연강의 열처리 온도와 두께 변화에 따른 피로귀렬성장거동에 관한 연구

오환교 한국산업안전학회 2000 한국안전학회지 Vol.15 No.3

The fatigue and tensile test were carried out with Mild steel using the Dump Frame of commercial car. The specimens were heat-treated at 810℃ and 930℃ and worked 4.5, 6.0, 8.0㎜ thickness in order to look over the mechanical properties and fatigue life by heat treatment and thickness from the tensile test result, the yield strength of the heat treated specimens was increased about 35% more than that of the non-heat treated specimen. The fatigue life of non-heated specimen was decreased 15% but that of heat treated specimens at 870℃ and 930℃ were decreased 16.38% and 13.16% respectably according to increasing the thickness from 4.5 to 8.0㎜.

Al 7075 合金의 피로파괴 인성치에 관한 연구

오환교 조선대학교 에너지.자원신기술연구소 1998 에너지·자원신기술연구소 논문지 Vol.20 No.2

Many researchers presented the probabilistic and statistical property of the material strength. However, the study on probabilistic and statistical property of fatigue fracture toughness has not been nearly presented. Major objectives in this paper are to compare the statistical test results of fatigue fracture toughness with those obtained in the tensile experiments, and to recognize the size effect for the probabilistic and statistical property by using specimens with various thickness. From the results of the tensile experiments, the distribution of the yield strength is higher than that of the tensile strength regardless of specimen sizes. The thicker the specimen thickness becomes, the smaller the distributions of the yield strength and the tensile strength. Those results show the dependency of the size. The distribution of the fatigue fracture toughness values at the specimen thickness of 6.0㎜ is higher than those of 3.0㎜ and 12.0㎜. It shows that the fatigue fracture toughness is affected by the mechanical factors of crack tip in the third region of crack propagation as well as the micro-defect inside the material.

가솔린 機關의 點火時期가 排氣가스에 미치는 影響

오환교,이종인 조선대학교 동력자원연구소 1996 動力資源硏究所誌 Vol.18 No.2

The summarized results as follow. Electronic Control System varied Spark plug Gap, and rpm, and catalyst apparatus, CO ,HC exhausted less and made the optimum control of the air-fuel ratio. In case of the Spark Plug Gap 1.0mm, Spark Timing 15 degree and rpm 3000. Exhaust gas such as CO, HC reduced and Electronic control Engine of feed back control was effective in the spark timing control and reduced the amount of CO, HC but carburetor didn't work on the same way.

SM45C鋼의 熱處理後 疲勞CRACK 發生 및 傳播擧動에 關한 硏究

吳奐敎,朴昌彦 조선대학교 동력자원연구소 1988 動力資源硏究所誌 Vol.10 No.1

Fatigue crack growth and propagation behavior in structual carbon steel (SM45C) was investigated by rotary bending test. Slip line cracking in the specimens was shown to be responsible for failure when surface origins dominated. It is suggested from fractographic and metallographic evidence that the same initiation mechanism produced internal origins during cycle fatigue. The results were as follows: 1. The fatigue strength, fatigue limit and fatigue life of post heat treated materials were considerably increased in comparison with them of annealed materials. 2. The fatigue limit of post quenched and tempered materials were improved about 35% and 20%, respectively. 3. Post quenched material showed very susceptibility of stress amplitude increment to fatigue fracture. 4. Under this experimetal conditions, the fatigue fracture behavior of structual carbon steel may be considered to composed of three-continuous staged: plastic deformation, formation of striations, and ductile dimple rupture.

피로파괴 인성치의 통계적 성질에 관한 연구

오환교,김희송 대한기계학회 1994 대한기계학회논문집 Vol.18 No.11

Many researchers presented a probabilistic and statistical property of the material strength. However, the study on probabilistic and statistical property of fatigue fracture toughness has not been nearly presented. Major objectives in this paper are to compare the statistical test results of fatigue fracture toughness with those obtained in the tensile experiments, and to recognize the size effect for the probabilistic and statistical property by using specimens with various thickness.

SM20C 강의 피로파괴인성치의 확률분포 특성에 관한 연구

오환교 한국산업안전학회 1997 한국안전학회지 Vol.12 No.3

The strength of material is scattered owing to the inhomogenity of microstructure, in spite of the same material. Therefore, in order to design the mechanical structure with the reliability engineering, it is important to grasp the statistic nature of material strength. In this paper, effects of grain sizes for the statistical nature of the fatigue crack growth was discussed. And the statistical of mechanical properties was compared with statistical nature of the fatigue crack growth rate.

ATOS 55강의 열처리 온도와 두께 변화에 따른 피로균열성장거동에 관한 연구

오환교 한국산업안전학회 1997 한국안전학회지 Vol.12 No.4

This study is to investigate the behavior of fatigue crack growth with ATOS 55 steel which can be applied to the commercial car Dump Frame. It is to obtain the material coefficients after tensile and fatigue crack growth test with the variation of thickness or heat treatment. Also, that is proved the Pari's law by experiment. The summarized results are as follows ; 1) Increasing thickness, tensile and yield strength measured highly regardless to heat treatment and measured lowly as variation of heat treatment temperature. 2) Specimen of thickness 8.0mm measured the faster of crack growth rate than another thickness according to the results of experiment. It was the different of stress conditions in crack tip. 3) It was found that the experimental constant m was range of 2∼5 to the relationship between fatigue crack growth rate and stress intensity factor range. Also, It was to prove the Paris's law by the experiment

헬멧의 安全性 評價에 對한 硏究

吳奐敎,崔秉起 조선대학교 동력자원연구소 1990 動力資源硏究所誌 Vol.12 No.2

Now a days, according that the occurrence of industrial disaster is on the increase, the necessity of Protective good is increasing. specially estimate of sefety helmet for protect of head is very important. On this, in this paper, amplification ratio and natural frequencies of fire safety he met and general safety helmet are estimated by falling impact test and frequency analysis. Also, trend of damping is estimated by using these test results. And we know that the fire safety helmet is less saft than general safety helmet for protect of head.

비틀림 荷重을 받은 Key Way Fillet 部의 塑性域 測定에 對한 硏究

吳奐敎 조선대학교 동력자원연구소 1986 動力資源硏究所誌 Vol.8 No.1

The failure of machine element is one of the most important cause of shaft deformation problems due to stress concentration. Stress concentration occured in key part due to the locallized plastic deformation during torsion. In order to investigate such a strain mechanism thoroughly, it is necessary to analyze the locallized plastic deformation and plastic zone at key way. In this study, the recrystallization technique has been extende to reveal plastic deformation at the Ground of key way tip of mild steel, and has been applied to observe the plastic zone at the around of the key way tip in the shaft. The results are summarized as follows: 1) The rcrystallization-etching technique has been sucessfully applied to measure the plastic strain and plastic zone quantitively under allowable stress. 2) The optimum condition of recrystallization treatment has been observed at 720 C for 3 hours in mild steel, at 950℃ for 24 hours in stainless steel. 3) The amount of equivalent plastic strain (ε´_p) was maximum value at the key way tip, the conditions of recrystallization technique was different, respectively according to material properties.

가솔린 엔진의 電子制御 特性과 排氣가스 減少에 關한 硏究

오환교(G. H. Oh),이종인(J. I. Lee) 한국자동차공학회 1996 한국자동차공학회 춘 추계 학술대회 논문집 Vol.1996 No.6_2

This paper deals with the improvement study for the automobile in fuel economy emission and exhaust gas. Electronic Control System is classified by Electronic Fuel Injection, Electronic Spark Timing, Electronic Idle Air Control and Electronic Exhaust Gas Recircuration Control system. To improve the characteristics ment in automobile, Electronin Control System and carburetor for engine were selected, and fuel injection characteristics and engine performance were studied experimentally. With the Electronic Control System and carburetor, We studied the efficiency of the Electronic Control System and function of the catalyst apparatus such as the change of Spark Plug Gap, Spark Timing, and RPM. We experimented carburetor engine such as changing the primary coil and setting the catalyst appartus and the mass of the Exhaust gas.<br/>