PSI - Issue 19

Yukio Miyashita et al. / Procedia Structural Integrity 19 (2019) 604–609

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Author name / Structural Integrity Procedia 00 (2019) 000–000

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4. Conclusion Fatigue strength test and fatigue crack growth test were carried out with non-combustible magnesium alloy containing Ca. Fatigue strength of TIG welds was lower than that of the base material. A weld defect was observed at fracture origin in all welds specimens tested and resulted in large scatter in fatigue strength with lower strength. Fatigue lives were well arranged by stress intensity factor calculated with size of defect and applied stress. Therefore, it is speculated that fracture mechanics approach is an effective way for fatigue design of the weld part. Fatigue crack growth resistance at weld part was higher than that of the base material even lower fatigue strength was observed in welds, thus presence of weld defect was significant on the fatigue strength. Moreover, in comparison of welds, weld part welded with higher heat input showed higher threshold stress intensity factor range compared to weld part welded with lower heat input. Those differences in fatigue crack growth resistance and threshold stress intensity factor rage were mainly due to difference in crack closure behavior. Therefore, it is proposed that effect of welding process could be taken into account by considering change in threshold stress intensity factor range in fatigue design of weld part in non-combustible magnesium alloy. Acknowledgements This work was carried out as a part of research project of “Innovative Structural Materials Research and Development” supported by New Energy and Industrial Technology Development Organization (NEDO). References S. Akiyama, H. Ueno, M. Sakamoto, H. Hirai, A. Kitahara, 2000, “Development of Noncombustible Magnesium Alloys”, Materia Japan, Vol. 39, No.1, pp.72-74. H. Ohara, 2016, “Development and application of flame-retardant and heat-resistant magnesium alloys”, Journal of Japan Institute of Light Metals”, Vol. 66, No.5, pp. 223-239. Y. Murakami, S. Aoki, N. Hasebe, Y. Itoh, H. Miyata, N. Miyazaki, H. Terada, K. Tohgo, M. Toya, R. Yuuki (Ed.), 1987, “STRESS INTENSITY FACTORS HANDBOOK”, Vol.1”, Pergamon Press, pp.3. S. Hamada, T. Kawazoe, K. Hayashi, H. Morita, M. Ueda, M. Sakamoto and H. Noguchi, 2010, “Proposal of Simple Determination Method for Welding Condition of Joint from Fatigue Limit Characteristics (lst Report , Application to TIG Butt Joint of Non Combustible Mg Alloy)” , Transactions of the Japan Society of Mechanical Engineers A, 76-772, pp.100-109 Y. Murakami, 1993, ”Metal fatigue effect of small defects and nonmetallic inclusions”, Yokendo co. ltd., pp.17. Fig.7 Relationship between fatigue crack growth rate, da / dN and (a) stress intensity factor range, Δ K and (b) effective stress intensity factor range, Δ K eff in T110A and T130A.