| 1. |
Norio KAWAGOISHI, Qiang CHEN, Nu YAN, Masahiro GOTO, Qingyuan WANG, Yoshihisa OHZONO, Fracture Mechanism in Fatigue of Nickel-Based Superalloy Inconel 718 at Elevated Temperatures, Journal of Solid Mechanics and Materials Engineering, 10.1299/jmmp.1.734, Vol.1, No.6, pp.734-743, 2007.06. |
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K. Morino, N. Kawagoishi, Q. Chen, K. Fukada, E. Kondo, Internal fracture process in fatigue of radical nitrided bearing steel, Computational and Experimental Methods, 10.2495/SURF030211, Vol.7, pp.213-222, 2003.06, Rotating bending fatigue tests were carried out for a radical nitrided bearing steel in order to investigate the initiation and propagation behavior of an internal crack. Surface fracture occurred under high stress levels and fish-eye fracture happened under low stress levels so that the S-N curve appeared in the shape of two-step lines. The depth of the origin of internal fracture was confined in a relatively narrow region near the boundary between the hardened and non-hardened matrix. By two-step loading fatigue tests in the internal fracture region, a circular trace corresponding to the stress change was observed within the fish-eye. In the internal fracture region, a crack was initiated at the early stage of the fatigue process, that is, most of the fatigue life of internal fracture was occupied by the growth life of an internal crack.. |
| 3. |
Q. Y. Wang, N. Kawagoishi, Q. Chen, R. M. Pidaparti, Probabilistic Modeling of Pitting Corrosion Fatigue Life, Proceedings of the International Offshore and Polar Engineering Conference, Vol.12, pp.253-256, 2002.05, Corrosion and fatigue are two types of damages found in aircraft and offshore structures. Corrosion fatigue processes are characterized by randomness due to the random nature of materials, initial defects, loading, and environmental condition. In this study, a mechanistically based probabilistic model for prediction of pitting corrosion fatigue life in aluminum alloys has been developed which captures the effect of the interaction of cyclic load and corrosive environment and all the stages of the corrosion fatigue process. Monte Carlo simulations were performed to define the failure probability distribution. Predicted cumulative distribution functions of fatigue life agreed reasonably well the experimental data.. |
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N. Kawagoishi, K. Morino, K. Fukada, Q. Chen, E. Kondo, On fish-eye fracture of radical nitrided die steel, Computational and Experimental Methods, 10.2495/SURF010201, Vol.6, pp.209-217, 2001.06, In order to investigate the effect of radical nitriding on fatigue strength of die steel, rotating bending fatigue tests were carried out at room temperature and 450°C. Fatigue strength was increased by nitriding at both temperatures due to surface hardening and compressive residual stress generated in the surface region. Comparing with the non-nitrided steel in which the fracture origin was at surface slip bands or surface defects, the nitrided steel fractured with the origin at inner inclusions at both temperatures. In the nitrided steel, cracks initiated from inclusions in the non-hardened layer or near the boundary between hardened and non-hardened layers. The difference in fatigue strength between the two temperatures was discussed based on the feature of fish-eye.. |
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Q. Chen, N. Kawagoishi, K. Othubo, E. Kondo, M. Sakai, T. Kizaki, Ultrasonic fatigue strength in Inconel 718, Proceedings of the International Symposium on Superalloys and Various Derivatives, 10.7449/2001/superalloys_2001_573_582, Vol.1, pp.573-582, 2001.06, The fatigue strength of a nickel-base superalloy, Inconel 718, was investigated at room temperature under an ultrasonic frequency (19.5 kHz) loading in ambient air environment. The endurance (S-N) data show that fatigue strength was enhanced at ultrasonic frequency as compared to those at conventional frequencies. Small crack initiation and propagation behavior was observed during the fatigue progress at both ultrasonic fatigue and conventional rotary bending fatigue. The effect of frequency on the fatigue fracture mechanism was examined from a microscopic viewpoint.. |
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Improvement of fatigue strength of maraging steel by nitriding
Rotating bending fatigue tests were carried out to investigate the influence of radical nitriding on the surface integrity and the fatigue strength for a maraging steel. Fatigue strength increased by nitriding. Although the initiation site of fracture was the surface in the aged steel, it was the specimen suface at high stress levels and the interior at low stress levels in the nitrided steel. The main reason for the surface fracture was the surface embrittlement and the one for the interior fracture was the surfce hardening due to nitriding. As the results, S-N curves of the nitrided maraging steel showed a double staged curve.. |
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近藤 英二, 皮籠石 紀雄, 大隈 博輝, 陳 強, 動的切削過程の特性値による工具摩耗の検出 (第2報, 測定条件の変化に対する特性値の適応性), 日本機械学会論文集. C編, 10.1299/kikaic.66.1700, Vol.66, No.645, pp.1700-1705, 2000.05, In-process measurement of tool flank wear is very important for judgment of tool life with the object of running fully automated machine tools economically. The purpose of this study is to propose a new method of detecting tool flank wear by using characteristic values of dynamic cutting process during steady-state cutting in turning operation. In this report, a simple calculation model of dynamic thrust force was proposed to derive equations of characteristic values from it, and effectiveness of the equations was experimentally verified under many cutting conditions and excitation conditions of a workpiece system. As a result of the calculations and the experiments, we reached conclusions that two characteristic values of dynamic cutting process, standard deviation of dynamic thrust force normalized by the standard deviation of workpiece vibration displacement and coefficient of correlation between dynamic thrust force and vibration displacement, have the following properties. (i)The characteristic values remained almost constant with variation of feed rate of a cutting tool and vibration amplitude of a workpiece. (ii)On condition that vibration frequency of a workpiece is constant, the characteristic values obtained under different cutting speeds can be standardized by normalizing the width of flank wear to the cutting speed. (iii)Tendency of calculated characteristic values with increase of vibration frequency was partly disagree with that of experimental values.. |
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Initiation and growth behavior of a fatigue crack in inconel 718 at elevated temperatures
Rotating bending fatigue tests were performed for Inconel 718 at room temperature and elevated temperatures of 300°C, 500°C and 600°C to investigate the influence of temperature on the fatigue crack initiation and its propagation. Although the propagation of a micro-crack smaller than about 20 um is suppressed at elevated temperatures, that of the larger-crack is accelerated inversely. These results were discussed from the viewpoints of the softening of matrix and the oxidation of surface caused by the high temperature.. |
