set equal to 2 mm, i.e. two times the imposed maximum element size. The TO process reaches a feasible solution, where all the constraints are satisfied, in 163 iterations. The final topology is shown under a different point of views in Fig. 3 with a filter on the intermated density equal to 0.5 (command ‘Iso’ in Hypermesh). Some considerations must be done on this solution: first of all, the tiny bar connecting the two grater masses may be removed in the CAD re-design of the model, however, it is crucial to guarantee the link between the bushings and keep the bracket mono-component. Secondly, one rivet connection is detached from the rest of the body since the number of constraints is highly redundant and this one it is not considered vital by the optimizer. Anyway, it can be easily linked afterwards in the CAD re-design not to lose the rivet connection. In Fig. 4, the von Mises equivalent stress and the maximum first principal stress distribution are