PSI - Issue 19

Masanori Nakatani et al. / Procedia Structural Integrity 19 (2019) 294–301 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

301

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estimated results may be reasonable. Further investigation and discussion are necessary to evaluate the effect of surface roughness quantitatively. As described previously, the fatigue strength of as-built AM sample is quite low compared with the ideal fatigue strength, preventing AM process from applying to actual mechanical components. Thus, it is significantly important to decrease or eliminate the surface roughness using some technique such as chemical etching, barrel polishing and so on. We are investigating the effect of polishing on the fatigue strength in Ti-6Al-4V alloy fabricated by AM process. The results will be also introduced in our presentation. 4. Conclusions The effect of surface roughness on the fatigue strength of Ti-6Al-4V alloys fabricated by two AM processes was investigated. As-built specimen has extremely rough surface with three-dimensional complex morphology. The surface roughness was dependent on the particle size used in AM process. The fatigue strength of as-built specimens decreased to the level of 1/3 of the fatigue strength of the ideal fatigue strength. Though HIP can eliminate the internal defects, the surface roughness was not improved by HIP. Therefore, surface roughness has a detrimental influence on fatigue strength. Thus, it is significantly important to decrease or eliminate the surface roughness. The evaluation method for the effect of surface roughness was also discussed. Even DMLS as-built specimen which surface roughness is relatively small does not fit the √ area parameter model. This suggests that the surface roughness of as-built specimen should be considered to be long crack rather than small defect. Baufeld, B., Biest, O.V., Gault, R., 2010. Additive manufacturing of Ti – 6Al – 4V components by shaped metal deposition: Microstructure and mechanical properties. Materials & Design 31, S106-S111. Frazier, W.E., 2014. Metal Additive Manufacturing: A Review. 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