PSI - Issue 7

Hiroshige Masuo et al. / Procedia Structural Integrity 7 (2017) 19–26 Hiroshige Masuo et Al./ Structural Integrity Procedia 00 (2017) 000–000

26 8

Where, the units are σ wl : MPa, HV : kgf/mm

2 , √ area

effmax : µ m.

4. Conclusions The fatigue properties of a Ti-6Al-4V manufactured by AMwere investigated and the perspective for fatigue design was discussed from the viewpoint of the effect of defects. 1. The Ti-6Al-4V manufactured by AM contained various defects which were observed by microstructural observation on the as-built material and also at fatigue fracture origins. 2. The defects were mostly defects made by lack of fusion. 3. Most of defects were eliminated by HIP and eventually HIP improved fatigue strength drastically to the level of the ideal fatigue limit expected from the hardness if the surface roughness effect was removed. 4. Surface roughness is more detrimental than defects which commonly exist in AM materials. 5. The shape of defects are mostly very irregular. The real size of defects does not reflect the true effect of defects. From the viewpoint of fracture mechanics, the method for estimating the effective size of defects expressed by √ area eff is proposed. The particular effect of surface on defects present near surface and the interaction effect of adjacent defects must be carefully considered from the viewpoint of √ area eff . 6. The statistics of extremes analysis based on the quantitative evaluation of defects is useful for the quality control of AM 7. It is suggested for practical fatigue design that considering the volume and number of productions of components, the lower bound of the fatigue limit σ wl based on √ area effmax can be predicted by the √area parameter model. References Aman, M., Okazaki, S., Matsunaga, H., Mariquis, G.B., and Remes. H., 2107. Interaction effect of adjacent defects on the fatigue limit of a medium carbon steel, Fatigue & Frac. Engng. Mater. & Struc., 40-1, 130-144. Beretta, S., Romano, S., 2017. A comparison of fatigue strength sensitivity to defects for materials manufactured by AM or traditional processes, Int. J. Fatigue, 94, 178–191. Günther,J., Krewerth, D., Lippmann, T., Leuders, S., Tröster, T., Weidner, A., Biermann, H., Niendorf, T., 2017. Fatigue life of additively manufactured Ti–6Al–4V in the very high cycle fatigue regime, International Journal of Fatigue 94, 236–245., and References included in this paper. Garwood, M.F. , Zurburg, H.H. and Erickson, M.A., 1951. Correlation of Laboratory Tests and Service Performance, Interpretation of Tests and Correlation with Service, ASM, Philadelphia, PA, pp. 1–77. Murakami, Y. and Endo, M., 1994. Effects of defects, inclusions and inhomogeneities on fatigue strength, Int. J. Fatigue, Vol.16, pp.163-182. Murakami, Y., Beretta, S., 1999. Small defects and inhomogeneities in fatigue strength: experiment, models and statistical implications, Extremes, 2(2), 123-147. Murakami, Y. and Nemat-Nasser, S. 1983. Growth and Stability of Interacting Surface Flaws of Arbitrary Shape, Engng. Frac. Mech., 17-1, 193 210. Nishijima, S., 1980. Statistical Analysis of Fatigue Test Data, J. Soc. Mater. Sci., Jpn., 29(316) , 24–29. Murakami, Y., 2002. Metal Fatigue: Effects of Small Defects and Nonmetallic Inclusions, Elsevier. Murakami, Y., 2012. Material defects as the basis of fatigue design, Int. J. Fatigue, Vol.41, pp.2-10