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- 저자 : 박경동 (검색결과 267 건)
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低合金鋼의 高溫波勞균열進展 下限界特性의 酸化被膜의 效果
朴卿東 釜山工業大學校 1992 論文集 Vol.34 No.-
At elevated temperature which is still below the creep operating region in air or water environment, characteristics of fatigue crack growth threshold for alloy-and carbon-steels are not well clarified. For the structural integrity operating at those temperature ranges, such as nuclear reactors, it is an urgent task to make clear them up. In the previous study, the fatigue crack growth rates and the crack closure were measured for a low alloy steel, JIS SFVV3 (A508-3), used for the pressure vessedl of the nuclear reactor. The temperature range examined was from foom temperature up to 350℃ which covers the operating temperature at 288℃ of the nuclear reactors. Further detailed studies were attempted by accumulating the threshold data for various alloy-and carbon-steels. Influencing factors are made clear and a simple method for predicting thresholds is developed by accounting for the above effects. The temperature dependence on the growth rate and the crack closure and the stress ratio effect are studied. Especially near the fatigue threshold where the temperature effect is significant, it is found that the oxidation produced on the crack surfaces at elevated temperaure have an important role. Their contribution is examined quantitatively. At room temperature, the fretting oxide debris (Fe??O??) cause the crack closure. Higher the temperature, the oxidation(Fe??O??) protects the crack surfaces from the ocurrence of fretting oxide. Thus the fatigue threshold decreases as increasing temperature up to around 100℃. Hereafter, it increases due to the increasing in thickness of oxidation which promotes the occurrence of crack closure. The dependencies of the yield stress and the cyclic frequency on the growth rates can be explained from the same view point.
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Deformation rigidity of odd Lagrangian Grassmannians
박경동 대한수학회 2016 대한수학회지 Vol.53 No.3
In this paper, we study the rigidity under K\"{a}hler deformation of the complex structure of odd Lagrangian Grassmannians, i.e., the Lagrangian case $\Gr_{\omega}(n, 2n+1)$ of odd symplectic Grassmannians. To obtain the global deformation rigidity of the odd Lagrangian Grassmannian, we use results about the automorphism group of this manifold, the Lie algebra of infinitesimal automorphisms of the affine cone of the variety of minimal rational tangents and its prolongations.
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圓孔으로된 스프링 鋼板의 反覆굽힘 疲勞强度에 關한 硏究
朴卿東 釜山工業大學 1974 論文集 Vol.14 No.-
In spite of Considerable amount of fracture phenomenon of machine and structure by fatigue, It is extremely difficult to obtain the surficient designing materials about fatigue intensity and deflection by fatigue fracture. The author has studied about the effect of heat treatment temperature and fatigue limit about the spring flat plate steel under the repeat bending load. Above all, I have extensively discussed the notched specimen and "O" hole form specimen. The content of this study is as follows. 1. After testing the unnotched specimen and the specimen of "O" hole form, I have examined the fatigue limit for example, I have made the radious of "O' hole form in 0.5mm, 1mm,2mm, and 4mm. 2. I have discussed the fatigue limit annealed specimen and tempered specimen.
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朴卿東 釜山工業大學校 1980 論文集 Vol.21 No.-
In spite of considerable amount of fracture phenomenon of machine and structure by torsion, It is extremely difficult to obtain the sufficient disinging materials of torsion strength and deflection by torsion fracture. There were a number of investigation recently oon behavior of Fatigue Fracture, but it was not yet clarified enough for torsion. The author has experimentally studied the torsion strength, torque, angle of twist, band structure, crack propagation and fractograph of structure steel on a torsion. 1) The experimental torsion test with smooth specimen resulted in the following. torque=2337kg-cm, angle of twist = 660˚ 2) In the case of a torsion fracture of structure steel. torion stress=68.88kg/mm² yielding stress=47.75kg/mm² 3) Band structure is to be seem appear tem degree of twisting angle.
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朴卿東 釜山工業大學校 1976 論文集 Vol.17 No.-
In spite of considerable amount of fracture phenomenon of machine and structure by fatigue, It is extremely difficult to obtain the sufficient designing materials of fatigue intensity, and deflection by fatigue fracture. there were a number of investigations recently on the behavior of rotary bending fatigue for spring steel, but it was not yet clarified enough for twisting fatigue. The author has experimentally studied the stress concentration factor, fatigue notch factor, notch sensitivity factor and fractograph of spring steel on a twisting fatigue. The results of this study are as follows; 1) The experimental twisting fatigue test with unnotched specimen, hole notched specimen, and U formed notched specimen resulted in the following fatigue limit; in case of Unnotched specimen:31.5(㎏/㎟) hole notched specimen:14-19.5(㎏/㎟) U formed notched specimen:14.5-20(㎏/㎟) 2) In the case of a twisting fatigue fracture of spring steel, the stress concentration factor (α), fatigue notch factor(β), and notch sensitivity factor(q), are calculated by the following equation. α=1.972∼2.866(hole notched specimen) α'=1.91∼2.81(U formed notched specimen) β=1.0∼2.22(hole notched specimen) β'=1.0∼2.18(U formed notched specimen) q=0∼0.651(hole notched specimen) q'=0∼0.6(U formed notched specimen) 3) In the spring steel unnotched, the fatigue crack propagates through two step on a twisting, the first along the axis, the second, along about 45℃ against the axis.
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反覆굽힘荷重下의 Unnotched & Notched 試片의 스프링平鋼에 對한 疲勞强度에 關한 硏究
朴卿東 國立釜山工業專門學校 1975 論文集 Vol.15 No.-
The author has Studied about the effect of fatigue limit about the spring flat plate steel under the repeat bending load, Above all, I have extensively discussed the notched specimen and unnotched specimen. The Content of this study is as follow. (1) After testing the unnotched specimen and the notched specimen of U form's. I have examined the fatigue limit, I have made the radious of notch in 0.5mm, 1mm, 2mm, 4mm, and 8mm. (2) I have discussed the ftigue limit about U form's notched specimen and O hole form's specimen. (3) I have examined mechanical properties after tension test about annealed specimen and tempered specimen. The specimen that used in this study is spring flat plate steel. (4) I have discussed the notch constant about U form's notched specimen and O hole form's specinen.
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