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유헌일(Heonil Yoo),천기정(T. Kawasaki),택목양삼(Y. Sawaki) 한국자동차공학회 1983 오토저널 Vol.5 No.1
In case of K_lmax < K_lscc, the corrosion fatigue of high strength steel in O.1N H₂SO₄ solution and 3.5% salt water is as follows.<br/> 1. The fatigue life shortens in order of 3.5% salt water and O.1N H₂SO₄ solution.<br/> 2. The fatigue crack growth rate in air is obtained as the following equation.<br/> (dc/dN)_?=7.23×10^-?(△K)^?<br/> 3. The corrosion fatigue crack growth rate in environment is divided into three regions, that is, First Region, Second Region and Third Region from the small cyclic stress intensity.<br/> 4. The formation rate of the active surface on metal is slower than the mechano-chemical reaction rate in First Region. The crack growth rate depends on time and the cyclic stress intensity and is expressed as the following equation.<br/> (dc/dN)=C(△K)^δ<br/> 5. The formation rate of the active surface is faster than the mechano-chemical reaction rate in Second Region and the synergistic effect by stress and corrosion becomes slow. In case the. fatigure load is large, we have the critical crack growth rate which is not<br/> related to the cyclic stress intensity. .<br/> 6. The corrosion crack growth rate by the mechano-chemical reaction is the same in H₂S0₄ solution and salt water, so Hydrogen accelerates the crack growth.<br/> 7. The environment has no effect on the corrosion. fatigue crack growth rate in Third Region.<br/> 8. In First Region and Second Region, dimple is observed on the fatigue fracture surface in O.lN H₂SO₄ solution.<br/> 9. The striation is observed in any environment as in air in Third Region and its interval approximately coincide with the crack growth rate.
외팔보 형식의 하중진폭 변화에 대한 Al 합금의 관통균열 거동에 관한 연구
유헌일,김엽래,Yoo, Heonil,Kim, Yeob-Rae 대한기계학회 1998 大韓機械學會論文集A Vol.22 No.4
This paper examines the crack growth behavior of 7075-T651 and 5052-H32 aluminum alloy under high-low block loading condition. The cantilever beam type specimen with a chevron notch is used in this study. The crack growth and closure ae investigated by compliance method. The applied stress ratios are R=0.15, 0.0, -0.15 and R=-0.15, 0.0, 0.15. The crack growth rate was found to increase as the load amplitude increases. However,${\bigtriangleup}K_eff$ was almost independent on the stress ratio. The experimental constants of 7075-T651 and 5052-H32 in Paris law were c`=1-1.3${\times}{10^-7},m`=3~3.2 and c`=4~6{\times}{10^-9}, m`=4.3-4.8$, respectively. $K_op$ of 7075-T651 and 5052-H32 becomes smaller as the stress ratio decreases. It seems that the crack closure affects $K_op$.
유헌일,김세환,서희강,Yoo, Heonil,Kim, Sei-Hwan,Seo, Hee-Kang 대한기계학회 1996 大韓機械學會論文集A Vol.20 No.2
It has been known that the life time of cold forging dies is shorten by the cracks and wear produced during the operation. Thus it is required to mak the same new one too often, At this time of making new ont the cutting work and electical discharge machining were mormally used. But the precision of product is declined in every times of making the mew dies due to the diffefence in dimensional accuracy arised from the electical discharge machining. Especially it can't meet the delivery date because the production was delayed for making another die. Furthemore it has the problem of increasing the production cost. Therfore inthis study we tried to solve these problems using the hobbing method instead of electical discharge machining.
김엽래,유헌일,서성원 서울産業大學校 1991 논문집 Vol.34 No.1
Through the rotary bending fatigue experiment of SM45C, widely applicable material to the machine, ship-building and airplane engineering, some mechanical properties were investigated such as fatigue limit, crack propagation, notch coefficient and fracture surface according to various type of notched specimen. Based on this study, the obtained results are summarized as follows: 1. Fatigue limit for Non-notched specimen was found 32.2kgf/㎟ and for U-notch and V-notch specimen, the limit values were 22.8kgf/㎟ 15.5kgf/㎟ respectively. In the case of transverse hole notch specimen, for 0.8㎜ and 1.6㎜ diameter of hole notch specimen the values were 17.6kgf/㎟ and 18.5kgf/㎟ respectively. Therefore, fatigue limit of notched specimen was 29.2-51.7% smaller than Non-notched specimen. 2. It was certified a fatigue crack length was more increase according to the repetition number of cycles. The slope was more steep in the S-N curve diagram and fatigue crack according time was more faster according to the stress level changed from lower stress level to high.