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In vitro plant regeneration from flower buds of populus deltoides and P. maximowiczii
정경호(Kyung Ho Chung),김주학(Joo Hag Kim),전영우(Young Woo Chun) 한국육종학회 1993 한국육종학회지 Vol.25 No.3
Small immature flower buds of Populus deltoides and P.maximowiczii were cultured on the MS medium containing 0.5㎎/ℓ BA and 0.5-1.0㎎/ℓ NAA for development and growth. Small slices of catkin 5-6㎜ in thickness prepared from the well-developed flower bud 3-4㎝ in length were culture on the MS medium containing 1.0㎎/ℓ BA+0.05㎎/ℓ NAA and 0.5㎎/ℓ BA+0.05㎎/ℓ NAA for adventitious shoot regeneration from P.deltoides and P.maximowiczii, respectively. Average 3.8 shoots from P.deltoedes and 4.1 from P.maximowiczii were regenerated from a slice of catkin. More than 20 shoots can be regenerated from a single mature catkin of poplar such as P.deltoides that is recalcitrant to shoot regeneration. Adventitious shoots were initiated from three different places of an explant, the outer and the cut surface of stalks, and the marginal part of small bracts. The development of immature flower buds in vitro was affected by collecting time. Those collecting in late March were not developed well into mature flower buds. among five different collecting times, July, Sep., Nov., Jan., and Mar.
김주학,김헌주,윤의박,김기철,조순형 대한금속재료학회(대한금속학회) 1989 대한금속·재료학회지 Vol.27 No.9
In multi-pass welding, the effect of 2nd pass on the microstructure and dynamic fracture toughness was discussed. The 2nd pass was found to enhance bond toughness in the range of 2.5 kJ/㎜ and 4.5 kJ/㎜ heat input. The reason seems to be that the size of Martensite -Austenite constituent was refined and its amount was decreased. The size of lower bainite and tempered martensite were also refined. TEM study revaled that the M-A constituent contained lath or twined martensite and it behaved as a crack path.
계장화충격시험법에 의한 구조용강 용접부의 동적파괴인성에 관한 연구 (4) : 이중열 cycle 재현법에 의한 Bond 부조직과 인성
김주학,김헌주,윤의박,김기철,조순형 대한금속재료학회(대한금속학회) 1989 대한금속·재료학회지 Vol.27 No.8
The relationships between the microstructure and dynamic fracture toughness, kid, were mainly investigated. In order to measure a fracture toughness using instrumented impact test, the necessity of low b1ow test for obtaining true energy by the compliance correction and Equivalent energy method were confirmed. It was proven that 2nd pass performance was capable of enhancing bond toughness. K_(Id) value decreased abruptly with increasing 1st pass heat input from 2.5KJ/㎜ to 9.0KJ/㎜. Bond toughness, however, improved noticeably when 2nd pass was carried, the heat input of which was between 2.5KJ/㎜ and 4.5KJ/㎜.
SA 508 Cl.3 원자로압력용기강 단위열영향부의 노치인성과 미세조직 변화
김주학,윤의박 대한금속재료학회(대한금속학회) 1998 대한금속·재료학회지 Vol.36 No.8
In order to study systematically the notch toughness and microstructural alterations across the heat-affected zone (HAZ) as functions of position and weld conditions, a unit HAZ concept was applied to a quenched and tempered SA 508 Cl. 3 reactor pressure vessel steel multipass weld. The unit HAZ, which consists of the width of HAZ (W_H) and the width of interpass (W_I), could be determined by the physical constants and welding variables of the materials. Weld HAZ thermal cycles, which correspond to the various HAZ regions, were simulated with a Gleeble 1500 thermal simulator. Seven typical positions were selected to evaluate the spatial distribution of notch toughness and microstructure in the unit HAZ. Three coarse-grained regions and two fine-grained regions showed relatively good toughness. On the contrary, an intercritically reheated region and a subcritically reheated region showed lower toughness than the base metal. The causes for the variations in toughness were discussed with reference to the microstructures and thermal cycles.
원자로압력용기장 용접열영향부의 미세조직 변화가 Magnetic Barkhausen Noise 거동에 미치는 영향
김주학,윤의박,문종걸,박덕근,홍준화 韓國非破壞檢査學會 1998 한국비파괴검사학회지 Vol.18 No.4
최근 자기적 특성의 변화가 재료의 미세조직적 상태에 민감하다는 보고가 있다. 재료의 미세조직은 상(phase), 결정립의 크기, 석출물 등의 다양한 인자로 구성되며, 본 연구에서는 이러한 인자들을 이용하여 재료의 특성과 Barkhausen noise(BN)의 관계를 연관시키기 위한 시도를 하였다. ASTM A 508 Gr.3 원자로압력용기강을 대상으로 용접열영향부의 미세조직적인 변화를 일곱가지 대표적인 영역으로 구분하였고, 각 영역에서의 미세조직과 기계적특성의 변화를 파악한 후, 각 조건별로 BN을 측정하였다. 통상의 보자력이나 잔류자화 같은 자기적 성질은 큰 변화가 없었지만, BN은 미세조직의 상태에 따라 현격한 변화를 보였다. 결정립과 석출물의 크기가 증가함에 따라 BN은 증가하였고, tempered martensite 보다는 tempered bainite 조직에서 높은 BN을 나타냈다. Recent study has demonstrated that some magnetic properties are sensitive to the microstructural state of material. The ASTM A 508 Gr. 3 reactor pressure vessel steel has various microstructural changes including martensitic and bainitic phases, and various sizes of grain and precipitates in the weld heat-affected zone (HAZ). To correlate the microstructural state with Barkhausen noise (BN), specimens were prepared through simulating various weld thermal cycles using a thermal simulator. The conventional magnetic properties, i.e. coercive force, remanence and maximum induction, did not change significantly. whereas the BN amplitude and energy during a magnetization cycle changed markedly with microstructural state. The BN increased with increasing grain and carbide sizes, and the tempered bainite structure showed higher BN parameter than tempered martensite.
원자로 용접부의 국부적 미세조직 변화에 따른 동적탄성계수 측정
정용무,김주학,홍준화,정현규 한국비파괴검사학회 2000 한국비파괴검사학회지 Vol.20 No.5
원자로 재료인 SA 508 Class 3 강용접부 및 열영향부 모사 시험편에 대해서 초음파공명분광법으로 동적탄성계수를 측정하였다. 등방성 탄성계수를 가정하여 초기 추정 탄성 계수, c11, c12 및 c44 로부터 장방형 시편의 공명 주파수를 계산하였으며 계산된 주파수와 초음파공명분광법으로 측정된 주파수를 비교, 반복 수렴 절차를 거쳐 정밀한 탄성계수를 구했다. 열처리 조건의 차이 및 미세 조직의 차이에 따라 영률 및 전단 계수의 차이가 확실하게 나타났다. 미세한 베이나이트 조직에서의 영률 및 전단 계수는 조대한 마르텐사이트 조직보다 높았으며 이러한 경향은 미세 경도 시험 등의 다른 실험 결과와도 일치하였다. The dynamic elastic constants of the simulated weld HAZ(heat-affected zone) of SA 508 Class 3 reactor pressure vessel (RPV) steel were investigated by resonant ultrasound spectroscopy (RUS). The resonance frequencies of rectangular parallelepiped samples were calculated from the initial estimates of elastic stiffness c11, c12 and c44 with an assumption of isotropic property, dimension and density. Through the comparison of calculated resonant frequencies with the measured resonant frequencies by RUS, very accurate elastic constants of SA 508 Class 3 steel were determined by iteration and convergence processes. Clear differences of Youngs modulus and shear modulus of shown from samples with different thermal cycles and microstructures. Youngs modulus and shear modulus of samples with fine-grained bainite were higher than those with coarse-grained tempered martensite. This tendency was confirmed from other results such as micro-hardness test.