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Journal Articles

Change in mechanical properties by high-cycle loading up to Gigacycle for 316L stainless steel

Naoe, Takashi; Harjo, S.; Kawasaki, Takuro; Xiong, Z.*; Futakawa, Masatoshi

JPS Conference Proceedings (Internet), 28, p.061009_1 - 061009_6, 2020/02

At the J-PARC, a mercury target vessel made of 316L SS suffers proton and neutron radiation environment. The target vessel also suffers cyclic impact stress caused by the proton beam-induced pressure waves. The vessel suffers higher than 4.5$$times$$10$$^8$$ cyclic loading during the expected service life of 5000 h. We have investigated fatigue strength 316L SS up to gigacycle in the previous studies. The cyclic hardening and softening behavior were observed. In this study, to evaluate the cyclic hardening/softening behavior, the dislocation densities of specimens were measured using the neutron diffraction method at the MLF BL-19. The result showed that the dislocation density of a 316L SS was increased with increasing the number of loading cycles. By contrast, in the case of cold-rolled 316L SS, annihilation and re-accumulation of dislocation by cyclic loading were observed. In the workshop, result of neutron diffraction measurement will be introduced with the progress of fatigue test.

Journal Articles

Effect of artificial defects on the very high cycle fatigue behavior of 316L stainless steel

Xiong, Z.*; Naoe, Takashi; Futakawa, Masatoshi

Metals, 9(4), p.412_1 - 412_11, 2019/04

 Times Cited Count:1 Percentile:66.53(Materials Science, Multidisciplinary)

The effect of surface defects on the very high cycle fatigue (VHCF) behavior were investigated on the solution annealed (SA) and cold-rolled (CW) 316L. Surface defects were artificially created using indentation. VHCF test was conducted using an ultrasonic fatigue method. The results showed that the fatigue crack initiation was independent of the indent with the applied range of depth in this research. Furthermore, the critical depth of the indent was evaluated based on an empirical formula. In the case of SA, the VHCF strength was not affected when the indent depth was less than 40 $$mu$$m, which is consistent with the value obtained from the empirical formula. In the case of 20% CW, VHCF strength was not affected when the indent depth was less than 80 $$mu$$m. The results were much larger than the results obtained from the empirical formula and might have been caused by the plastic deformation, residual stress and probable deformation induced martensite transition around the indent.

Journal Articles

Temperature measurement for in-situ crack monitoring under high-frequency loading

Naoe, Takashi; Xiong, Z.*; Futakawa, Masatoshi

Journal of Nuclear Materials, 506, p.12 - 18, 2018/08

 Times Cited Count:3 Percentile:36.93(Materials Science, Multidisciplinary)

A mercury target for neutron source (made of 316L SS) suffers not only proton and neutron radiation damage, but also cyclic impact stress caused by pressure waves. In the previous study, we carried out an ultrasonic fatigue test to investigate the gigacycle fatigue strength of 316L SS, concluding that specimen surface temperature rose abruptly more than 300$$^{circ}$$C just before failure. In this study, to clarify the mechanism of the temperature rise, we measured temperature distribution with a thermography during the fatigue test. The experimental results showed that the temperature rose locally only at the crack tip and the peak position moved with the crack propagation. We also carried out a nonlinear structural analysis by LS-DYNA to estimate the temperature rise with strain energy of elements. The analytical result showed that the heat due to plastic deformation at the crack tip is dominant for the temperature rise rather than the friction between crack surface.

Journal Articles

Gigacycle fatigue behaviour of austenitic stainless steels used for mercury target vessels

Naoe, Takashi; Xiong, Z.; Futakawa, Masatoshi

Journal of Nuclear Materials, 468, p.331 - 338, 2016/01

BB2014-2666.pdf:0.65MB

 Times Cited Count:11 Percentile:12.18(Materials Science, Multidisciplinary)

Mercury enclosure vessel of the JSNS made of an austenitic stainless steel suffers radiation damage in the proton and neutron environment. In addition to the radiation damage, the vessel suffers the cyclic impact loading caused from the pressure waves. The JSNS target vessel suffers higher than 2$$times$$10$$^8$$ cyclic loading. Furthermore, strain rate of the beam window portion of the target vessel reaches to 50s$$^{-1}$$ at the maximum, which is much higher than the conventional fatigues. Very high cycle fatigue strengths up to 10$$^9$$ cycles for solution annealed (SA) and 10% cold-worked 316L (CW) were investigated through the ultrasonic fatigue test. The result showed that the fatigue strengths of SA and CW tested in high-strain rate were higher than that of the conventional fatigue. On the other hand, the fatigue failure occurred regardless of material and temperature in the very high-cycle region ($$10^7 sim 10^9$$ cycles) at the stress amplitude of below the conventional fatigue limit.

Journal Articles

Mechanical property change in the region of very high-cycle fatigue

Xiong, Z.; Naoe, Takashi; Wan, T.; Futakawa, Masatoshi; Maekawa, Katsuhiro*

Procedia Engineering, 101, p.552 - 560, 2015/03

BB2014-3103.pdf:0.47MB

 Times Cited Count:1 Percentile:29.52

Very high-cycle fatigue behaviour of SUS316L, which is used as the structural material of the spallation neutron sources, was investigated through the ultrasonic fatigue test with the strain rate of 10$$^2$$ s$$^{-1}$$. Cross-sectional hardness distributions of the fatigue-failed specimens for solution annealed (SA) and cold worked (CW) 316L were measured to understand the cyclic hardening or softening. In addition, the tensile tests of the fatigue-failed specimens were performed at room temperature. Furthermore, the nonlinear ultrasonic system was used for evaluating the dislocation density variation. The results showed the cyclic hardening in the region of very high-cycle fatigue in the case of SA. In contrast, in the case of 10%CW, cyclic softening occurred when the number of cycles below 10$$^6$$ and followed by cyclic hardening. In the case of 20%CW, cyclic softening was observed when the number of cycles below 10$$^7$$, while cyclic hardening occurred subsequently.

Journal Articles

Very high cycle fatigue in pulsed high power spallation neutron source

Xiong, Z.*; Futakawa, Masatoshi; Naoe, Takashi; Maekawa, Katsuhiro*

Advanced Materials Research, 891-892, p.536 - 541, 2014/03

 Times Cited Count:6 Percentile:3.28

Very high cycle fatigue degradation of type 316L austenitic stainless steel, which is used as the structural material of neutron spallation sources under intensive neutron irradiation environment, is investigated by using an ultrasonic fatigue testing machine. The strain rate imposed on the structure of neutron spallation source is almost equivalent to that produced in the testing machine. The temperature on the surface was controlled by the air-cooling. The effect of strain rate on the fatigue strength is recognized to increase the fatigue limit.

Oral presentation

Investigation on HIP diffusion bonding of invar alloy and stainless steel

Wakui, Takashi; Ishii, Hideaki*; Naoe, Takashi; Wan, T.*; Xiong, Z.*; Haga, Katsuhiro; Takada, Hiroshi; Futakawa, Masatoshi

no journal, , 

no abstracts in English

Oral presentation

Investigation on HIP diffusion bonding of invar alloy and stainless steel

Ishii, Hideaki*; Wakui, Takashi; Naoe, Takashi; Wan, T.; Xiong, Z.*; Haga, Katsuhiro; Takada, Hiroshi; Futakawa, Masatoshi

no journal, , 

no abstracts in English

Oral presentation

Change in mechanical properties of austenitic stainless steels due to very high cycle fatigue

Xiong, Z.; Naoe, Takashi; Futakawa, Masatoshi; Maekawa, Katsuhiro*

no journal, , 

An austenitic stainless steel, SUS316L is currently being used in the liquid mercury pulsed spallation neutron source as the structural material of the mercury enclosure vessel, so called target vessel. The target vessel suffers cyclic loading in which the total number of cycles in the service life is higher than 2$$times$$10$$^8$$, with a high strain rate of 50 1/s at maximum under intensive proton and neutron irradiation environment. In present work, the very high cycle fatigue strength was investigated using the specimens that had the different dislocation density at room temperature. The tensile strength and hardness of the failed specimen were measured to understand the change in mechanical properties during fatigue test in addition to the fatigue strength evaluation. It was found that the fatigue failure still occurred in the very high cycle region. The fatigue strength was increased with the dislocation density. For the SA 316L, cyclic hardening, the hardness was increasing with the number of cycles, was observed. However, 10% CW316L showed obvious softening, the hardness decreased while the number of cycles was less than 10$$^6$$6 and then increased while the number of cycles was beyond 10$$^6$$.

Oral presentation

Very high-cycle fatigue behavior in mercury target vessel for high-power pulsed spallation neutron source

Xiong, Z.; Naoe, Takashi; Futakawa, Masatoshi; Wakui, Takashi; Kogawa, Hiroyuki; Haga, Katsuhiro; Maekawa, Katsuhiro*

no journal, , 

An enclosure vessel of liquid mercury spallation target, which is made of 316L stainless steel, is suffered from the cyclic loading due to the proton beam-induced pressure waves. The number of loading cycles will be beyond 10$$^8$$ to giga-cycle region throughout the expected service life. In and around giga-cycle region, the fatigue failure occurs under the conventionally defined fatigue limit. In addition to the cyclic loading, the strain rate at the beam window of the target vessel reaches to 50 1/s at the maximum, which is much higher than the conventional fatigues. In this work, ultrasonic fatigue tests were conducted with controlling specimen surface temperature to investigate effects of the temperature and the work hardening that simulates the irradiation embrittlement on very high-cycle fatigue strength of 316L SS. The experimental result showed that the obvious fatigue limit was not observed up to 10$$^9$$ cycles, and the fatigue strength was reduced about 75% of R.T. around 250 $$^circ$$C regardless of the work hardening, which was the conceivable maximum temperature of the beam window at the 1 MW operation.

Oral presentation

Gigacycle fatigue behavior of structural material for the mercury target vessel

Naoe, Takashi; Xiong, Z.*; Futakawa, Masatoshi

no journal, , 

At J-PARC, a mercury target for neutron source (made of 316L SS) suffers not only proton and neutron radiation damage by proton and neutron but also cyclic impact stress caused by pressure waves. The number of impact stresses exceeds $$2 times 10^9$$ in the design operating period for 2500 hours at 1 MW. Recently, it was reported that the fatigue failure occurs below the fatigue limit which was determined by a test up to 10$$^7$$ cycles. In this study, we carried out an ultrasonic fatigue test to investigate the gigacycle fatigue strength of 316L SS and its welded material, concluding that an obvious fatigue limit was not observed below 10$$^9$$ cycles for 316L SS. Smoothed weld material which removed weld bead showed higher fatigue strength than that of base metal. By contrast, the fatigue strength of the weld material with bead decreased below that of base metal due to the stress concentration at the weld toe.

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