旋削工具에 發生하는 Chatter 振動의 實驗的 解析

鄭在康,曺圭宰 조선대학교 동력자원연구소 1984 動力資源硏究所誌 Vol.6 No.1

A mechanism and energy of the self-excited tool chatter vibration is experimentally investigated in this paper. The results obtained are as follows ; 1. The tool vibration of the primary chatter vibration where the exciting energy is supplied by contact of the flank surface with the workmaterial due to the bending of the tool shank. 2. Exciting energy of the tool chatter vibration is supplied during the tool moves to lower direction and consumed in the next half cycle to upper direction. 3. The frequency of tool chatter vibration is related with cutting speed

Al5083-O 알루미늄합금의 보호가스 혼합비율 및 입열량에 따른 GMA용접 특성에 관한 연구

정재강,양훈승,이동길 대한용접접합학회 2002 대한용접·접합학회지 Vol.20 No.2

This study was to evaluate GMA welding characteristics of the A15083-O aluminum alloy according to the shield gas mixing ratio and heat input change. The GMA welding of the base metal was carried out with flour different shield gas mixing ratios(Ar100%+He0%, Ar67%+He33%, Ar50%+He50%, and Ar33%+He67%). Regarding the if1uence on the bead shape of the shield gas mixing ratio and heat input, the bead width was greatest in Ar100%+He0% mixture. But the penetration depth and area were greatest in Ar33%+He67% mixture considering that the lower Ax gas ratio, the higher bead depth and area. Also, dilution was also best in the shield gas mixing ratio. The size and number of deflects were least in Ar33%+He67% mixture. Higher He gas ratio resulted in less deflects detected by the radiographic inspection.

미소원공결함을 갖는 자동차 전륜구동 축재의 피로수명 예측

이동길,오환교,정재강 朝鮮大學校 機械技術硏究所 1998 機械技術硏究 Vol.1 No.1

본 연구에서는 현재 생산되고 있는 자동차의 전륜 구동축재료 S43C와 S50C를 대상으로 회전굽힘피로시험을 통해 고주파열처리와 온도조건에 따른 피로크랙 전파거동을 고찰하고, Nisitani가 제안한 역학적 변수에 의해 재료상수를 구한 후 그 적용성을 검토해 보았다. 비열처리재 S43C 및 S50C의 피로한도는 각각 98.1MPa, 107.9MPa이었으며, 열처리재는 각각 147.1MPa, 156.9MPa로서 열처리 후 두 재료 모두 피로한도가 약 49MPa씩 증가하였으며, 저온(-30℃)에서의 피로수명은 상온(25℃)에서보다 두 재료 모두 비열처리재는 약 110%, 열처리재는 약 120% 증가하였다. 또한 본 재료에 실험으로부터 얻어진 재료상수를 Nisitani의 피로크랙전파속도 예측식에 적용하여 피로수명을 예측한 결과 고주파 열처리 여부와 실험온도 조건에 관계없이 약 5% 내외의 낮은 오차를 보이며 잘 일치함을 알았다. In this study, the rotary bending fatigue test was carried out with two kinds of materials, S43C and S50C, using in the front engine and front drive shaft of vehicle. The specimens were heat-treated by high frequency induction method and tested at +25℃ and -30℃ in order to look over the influence of the heat treatment and the temperatures. The mechanical factor, C(2a)p, proposed by Nisitani was employed in the present study to compare the results of fatigue life obtained from experiment and prediction. The fatigue limit of the as-received specimens S43C and S50C were 98.1MPa and 107.7MPa, and that of the heat-treated S43C and S50C were shown 147.1MPa and 156.9MPa respectably. It means that the fatigue limit was increased about 49MPa by high frequency heat treatment. Fatigue lifes of the specimens tested at low temperature(-30℃) showed about 110% for as-received, 120% for heat-treated higher than at room temperature(25℃). It was found the crack length at onset or final fracture tested at low temperature was shorter than the crack length at room temperature(+25℃). The fatigue lifes were predicted with an equation of the fatigue crack propagation proposed by Nisitani, d(da/dN)=C(2a)p, the results were found to be within 5.0% error by comparison with experimented results.

旋削加工에서의 Burrs의 生成原因과 特性에 관한 硏究

鄭在康 조선대학교 생산기술연구소 1982 生産技術硏究 Vol.1982 No.-

The mechanisms causing machining burrs and two typical analistical models that predict burr properties are presented. The experimental study has been made to prevent the burrs produced on workpiece edges in turning operations. The effect and correlations between cutting conditions and burr sizes, and a mechanism of burr formation are discussed. The experimental results obtained are as follows; 1) The deformation of a workpiece edge by cutting force causes burrs. And there are two type of burrs, large size burrs and extremely small size burrs. 2) Small size burrs are produced at large depth of cut, small feed rate, large nose radius and small side cutting edge angle. 3) Brittle materials easily produce the small size burrs and ductile materials easily produce the large size burrs.

탄소강 단조재의 피로크랙 전파 거동에 관한 연구

정재강,김건호,이동길 조선대학교 생산기술연구소 1995 生産技術硏究 Vol.17 No.2

For the purpose of the prevention of fatigue fracture in the carbon steel forging materials which are used in the marine propeller shaft, this paper was analyzed behavior, rate and life of fatigue crack propagation, and was performed fatigue test in order to investigate date. The results are as follows: Smaller the grain size and larger the pearlite rate increases the fatigue strength was increased. Initial time of fatigue crack was lag and fatigue life was long due to increase in fatigue strength. Fatigue crack propagation life from initiation of slip band to growth of small crack, 2α= 1.30㎜, was occupied the most of fatigue crack propagation life. Fatigue crack propagation rate was able to express by d(2α)/dN = B2α/N_(f) because of the possibility of differentiation in the relation between fatigue crack length and cycle ratio. Fatigue crack propagation rate was able to express by d(2α)/dN = Cδ_(α)^(m)(2α)^(m) and this equation was the possibility of application of fatigue crack propagation life prediction in the experimental materials.

SS41강 용접부의 동적균열개시인성 평가

정재강,김건호 대한용접접합학회 1994 대한용접·접합학회지 Vol.12 No.2

In the present study, the dynamic crack initiation toughness and total absorbed energy behavior of Heat Affected Zone(HAZ) was experimentally evaluated for SS41 steel welding. The materials were submerged arc-welded SS41 steel plate with thickness 19mm. The test temperature range was from $20^{\circ}C$(room temperature) to $-70^{\circ}C$ The HAZ of welding were divided into three sub-zones for analysis; H1, H2, H3, according to the distance from the fushion line. From the experimental studies, the reference value of dynamic crack initiation toughness $(J_{Id(R)})$ can be use to estimate dynamic fracture toughness characteristics of steel welding.

보호가스 혼합비율에 따른 Al5083-O 용접부의 저온 인성에 관한 연구

정재강,양훈승,이동길 대한용접접합학회 2002 대한용접·접합학회지 Vol.20 No.6

In this study, the low temperature toughness was evaluated by using the instrumented Charpy impact testing procedures for A15083-O aluminum alloy used in the LNG carrying and storage tank. The specimens were GMA(Gas Metal Arc) welded with four different mixing shield gas ratios (Ar100%+He0%, Ar67%+He33%, Ar50%, and Ar33%+He67%), and tested at four different temperatures(+25, -30, -85, and $-196^{\circ}C$) in order to investigate the influence of the mixing shielding gas ratio and the low temperature. The specimens were divided into base metal, weld metal, fusion line, and HAZ specimen according to the notch position. From experiment the maximum load and displacement were shown the highest and He lowest at $-196^{\circ}C$ than the other test temperatures. The absorption energy of weld metal notched specimens was not nearly depends on test temperature and mixing shield gas ratio because the casting structure was formed in weld metal zone by melting welding wire. On the other hand, the others specimens was shown that the lower temperature, the higher absorption energy slightly up to $-85^{\circ}C$ but the energy was decreased so mush at $-196^{\circ}C$.

구조용강의 유한요소해석 및 온도변화에 따른 피로수명 평가에 관한 연구

이동길,이상열,정재강 朝鮮大學校 機械技術硏究所 1999 機械技術硏究 Vol.2 No.2

본 연구에서는 국산 승용차의 전륜구동축 재료인 S43C와 S5OC를 대상으로 유한요소해석과 회전굽힘피로실험을 통해 고주파열처리와 온도조건에 따른 피로크랙의 발생, 전파거동을 고찰하였다. 유한요소해석 결과 하중이 가해지는 방향에 따라 반복적으로발생되는 인장응격 및 압축응력은 미소원공결함 부분에서 가장 크게 나타났다. 이러한원인은 미소원공결함이 응력의 국부적인 집중원으로 작용했기 때문으로 생각되며, 이러한 응력의 반복으로 인하여 미소원공결함을 기점으로 크랙이 발생∙성장하였음을 알 수있다. 회전굽힘피로실험 결과 두가지 재료 모두 저온(-3O℃) 피로수명은 비열처리재의 경우 상온(25℃)보다 약 110% 증가하였고, 열처리재는 약 120% 증가함으로서 온도의 저하가 피로수명을 크게 증가시킨 반면 고온(80℃) 피로수명은 상온 피로수명과 비교시 비열처리재가 약 35%. 열처리재가 약 5%의 피로수명 감소를 나타냈다. In this study, the rotary bending fatigue test was carried out with two kind of material, S43C and S5OC, using in the front engine and front wheel drive shaft of vehicle. The specimens were heat-treated by high frequency induction method and tested at room(+25℃), high(+80) and low temperature(-3O℃) in order to look over the fatigue crack initiation and propagation behavior by the heat treatment and the temperatures. Based on the FEM result, the tensile and compressive stress repeatedly generated by load direction were largest on the small circular defect due to the stress concentration. So the small crack was initiated and grew from the defect Fatigue lifts of the specimens tested at low temperature showed about 110% for as-received. 120% for heat-treated higher than at room temperature, It was found that low temperature increased so much the fatigue life. At room and high temperature, the fatigue life of as-received specimens were decreased about 35%, but that of heat-treated specimens were decreased about only 5% at high temperature more than at room temperature, Therefore, fatigue life under high temperature will be considered at design of front engine and front wheel drive shaft materials of vehicle.

Submerged Arc 鎔接部의 動的破壤靭性 評價에 關한 硏究

鄭在康,洪錫柱 조선대학교 생산기술연구소 1991 生産技術硏究 Vol.13 No.1

In the present study, the dynamic fracrure behavior of steel weldments was experimentally evaluated with an instrumented Charpy impact test using pre-cracked Charpy V-notched specimens. The materials are submerged arc-weled plates of SM45C steel with a thickness of 19mm. The tested temperature renge was from +20℃(room temperature)to -160℃ The weldments were divided into the sub-zones for analysis : weld metal, grain coarsened HAZ, grain-refined HAZ, partially transformed HAZ and unchanged base metal. Empirical correlations were investigated between the dynamic fracture toughness (K_(Id)) and both the crack initiation energy(K_(Id)) and the total absorbed energy of fracture (Ei/A), and K_(Id) was estimated from the energy Ei/A or Et/A using the empirical equations determined.

미소원공을 갖는 선박 추진축재의 피로크랙 전파 거동에 관한 연구

정재강,김건호 한국마린엔지니어링학회 1995 한국마린엔지니어링학회지 Vol.19 No.2

In this paper, fatigue crack propagation behaviors were investigated experimentally for the materials, carbon steel forgings (SF45A, SF50A, SF60A) which are used in the marine propeller shaft. The results obtained are as follows: The number of cycles required to grow crack length 1.30mm from microcrack initiation was about 60% of the total fatigue life. Fatigue crack propagation rate was expressed by the equation d(2a)/dN_B 2a/$N_f$ and the result was agreed well with the experimented data. And the equation d(2a)/dN=$C{\sigma}_a^m(2a)^n$ was evaluated also. Obtained material property m and n are 3~5 and 1-1.5 respectably, and the result was reasonably agreed to the data obtained from experiments.