• Smart Structures and Systems
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• 제22권6호
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• pp.643-662
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• 2018

One of the methods for investigation of mechanical behavior of materials is numerical simulation. For simulation, its need to model behavior is close to real condition. PFC is one of the rock mechanics software that needs calibration for models simulation. The calibration was performed based on simulation of unconfined compression test and Brazilian test. Indeed the micro parameter of models change so that the UCS and Brazilian test results in numerical simulation be close to experimental one. In this paper, the effect of four micro parameters has been investigated on the uniaxial compression test and Brazilian test. These micro parameters are friction angle, Accumulation factor, expansion coefficient and disc distance. The results show that these micro parameters affect the failure pattern in UCS and Brazilian test. Also compressive strength and tensile strength are controlled by failure pattern.

• 한국재료학회지
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• 제22권10호
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• pp.513-518
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• 2012

Recently, automobile parts have been required to have high strength and toughness to allow for weight lightening or improved stability. But, traditional micro-alloyed steel cannot be applied in automobile parts. In this study, we considered the influence of quenching temperature and cooling rate for specimens fabricated by vacuum induction furnace. Directly quenched micro-alloyed steel for hot forging can be controlled according to its micro structure and the heat-treatment process. Low carbon steel, as well as alloying elements for improvement of strength and toughness, was used to obtain optimized conditions. After hot forging at $1,200^{\circ}C$, the ideal mechanical properties (tensile strength ${\geq}$ 1,000 MPa, Charpy impact value ${\geq}\;100\;J/cm^2$) can be achieved by using optimized conditions (quenching temperature : 925 to $1,050^{\circ}C$, cooling rate : ${\geq}\;5^{\circ}C/sec$). The difference of impact value according to cooling rate can be influenced by the microstructure. A fine lath martensite micro structure is formed at a cooling rate of over $5^{\circ}C/sec$. On the other hand, the second phase of the M-A constituent microstructure is the cause of crack initiation under the cooling rate of $5^{\circ}C/sec$.

• 한국구조물진단유지관리공학회 논문집
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• 제28권3호
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• pp.47-58
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• 2024

본 연구에서는 마이크로 강섬유와 다중벽 탄소나노튜브(multi-walled carbon nanotube, MWCNT)를 혼입한 전도성 모르타르의 발열성능, 휨강도 및 미세구조를 분석하기 위해 실험적으로 수행하였다. 전도성 모르타르 발열성능 및 휨강도 시험에서 MWCNT의 혼입 농도는 시멘트 중량 대비 0.0wt%, 0.5wt% 및 1.0wt%로 선정하였으며, 마이크로 강섬유는 부피 대비 2.0vol%로 혼입하였다. 발열성능 실험은 다양한 인가전압 (DC 10V, 30V, 60V) 및 상이한 전극간격 (40 mm, 120 mm)을 매개변수로 수행하였으며, 양생 재령 28일에서 휨강도를 측정하여 일반 모르타르와 비교, 분석하였다. 더 나아가, 전계방사 주사전자현미경(field emission scanning electron microscope, FE-SEM)을 이용하여 전도성 모르타르의 표면 형상과 미세구조를 분석하였다. 그 결과 MWCNT의 혼입 농도와 인가전압이 증가할수록 발열성능이 향상되었으며, 전극간격이 좁을수록 발열성능이 더욱 향상되는 것으로 나타났다. 하지만 MWCNT의 혼입 농도를 1.0wt%까지 추가하더라도 발열성능은 크게 향상되지 못하였다. 휨강도 시험결과, PM 시편과 MWCNT를 혼입한 시편을 제외한 모든 시편의 평균 휨강도가 4.5 MPa 이상으로 나타나 마이크로 강섬유 혼입에 따른 높은 휨강도를 보였다. FE-SEM 이미지 분석을 통해 시멘트 매트릭스 내 마이크로 강섬유와 MWCNT 입자 사이에 전도성 네트워크가 형성되는 것을 확인하였다.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 1998년도 추계학술대회 논문집
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• pp.273-278
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• 1998

In this paper, basic micro-mechanical properties of unidirectional CFRP composite shell such as bonding strength, fiber volume fraction and void fraction are measured and tensile strength test is performed with a fixture. And then fracture surfaces are observed by SEM. In case of basic micro-mechanical properties, bonding strength is reduce with decreasing of radius of each ply in a shell for the effect of residual stress, fiber volume fraction is smaller than plate, and void fraction is vise versa. For these reason, tensile strength of shell is smaller than plate fabricated with same prepreg. For failure mode shell has many splitted part along its length, and it is assumed that this phenomenon is caused by the difference of bonding strength for residual stress.

• 한국건축시공학회지
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• 제21권4호
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• pp.269-279
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• 2021

Palm Oil Fuel Ash(POFA)는 콘크리트의 물리적 특성 및 내구성을 향상시키기 위해 일정량 시멘트를 치환하여 사용된다. 그러나 높은 강열감량과 각진 입자 형상으로 인해 POFA를 사용한 콘크리트의 워커빌리티가 감소한다. 본 연구에서는 micro-POFA를 혼입한 시멘트 페이스트의 초기 물리적, 수화 특성에 감수제 종류 및 사용량이 미치는 영향을 mini-slump 실험, 초기 압축 강도, TGA, XRD, SEM을 이용하여 검토하였다. micro-POFA 치환율이 증가함에 따라 시멘트 페이스트의 유동성은 감소하였으며, 감수제의 사용량이 증가할수록 시멘트 페이스트의 유동성은 증가하였다. 또한, 감수제의 사용은 시멘트 페이스트의 초기 압축 강도를 저하시켰으며, 사용량이 증가할수록 압축 강도 저하가 뚜렷하게 나타났다. 미세분석을 통해 감수제가 C-S-H 형성을 억제하고 상대적으로 Ca(OH)₂의 생성량을 증가시켰기 때문이라고 사료된다.

• Geomechanics and Engineering
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• 제20권1호
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• pp.29-41
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• 2020

It is extremely important to obtain rock strength parameters for geological engineering. In this paper, the evolution of sandstone cohesion and internal friction angle with plastic shear strain was obtained by simulating the cyclic loading and unloading tests under different confining pressures using Particle Flow Code software. By which and combined with the micro-crack propagation process, the mesoscopic mechanism of parameter evolution was studied. The results show that with the increase of plastic shear strain, the sandstone cohesion decreases first and then tends to be stable, while the internal friction angle increases first, then decreases, and finally maintains unchanged. The evolution of sandstone shear strength parameters is closely related to the whole process of crack formation, propagation and coalescence. When the internal micro-cracks are less and distributed randomly and dispersedly, and the rock shear strength parameters (cohesion, internal friction angle) are considered to have not been fully mobilized. As the directional development of the internal micro-fractures as well as the gradual formation of macroscopic shear plane, the rock cohesion reduces continuously and the internal friction angle is in the rise stage. As the formation of the macroscopic shear plane, both the rock cohesion and internal friction angle continuously decrease to a certain residual level.

• 한국건설순환자원학회논문집
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• 제12권1호
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• pp.33-39
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• 2024

본 연구에서는 나노소재의 콘크리트 혼화재로 사용하기에 적합한지 확인하기 위해 마이크로 실리카 및 흄드 실리카 대체율 변화에 따른 시멘트 페이스트의 기본 특성을 분석하였다. 초고강도용 배합을 참고하여 나노소재 대체율에 따른 시멘트 페이스트의 유동성을 평가와 압축강도 특성을 비교 분석하였다. 반응성 나노소재의 시멘트 수화물과의 관련 특성은 SEM, EDS 분석 이용하여 미세구조를 관찰과 수화 생성물의 구성요소 확인하였다. 본 연구에 사용한 반응성 나노소재는 탭밀도가 0.061~0.264 g/cm³ 수준으로 SF 대비 낮게 측정되었다. 마이크로 실리카의 경우 대체율이 증가할수록 우수한 압축강도 특성을 나타냈지만 흄드 실리카는 마이크로 화이트와는 달리 대체율 0.01~0.1 %에서 우수한 압축강도를 확보하였다. 수화특성 분석결과에서도 동일한 경향을 확인할 수 있었다.

• 열처리공학회지
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• 제33권3호
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• pp.117-123
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• 2020

Due to high corrosion resistance, Zinc has been widely used in the automobile, shipping or construction industries as a galvanizing material. Zinc is popular as a coating element, but its low mechanical strength impede the expansion of applications as a load-bearing structure. The mechanical strength of Zinc can be increased through zinc based alloy process, but the ductility is significantly reduced. In this study, the mechanical strength and ductility of Zinc-Magnesium alloys with respect to heat treatment hold time was investigated. In order to enhance the mechanical strength of Zinc, a Zinc-Magnesium alloy was fabricated by a melting process. The heat treatment process was performed to improve the ductility of Zinc-Magnesium alloy. The microstructure of the heat-treated alloy specimen was analyzed using SEM. The hardness and compressive strength of the specimen were measured by a micro-hardness tester and a nano-indenter, respectively.

• 전기학회논문지
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• 제67권10호
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• pp.1330-1337
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• 2018

In this study, 40, 50, 60, and 70 wt% filler dispersed samples were prepared for the current GIS Spacer or environmentally friendly GIS. In the AC electrical breakdown, EMSC and EMAC decreased with increasing filler content, and EMSC showed better breakdown strength than EMAC. The mechanical properties such as tensile strength and flexural strength of EMSC and EMAC were also increased with increasing filler content. In addition, EMSC results in better mechanical properties than EMAC. The reason for this is considered to be one in which the influence of the interface is important.

• 콘크리트학회논문집
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• 제12권4호
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• pp.41-48
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• 2000

This study is to investigate for the frost resistance of high-strength concrete using finely ground granulated blast-furnace slag with experimental parameters, such as water/binder ratio, replacement proportion of granulated blast-furnace slag, air content and methods of curing. The high-strength concrete using granulated blast-furnace slag is effective to resist frost and decrease scaling. The more increasable replacement proportion of granulated blast-furnace slag is, the better the effect is. The high-strength concrete using granulated blast-furnace slag needs hydrating adequately to prevent deterioration by drying in the early curing period. The micro structure of high-strength concrete, increased to the pore number with diameter of 0.03~0.1mm, is changed by using granulated blast-furnace slag, but is presented differently according to water/binder ration and replacement proportion of granulated blast-furnace slag.