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최병학,심종헌,김승언,현용택,박찬희,강주희,이용태,김영욱,Choe, Byung Hak,Shim, Jong Heon,Kim, Seung Eon,Hyun, Yong Taek,Park, Chan Hee,Kang, Joo-Hee,Lee, Yong Tai,Kim, Young Ouk 한국재료학회 2015 한국재료학회지 Vol.25 No.8
Metastable phase characteristics of beta Ti alloys were investigated to consider the relationship of the microstructure and diffraction pattern in TEM. TEM analysis showed that the microstructure was mottled as a modulated structure, and the diffraction pattern was composed of spot streaks between the main spots of a stable beta phase with a specific lattice relationship. The modulated structure may be induced by short distance slip or atom movement during a very short interval of solution treated and quenched (STQ) materials. The athermal ${\omega}$ phase, which could be precipitated at low temperature aging, is also analysed by the metastable phase. The metastable phases including athermal ${\omega}$ phase had a common characteristic of hardened and brittle behavior because the dislocation slip was restricted by a super lattice effect due to short distance atom movement at the metastable state.
최병학,최원열,심종헌,박찬희,강주희,김승언,현용택,Choe, Byung Hak,Choi, Won-Youl,Shim, Jong Heon,Park, Chan Hee,Kang, Joo-Hee,Kim, Seung Eon,Hyun, Yong Taek 한국재료학회 2015 한국재료학회지 Vol.25 No.8
Microstructural analysis of a (${\alpha}+{\beta}$) Ti alloy was investigated to consider phase transformation in each step of the thermo-mechanical process using by SEM and TEM EDS. The TAF (Ti-6Al-4Fe) alloy was thermo-mechanically treated with solid solution at $880^{\circ}C$, rolling at $880^{\circ}C$ and annealing at $800^{\circ}C$. In the STQ state, the TAF microstructure was composed of a normal hcp ${\alpha}$ and metastable ${\beta}$ phase. In a rolled state, it was composed of fine B2 precipitates in an ${\alpha}$ phase, which had high Fe segregation and a coherent relationship with the ${\beta}$ matrix. Finally, in the annealing state, the fine B2 precipitates had disappeared in the ${\alpha}$ phase and had gone to the boundary of the ${\alpha}$ and ${\beta}$ phase. On the other hand, in a lower rolling temperature of $704^{\circ}C$, the B2 precipitates were more coarse in both the ${\alpha}$ and the boundary of ${\alpha}$ and ${\beta}$ phase. We concluded that microstructural change affects the mechanical properties of formability including rolling defects and cracks.
AUTODYN을 이용한 LNG 폭발 사고 위력 평가에 관한 법공학적 연구
김의수 ( Eui Soo Kim ),김종혁 ( Jong Hyuk Kim ),심종헌 ( Jong Heon Shim ),김진표 ( Jin Pyo Kim ),고재모 ( Jae Mo Goh ),박남규 ( Nam Kyu Park ) 한국안전학회(구 한국산업안전학회) 2015 한국안전학회지 Vol.30 No.4
Gas explosion accidents could cause a catastrophe. we need specialized and systematic accident investigation techniques to shed light on the cause and prevent similar accidents. In this study, we had performed LNG explosion simulation using AUTODYN which is the commercial explosion program and predicted the damage characteristics of the structures by LNG explosive power. In the first step, we could get LNG’s physical and chemical explosion properties by calculation using TNT equivalency method. And then, by applying TNT equivalency value about the explosion limit concentration of LNG on the 2D-AUTODYN simulation, we could get the explosion pressure wave profiles (explosion pressure, explosion velocity, etc.). In the last step, we performed LNG explosion simulation by applying to the explosion pressure wave profiles as the input data on the 3D-AUTODYN simulation. As a result, we had performed analyzing of the explosion characteristics of LNG in accordance with concentration through the 3D-AUTODYN simulation in terms of the explosion pressure behavior and structure’s destruction and damage behavior.
가상 피트데이터 통계처리를 통한 가스배관 고장확률 및 수명평가
최병학 ( Byung Hak Choe ),김성준 ( Seong Jun Kim ),심종헌 ( Jong Heon Shim ),김우식 ( Woo Sik Kim ),김철만 ( Chul Man Kim ) 대한금속재료학회(구 대한금속학회) 2015 대한금속·재료학회지 Vol.53 No.6
Corrosion data obtained from in-line inspection can be applied to assess present integrity as well as to predict future integrity of gas pipelines. This can be accomplished by using a combination of probabilistic analyses and simulation. With a deterministic method, failure models (e.g., NG 18 or ASME B31G)can only provide “Safe or Fail” criteria for corroded pipelines. However, a probabilistic method can offer “Probability of Failure (POF)” using the same models. This paper is focused on determining the POF for hypothetical corrosion-pit data of a gas pipeline. The study presented a ten-step procedure for obtaining the POF of a gas pipeline using three statistical methods (i.e., Monte Carlo, FOSM: First-Order Second-Moment, and FORM: First-Order Reliability Method). Furthermore, the coefficient of variance, regarding the value of POF sensitivity in relation to data variation, was mostly affected by the corrosion-depth parameter of the pit data.
ADINA & WINLIFE 활용한 압력용기 용접부 피로파괴 해석
최병학(Byung Hak Choe),이범규(Bum Gyu Lee),심종헌(Jong Heon Shim),박찬성(Chan Sung Park),김진표(Jin Pyo Kim),박남규(Nam Gyu Park) 대한용접·접합학회 2016 대한용접·접합학회지 Vol.34 No.5
The aim of this study is to consider effect of weld elastic modulus on simulations of stress concentration and fatigue life for pressure vessel. The investigations include analysis with ADINA and WINLIFE softwares for whole body model about using condition of the boiler vessel. Values of weld elastic modulus were divided by 5 steps in butt weld area of the boiler vessel body. The stress concentration of the butt weld more was increased in case of higher elastic modulus of weld area because of higher difference of material properties between matrix and weld. It was concluded that the fatigue lives were decreased along increasing stress concentration due to high elastic modulus of weld. The matrix microstructure was estimated as pearlitic structure of α·ferrite and pearlite. And the microstructures of welds along 5 steps of elastic modulus were estimated as bainitic fine pearlite and martensite as increasing elastic modulus.