PSI - Issue 19

Yukitaka Murakami et al. / Procedia Structural Integrity 19 (2019) 113–122 Yukitaka Murakami et al./ Structural Integrity Procedia 00 (2019) 000–000

122 10

Table 1 Tensile properties of Ni based superalloy 718.

Manufacture angle

Specimen №

Tensile strength (MPa)

Elongation (%)

Reduction of area (%)

1 6 11 24 29 32

895 900 885

35.8 31.4 23.4 26.6 22.4 21.2

47 37 25 37 28 26

90°

1020 1020 985

0°

10. Summary Effects of AM defects and surface roughness on fatigue properties were discussed from the viewpoint from the mechanics of small crack. Conclusions can be summarized as follows. 1. Control of presence of defects or size of defects and surface roughness is the key solution for the safe development of AM parts. Currently, the ideal fatigue strength (Fatigue-Grade 5) expected from Vickers hardness HV can be obtained only by the combination of HIP and surface polish. 2. Depending on the decrease amount from the ideal fatigue strength expected from Vickers hardness HV , the quality scale Fatigue-Grade 5 (90-100% of the ideal fatigue strength) to Fatigue-Grade 1 (10-30% of the ideal fatigue strength) was proposed. This Fatigue-Grade will be useful for sharing common understanding of fatigue performance among AM researchers. 3. As-built surface roughness is more detrimental than AM defects. Fatigue strength of AM defects must be treated as the small crack problem. Efficient surface polish techniques exclusively for AM parts must be developed. Tensile test cannot detect the influence of small defects on fatigue and is not relevant for the quality control of AM materials. Statistics of extremes can be used for the quality control and the standardization for the evaluation of AM defects. References Garwood, M.F., Zurburg, H. H., Erickson, M. A., 1951, Correlation of Laboratory Tests and Service Performance, Interpretation of Tests and Correlation with Service, ASM, Philadelphia, PA, pp. 1-77. Masuo H., Tanaka, Y., Morokoshi, S., Yagura, H., Uchida, T., Murakami, Y., 2018, Influence of defects, surface roughness and HIP on the fatigue strength of Ti-6Al-4V manufactured by additive manufacturing, Int. J. Fatigue 117, 163-178. Murakami, Y., 2002, Metal Fatigue: Effects of Small Defects and Nonmetallic Inclusions, First edition, Elsevier. Murakami, Y., 2019, Metal Fatigue: Effects of Small Defects and Nonmetallic Inclusions, Second edition, Academic Press & Elsevier. Murakami, Y. , Endo, M., 1994, Effects of Defects, Inclusions and Inhomogeneities on Fatigue Strength, Int. J. Fatigue 16, 163-182. Murakami, Y., Endo, T., 1980, Effects of small defects and on fatigue strength of metals, Int. J. Fatigue 2, 23-30. Murakami, Y., Machida, H., Miyakawa, S., Takagi, T., 2017, A new quality control method based on statistics of extremes for preventing recalls for mass production products, Trans. Japan Soc., Mech. Engrs. 83, 17-00231 (in Japanese). Murakami, Y., Miller, K.J., 2005, What is fatigue damage? A view from the observation of low cycle fatigue process, Int. J. Fatigue, 27, 991 1005. Nishijima, S., 1980, Statistical Analysis of Fatigue Test Data, J. Soc. Mater. Sci. Jpn. 29, 24-29 (in Japanese). Romano, S., Miccoli, S., Beretta, S., 2019, A new FE post-processor for probabilistic fatigue assessment in the presence of defects and its application to AM parts, Int. J. Fatigue 125, 324-341. Seifi, M., Gorelik, M., Waller, J., Hrabe, N., Shamsaei, Daniewicz, S., Lewandowski, J. J., 2017, Progress Toward Metal Additive Manufacturing Standardization to Support Qualification and Certification, JOM 69, 439-455. Serrano-Munoz, I., Buffiere, J.Y., Mokso, R., Verdu, C., Nadot, Y., 2017, Location, location and size : Defects close to surfaces dominate fatigue crack initiation. Scientific Reports 7, 45239. Yamashita, Y., Murakami, T., Mihara, R., Okada, M., Murakami, Y., 2018, Defect analysis and fatigue design basis for Ni-based superalloy 718 manufactured by selective laser melting, Int. J. Fatigue 17, 485-495.