• Journal of Animal Environmental Science
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• v.14 no.1
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• pp.61-68
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• 2008

The roof structural model of liquid manure storage tank was designed to improve a structural safety and an ability of resistance to corrosion by the bad environmental condition with high humidity and high gas concentration. Due to corrosion of a general steel, the 5 years used materials were reduced to one-third of a new material in the result of a bending strength test. Some structural materials were tested to evaluate a strength and an anti-corrosion, and stainless steel pipe (STS439), steel angle with zinc hot dipping, rectangular steel pipe covered with FRP (Fiberglass Reinforced Plastics) resin were selected finally. A stainless steel is more expansive about $3{\sim}5$ times than general structural steel. But its durability under heavy corrosive environment is expected twice as long as general steel. The roof models were designed as closed cone type for each of the three structural materials. In the result of a FEM (Finite Element Method) structural analysis for the developed models, the safe snow depth was higher 2.3 times than a general roof structure, when elements of equal section modulus were used.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2018.06a
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• pp.116-116
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• 2018

부식은 재료와 사용 환경과의 상호작용에 의한 결과로서 일반적으로 두께의 감소와 균열의 발생 및 파손 등의 문제로 나타난다. 특히 사용환경 중에서 해수 분위기는 금속의 부식에 가장 유리한 조건이다. 따라서 해양환경 중 항만이나 조선 및 해양 산업 등에 많이 이용되는 강 구조물은 이에 대응하기 위하여 도장방식이나 음극방식을 사용하고 있다. 여기서 음극방식은 피방식체를 일정전위로 음극 분극하는 원리로써 외부전원을 인가하거나 비전위의 금속을 전기적으로 연결하여 방식하는 방법이다[1]. 한편, 해수 중에서 이와 같은 원리로 음극방식 할 경우에는 피방식체인 강재표면에 부분적으로 칼슘 또는 마그네슘 화합물 등의 생성물이 부착하는 현상을 볼 수 있게 된다. 이와 같이 수산화마그네슘($Mg(OH)_2$)및 탄산칼슘($CaCO_3$)을 주성분으로 하여 석출되는 석회질 피막(calcareous deposits)은 피방식체에 유입되는 음극방식 전류밀도를 감소시켜 주거나 물리적 장벽의 역할을 함으로써 외부의 산소와 물 등 부식환경으로부터 소지금속을 보호한다[2]. 그러나 석회질 피막은 소지금속과의 결합력, 막의 균일한 분포, 내식성 및 제작시간의 단축 등 해결해야 할 과제가 있다. 또한 여러 가지 환경 조건 등의 영향을 받아 그 피막의 형성 정도도 가늠하기 어렵기 때문에 음극방식 설계 시 그 정도에 따른 영향을 고려-반영하기가 곤란하다. 따라서 본 연구에서는 석출속도, 밀착성 및 내식특성을 향상시키기 위해 전착프로세스를 통해 해수 중 기체를 용해시켜 석회질 피막을 제작하고 막의 결정구조 제어 및 특성을 분석-평가하였다. 본 연구에 사용된 강 기판(Steel Substrate)은 일반구조용강(KS D 3503, SS400)을 사용하였으며, 외부전원은 정류기(Rectifier, xantrex, XDL 35-5T)를 사용하여 3 및 $5A/m^2$의 조건으로 인가하였다. 양극의 경우에는 해수에 녹아있는 이온 이외에 다른 성분들이 환원되는 것을 방지하기 위해 불용성 양극인 탄소봉(Carbon Rod)을 사용하였다. 이때 석출속도, 밀착성 및 내식특성 향상을 위해 해수에 주입한 기체의 양은 0.5 NL/min였으며, 기판 근처에 고정하여 음극 부근에서의 반응을 유도하였다. 각 조건별로 제작된 막의 표면 모폴로지, 조성원소 및 결정구조 분석을 실시하였으며, 석회질 피막의 밀착성과 내식특성을 평가하기 위해 규격에 따른 테이핑 테스트(Taping Test, ISO 2409)와 3 % NaCl 용액에서 전기화학적 양극 분극 시험을 진행하여 제작된 막의 내구성과 내식성을 분석-평가하였다. 시간에 따른 전착막의 외관관찰 결과 전류밀도의 증가와 함께 상대적으로 많은 피막이 형성되었고, 용해시킨 기체에 의해 더 치밀하고 두터운 피막이 형성됨을 확인할 수 있었다. 성분 및 결정구조 분석 결과 $Mg(OH)_2$ 성분의 Brucite 및 $CaCO_3$ 성분의 Calcite 및 Aragonite 구조를 확인하였으며, 용해시킨 기체의 영향으로 $CaCO_3$ 성분의 Aragonite 구조가 상대적으로 많이 검출되었다. 밀착성 및 내식성 평가를 실시한 결과 해수 중 용해시킨 기체에 의해 제작한 시편의 경우 견고하고 화학적 친화력이 높은 Aragonite 결정이 표면을 치밀하게 덮어 전해질로부터 산소와 물의 침입을 차단하는 역할을 하여 기체를 용해시키지 않은 3 및 $5A/m^2$ 보다 비교적 우수한 밀착성 및 내식 특성을 보이는 것으로 사료된다.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.43 no.1
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• pp.9-20
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• 2023

For highway concrete structures, the deterioration of the structure is accelerated due to the increase in the use of deicing materials, and sectional repair work is being frequently carried out to restore performance. However, after the repair work, re-damage such as cracks, delamination, and poor bond performance is exhibited in the repaired sectional area. In this study, overseas repair material requirements were first analyzed, and present domestic requirements were improved repair material performance through field surveys of common concrete structures, laboratory experiments, and test construction on a disused concrete bridge. In addition, performancebased quality requirements were presented so that all materials that meet the required performance can be applied, and different test methods for each material were unified into concrete test methods for consistent test results analysis. The considered performance requirements were compression strength, bending strength, and bond strength for structural properties, and length change rate, crack resistance, thermal expansion coefficient, and elasticity coefficient were for dimensional behavior. For resistance to chloride penetration resistance and freeze-thaw resistance were presented as durability. The proposed requirements for concrete repair materials are expected to contribute to the improvement of the quality of concrete sectional repair work in Korea.

• Journal of the Korean Society of Marine Environment & Safety
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• v.29 no.6
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• pp.704-711
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• 2023

This paper discusses the control method of BLDC(Brushless Direct Current) motor that has similar electrical characteristics with DC motor but has improved its lifespan and reliability. The BLDC motor can improve durability and speed stability by using rotor position information to eliminate commutators that require mechanical contact with DC motors. In this study, a controller for a DC motor was designed based on the fact that the current in the windings of a BLDC motor is a square-wave current like the current flowing in the armature of a DC motor. Next, the designed controller was applied to a 3-phase BLDC motor to confirm the effectiveness of the controller. In detail, a single-phase DC motor with electrical parameter values of a three-phase BLDC motor was modeled and a PI controller for motor speed control was designed by applying the root locus method to the derived system. The speed control simulation of the DC motor was performed to confirm the validity of the controller, and the same controller was applied to the speed control of the 3-phase BLDC motor implemented in MATLAB. From the simulation, similar results of the DC motor were obtained in the 3 phase BLDC motor and confirmed the usefulness of the proposed control scheme.

• Journal of the Korea Concrete Institute
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• v.21 no.6
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• pp.689-696
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• 2009

In this study, electro-deposition method was applied to heal cracks in various blended concrete. The performance of the method was indirectly monitored by measuring impressed voltage, electrolyte, galvanic current monitoring, linear polarization resistance, and directly by image analysis of the cracks. The indirect and direct monitoring values are compared to develop guidelines for relating the indirect measures to actual crack healing. As a result, It was found that impressed voltage was convergence to 2.9V after 20000 minutes. From the galvanic current test results of artificial crack healing, the corrosion resistance showed that the order of 0.4 $>$ 0.6 $>$ 0.5 water to cement ratio. Furthermore, in view of binder, the corrosion resistance order was calculated OPC $>$ 60%GGBS $>$ 10%SF $>$ 30%PFA. Finally, It was found that 76.47% of healed crack surface calculated from the artificial crack healing technique using electrochemical deposition method.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.353-356
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• 2008

UHPC which was a structural material exhibiting very remarkable mechanical performances with compressive strength, tensile strength and flexural strength rising up to 200MPa, 15MPa and 35MPa, respectively. In addition, this material presents exceptional durability regard to the very low diffusion and penetration speeds of noxious substances like chloride ions This study was carry out to evaluate the effect of flexural behavior according to steel fiber type in UHPC. The results is showing that the steel fiber type have remarkable influence flexural strength Addition to it is showing that steel fiber type made little difference in the first cracking strength but considerable gap in the ultimate flexural strength to use the steel fiber of wave type.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.357-360
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• 2008

UHPC which was a structural material exhibiting very remarkable mechanical performances with compressive strength, tensile strength and flexural strength rising up to 200MPa, 15MPa and 35MPa, respectively. In addition, this material presents exceptional durability regard to the very low diffusion and penetration speeds of noxious substances like chloride ions This study was carry out to evaluate the effect of flexural behavior according to placement method in UHPC. The results is showing that the placement methods have remarkable influence flexural strength Addition to it is showing that the placement methods made little difference in the first cracking strength but considerable gap up to 2 or 3 times in the ultimate flexural strength.

• Elastomers and Composites
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• v.47 no.1
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• pp.65-74
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• 2012

Recently, the need of developing eco-friendly materials has been required with restriction strengthening on environment and energy saving by the resource depletion worldwide. These trends are not an exception in transport industry including automobile. In addition, these materials have to fulfill not only the high quality and cheap price but also the high-performance which meet the needs of costumer and society. Among the various materials, carbon fiber-reinforced composite which is actively studying for lightweight of the automobile is one of the most suitable candidates. Indeed, the carbon fiber-reinforced composites are used as the essential materials to substitute body and other parts in automobile and the demand is increasing largely. Carbon fiber-applied automobile has improved brake, steering, durability and high fuel efficiency, leading to the energy conservation and minimizing carbon dioxide emissions. This paper focuses on the necessity of carbon fiber-reinforced composites for lightweight of automobile and its technical trends.

• Journal of the Korean Wood Science and Technology
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• v.40 no.6
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• pp.418-423
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• 2012

In order to develop the end use of cylindrical laminated veneer lumber (LVL) such as wooden crafts, the water proof-bonding strength, the resistance to abrasion and the surface hardness by painting the surface of LVL were investigated. The study results were as follows; The water proof-bonding strength through 5 cyclic test by boiling in water immersion and drying were favorable without delamination of glue line. Then the formulation of glue was resorcinol resin (100) to hardener of paraformaldehyde (5) by mixed weight percentage. The resistance to abrasion was relatively higher at cross section than tangential section. When tangential section of LVL was painted by UV protection oil, the resistance to abrasion was improved. In case of an cross section of LVL, the higher surface hardness appeared at larch core than radiata pine LVL. Also, in case of an tangential section of LVL, the higher surface hardness appeared at glue line than veneer side.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2016.11a
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• pp.143-143
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• 2016

알루미늄 합금은 내구성과 내식성이 우수할 뿐만 아니라 다양한 표면개질을 통해 그 표면 특성을 더욱 향상시킬 수 있다. 특히 Al-Mg계 5083-H321 Al 합금의 경우 가공성 및 용접성이 우수하여 선체 재료로 널리 이용되는데, 이는 선체중량의 경량화가 가능하여 연료비 절감과 빠른 선속 등 다양한 이점을 지니기 때문이다. 그러나 선속의 고속화에 따라 선체에 가해지는 유체충격이 증가하고 정압 저하에 기인하여 캐비테이션-침식 손상이 증가할 뿐만 아니라 해수환경 특성 상염소이온의 존재로 부식이 가속화되는 등 침식 및 부식의 시너지효과로 손상은 크게 증가한다. 이에 대한 방지대책으로 다양한 표면개질 기법이 제안되고 있으나 강한 충격압이 동반된 캐비테이션 침식-부식 복합 손상 환경에서는 표면처리만으로는 불가능할 수 있다. 따라서 본 연구에서는 양극산화된 5083-H321을 대상으로 캐비테이션 환경 하에서 일정 전위를 인가하여 침식-부식 손상이 최소화되는 최적전위를 규명하고자 한다. 이를 위해 먼저 분극 실험을 통해 재료의 전기화학적 거동을 바탕으로 임의의 전위를 선정하고 해당 전위를 인가한 상태에서 캐비테이션 실험을 실시하였다. 이때 분극실험과 캐비테이션-전기화학 복합실험 모두 $25^{\circ}C$의 해수에서 실시하였으며, 전기화학적 분극실험은 유효면적이 $3.24cm^2$인 시편에 2 mV/s의 분극속도로 0 ~ -3 V 까지 인가하였고, Ag/AgCl 기준전극과 백금대극을 사용하였다. 캐비테이션-전기화학 복합 실험은 정전위를 인가한 상태에서 $30{\mu}m$의 진폭으로 20분간 실시하였으며, 혼팁과 시험편 사이의 거리는 1 mm로 일정하게 유지하였다. 실험 후 표면 손상의 정량적 분석을 위해 인가된 전위별 전류밀도를 비교하고, 무게감소량을 측정하였으며, 손상특성 분석을 위해 3D현미경과 주사전자현미경(SEM)을 통해 표면을 분석하였다.