Current Trends in Atomistic Study on Fatigue (original) (raw)
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ボルト∙ナット締結体の疲労強度に及ぼすピッチ差の影響とその解析モデルの提案
Transactions of the JSME (in Japanese), 2015
The high strength bolts and nuts are widely used in engineering structures. To investigate the pitch difference on the fatigue strength of bolt, a slight pitch difference is considered between the bolt and nut. Here, the pitch of the nut is α μm larger than the pitch of the bolt. The fatigue experiment is conducted with varying pitch difference. The results show that the fatigue life is extended to about 1.5 times of the one of normal bolt and nut by introducing the suitable pitch difference under the high stress amplitude. According to the detailed observation on the fractured specimens, it is found that the fractured positions and the crack distributions vary depending on the pitch difference. To clarify the improvement mechanism of the fatigue strength, the finite element method is applied to calculate the stress amplitude and mean stress at each bottom of bolt threads. It is found that the finite element analytical model considering the incomplete nut threads is useful for predicting the crack initiation under different pitch difference introduced.
Notch fatigue properties of a Ti-29Nb-13Ta-4.6Zr alloy for biomedical applications
Journal of Japan Institute of Light Metals, 2005
The effects of microstructures on notch fatigue propertes of a Ti-29Nb-13Ta-4.6Zr alloy TNTZ subjected to various thermo-mechanical treatments were investigated in this study. The notch fatigue strengths of TNTZ subjected to aging at 673 K and 723 K after solution treatment or cold rolling at stress concentration factors of 1 without the notch , 2 and 6 in both low and high cycle fatigue life regions are greater than those of as-cold rolled and as-solutionized TNTZ, and TNTZ subjected to aging at 598 K after solution treatment or cold rolling. A single fatigue crack initiates on a specimen surface and at the tip of the notch at stress concentration factors of 1 and 2. While, a few cracks initiate the tip of the notch having a stress concentration factor of 6. Notch sensitivity factor of TNTZ is almost equal to or smaller than those of other materials such as Ti-6Al-4V, CP-Ti, S35C, S45C and SUS304. It is considered that the notch sensitivity factor decreases with decreasing the width of lath like a phase and its volume fraction.
Journal of Japan Institute of Light Metals, 2005
The effects of microstructure and contact pressure on fretting fatigue characteristics of a Ti-4.5Al-3V-2Mo-2Fe alloy with a Widmanstätten a structure were investigated in comparison with that with an equiaxed a structure in this study. In fretting fatigue of the Ti-4.5Al-3V-2Mo-2Fe alloy with a Widmanstätten a structure in a high cycle fatigue life region, and that with an equiaxed a structure in low and high cycle fatigue life regions, the fretting fatigue life does not change linearly with contact pressure, and the fretting fatigue life shows the minimum at a certain contact pressure. In a low cycle fretting fatigue region of the alloy with Widmanstätten a structure, the fretting fatigue life changes linearly with changing in contact pressure. At contact pressures over a certain value, fretting fatigue life of the alloy tends to become nearly constant in each fatigue life region. At relatively lower contact pressures, the main small crack in the alloy with equiaxed a structure tends to be formed at uneven wear damaged parts by fretting wear in the slip region in each fatigue life region. At relatively higher contact pressures, the main small crack in the alloy with equiaxed a structure tends to be formed at the boundary between slip and stick regions in each fatigue life region. The main small crack in the alloy with Widmanstätten a structure tends to be formed in the slip region in each fatigue life region.