PSI - Issue 5

David Palousek et al. / Procedia Structural Integrity 5 (2017) 393–400 Vendula Kratochvilova et al. / Structural Integrity Procedia 00 (2017) 000 – 000

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2.3. Fatigue bending test and acoustic emission measurement

All specimens were machined according the picture on the Fig. 4a and fatigue tested. Fatigue bending test were carried out by electro-resonance testing machine RUMUL Cracktronic 8204 at room temperature. The fatigue cycle was sinusoidal and the stress ratio was symmetrical (R = -1). These measurements were supplemented by scanning electron microscope (SEM) factography analysis. For continuous monitoring of AE signal a device DAKEL-XEDO and two piezo-electric sensors DAKEL-MIDI with 35 dB preamplifiers was used. XEDO system allows 12-bit synchronous sampling with sampling frequency 2MHz and continuous saving data to a computer. The sensors were attached at both ends of the sample with Loctite adhesive to create a two-channel linear localization system. In post processing, the threshold detection of the AE hits was applied. Measuring station is shown on the Fig. 4b.

Fig. 4. (a) drawing of a specimen; (b) measuring station

3. Results and discussion

3.1. Fatigue testing

Results of fatigue testing were compared using S-N curves. The comparison of SLM and conventionally produced Al alloys AlCu2Mg1.5Ni in shown on the Fig. 5a. The difference between reference material after and before T6 treatment is insignificant, so the treatment did not improve fatigue resistance. Fatigue limit of both material is approximately 150 MPa. The fatigue resistant of SLM Al alloy is much worse than the reference material. 3 rd batch made from recycled powder is the worst. Even though the fatigue resistance of 2 nd batch seems to be the best of SLM material, the different quality of individual samples was observed. As the amount of samples is very low, it is not possible to determine the fatigue limit. The fatigue resistance of SLM alloy AlSi10Mg is similar to new powder batches of AlCu2Mg1.5Ni, see Fig. 5b. Quality of individual samples is consistent. These results are also comparable to those of study by Brandl et al. (2012). It suggests that alloy AlCuMg1.5Ni is not suitable for production by SLM technology. Results of fatigue testing of Cu alloy are compared on the Fig. 6. As expected, the quality of SLM material is worse than reference material. Fatigue limit of extruded material is about 285 MPa and 235 MPa for SLM material. However, the difference is not as significant as that observed in material AlCu2Mg1.5Ni and the quality of individual samples is stable. This Cu alloy is also more suitable for SLM production than AlCu2Mg1.5Ni.