• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2002년도 추계학술강연 및 발표대회
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• pp.34-35
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• 2002

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2004년도 International Symposium on Powder Materials and Processing
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• pp.25-25
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• 2004

• 한국구조물진단유지관리공학회 논문집
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• 제23권6호
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• pp.18-25
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• 2019

콘크리트는 인장력에 취약한 재료적 특징을 갖기 때문에 콘크리트 구조물의 사용기간 중에 발생하는 균열은 내구성능 평가 시 필히 고려되어야 한다. 본 연구에서는 두 수준의 강도를 고려한 플라이애시 콘크리트를 배합하여 옥외 폭로 시험을 실시하였다. 노출 환경은 비말 조건으로 설정하였으며, 균열 폭이 콘크리트의 염화물 확산 거동에 미치는 영향을 평가하고자 각 배합의 시편에 0.1 mm 간격으로 최대 1.0 mm 까지의 균열 폭을 야기하였다. 그 후 3가지 수준의 노출기간(180일, 365일, 730일)을 고려하여 겉보기 염화물 확산계수 및 표면 염화물량을 산출하였다. 균열 폭의 증가에 따라 두 배합 모두 확산계수가 증가하였으며, 노출기간이 증가함에 따라 확산계수는 감소하였다. 또한 노출 기간이 증가함에 따라 균열 폭이 확산계수에 미치는 영향이 감소하였는데, 이는 염소 이온 기반 수화물이 콘크리트의 확산성을 저감시키기 때문으로 사료된다. 표면 염화물량 거동은 겉보기 염화물 확산계수 거동 대비 균열 폭의 증가에 따른 뚜렷한 변화 거동이 발생하지 않았으며, 고강도 배합에서 보통 강도 배합 대비 78.9 % ~ 90.7 %의 표면 염화물량을 나타내어 강도와의 상관관계를 갖는 것으로 판단된다.

• 한국지반공학회논문집
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• 제27권3호
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• pp.85-94
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• 2011

다양한 모래부피비($sf=V_{sand}/V_{total}$)를 가지는 시료를 조성하여 변형률 크기에 따른 모래-고무 혼합재($D_{sand}/D_{rubber}=1$)의 거동을 분석하였다. 공진주시험, 압밀시험, 그리고 직접전단시험을 실시하였다. 변형률 크기에 따라 모래와 고무는 혼합재 전체 거동을 서로 다르게 제어한다. $sf{\geq}0.4$의 혼합재는 비선형 전단강성의 감소가 관찰되는 반면, $sf{\leq}0.2$의 낮은 모래부피비를 가지는 혼합재는 상당히 높은 탄성한계변형률을 보인다. 고무 입자가 force chain의 역할을 수행할 때 수직변형은 급격한 증가를 보인다. 혼합재 내의 고무부피비가 감소함에 따라 혼합재의 강도는 증가하는 경향을 보이며 $sf{\leq}0.8$의 혼합재는 전단변형에 따라 부피 수축 거동을 보인다. 고무 입자는 변형률 크기에 따라 혼합재 내에서 서로 다른 역할을 수행한다: 미소변형률 영역에서는 혼합재 내의 접촉수 증가 및 소성의 제어; 중간변형률 영역에서는 force chain의 좌굴 방지; 그리고 대변형률 영역에서는 혼합재의 부피수축 거동을 이끈다.

• 한국구조물진단유지관리공학회 논문집
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• 제21권3호
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• pp.54-59
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• 2017

고로슬래그 미분말은 공학적으로 우수한 건설산업 부산물이며, 최근들어 환경부하 저감 및 사용 활성화를 위해 대단위 슬래그 치환 콘크리트가 많이 연구되고 있다. 본 연구에서는 목표 강도를 50 MPa로 설정하고 고로슬래그미분말 치환률을 65%로 고려한 대단위 치환 슬래그 콘크리트를 제조하여 건조수축특성과 초지재령 특성을 평가하였다. 이를 위해 3 수준의 콘크리트를 제조하였으며, 슬럼프 플로우, 강도, 건조 및 자기수축에 대한 실험을 수행하였다. 실험결과, 보통 포틀랜트 시멘트를 100% 함유한 콘크리트(OPC 100)에 비하여 재령 7일전의 강도는 약간 감소하였으나, 슬래그 치환 배합은 수화에 필요한 충분한 자유수를 가졌으므로 28일 재령에서는 우수한 강도 발현을 나타내었다. 또한 재령 3일까지 큰 자기수축으로 인하여, OPC 100 배합에서는 건조수축이 크게 평가되었지만, 65% 고로슬래그 미분말을 치환한 배합에서는 초기재령의 자기수축 성능이 개선되어 우수한 건조수축거동을 나타내었다. 특히 단순 질량 치환배합(BS 65)보다 물-결합재비(0.27)와 단위수량($163kg/m^3$)을 낮춘 OPTBS 65에서 더욱 우수한 건조수축 및 자기수축 거동을 나타내었다.

• 한국연소학회:학술대회논문집
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• 한국연소학회 제26회 KOSCO SYMPOSIUM 논문집
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• pp.65-73
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• 2003

An experimental study on flame lift-off characteristics of propane jet flame highly diluted with nitrogen has been conducted introducing acoustic forcing with a tube resonant frequency. A flame stability curve is attained according to forcing strength and nozzle exit velocity for $N_2$ diluted flames. Flame lift-off behavior with forcing strength and nozzle exit velocity is globally categorized into three; a well premixed behavior caused by a collapsible mixing for large forcing strength, a coexistent behavior of well-premixed and edge flames interacting with well-organized inner fuel vortices for moderate forcing strengths, and edge flame behavior for small forcing strengths. Special focus is concentrated on the coexistent behavior of the flame base in lifted flame since this may give a hint to a possibility which the flame base behaves like a well-mixed premixed flame in highly turbulent lifted flames. It is also shown that the acoustic forcing to self-pulsating laminar lifted flame affects flame lift-off behavior considerably which is closely related to downstream flow velocity, mixture strength, effective fuel Lewis number, and flame stretch.

• 대한기계학회논문집B
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• 제28권5호
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• pp.569-579
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• 2004

The lift-off characteristics of lifted laminar propane jet flames highly diluted with nitrogen are investigated introducing acoustic forcing with a fuel tube resonance frequency. A flame stability curve is obtained according to forcing strength and the nozzle exit velocity for N2 diluted flames. Flame lift-off behavior is globally classified into three regimes; 1) a weakly varying partially premixed behavior caused by a collapsible mixing for large forcing strength, 2) a coexistent behavior of the edge flame and a weakly varying partially premixed behavior for moderate forcing strength, and 3) edge flame or triple flame behavior for small forcing. It is shown that the laminar lifted flame with forcing affects flame lift-off behavior considerably, and is also clarified that the flame characteristic of flame base is well described with the penetration depth of the degree of mixing, ${\gamma}$$\_$$\delta$/. It is also confirmed that the weakly varying partially premixed flame caused by a collapsible mixing fur large forcing strength behaves as that just near flame blow-out in turbulent lift-off flame.

• 대한기계학회논문집B
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• 제26권8호
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• pp.1138-1144
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• 2002

Recently GDI(Gasoline Direct Injection) engine is spot-lighted to achieve higher thermal efficiency under partial loads and better performance at full loads. To realize this system, it is essential to make both stratified combustion and homogeneous combustion. Spray pattern must be optimized according to injection timing because ambient pressure in combustion chamber is varied with crank angle. In this experimental study, two types of visualization system such as laser scattering method and schlieren method were developed to clarity the spray behavior during on intake stroke. As the ambient pressure increases, thepenetration length and spray angle show a tendancy to decrease due to rising resistance caused by the drag force of the ambient air. Distribution of injected fuel on intake stroke has a significant effect on homogeneous mixture in the cylinder. These results provide the information on macroscopic wall-wet growth in the cylinder and design factors for developing GDI injector.

• 대한기계학회논문집B
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• 제26권4호
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• pp.614-621
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• 2002

This study was performed to investigate the behavior of vapor phase of fuel mixtures with different piston bowl shapes(F, B and R-type) in a optically accessible engine. The images of liquid and vapor phases were captured in the motoring engine using exciplex fluorescence method. Fuel was injected into atmospheric nitrogen to prevent quenching phenomenon by oxygen. Injection pressure was 5.1MPa. Two dimensional spray fluorescence image of vapor phase was acquired to analyze spray behaviors and fuel distribution inside of cylinder. Four injection timings were set at BTDC 90$^{\circ}$, 80$^{\circ}$, 70$^{\circ}$, and 60$^{\circ}$. With a fuel injection timing of BTDC 90$^{\circ}$, fuel-rich mixture level in the center region was highest in a B-type piston. With a fuel injection timing of BTDC 60$^{\circ}$, R-type piston was best. R-type piston shape was suitable under enhanced swirl ratio and late injection condition and B-type piston shape was right in a weak swirl ratio. It was found that the piston bowl shape affected the mixture stratification inside of cylinder.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집B
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• pp.915-920
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• 2001

This study was performed to investigate the behavior of vapor phase of fuel mixtures with different piston bowl shapes(F, B, and R-type) in a optically accessible engine. The images of liquid and vapor phases were captured in the motoring engine using exciplex fluorescence method. Fuel was injected into atmospheric nitrogen to prevent quenching phenomenon by oxygen. Injection pressure is 5.1MPa. Two dimensional spray fluorescence image of vapor phases was acquired to analyze spray behaviors and fuel distribution inside of cylinder. Four injection timings were set at BTDC $90^{\circ},\;80^{\circ},\;70^{\circ},\;and\;60^{\circ}$. With a fuel injection timing of BTDC $90^{\circ}$, fuel-rich mixture level in the center region was highest in a B-type piston. With a fuel injection timing of BTDC $60^{\circ}$, R-type piston was best. R-type piston shape was suitable under enhanced swirl ratio and late injection condition and B-type piston shape was right in a weak swirl ratio. It was found that the piston bowl shape affected the mixture stratification inside of cylinder.