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N. Yan¹, N. Kawagoishi², Y. Maeda³, Q. Chen⁴
Structural Longevity, Vol.2, No.3, pp. 139-146, 2009, DOI:10.3970/sl.2009.002.139
Abstract Fatigue tests under rotating bending and ultrasonic loading were carried out using plain specimens with different grain sizes of Ni-base super alloy, Inconel 718, in order to investigate the effects of grain size and loading frequency on fatigue properties. Fatigue strength was increased with decreasing in grain size under both tests. Moreover, the fatigue strength under ultrasonic loading was higher than that under rotating bending. The resistance to crack initiation was larger in smaller grain sized alloy under both tests, and larger under ultrasonic loading than under rotating bending. Effects of loading frequency and grain… More >

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Y. Furuya¹
Structural Longevity, Vol.2, No.3, pp. 147-156, 2009, DOI:10.3970/sl.2009.002.147
Abstract This paper introduces results of researches on gigacycle fatigue using ultrasonic fatigue testing in NIMS. The first step was investigations of validity of the ultrasonic fatigue testing. As the result, the validity was conformed on conditions where fish-eye fracture occurred. The second step was additional developments on the ultrasonic fatigue testing, such as superimposing mean stress, enlargement of specimens and so on. This step elucidated the mean stress effects and size effects on the fish-eye fracture properties. More >

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Chengqi Sun¹, Aiguo Zhao¹, Youshi Hong^1,2
Structural Longevity, Vol.2, No.3, pp. 157-168, 2009, DOI:10.3970/sl.2009.002.157
Abstract The researches on the behavior of very-high-cycle fatigue (VHCF) for high strength steels have become a new branch in the field of metal fatigue since 1980s. The characteristics of crack initiation and propagation for high strength steels in VHCF regime differ from those in low cycle regime. One of the most distinct phenomena for VHCF regime is the interior or subsurface crack initiation at inclusions or at other inhomogeneities. This paper attempts to further investigate the crack initiation with the morphology of so-called fish-eye and fine granular area (FGA) or optical dark area (ODA) for… More >

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Y.J. Liu¹, Q.L. Ouyang², R.H. Tian³, Q.Y. Wang⁴
Structural Longevity, Vol.2, No.3, pp. 169-175, 2009, DOI:10.3970/sl.2009.002.169
Abstract Fatigue properties of Ti-6Al-4V subjected to simulated body fluid (SBF) environment were presented in this paper. Using the ultrasonic fatigue testing technique, the ultra-high cycle fatigue properties of Ti-6Al-4V alloy subjection to SBF in two groups for two days and six days respectively in body temperature were studied and the initiation mechanisms of fatigue cracks were investigated and analyzed with scanning electron microscopy (SEM) and energy dispersive atomic X-ray (EDX). Then, a comparison with corresponding behaviors of the Ti-6Al-4V alloy with no treatment was made. The results show that, the S-N curves of the Ti-… More >

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