Ti재의 용접조건에 따른 기계적 특성에 관한 연구

최병기,장경천,정장만 朝鮮大學校 機械技術硏究所 2002 機械技術硏究 Vol.5 No.1

Ti재를 이용하여 여러 가지 용접조건 시험편을 제작하여 특서을 측정해 본 결과 다음과 같은 결론을 얻을 수 있었다. 1) 동일한 용접조건에서 패스 수에 따라 4패스는 7패스와 비교하였을 경우 인장강도가 10%정도 높게 나타났고, 연신율은 30%정도 감소함을 알 수 있었다. 또한 실딩가스량이 많고, 용접 후 자연냉각 시간간격이 길수록 인장강도는 높게 나타났고, 연신율은 감소하였다. 2) 충격 흡수에너지값은 4패스는 7패스에 비해 50%정도 감소하였으나, 실딩가스량이 많을수록 높게 나타났다. 또한 경도값은 패스 수가 적을수록 높게 나타났으며, 용접 후 자연냉각 시간간격에는 비숫하였으나 용접 후 자연냉각 시간간격이 적은 것은 조금 감소하였다. The purpose of this paper was to investigate the welding characteristics of titanium commonly using power station, aircraft and ship. The experimented material was TIG welded in order to look over the mechanical properties. The tensile strength and elongation of the 4 pass welded specimens was shown about 10% and 30% higher than those of the 7 pass welded specimens at the same welding conditions. Also, the more shielding gas and the shorter natural cooling time, the higher tensile strength but the lower elongation. The absorption enery of the 4 pass welded specimens was decreased about 50% more than that of the 7 pass welded specimens, and the more shielding gas, the higher impact absorption energy value. The higher hardness, the lower pass, but the natural cooling time almost had no relation to the hardness.

Ti 鎔接材의 機械的 特性 및 疲勞크랙 進展擧動에 關한 硏究

최병기,장경천,정장만 朝鮮大學校 機械技術硏究所 2001 機械技術硏究 Vol.4 No.2

Ti 용접재 시험편을 통하여 용접조건에 따른 기계적 성질 및 피로크랙 진전거동을 각각 비교·검토한 결과 다음과 같은 결론을 얻을 수 있었다. 동일한 용접조건에서 패스 수에 따라 4패스는 7패스와 비교하였을 경우 인장강도가 10%정도 높게 나타났고, 연신율은 30%종도 감소함을 알 수 있었다. 또한 실딩가스량이 많고, 용접 후 자연냉각 시간간격이 길수록 인장강도는 높게 나타났고, 연신율은 감소하였다. 충격 흡수에너지값은 4패스는 7패스에 비해 50%정도 감소하였으나, 실딩가스량이 많을수록 높게 나타났다. 또한 경도값은 패스 수가 적을수록 높게 나타났으며, 용접 후 자연냉각 시간간격에는 비슷하였으나 용접 후 자연냉각 시간간격이 적은 것은 조금 감소하였다. 초기크랙 진전속도는 Bond부, 용착부, HAZ, 온도영향부 순으로 느리게 나타났으나, 피로수명은 Bond부, HAZ부, 용착부, 온도영향부 순으로 높게 나타났다. The purpose of this thesis was to investigate the welding characteristics and the fatigue crack propagation behavior of titanium commonly using power station, aircraft and ship. The experimented material was TIG welded in order to look over the characteristics according to the notch position and compare with other materials. We compared and reviewed the fatigue crack propagation behavior of nonwelded base metal and welded specimens having different notch position to evaluate the fatigue crack propagation behavior by welding condition. The tensile strength and elongation of the 4 pass welded specimens was shown about 10% and 30% higher than those of the 7 pass welded specimens at the same welding conditions. Also, the more shield gas and the lower natural cooling time, the higher tensile strength but the lower elongation. The absorption energy of the 4 pass welded specimens, was decreased about 50% more than that of the 7 pass welded specimens, and the more shield gas, the higher impact absorption energy value. The higher hardness, the lower pass, but the natural cooling time almost had no relation to the hardness. The fatigue life was shown higher as following the order, boundary zone > HAZ > welding zone > base metal. Especially the fatigue life of boundary zone notched specimen was shown 700% higher than that of base metal.

Ni-Co 합금강의 탄소함량에 따른 기계적 특성에 관한 연구

최병기,정장만,최병희 朝鮮大學校 機械技術硏究所 2005 機械技術硏究 Vol.8 No.1

This study was to evaluate the effect of carbon content on metallic change and fatigue characteristics with Fe-29%Ni-17%Co, low heat expansion alloy, widely using electronic components, precision machines, and sealing with glass and metal etc. The steels were fabricated with variation of carbon content, 0, 0.03, 0.06, 0.1, and 0.20% with VIM and tensile test and fatigue test were performed to achieve the above purpose. The more carbon content, the higher hardness value and yield strength. But elongation of 0.03%C, 0.06%C. and 0.10%C specimen decreased about 2.2%, 1.5% and 0.8% respectively more than that of the base metal. Especially the strength and elongation of 0.20%C specimen increased simultaneously about 14.4% and 7.5%. Fatigue life of 0.03%C specimen decreased but the more carbon content, the higher fatigue life over 0.06% carbon content more than that of base metal.

순수 Ti 용접재의 기계적 특성 및 피로크랙 성장특성에 관한 연구

최병희,이종범,정장만,장경천,최병기 朝鮮大學校 機械技術硏究所 2007 機械技術硏究 Vol.10 No.2

In this study, fatigue fracture often occurs due to the fatigue crack in the machine and welding structure and this is the result of severe operational environment, operational condition, and design condition caused by the large scaled and light weighted machine and structure in recent days. Therefore, safety and reliability should be secured to prevent the fatigue fracture of machine and structure, and the use of titanium has been increased in the metal material for the safety and reliability. The purpose of this thesis was to investigate the welding characteristics and fatigue crack growth characteristics of titanium, commonly using power station, aircraft and ship. The experimented material was TIG welded in order to look over the characteristics according to the notch position and compare with other material. The results, at the same welding condition, 4 pass specimen which had the smallest number of welding pass had the highest tensile strength with 51kgf/㎟ and the tensile strength of 4 pass specimen was 10% higher than the one of 7 pass specimen, and its elongation reduced about 30%. The initial fatigue crack growth characteristic is slower in this order, boundary zone < welding zone < HAZ < base metal. Especially boundary zone's growth speed is slower about 30 times than base metals.

잔류응력을 고려한 SS400재의 피로특성에 관한 연구

최병희,이종범,정장만,장경천,최병기 朝鮮大學校 機械技術硏究所 2007 機械技術硏究 Vol.10 No.2

In this study is about the fatigue characteristics which appears in the welding residual stress field. The welding residual stress takes place mostly at the portion where SS400 materials are automatical welded. The effects of the welding residual stress in the growth and propagation of fatigue crack, so as to study the fatigue behavior in the welding residual stress field. The results, in case of the load range is constant, as the stress ratio is changing to 0.1, 0.33. 0.5 the propagation life is constant but the growth life decreases. And than, when maximum load or minimum load is constant, as the stress ratio increases the growth life and propagation life increase. The fatigue crack propagations rate da/dN appears to accelerate when the stress intensity factor range △K is less than 15MPa-m^(1/2). The growing and propagation fatigue crack in the welding residual stress field is similar to original specimen after being passed the original residual stress field.

Ni-Co 합금강의 기계적 특성에 대한 탄소함량의 영향

장경천,국중민,정장만,권택용,최병기 한국공작기계학회 2004 한국공작기계학회 춘계학술대회논문집 Vol.2004 No.-

This study was to evaluate the effect of carbon content on metallic change and fatigue characteristics with Fe-29%Ni-17%Co, low heat expansion alloy, widely using electronic components, precision machines, and sealing with glass and metal etc. The steels were fabricated with variation of carbon content, 0, 0.03, 0.06, 0.1, and 0.20% with VIM and tensile test and fatigue test were performed to achieve the above purpose. The more carbon content, the higher hardness value and yield strength. But elongation of 0.03%C, 0.06%C, and 0.10%C specimen decreased about 2.2%, 1.5% and 0.8% respectively more than that of the base metal. Especially the strength and elongation of 0.20%C specimen increased simultaneously about 14.4% and 7.5%. Fatigue life of 0.03%C specimen decreased but the more carbon content, the higher fatigue life over 0.06% carbon content more than that of base metal.

Ti 鎔接材의 機械的 特性 및 殘留應力의 分布에 關한 硏究

최병기,장경천,국중민,정장만,구남열 한국산업안전학회 2003 한국안전학회지 Vol.18 No.1

The objective of this paper was to investigate the welding characteristics according to the restraint condition, the pass number, and the shield gas quantity with titanium commonly using in power stations, aircrafts, ships, and so forth. The residual stress distribution was measured under restraint and nonrestraint welding conditions. The tensile strength and elongation of the 4 pass welded specimen were shown higher about 10% and 30% than those of the 7 pass welded specimen at the same welding conditions respectably. Also, the more shield gas quantity and the shorter natural cooling time, the higher tensile strength and the lower elongation.

殘留應力을 考慮한 鎔接材의 疲勞龜裂 進展擧動에 關한 硏究

최병기,이을호,국중민,기준호,임선빈,정장만 朝鮮大學校 機械技術硏究所 2000 機械技術硏究 Vol.3 No.1

The effect of welding residual stress on the initiation and propagation of fatigue crack is investigated so as to study the fatigue behavior in welding residual stress field. Especially, the relation between welding residual stress and fatigue crack opening behavior is investigated and the redistribution of residual stress as a fatigue crack propagates is examined. Following results are obtained. 1) In case of the load range is constant, as the stress ratio is changing to 0.1, 0.33, 0.5 the propagation life is constant but the growth life decreases. And than, when maximum load or minimum load is constant, as the stress ratio increases the growth life and propagation life increase. 2) The fatigue crack propagations rate da/dN appears to accelerate when the stress intensity factor range ΔK is less than 15MPa-m^1/2. 3) The residual stress that is appeared by welding decreases after cutting. 4) Fatigue crack propagation ratio is affected by tensional and compressible residual stress at the initial time, but it's similar to the original in the more than 20mm of crack length.

전기/하이브리드 자동차에 적용이 가능한 높은 강압비와 효율을 갖는 3kW급의 절연형 DC-DC 컨버터 설계 방법

신무철(Shin, Moo Chul),조은석(Cho, Eun Seok),정장만(Jung, Jang Man),이용근(Lee, Yong Keun) 한국전시산업융합연구원 2015 한국과학예술융합학회 Vol.19 No.-

본 논문에서는 전기 자동차에 적용 가능한 높은 효율을 갖는 3kW급의 양방향 Inverter, DC-DC Converter를 제안하였다. 제안된 시스템은 입력과 출력을 절연시키기 위한 Full-Bridge Part, 피드백에 의한 전압 조절을 위한 Push-Pull Part, 그리고 Inverter Part로 총 3개의 파트로 구성된다. 고전류 컨버터에서 상당한 손실을 야기하는 인덕터를 저 전류 측으로 옮기고, MOSFET의 개수를 줄임으로써 획기적으로 효율을 증가시켰다. 또한 Full Bridge Part 에서 높은 고정 듀티(Duty)의 Phase Shift 방식을 사용하여 낮은 Turn ON 손실과 낮은 스위치 도통손실을 달성하였다. 추가적으로 기존의 인버터의 스위칭 문제점을 개선하여 적절한 Dead Time을 추가하였으며, 이로 인한 상당한 효율증가를 보여주었다. 제안된 토플로지는 하이브리드(전기)자동차의 전력 변환 시스템이나, 배터리 충·방전 테스트 장비에 효과적으로 적용될 수 있겠다. We proposed 3kW bi-directional inverter and DC-DC converter system with high step down ratio and efficiency in this paper. The proposed system is consisted to 3 parts. The first one is Full-Bridge part to isolate input and output and 2nd part is Push-Pull topology to control the output voltage. The last one is the inverter part to transfer the power from DC to AC. The inductor and MOSFET cause conduction loss especially in high current condition. We moved the inductor to lower current part and decreased the number of MOSFET in high current part to decease power loss. And we decreased power loss by using phase shift switching and add the proper dead time for the inverter part. The proposed system can be used for wide application such as electronic(hybrid) car, BMS and any power transfer system.