PSI - Issue 34

Riccardo Caivano et al. / Procedia Structural Integrity 34 (2021) 221–228 Riccardo Caivano et al./ Structural Integrity Procedia 00 (2019) 000 – 000

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the literature to show the weaknesses of the TO algorithms. As a matter of fact, the TopFat original algorithm is tested under these severe conditions with the precise purpose of showing the reliability and efficiency of the method. On the contrary, the HyperWorks TO solver is easily extendible to many other different TO problems but it is less specific than the original TopFat algorithm. Overall, it can be concluded that the TopFat original algorithm is extremely efficient even with hard geometry conditions but its extendibility to other TO problems is complicated and the software is not available for most companies and industries. On the contrary, HyperWorks TO can include the TopFat procedure, i.e. including the defect population analysis within the TO framework, but it may not reach a feasible solution in specific complex problems (or the set of TO settings can be hardly defined). However, this partial limitation in HyperWorks can be quite easily overcome with an appropriate problem set-up, generally followed when components are to be designed with TO algorithms. For example, the re-entrant corners can be round by the designer before the optimisation, reducing stress concentrations. Additionally, the re-design phase after the optimisation, which has not been considered in the present paper, would permit to reduce possible peak stresses and to obtain a feasible topology.

a)

b)

= 2133  = 659 MPa 1 = 510 MPa = 2363 = 769 MPa 1 = 550 MPa Fig. 4 - Corbel benchmark: a) final topology obtained in TopFat and data; b) final topology obtained in HyperWorks and data. Notation : : compliance; : maximum von Mises equivalent stress; 1 : maximum first principal stress 4. Conclusion In the present paper, a novel methodology that permits to take into account the detrimental influence of defects on the fatigue response in the topology optimisation (TO) set-up is implemented in the HyperWorks commercial software. The Murakami theory is employed to include the defect population as a fatigue constraint in the TO, with a limit on the maximum first principal stress. The proposed method has been validated by considering the results obtained by applying a pre-existing algorithm, named TopFat, on literature benchmarks. The results show that the commercial software can be reliably used to design and optimise parts by considering the presence of defects. The original TopFat algorithm can solve problems with extreme geometries and loading conditions, whereas the HyperWorks commercial software may fail. However, this is reasonable since the original TopFat algorithm has been developed to be applicable in almost every conditions. On the contrary, the extension of this methodology to commercial software has the purpose of reaching wide-ranging applications and industrial users. To conclude, the possibility to apply stress limits defined by considering the defect population in TO algorithms implemented in commercial software will permit a safe design of AM components and contribute to their further diffusion in structural applications.