PSI - Issue 19

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

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3. Fatigue tests

3.1 Stress-controlled fatigue tests

The stress-controlled fatigue tests have been carried out with a stress-ratio of R  = -1 for an expected fatigue life in the regime between 3 ∙ 10 4 ≤ N f ≤ 1 ∙ 10 7 cycles. The crack initiation is defined as an increase of 20µm of the actuator displacement at constant load amplitudes.

Figure 7: Influence of the load orientation on the Wöhler-curve of AlSi10Mg

The comparison of the Wöhler-curves in Fig. 7 shows an anisotropic fatigue behavior, because the fatigue strength of Z-orientation in the low and medium cycle range is lower than of the X-orientation; in case of X-orientation the built direction is perpendicular to the load direction, but the layers are parallel to the load direction. From the point of view of system reliability, the individual layers are parallel, that means, even if in one layer contains imperfections, the impact on the structural durability is not decisive. In opposite in case of Z-orientation the strength depends on the weakest link, that means the layer with the most severe defects. With the scope on serial production, the reproducibility becomes a matter of particular interest. Therefore, further sets of specimens were built and tested. Fig. 8 shows the results of Wöhler-tests with Z-orientation of different built jobs with the same nominal scanning parameters. The fatigue strength of built job b is twice as high than of built job a. Due to this reason, the documentation of the nominal scanning parameters is not satisfying with regard to fatigue.