PSI - Issue 19

Rainer Wagener et al. / Procedia Structural Integrity 19 (2019) 380–387 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

387

8

lower structural strain amplitude in case of X-orientation than of Z-orientation. For the so-called cyclic stabilized stress-strain state the stress-strain curve of an Incremental Step Test with  a,t,max = 0.4% shows a small proportion of plasticity whereas the stress-strain behavior of the Z-orientation is still elastic at macroscopic level. At higher loads, both orientations show elastic-plastic stress-strain behavior, with lower cyclic yield strength in X-orientation.

4. Conclusions

Additive manufacturing by laser powder bed fusion offers new options for lightweight design for safety parts under cyclic loading conditions. In order to utilize all advantages and exploit the full potential of this new production technology, the main impact factors on the fatigue behavior have to be identified and considered. This means in case of AlSi10Mg to consider influences related to the exposure strategy, heat treatment, microstructure, support structure and surface conditions, as well as the influence of the load history. Overall, the number of impact factors is important. Within the scope of the realization of a full virtual product development, structure elements are helpful to describe the component-related material behavior especially under cyclic loading conditions. Based on the layer by layer production process anisotropic material behavior occurs. Therefore, the stress-strain as well as the fatigue life could be depending on the orientation of the built to the load direction. A high quality fatigue approach is getting more challenging, because up to now the reproducibility is limited. Due to this reason, the main impact factors on the local fatigue properties are not identified so far. Finally yet importantly, the Incremental Step Test enables to identify the impact factors on the cyclic material behavior with less experimental effort and for that reason, a cyclic test with this load sequence enables a production accompanying quality checks. Acknowledgement The research and development project “VariKa” that forms the basis for this report is funded within the scope of the “PAiCE Digitale Technologien für die Wirtschaft” technology programme run by the Federal Ministry for Economic Affairs and Energy and is managed by the DLR project management agency „Gesellschaft, Innovation, Technologie- Informationstechnologien / Elektromobilität“ at the German Aerospace Center in Cologne.

Nomenclature  a,t,max max. strain amplitude within an Incremental Step Test K t stress concentration factor k slope of the Wöhler-curve N f number of cycles to failure N k number of cycles at the knee-point of the Wöhler-curve R  load ratio R  strain ratio  a,k stress amplitude at the knee-point of the Wöhler-curve

References

Landgraf, W.R., Morrow, J.D., Endo, T. (1969): Determination of the cyclic stress-strain curve, Journal of Materials, No. 4, pp. 176-188 Wagener, R., Melz, T. (2017): Deriving a continuous fatigue life curve from LCF to VHCF, SAE 2017-01-0330, DOI: 10.4271/2017-01-0330 Ramberg, W., Osgood, W. R.: Description of stress-strain curves by three parameters, Technical Note No. 902 (1943), NACA