PSI - Issue 13

J.-P. Brüggemann et al. / Procedia Structural Integrity 13 (2018) 311–316 J.-P. Brüggemann et al. / Structural Integrity Procedia 00 (2018) 000 – 000

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To evaluate the fracture mechanical behavior of the mixed aluminum alloy CT-specimens were built. In order to investigate the influence of the building direction regarding possible anisotropic behavior, two different orientations were analyzed, Building Direction parallel to Crack Path (BD ∥ CP) and Building Direction perpendicular to Crack Path (BD ⊥ CP), see Fig. 4. The fracture mechanical characterization of the produced mixed aluminum alloy compared to fatigue crack growth curves of the conventional EN AW-7075 alloy from literature is illustrated in Fig. 4.

Fig. 4. Crack growth curves for SLM-processed mixed aluminum alloy for the heat-treated condition and with the building directions BD ∥CP as well as BD ⊥ CP. Data for conventionally processed reference material by Sander (2008) and Eberlein (2016). The da/dN - Δ K -curves for specimen with building direction perpendicular to the crack path (BD ⊥ CP) are located further to the right in comparison to those with building direction parallel to the crack path (BD ∥ CP) and represent better fracture mechanical characteristics. A comparison of the threshold values clarifies the better material behavior. Both curves show the aluminum-typical double-S-shaped course of the crack propagation curve, Richard and Sander (2012). The threshold value for the BD ⊥ CP is Δ K I,th = 4.1±0.31 MPa·m 1/2 , for the BD ∥ CP the threshold for fatigue crack propagation is Δ K I,th = 3.3±0.21 MPa·m 1/2 . Compared to literature data by Eberlein (2016) and Sander (2008), the produced mixed alloy has fracture mechanical properties comparable to the conventionally processed EN AW-7075 alloy. The literature characteristics also show a typical variation in the threshold range for this alloy, so that there is good performance of the mixed alloy regarding fracture mechanical properties. The production of an aluminum alloy based on the high-strength alloy EN AW-7075 led to process-reliable processing using SLM. When using an adequate process parameter set, the samples produced have an almost pore free appearance without detectable hot cracks. A subsequent heat treatment leads to an increase in the mechanical characteristics of the mixed aluminum alloy. Nevertheless, these are below those of the conventional high-strength EN AW-7075 alloy. The investigation of the fracture mechanical characteristics shows a slight anisotropy with respect to the threshold value Δ K th . Nevertheless, the characteristics of the mixed alloy regarding fracture mechanics are comparable to conventional EN AW-7075. 4. Conclusions

References

ASTM, 2008. Annual book of ASTM standards. Section 3: Metals test methods and analytical procedures, vol 03.01. Metals - Mechanical testing, elevated and low-temperature tests. Metallography, 2008: E 647-08.