PSI - Issue 34

Federico Uriati et al. / Procedia Structural Integrity 34 (2021) 184–190 Author name / Structural Integrity Procedia 00 (2021) 000–000

189

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Figure 6. a) contour plot of the component under experimental loading condition b) optimized part after fatigue \testing; failure initiation at the connection to the organic part with non-design volume (right joint) The fatigue data of as-built AlSi10Mg alloy were obtained using the miniature specimens displayed in Fig. 5b, [9]. The fatigue response was highly directional with a large difference in fatigue strength between the vertical and the horizontal specimens. These large differences are only partly attributable to the surface quality. A more significant contribution is due to the residual stresses that are especially high in the vertical specimens and almost absent in the horizontal specimens as determined by simulation and confirmed experimentally. Tab. 1 summarizes the data useful for the structural integrity assessment of the optimized lower arm. Since the tensile residual stresses in the vertical specimens play a negative role on fatigue strength, the local strength of the part at the failure location is defined by the horizontal specimens. The significant remaining difference between specimens and part data ( σ max,spec = 220 MPa @ 1.56 10 5 cycles vs. σ max,comp = 280 MPa, respectively) is however consistent with two additional factors: i) as-built vs. sand-blasted surfaces and ii) localized plasticity not considered in FEA of part.

Tab. 1 –Reference information from fatigue testing of miniature specimens [9] Vertical Mini specimens Horizontal Mini Specimens Surface quality As-built As-built Fatigue strength at 1.56 10 5 cyles 140 MPa 200 MPa Residual stresses 180 MPa 20 MPa

5. Conclusions This contribution presented an integrated design workflow of a metal AM part followed by the actual part fabrication in an industrial-grade L-PBF system using the AlSi10Mg alloy powder and its structural qualification by fatigue testing. Basic fatigue testing was required for the structural integrity assessment of the additively manufactured part [9]. The main conclusions reached in this work are the following: - Design of components to be produced by L-PBF is an iterative process involving topological optimization, CAD remodeling, FE analysis, part orientation analysis and PBF process simulation prior to actual part production. - A composite job incorporating actual parts, fatigue test specimens and calibration specimens has been developed and used for extensive testing. - The anisotropic fatigue behavior of as-built L-PBF AlSi10Mg obtained with directional specimens was attributed to the key role of fabrication residual stresses. - Prediction of the fatigue response of the optimized L-PBF part benefited from extensive modeling and simulation activities and ad-hoc material testing. Acknowledgement

Additive Works GmbH, Germany, is acknowledged for freely providing a license of Amphyon software.

References

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