PSI - Issue 34

Sigfrid-Laurin Sindinger et al. / Procedia Structural Integrity 34 (2021) 78–86

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S.-L. Sindinger et al. / Structural Integrity Procedia 00 (2019) 000–000

One aspect that likely contributed to an overestimation of stresses is related to discretization of the component. Namely, the representation of rib connections as shells. As can be seen in the detail view of Fig. 4a, the connection of three ribs leads to a material accumulation. In the real structure this firstly evokes higher ultimate strength due to the thickness e ff ect and secondly lower apparent stresses, since the cross section that loads act upon is larger. Hence, the part is not prone to fail in this exact location but rather towards the transition to single-rib thickness (compare Fig. 4a), which is furthermore a ff ected by a local change in sti ff ness. On the contrary, in the discretized model three ribs are connected via a single node path and no thickness accumulation can be accounted for, which leads to an unrealistic stress concentration. As can be seen in Figs. 5c- 5d, first element failure is estimated exactly in such a region. Omitting elements that constitute these rib connections reduces the deviation between predicted and measured failure displacement from 18 to approximately 6 % in the current part. Since general negligence of these critical regions cannot be justified, more sophisticated approaches using specialized shell or solid elements should be considered for modeling such rib interconnections. This highlights the fact that structural integrity of components can be dictated by highly local phenomena, while the load-displacement response of entire structures may be governed by the interplay of all structural members. The fact that in the present simulations linear material behavior was assumed until fracture certainly diminished prediction accuracy as well. While the stress-strain graphs obtained in the tensile tests for the most part showed a close to linear progression, a slight degressive trend manifested towards specimen fracture. Unfortunately, at present Optistruct ™ does not support orthotropic and elasto-plastic material laws for 2D elements. The implementation of thickness dependent and orthotropic behavior for elasto-plastic shells should be addressed in future research using solvers with more advanced material modeling capabilities (e.g. Altair RADIOSS ™ ). In conclusion, it can be said that the proposed approach yields adequate results for prediction of sti ff ness, but further improvements are necessary to e ff ectively asses the load bearing capacity of thin-walled additively manufactured structures.

Acknowledgements

The financial support of the Christian Doppler Research Association, the Austrian Federal Ministry of Digital and Economic A ff airs and the National Foundation for Research, Technology and Development is gratefully acknowl edged. Furthermore, the authors are grateful to KTM E-TECHNOLOGIES GmbH for fabricating the samples used for the experiments.

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