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Hasegawa, Kunio; Usami, Saburo*; Lacroix, V.*
Proceedings of 2019 ASME Pressure Vessels and Piping Conference (PVP 2019) (Internet), 6 Pages, 2019/07
Fatigue crack growth thresholds are provided by several fitness-for-service (FFS) codes. When evaluating cracked components subjected to cyclic loading, maximum stress intensity factor and/or minimum stress intensity factor are required. However, the definitions of the thresholds under negative stress ratio 
are not clearly written. In addition, the thresholds are given by constant values under negative . This paper shows that the maximum stress intensity factor converted by the thresholds obtained by experimental data are not constant values under negative . The thresholds for the FFS codes are less conservative. The definition of the thresholds under negative ratio are discussed.
Suzuki, Takayuki*; Usami, Saburo*; Kimura, Takae*; Koizumi, Koichi; Nakahira, Masataka; Takahashi, Hiroyuki*
Proceedings of 55th Annual Assembly of International Institute of Welding (IIW2002), 16 Pages, 2002/06
A new type of welded joint for the outer wall and rib of a double-walled vacuum vessel of a fusion reactor has been developed. The joint is manufactured by through-wall electron-beam welding (TW-EBW), in which the beam is injected from the outside of the outer wall. Static and fatigue tests are carried out on one-bead-specimens under an axial load and two-bead-specimens under a bending load. The experimental results are analytically investigated by FEM. Although this joint is partially penetrated, the net yield strength of the bead is increased by the plastic constraint due to triaxial tensile stress in the weldment. This phenomenon reduces the mean equivalent stress on the bead cross section, and the gross strength of the joint is close to that of a full thickness welded joint. The fatigue-strength reduction factor for low-cycle fatigue life is a little larger than four. The calculated fatigue-crack growth rate in the joint is conservatively calculated by using the maximum stress intensity factor of the crack and the fatigue-crack growth rate given in ASME Code Section XI.