• 한국신뢰성학회:학술대회논문집
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• 한국신뢰성학회 2004년도 정기학술대회
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• pp.335-342
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• 2004

The failures such as flaking, wear, crack and seizing caused by the high contact pressure accompanied with sliding motion between inner or outer ring and ball are potential failures of ball bearing. In this research, we have qualitatively selected the efficient test items through the analysis of the life and potential failures of ball bearing. The bearing's failures are related closely to the whole system in using the bearing. So, the bearing itself requires an estimation of life in order to opreate the system safely. We have tested ten ball bearings. Our research has applied both radial and axial direction force of maximum torque conditions simultaneously for the accelerated life testing. The result is established by employing the weibull plot and compared the predicted life of ball bearing to the experimental result.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2006년도 추계 학술발표회 논문집
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• pp.253-256
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• 2006

The HPFRCCs show the multiple crack and damage tolerance capacity due to the interfacial bonding of the fibers to the cement matrix. For practical application, it is needed to investigate the fractural behavior and of HPFRCCs and understand the micro-mechanism of cement matrix with reinforcing fiber. The objectives of this paper are to examine the compressive behavior, fracture and damage process of HPFRCC by acoustic emission technique. Total four series were tested, and the main variables were the hybrid type, polyethylene (PE) and steel cord (SC), and fiber volume fraction. The damage progress by compressive behavior of the HPFRCCs is characteristic for the hybrid fiber type and volume fraction. And from acoustic emission (AE) parameter value, it is found that the second and third compressive load cycles resulted in successive decrease of the ring-down count rate as compared with the first compressive load cycle.

• Tribology and Lubricants
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• 제34권5호
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• pp.197-207
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• 2018

Thermal deterioration of fuel due to long-term storage influences engine performance and causes malfunctions. Fuel stability is usually evaluated via heat resistance and thermal stability during a brief heat shock at high temperature; storage stability in this scenario means that there is very little change in the quality of the fuel during long-term storage. In addition, rubber-based products such as oil seals, O-rings, and rubber hoses can influence the quality of the fuel. When these rubber products are in contact with fuel, they can swell, mechanically weaken, and occasionally crack, thus leaking low molar weight rubber and additives including plasticizer and antioxidant into the fuel to degrade its properties and shorten its useful lifetime. This study determines the thermal stabilities of three kinds of synthetic fuels by evaluating their low temperature kinematic viscosities, chemical composition changes via GC analyses, gross heat of combustion, and color changes. We evaluate the compression set of O-rings by immersing one NBR and two FKM rubber O-rings in the three synthetic fuel samples in airtight containers at variable storage temperatures for six months; from this, we estimate the lifetimes of the O-rings using the Power law model. There were very little changes in the chemical compositions and gross heat of combustion after six months of the experiment. The lifetimes are thus dependent on the materials of the rubber products, and in particular, the FKM O-ring was calculated to have a theoretical lifetime of 200 to 5,700 years. These results indicate that the synthetic fuels maintain their physical properties even after long-term storage at high temperatures, and the FKM O-ring is suitable for long-term sealing of these fuels.

• 한국전산구조공학회논문집
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• 제29권5호
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• pp.483-490
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• 2016

플랜트의 유황 저장 탱크는 강재로 구성되며, 탱크 저면은 앵커볼트에 의해 Ring Wall 형상의 콘크리트 기초와 연결된다. 탱크 내 유황이 내부 열원에 의해 고온상태를 유지하기 때문에, 유황 저장 탱크는 상온의 유체를 저장하는 다른 탱크에 비해 큰 체적팽창을 겪게 된다. 일반적으로 탱크 기초의 구조설계는 기초의 내외부의 온도차를 하중으로 적용한 구조해석이 수행되는데, 이 방법은 탱크의 열팽창 특성이 앵커볼트에 의해 집중하중 형태로 콘크리트 기초에 전달되는 현상을 고려할 수 없다. 이는 온도하중의 영향을 과소평가하게 되며, 앵커볼트에 인접한 콘크리트의 균열을 야기한다. 본 연구는 앵커볼트에 의한 온도 하중전달 메커니즘을 고려한 하중 평가식을 제안함으로써, 콘크리트 기초에 작용하는 하중을 보다 합리적으로 결정하고자 한다. 이를 위해 탱크 바닥판과 앵커볼트가 포함된 유한요소모델을 이용해 앵커볼트 개수 증감에 따른 온도하중의 변화를 분석하였으며, 분석결과를 이론해와 결합해 앵커볼트에 의해 전달되는 하중을 평가할 수 있는 명시적인 형태로 해를 제시하였다. 제안된 식의 유효성을 확인하기 위해 실제 플랜트 현장의 유황 저장 탱크 설계에 적용하였으며, 실무적으로 사용 가능함을 보였다.

• 콘크리트학회논문집
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• 제21권4호
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• pp.523-530
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• 2009

콘크리트를 설계하기 위해 설계자는 설계의 효율성을 위하여 일축휨강도에 기초한 설계를 하고 있지만, 포 장체 및 바닥판과 같은 실제 구조요소의 응력상태는 재료전반에 작용하는 이축응력이 발생하게 된다. 따라서 콘크리트 의 이축휨시험은 사용하중상태에서 콘크리트의 거동을 평가할 수 있는 중요한 설계인자로서 사용될 수 있다. 이 연구 에서 저자들은 콘크리트 이축휨강도를 평가할 수 있는 BFT 시험법의 최적 구성을 제안하였다. 이 기법은 세라믹 또는 바이오 재료 분야에서 사용되어온 링온링 시험법을 콘크리트 재료에 적합하도록 수정, 제시한 것이다. 이를 위하여 유 한요소해석과 정밀해에 대한 분석을 통하여 시험체의 형상과 시험법을 제시하였다. 제안된 방법에 의한 실험 결과, 이 축휨실험을 통하여 콘크리트 재료의 휨강도를 충분히 판정할 수 있는 것을 증명할 수 있었다.

• Journal of Advanced Marine Engineering and Technology
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• 제22권2호
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• pp.139-145
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• 1998

Filament winding method is widely used for composite fabrications using low viscosity liquid for-mation and processing asymmetrical structures of pressure vessel pipe rocket motor case etc. The filament winding method is affected by several parameters such as pot life of process time viscosi-ty of resin filament winding temperature and schedules curing condition and post curing condi-tion of resin. To develope high functional composite materials the rotation(5, 15, 20, 30rpm) of the winding machine was controlled by D.C motor. And the wiper to give proper tension was equipped between strand and resin bath. The resin is hooked by the design wiper. The adequate cure schedule was found by DSC. NOL ring test is carried out to investigate the basic physical properties such as design technology. The void contents in filament winding is generally higher than that of the prepreg laminated plate. These high contents of void can make a crack in resin in spite of low deformation. These problem was solved by giving tension in processing. To improve the characteristics of fiber volume fraction void contents resin/fiber bonding the winding speedc is changed under constant tension. It was found that resin impregnation was not different from in fiber contents void contents at the range of 0.5~1kg tension but it was found that resin was not impregnated at the above of 1.5kg tension. In burst test a pure PE liner was failed at a nozzle part under the $14kg/\textrm{cm}^2$ pressure but a pressure vessel of CNG was failed at a cylinder part under the $200kg/\textrm{cm}^2$ pressure.

• Advances in concrete construction
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• 제14권2호
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• pp.93-102
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• 2022

In this study, limestone powder (LS) and fly ash (FA) were used as powder materials in self-compacting concrete (SCC) in increasing quantities in addition to cement, so that the two powders commonly used in the production of SCC could be compared in the same study. Considering the reduction of the maximum aggregate size in SCC, 10 mm or 16 mm was selected as the coarse aggregate size. The properties of fresh concrete were determined by slump flow (including T₅₀₀ time), V-funnel and J-ring experiments. The experimental results showed that as the amount of both LS and FA increased, the slump flow also increased. The increase in powder material had a negative effect on V-funnel flow times, causing it to increase; however, the increase in FA concretes was smaller compared to LS ones. The increase in the powder content reduced the amount of blockage in the J-ring test for both aggregate sizes. As the hardened concrete properties, the compressive and splitting strengths as well as the modulus of elasticity were determined. Longitudinal and transverse deformations were measured by attaching a special frame to the cylindrical specimens and the values of Poisson's ratio, initiation and critical stresses were obtained. Despite having a similar W/C ratio, all SCC exhibited higher compressive strength than NVC. Compressive strength increased with increasing powder content for both LS and FA; however, the increase of the FA was higher than the LS due to the pozzolanic effect. SCC with a coarse aggregate size of 16 mm showed higher strength than 10 mm for both powders. Similarly, the modulus of elasticity increased with the amount of powder material. Inelastic properties, which are rarely found in the literature for SCC, were determined by measuring the initial and critical stresses. Crack formation in SCC begins under lower stresses (corresponding to lower initial stresses) than in normal concretes, while critical stresses indicate a more brittle behavior by taking higher values.

• 멤브레인
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• 제20권1호
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• pp.62-68
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• 2010

Cermet 분리막 제조를 위한 혼합 분말은 60 vol.% vanadium과 $Y_2O_3$-stabilized $ZrO_2$ (YSZ)를 기계적으로 혼합하여 준비하였다. 혼합 분말을 원판으로 압축한 후 진공 분위기에서 $1600^{\circ}C$로 2시간동안 소결하였다. 소결 분리막은 치밀하였고, 브레이징 필러를 이용하여 스테인레스 링에 장착되었다. V/YSZ 분리막의 수소 투과량은 100% 수소를 흘려 $200{\sim}350^{\circ}C$ 범위에서 측정되었다. $350^{\circ}C$, 0.5 bar압력에서 분리막의 양 표면에 균열이 형성되었다. 투과실험 동안에 V/YSZ 분리막의 vanadium은 수소와 반응하여 $V_2H$를 생성하였으며, 이로 인해 분리막이 균열되는 것을 알 수 있었다.

• Steel and Composite Structures
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• 제27권5호
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• pp.577-598
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• 2018

The imperfect steel-concrete interface bonding is an important deficiency of the concrete-filled double skin tubular (CFDST) columns that led to separating concrete and steel surfaces under lateral loads and triggering buckling failure of the columns. To improve this issue, it is proposed in this study to use longitudinal and transverse steel stiffeners in CFDST columns. CFDST columns with different patterns of stiffeners embedded in the interior or exterior surfaces of the inner or outer tubes were analyzed under constant axial force and reversed cyclic loading. In the finite element modeling, the confinement effects of both inner and outer tubes on the compressive strength of concrete as well as the effect of discrete crack for concrete fracture were incorporated which give a realistic prediction of the seismic behavior of CFDST columns. Lateral strength, stiffness, ductility and energy absorption are evaluated based on the hysteresis loops. The results indicated that the stiffeners had determinant role on improving pinching behavior resulting from the outer tube's local buckling and opening/closing of the major tensile crack of concrete. The lateral strength, initial stiffness and energy absorption capacity of longitudinally stiffened columns with fixed-free end condition were increased by as much as 17%, 20% and 70%, respectively. The energy dissipation was accentuated up to 107% for fixed-guided end condition. The use of transverse stiffeners at the base of columns increased energy dissipation up to 35%. Axial load ratio, hollow ratio and concrete strength affecting the initial stiffness and lateral strength, had negligible effect of the energy dissipation of the columns. It was also found that the longitudinal stiffeners and transverse stiffeners have, respectively, negative and positive effects on ductility of CFDST columns. The conclusions, drawn from this study, can in turn, lead to the suggestion of some guidelines for the design of CFDST columns.

• 대한조선학회논문집
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• 제47권1호
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• pp.67-75
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• 2010

Submarine and deep sea diving structures are generally designed based on their ultimate strength. Fatigue strength at welded joint must be also taken into account because working stress is increased due to the increasing of diving depth and using high yield steel. The pressure hulls of submarine are subjected to fluctuating compressive loading. But in addition to the calculated stresses, high residual tensile stresses at welded part have to be considered. The state of stress level of pressure hull is tensile at surface and compressive at deep diving depth. This paper presents the results of an experimental investigation on the crack initiation and growth at the weld toe of T welded joints of HY-100 steel plate under constant amplitude loading. It is also investigated the phenomenon of the fatigue failure and test methods. Fatigue tests have been using real scaled local structural models of full penetration T-welded joint, which is a part of the cylindrical shell structures reinforced by ring stiffeners. Several load ratios under constant amplitude loading are considered in the tests. Crack initiation and growth characteristics are examined based on the beach marks of the cracked section of the test specimens. A design stress-life curve including the design formula is suggested according to tested data.