PSI - Issue 13

Catrin M. Davies et al. / Procedia Structural Integrity 13 (2018) 1384–1389 Author name / Structural Integrity Procedia 00 (2018) 000 – 000

1389

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For samples built in the vertical orientation more unusual trends are seen. The as-built vertical sample data Fig. 6 (c) deviates from the FE prediction at a load-of 2kN, indicating early stages of crack growth. For the heat treated vertical sample Fig. 6 (d), the experimental data agrees with the plane strain prediction until a load of approx. 5.8 kN is achieved, where crack growth is initiated. In this case higher fracture strength is observed in the heat treated sample compared to the as-built sample. This may be due to the low ductility of the vertical as-build samples (<5%) which is substantially increased (up to 15%) with 700 °C heat treatment (Ronnerberg et. al., 2018). Note that in the horizontal orientation, the tensile ductility of both AB and 700 °C were similar and around 28% on average (Ronnerberg et. al., 2018), which may explain the similarity in the fracture results in Fig. 6 (a) and (b), assuming the sample fractures due to ductility exhaustion. Further tests are required to confirm these finding and a ductility exhaustion model needs to be implemented into the FE analysis to simulate the test results. The influence of sample orientation and heat treatment have been examined on SLM built Charpy impact sample and single edge notched bend, SEN(B), fracture samples. Generally it has been found that the Charpy impact energy of samples with the crack plane parallel to the build layers (vertical) is a factor of 3 less than that of samples with the crack plane normal to the build layers (horizontal). Heat treatment has been found to increase the impact toughness of the horizontal samples but significant variability in the results exists. The fracture resistance of SEN(B) samples had similar trends to the tensile ductility of the material in the as-built and heat treated conditions in both horizontal and vertical orientations, signifying that crack growth is consistent with a ductility exhaustion model. Further tests are required to confirm these trends. 5. Conclusions

Acknowledgements

The authors would like to thank AWE for supporting this research.

References

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