過大, 過小應力下에서의 內部크랙 傳播擧動

元時太 서울産業大學校 1985 논문집 Vol.22 No.1

With respect to structural carbon steel(SM22C), it was studied how overstress or the understress has effects on fatigue inside crack propagation curve of a two level stress. Obtained results are summarized as follows. 1) The overstress or the Understress, at a slip band occurrence stage, does not change the inside crack propagation curve because the crack closure and opening phenomena do not happen. 2) The overstress, at a crack propagation stage, does not change the inside crack propagation curve because crack closure of overstress in compressive state is nearly same that of base stress in compressive state. 3) The understress. at a crack propagation stage, give rise to an acceleration of crack growth because the crack closure of understress in compressive state is more open than that of base stress in compressive state.

異種熔接材의 疲勞크랙傳播擧動에 關한 硏究

元時太 서울産業大學校 1989 논문집 Vol.29 No.1

In order to investigate the fatigue crack propagation behaviors of dissimilar weld joints, submerged arc butt welding is used for welding mild steel (SB 34) and austenitic stainless (STS 304). The dissimilar weld joint consists of (1) the unaffected base metal of mild steel (SB 34), (2) the unaffected base metal of stainless steel (STS 304), (3) the heataffected zone of mild steel (HAZ), and (4) the deposit metal zone (DMZ). Unidirectional bending fatigue tests have been carried out in these four zones with quarter-circular shape corner crack. Obtained results are summarized as follows. (1) The relation between the crack aspect ratio ?? and crack depth to plate thickness ratio ?? of dissimilar weld joints are expressed by following eq. in the range of 0.2<??<0.7 ?? Where G and αare material constant dependent upon the magnitude of bending stress. (2) The relationship between the fatigue crack propagation rate and stress intensity factor range ?? is properly applied to dissimilar weld joint, where its exponent (m) are 2.46 to 3.25. (3) The fatigue crack propagation rate of dissimilar weld joint within the same stress intensity factor range is the largest at the heat-affected zone of mild steel and nexts are the unaffected base metal of mild steel, the unaffected base metal of stainless steel and the deposit metal zone in order.

過大, 過小 應力下에서의 疲勞크랙傳播擧動 : 크랙 先端部 表面變形層 除去의 영향을 中心으로

元時太 서울産業大學校 1993 논문집 Vol.38 No.1

Fatigue crack behavior is studied though overstressing or understressing after surface damage layer is removed around crack tip with the deep non-through radial holed notch specimens of low carbon steels(SM22C). The main factors investigated are the effects of duration and applying order of two loads of different magnitude, surface damage layer around crack tip, phenomena of closing or opening of the crack tip schematic shapes of cracked surface. Obtained results are summarized as follows. At the crack propagation stage, fatigue crack propagation is slower in overstressing and faster or slower in understressing respectively than that in single-level stressing. Important factors observed are closing effect of crack tip, schematic shapes of cracked surface, charteristic of surface and inside crack are propagated under the applying stress.

한국 전통 도깨비 문양을 고려한 팬던트 생산용 금형 제작 및 상품화 방안 연구

원시태,강민아,최우정,강미로 서울産業大學校 2005 논문집 Vol.54 No.1

Korean traditional ogre patterns generally have a meaning of protecting from demons and charming away unfortunates. However, their threatening faces and complexity of shapes have not appealed to the general public as personal accessories. In order to make use of their aesthetic and peculiar beauty of figures, a new concept of ogre accessory having a friendly-butterfly shape pendant is develope This study demonstrates whole processes of a capstone design case study, that is, conceptualization of the butterfly ogre pattern, die design and manufacturing for mass production, real production and quality progress, and commercialization process.

편진굽힘應力下에서 ¼円모서리크랙材의 疲勞크랙傳播擧動

元時太 서울産業大學校 1988 논문집 Vol.27 No.1

Fatigue crack growth in machine parts generally involves surface initiated crack of semielliptical shape( surface crack ) or quarter-elliptical shape. Such cracks initiate in regions of locally high stresses and stress gradients. In this study, unidirectional bending fatigue tests have been carried out in two kinds of SB 34 and 304 plates with quarter-circular shape corner crack. Surface crack (a) and side crack (b) propagated from the corner crack have been observed in order to investgate the correlation of crack aspect ratio (?) and crack depth to plate thickness ratio (?) and derived the correlation eq. of surface and side fatigue crack propagration rates(?,?) and stress intensity factors range(△K ?, △K?). Obtained results are summarized as follow. (1) The relation between the crack aspect ratio(?) and crack depth to plate thickness ratio (?) are expressed by following eq. in the range of 0.2<?<0.7 (?)=G(?)? Where G and аare material constant dependant upon the magnitude of bending stress. (2)The following eq. are derived on the surface and side fatigue crack propagation rate and stress intensity factors range. ????????

마찰 교반 용접된 철도 차량용 A6005 압출재의 기계적 성능 향상을 위한 최적 공법 설계

원시태,김원경,Won, Si-Tea,Kim, Weon-Kyong 대한용접접합학회 2009 대한용접·접합학회지 Vol.27 No.5

Recently, extruded aluminium-alloy panels have been used in the car bodies for the purpose of the light-weight of railway vehicles and FSW(Friction Stir Welding), which is superior to the arc weldings, has been applied in the railway vehicles. This paper presents the optimum design of the FSW process on A6005 extruded alloy for railway vehicles to improve its mechanical properties. Rotational speed, welding speed and tilting angle of the tool tip were chosen as design parameters. Three objective functions were determined; maximizing the tensile strength, minimizing the hardness and maximizing the difference between the normalized tensile strength and hardness. The tensile tests and the hardness tests for fifteen FSW experiments were carried out according to the central composite design table. Recursive model functions on three characteristic values, such as the tensile strength, the hardness difference(${\Delta}Hv$) and the difference of normalized tensile strength and ${\Delta}Hv$, were estimated according to the classical response surface analysis methodology. The reliability of each recursive function was verified by F-test using the analysis of variance table. Sensitivity analysis on each characteristic value was done. Finally, the optimum values of three design parameters were found using Sequential Quadratic Programming algorithm.

박판 스프링용 탄소공구강재(SK4M)의 시험온도에 따른 기계적 특성평가에 관한 연구

원시태,임철록 서울産業大學校 2005 논문집 Vol.54 No.1

This study examined the effects of the testing temperature on the mechanical properties of the carbon tool steel (SK4M) for flat spring. Hardness test and fatigue test were performed at room temperature (20°C). Tensile test and creep test were performed at temperature range 20°C~160°C. The micro-vickers hardness values of SK4M was Hv = 584. The Elastic modulus, tensile strength and yield strength of SK4M at 160 °C test temperature were decreased 0.92 time, 0.97 time and 0.82 time those of SK4M at 20 °C test temperature, respectively. The maximum creep strain for lOOhr at creep temperature (80°C~160°C) and creep stress (37.4Kgf/mm²~93.6Kgf/mm²) was 0.572%. The fatigue limit of SK4M was 94Kgf/mm².

알루미늄 5182, 5052 및 3003 합금 판재의 어닐링 조건에 따른 기계적 특성 변화 및 집합 조직 해석

원시태,김기주 대한기계학회 2020 大韓機械學會論文集A Vol.44 No.1

To fabricate aluminum alloys with good formability and toughness, it is crucial to establish proper heat treatment conditions. Among the various heat treatment conditions, in the case of annealing, if the heat treatment temperature is too high, the crystal grains of the cold rolled material may coarsen and lose their mechanical properties, whereas if the temperature is too low, the work hardening of the cold rolled material may not be released, and the ductility may deteriorate. This results in the same tendency regarding not only the heat treatment temperature, but also the heat treatment time. Therefore, in the present study, cold rolled sheets of 3003, 5052, and 5182 aluminum alloys were annealed at a temperature of 350 °C. Microhardness and tensile tests were performed according to various annealing times of 0–1,200 s, and the results were compared. The tensile test results were similar to those of the microhardness test, which confirmed that abrupt softening occurred between 60 and 70 s. Comparing the three alloy sheets, the 5182 aluminum alloy sheet demonstrated excellent mechanical properties. 알루미늄 합금이 성형성과 인성이 우수하도록 제조하려면 적절한 열처리 조건을 확립하는 것이 매우 중요하다. 다양한 열처리 조건 중에서 어닐링은 열처리 온도가 충분히 높은 경우 냉간압연 재료의 결정립들이 조대화 될 수 있으며 그들의 기계적 물성을 잃을 수 있다. 반면에 열처리 온도가 너무 낮으면 냉간압연으로 가공 경화된 소재의 강도가 풀리지 않아 연성을 떨어뜨리게 된다. 이 결과는 열처리 온도의 경우뿐만 아니라 열처리 시간에서도 동일한 경향을 나타낸다. 그러므로 본 연구에서는 3003, 5052 및 5182 알루미늄 합금의 냉간압연 후 350℃에서 어닐링 열처리를 행하였으며 0초~1,200초 동안의 다양한 열처리 후 미소 경도와 인장 시험을 행하여 그 결과를 비교하였다. 미소 경도 시험 결과 열처리 시간 60초~70초 사이에 급작스러운 연화가 나타났으며 이것은 인장 시험에서의 결과와 부합하였다. 이들 세 가지 합금계 판재의 비교로부터 5182 알루미늄 합금이 가장 우수한 기계적 강도를 갖는 것을 확인하였다.

내시경 수술용 혈관집게 개발에 관한 연구

원시태,이정철 서울産業大學校 2005 논문집 Vol.54 No.1

Traditionally, open surgery requires a lot of time for operation and recovery. The comparision with open surgery and endo surgery is getting popular due to economy, time and cosmetics. This technique can reduce operation and recovery time. Scars due to operation are minimized by using small holes. Popular devices for endo surgery have stick shape, and surgeons are watching the inner space of patient through video scope. For that, the vessel holding is essential process, and endo-clip should hold the vessel tightly and stay in the patient body for very long time. The endo clip applier has the stick shape which can operate the endo clip. In order to improve performance of endo clip and applier, new technique and product was developed in this study, which provides 1) vessel clipping method by using elastic force of clip 2) moving method of clip forwarding and 3) counting method for remaining clip.

박판 스프링용 스테인레스강재(STS301CSP-3/4H, STS301CSP-H)의 시험온도에 따른 기계적 특성평가에 관한 연구

원시태,임철록 서울産業大學校 2005 논문집 Vol.54 No.1

This study examined the effects of the testing temperature on the mechanical properties of the stainless steels (STS301CSP-3/4H and STS301CSP-H) for flat spring. Hardness test and fatigue test were performed at room temperature (20°C). Tensile test and creep test were performed at temperature range 20°C~200°C. The micro-vickers hardness values of STS301CSP-3/4H and STS301CSP-H were HV = 443 and HV = 488, respectively. The Elastic modulus, tensile strength, yield strength and strain of these materials were decreased with increasing testing temperature, respectively. The maximum creep strain for lOOhr at creep temperature (100°C~200°C) and creep stress (Tensile strength*50%) of these materials were 0.53%-0.58%. The fatigue limit of STS301CSP-3/4H and STS301CSP-H were 64.5Kgf/mm² and 67.4Kgf/mm², respectively.