Unique Appearance of Lamellar Cleavage Patterns on Fracture Surfaces of Ti-Based Amorphous Matrix Composite

Jeon, Changwoo,Suh, Byeong-Chan,Kim, Choongnyun Paul,Kim, Hyoung Seop,Kim, Nack J.,Lee, Sunghak Springer-Verlag 2015 Metallurgical and Materials Transactions A - Physi Vol.46 No.6

Failure and Phase Transformation Mechanism of Multi-Layered Nitride Coating for Liquid Metal Injection Casting Mold

Jeon, Changwoo,Lee, Juho,Park, Eun Soo Materials Research Society of Korea 2021 한국재료학회지 Vol.31 No.6

Ti-Al-Si target and Cr-Si target are sputtered alternately to develop a multi-layered nitride coating on a steel mold to improve die-casting lifetime. Prior to the multi-layer deposition, a CrN layer is developed as a buffer layer on the mold to suppress the diffusion of reactive elements and enhance the cohesive strength of the multi-layer deposition. Approximately 50 nm CrSiN and TiAlSiN layers are deposited layer by layer, and form about three ㎛-thickness of multi-layered coating. From the observation of the uncoated and coated steel molds after the acceleration experiment of liquid metal injection casting, the uncoated mold is severely eroded by the adhesion of molten metallic glass. On the other hand, the multi-layer coating on the mold prevents element diffusion from the metallic glass and mold erosion during the experiment. The multi-layer structure of the coating transforms the nano-composite structured coating during the acceleration test. Since the nano-composite structure disrupts element diffusion to molten metallic glass, despite microstructure changes, the coating is not eroded by the 1,050 ℃ molten metallic glass.

Improvement of Mechanical Properties of Zr‑Based Bulk Amorphous Alloys by High Temperature Heat Treatment

Changwoo Jeon,Min Chul Jo,Juho Lee,Eun Soo Park,Junho Park,Sang Yong Shin 대한금속·재료학회 2020 METALS AND MATERIALS International Vol.26 No.8

Zr-based bulk amorphous alloys which were heat-treated from 673 to 1073 K were investigated, and compressive fracturemechanisms related with improvement of mechanical properties were investigated by observing how the type, size and volumefraction of crystalline particles which is generated during the heat treatment affected the fracture mode. The Zr-based bulkamorphous alloys contained nano-sized crystalline particles showed excellent mechanical properties of compressive fracturestrength over 2.0 GPa and compressive plastic strain of approximately 1%. The fracture modes of the alloys are changeddepending on the heat treatment temperature and their microstructure. When the alloy is heat-treated at 673 K, the nanosizedZr2Cuparticles are generated in amorphous matrix. According to the observation of fractured specimens, in the alloyheat-treated at 673 K, the fine and elongated vein patterns were well developed. The heat treatment temperature increasedabove Tx,the Zr2Cuparticles as well as complex crystalline particles are consist in the heat-treated alloy, which lead to thebrittle fracture and the alloy show the low strength of 605 MPa. In the fractured surface of the alloy, large cleavage facetswere evenly developed. When the heat treatment temperature up near Tm,the size of Zr2Cuand complex crystalline particlesincreased to approximately 1 μm and the volume fraction of complex crystalline particles increased up to 52.3%. As the sizeof crystalline particles change, the size of facet decreased similarly to the size of crystalline particles.

Effects of dendrite size on dynamic tensile deformation behavior in Zr-based amorphous alloys containing ductile dendrites

Jeon, Changwoo,Kang, Minju,Paul Kim, Choongnyun,Seop Kim, Hyoung,Lee, Sunghak Elsevier 2016 Materials science & engineering. properties, micro Vol.650 No.-

<P><B>Abstract</B></P> <P>In this study, dynamic tensile properties of Zr-based amorphous alloys whose dendrite size was varied with plate thickness (or cooling rate) were investigated, and effects of dendrite size on dynamic deformation mechanisms were verified. The dendrite size of the amorphous alloys was varied from 14.7μm to 42.8μm, while their volume fraction was almost constant. The dynamic tensile test results indicated that the ultimate tensile strength increased up to 2.6GPa because of strain rate hardening effect, whereas the elongation decreased to 1.1–1.6%, although the overall strength and elongation trends followed those of the quasi-static tensile test. According to the observation of dynamic tensile deformation behavior, the dendrite size greatly affected the dynamic tensile strength and elongation by the formation of deformation bands at dendrites, while dendrites themselves took over a considerable tensile load. However, the elongation was deteriorated when dendrites were large above a certain size level. In the alloy containing large dendrites, deformation bands were formed at dendrites in two intersected directions, but the amount of intersected deformation bands was reduced because deformation bands showed slip characteristics on a few slip planes of dendrite.</P>

Effects of Effective Dendrite Size on Dynamic Tensile Properties of Ti-Based Amorphous Matrix Composites

Jeon, Changwoo,Park, Jaeyeong,Kim, Choongnyun Paul,Kim, Hyoung Seop,Lee, Sunghak Springer-Verlag 2016 Metallurgical and Materials Transactions A - Physi Vol.47 No.4

Atomization Technology for High-Permeability Amorphous Fe-Based Magnetic Powder

Changwoo Jeon,Kwanghyun Lee,Juho Lee,Eun-Soo Park 한국자기학회 2023 한국자기학회 학술연구발표회 논문개요집 Vol.33 No.2

색상 배색 테크닉에 의한 3 색 배색의 확장에 관한 연구

전창우(Changwoo Jeon),윤경현(Kyunghyun Yoon) 한국HCI학회 2016 한국HCI학회 학술대회 Vol.2016 No.1

회화에는 화가의 느낌이나 생각, 사상, 감성 등이 표현된다. 회화를 구성하는 기본적인 요소로는 색, 재질감, 구도 등이 있는데 그중에 색은 회화의 감성을 분석하는 중요한 요소 중 하나이다. 우리는 이러한 색이라는 분야를 시스템적인 분야로 이해함으로써 회화로부터 어떠한 감성을 느낄 수 있는지를 분석해 볼 수 있다. 일본의 디자인 연구자 시게노부 고바야시(Shigenobu Kobayashi)는 인간과 색과의 상관관계에 대해 오랜 시간에 걸쳐 연구해 왔다. 고바야시는 설문조사를 통해 130 가지의 색을 기준으로 178 개의 감성형용사를 표현할 수 있는 936 가지의 3 색 배색을 제시하였다. 하지만 130 가지 색을 기준으로 만들 수 있는 357,760 가지의 3 색 배색에 비하면 936 가지의 3 색 배색은 우리들의 느끼는 세밀한 정서를 적절하게 표현하기에는 어렵다. 고바야시가 제시한 936 가지의 3 색 배색은 색상 배색 테크닉이라는 규칙성을 가진다. 이 논문에서는 색상 배색 테크닉을 이용하여 178 개의 감성 형용사를 표현할 수 있는 새로운 감성 배색을 제안함으로써, 회화를 구성하고 있는 색으로부터 표현되는 감성을 보다 정확하게 예측이 가능하게 한다. The artist"s thoughts, philosophy, emotions etc. are expressed in a painting. The basic elements that consist a painting include color, texture, and structure. Among these elements, color is one of the important factors in analyzing the emotion expressed in a painting. We may view the field of color as a systematic field and attempt to analyze what emotions can be felt from a painting. Shigenobu Kobayashi, a Japanese design specialist, has done a lot of research on the relation between humans and color. Kobayashi conducted surveys and using 130 different colors, he came up with 936 types of 3-color combinations that can express 178 emotion-related adjectives. But compared to the 357,760 different kinds of 3-color combinations that can be created with 130 colors, the 936 types of 3-color combinations are not enough to express our subtle emotions adequately. Kobayashi"s 936 types of 3-color combinations follow the pattern of color combination technique. In this paper, I will propose a new set of 3-color combinations, using the color combination technique that can express the 178 emotion-related adjectives, thereby enabling a more precise prediction of the emotion that is expressed by the color in a painting.

고령인구의 이동편의 증진을 위한 무료셔틀버스 노선 최적화 연구: 서울시 관악구를 사례로

전창우 ( Changwoo Jeon ),이건학 ( Gunhak Lee ) 한국지리학회 2017 한국지리학회지 Vol.6 No.2

최근 고령인구가 급격히 증가함에 따라 이들을 위한 복지서비스를 어떻게 효과적이고 효율적으로 공급할 것인가에 대한 논의가 활발히 진행 중이다. 무료셔틀버스는 고령자의 교통 복지와 관련하여 이동편의 증진에 도움이 되는 수단 중 하나로 도입이 되었지만, 제한된 접근성, 지역적 편중된 노선 운행 등으로 고령인구의 수요를 제대로 충족시키지 못하고 실제적인 효용성을 발휘하지 못하고 있는 실정이다. 따라서 본 연구에서는 공간 최적화 모델링을 통해 고령인구의 이동성 및 교통 복지 서비스의 효율적 개선을 위한 최적화된 무료셔틀버스 노선을 제시하고자 한다. 보다 구체적으로 서울시 관악구를 대상으로 고령인구의 접근성을 최대화할 수 있는 버스 정거장 입지를 도출하고, 고령자의 현실적 수요를 고려한 장소들을 효율적으로 순회할 수 있는 무료셔틀버스의 최적 노선을 보여준다. 본 연구는 향후 고령자를 포함한 다양한 교통약자의 이동성을 향상시키는 데 필요한 구체적이고 실천적인 가이드라인을 제공할 것으로 기대된다. As the elderly are rapidly increasing in recent years, the effective and efficient provision of welfare services for the elderly has been substantially discussed. Although the free shuttle bus was basically deployed as one of the modes to improve the travel convenience related to the transportation welfare for the elderly, it does not meet the demand for the elderly and is not utilized well due to the limited accessibility, uneven routing of the shuttle bus, etc. This paper aims to provide optimal routes for the free shuttle bus to improve the mobility of elderly people and to enhance the transportation welfare service using spatial optimization modeling. More specifically, as a case of Gwanak-gu, Seoul, we first present optimal locations of bus stops maximizing spatial accessibility, and provide optimized routes for the free shuttle bus which are made of important places considering elderly actual demands. It is expected that this study will provide a tangible and practical guideline for improving the mobility of various traffic disadvantages including elderly people.

Optimal estimation of rock joint characteristics using simulated annealing technique - A case study

Changwoo Hong,Seokwon Jeon 한국암반공학회 2003 한국암반공학회 학술대회 및 세미나 자료집 Vol.- No.-

유전알고리즘을 이용한 암반 물성의 최적 평가에 관한 연구

홍창우(Changwoo Hong),전석원(Seokwon Jeon) 한국암반공학회 2005 터널과지하공간 Vol.15 No.2

터널이나 지하구조물의 건설시 필요한 지보의 설계는 보통 시추에 의한 지반조사결과에 기초하고 있다. 지반조사 자료가 부족한 지역에서의 암반 물성을 보다 객관적이고 추계학적(stochastic)으로 예측하기 위해 유전 알고리즘(genetic algorithm)과 조건부 모사 기법(conditional simulation)을 사용하였다. 지구통계학적 모델링의 방법으로 조건부 모사를 실시한 후에 공간상관관계의 최적화과정을 통해 암반 물성을 구하였다. 유전알고리즘을 이용할 경우 크리깅에 의한 분산의 감소 현상을 극복하고 확률적으로 값을 제시할 수 있었다. 또한 30번의 확률적 등가치(equi-probable) 모사를 통해 유전알고리즘으로 구한 값의 불확실성을 정량적인 확률분포 값으로 제시하였고, 교차검증(cross validation) 방법으로 유전알고리즘의 신뢰도를 검증하였다. This paper describes the implementation of rock mass rating evaluation based on genetic algorithm(GA) and conditional simulation technique to estimate RMR in the area without sufficient borehole data. RMR were estimated by GA and conditional simulation technique with reflecting distribution feature and spatial correlation. And RMR determined by GA were compared with the results from kriging. Through the analysis of the results from 30 simulations, the uncertainty of estimation could be quantified.