PSI - Issue 53

Rainer Wagener et al. / Procedia Structural Integrity 53 (2024) 161–171 Author name / Structural Integrity Procedia 00 (2019) 000–000

170 10

For example, Fig. 9 shows the comparison of cyclic stress-strain curves of a polished and thus smooth specimen and a specimen with as built surface from the Incremental Step Test. Independ of the surface in both cases a cyclic hardening occurs. Due to the small differences between the curves, it is advisable in this case not to consider the surface topology in the stress simulation and only in post-processing with the help of a reduced SN-curve.

Fig. 9: Influence of surface roughness on the cyclic stress-strain curve of different surface conditions

7. Conclusions The decisive factor for the quality of a numerical fatigue approach is the correct consideration of the material behavior. The advantage and disadvantage at the same time of additively manufactured structures is their heterogeneous microstructure. On the one hand, different local properties can be set in order to optimize the component behavior and reliability, on the other hand, these must also be evaluated correctly and included in the design process as well as fatigue assessment. In addition, additive manufacturing and, thus, WAAM offer freedom of design, which must be used in the sense of lightweight construction and resource conservation. At the same time, the requirements for a design concept that not only fulfills the material properties but also the industrial interests are increasing. The use of Representative Structural Elements can help to meet these requirements, provided such that the boundary conditions for which the RSE application can be described accurately. Sometimes it is necessary to break new grounds, for example with the counting of the peak-to-valley length to height quotient K R instead of the use of a conventional roughness parameter. Its cumulative distribution and maximum value can be used in a data-driven weakest-link approach. Concluding from the results shown, a local fatigue approach using Representative Structural Elements instead of cyclic material properties seems to applicable for WAAM structures, too. Acknowledgements This project has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No 862617 – MULTI-FUN. References

Basquin, O.H., 1910, The exponential law of endurance tests, Proceeding ASTM, 10, p. 625-630 Christ, H.-J., 1998, Materialermüdung und Werkstoffmikrostruktur, Werkstoff-Informationsgesellschaft, Frankfurt am Main.