• 수산해양기술연구
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• 제14권2호
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• pp.69-78
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• 1978

알루미나이징강에 대하여 초기마모영역에서 rolling-sliding 마모시험을 한 결과를 요약하면 다음과 같다. 1) 2차 확산재의 내마모성이 가장 우수하고 처녀재에 비하여 저응력 레벨에서 약 18%, 고응력에서 약 40%의 마모감소를 나타낸다. 2) 2차 확산재는 피복층과 합금층 경계부근의 공공생성으로 인하여 예상보다 내마모성이 낮다. 3) 알루미나이징강의 rolling-sliding 접촉에 의한 마모파양의 형태는 spalling 이며 spalling crack은 합금속의 경계부근에서 발생한다.

• Computers and Concrete
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• 제15권6호
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• pp.951-972
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• 2015

The focus of the present study is to investigate both local and global behaviour of a precast concrete sandwich panel. The selected prototype consists of two reinforced concrete layers coupled by a system of cold-drawn steel profiles and one intermediate layer of insulating material. High-definition nonlinear finite element (FE) models, based on 3D brick and 2D interface elements, are used to assess the capacity of this technology under shear, tension and compression. Geometrical nonlinearities are accounted via large displacement-large strain formulation, whilst material nonlinearities are included, in the series of simulations, by means of Von Mises yielding criterion for steel elements and a classical total strain crack model for concrete; a bond-slip constitutive law is additionally adopted to reproduce steel profile-concrete layer interaction. First, constitutive models are calibrated on the basis of preliminary pull and pull-out tests for steel and concrete, respectively. Geometrically and materially nonlinear FE simulations are performed, in compliance with experimental tests, to validate the proposed modeling approach and characterize shear, compressive and tensile response of this system, in terms of global capacity curves and local stress/strain distributions. Based on these experimental and numerical data, the structural performance is then quantified under various loading conditions, aimed to reproduce the behaviour of this solution during production, transport, construction and service conditions.

• Tribology and Lubricants
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• 제22권3호
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• pp.144-148
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• 2006

The experimental investigation was performed to find the associated changes in characteristics of fretting wear with various water temperatures. The fretting wear tests were carried out using the zirconium alloy tubes and the grids with increasing the water temperature. The tube materials in water of $20^{\circ}C,\;50^{\circ}C\;and\;80^{\circ}C$ were tested with the applied load of 20 N and the relative amplitude of $200{\mu}m$. The worn surfaces were observed by SEM, EDX analysis and 2D surface profiler. As the water temperature increased, the wear volume was decreased, but oxide layer was increased on the worn surface. The abrasive wear mechanism was observed at water temperature of $20^{\circ}C$ and adhesive wear mechanism occurred at water temperature of $50^{\circ}C,\;80^{\circ}C$. As the water temperature increased, surface micro-hardness was decreased, but wear depth and wear width were decreased due to increasing stick phenomenon. Stick regime occurred due to the formation of oxide layer on the worn surface with increasing water temperatures

• 대한기계학회논문집B
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• 제31권11호
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• pp.895-903
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• 2007

CMBT(Curved Moving Boundary Treatment) is a newly developed scheme for the treatment of a no slip condition on the curved solid wall of moving obstacle in a flow field. In our research CMBT was used to perform LBM simulation of a flow over a moving circular cylinder to determine the flow feature and aerodynamics characteristic of the cylinder. To ascertain the applicability of CMBT on the complex shape of the obstacle, it was first simulated for the case of the flow over a fixed circular cylinder in a channel and the results were compared against the solution of Navier-Stokes equation with deforming mesh technique. The simulations were performed in a moderate range of reynolds number at each moving cylinder to identify the flow feature and aerodynamic characteristics of circular cylinder in a channel. The drag coefficients of the cylinder were calculated from the simulation results. We have numerically confirmed that the critical reynolds number for vortex shedding is ar Re=250 and the result is the same as the case of fixed cylinder. As the cylinder approaching to one wall, the 2nd vortex is developed by interacting with the wall boundary-layer vorticity. As the velocity ratio increase the third vortex are generated by interacting with the 2nd vortexes developed on the upper and lower wall boundary layer. The resultant $C_d$ decrease as reynolds number increasing and the Cd approached to a value when Re>1000.

• 한국세라믹학회지
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• 제20권3호
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• pp.211-216
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• 1983

This work aims at characterizing silicon grains and its compacts. In order to remove iron silicon grains were washed with 5N hydrochloride at 60-7$0^{\circ}C$ for 170 hrs, and then followed the chemical analysis by atomic absorption spectrophotometer X-ray diffraction analysis SEM observation and specific surface area determination by B. E. T. Mixtures of graded silicon particles with two or three different sizes were made into packings by mechanical vibration. The mixtures were used to make compacts with 10 mm in diameter and 70mm in length by isostatically pressing at 1, 208 kg/$cm^2$ (20 kpsi) and 4, 255kg/$cm^2$ (60 kpsi) respectively. Bulk densities of packings and compacts were measured. A slip made of magnesium nitrate solution and fine silicon particles was spray-dried and then decomposed at 30$0^{\circ}C$ for the purpose of coating the uniform layer of magnesium oxide on the surface of particles. The results obtained are as follows: (1) About two thirds of iron content could be removed from silicon by washing silicon powders with hydrochloride. (2) Uniform layer of magnesium oxide on the surface of silicon could be prepared by spray-drying suspension and by decomposing it. (3) B. E. T. specific surface area of fine silicon particles was 2, 826.753$m^3$/kg. (4) In the binary system with two sizes of 40-53$\mu\textrm{m}$ particles and <10$\mu\textrm{m}$ particles the maximum bulk density of packing was 55% of theoretical value and that of compacts made at the pressure of 4, 255 kg./$cm^2$ (60 kpsi) was 73% of theoretical value. (5) In the ternary system with three sizes the maximum bulk density of packing was 1.43 g/$cm^3$and that of compacts was 1.80g/$cm^3$which is equivalent to 77.6% of theoretical value. The composition of the closest compact was consisted of 50% of 40-53$\mu\textrm{m}$ particles 20% of 10-30$\mu\textrm{m}$ particles and 30% of <10$\mu\textrm{m}$ parti-cles.

• Steel and Composite Structures
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• 제21권2호
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• pp.357-371
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• 2016

Column base connections are critical components in steel structures because they transfer axial forces, shear forces and moments to the foundation. Exposed column bases are quite commonly used in low- to medium-rise buildings. To investigate shear transfer in exposed column base plates, four large scale specimens were subjected to a combination of axial load (compression or tension) and lateral shear deformations. The main parameters examined experimentally include the number of anchor rod, arrangement of anchor rod, type of lateral loading, and axial force ratio. It is observed that the shear resisting mechanism of exposed column base changed as the axial force changed. When the axial force is in compression, the resisting mechanism is rotation type, and the shear force will be resisted by friction force between base plate and mortar layer. The specimens could sustain inelastic deformation with minimal strength deterioration up to column rotation angle of 3%. The moment resistance and energy dissipation will be increased as the number of anchor rods increased. Moreover, moment resistance could be further increased if the anchor rods were arranged in details. When the axial force is in tension, the resisting mechanism is slip type, and the shear force will be resisted by the anchor rods. And the shear resistance was reduced significantly when the axial force was changed from compression to tension. The test results indicated that the current design approach could estimate the moment resistance within reasonable acceptance, but overestimate the shear resistance of exposed column base.

• 한국지구과학회지
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• 제33권5호
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• pp.434-449
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• 2012

The Mesozoic leucocratic granite in the northeastern margin of the Taebaeksan Basin was transformed to protomylonite and mylonite. Mylonitic foliations generally strike to NWWNW and dip to NE with the development of a sinistral strike-slip (top-to-the-northwest) shear sense. Grain-size reduction of feldspar in the mylonitized leucocratic granite occurred due to fracturing, myrmekite formation and neocrystallization of albitic plagioclase along the shear fractures of K-feldspar porphyroclasts. As the deformation proceeded, compositional layering consisting of feldspar-, quartz- and/or muscovite-rich layers developed in the mylonite. In the feldspar-rich layer, fine-grained albitic plagioclase and interstitial K-feldspar were deformed dominantly by granular flow. On the other hand, quartz-rich layers containing core-mantle and quartz ribbons structures were deformed by dislocation creep. Based on calculations from conventional two-feldspar and ternary feldspar geothermometers, mylonitization temperatures of the leucocratic granite range from 360 to $450^{\circ}C$. It thus indicates that the mylonitization has occurred under greenschist-facies conditions. Based on the geochemical features and previous chronological data, the leucocratic granite was emplaced during the Middle Jurassic at volcanic arc setting associated with crustal thickening. And then the mylonitization of the granite occurred during the late Middle to Late Jurassic (150-165 Ma). Therefore, the mylonitization of the Jurassic granitoids in the Taebaeksan Basin was closely related to the development of the Honam shear zone.

• 한국세라믹학회지
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• 제33권6호
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• pp.700-708
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• 1996

TiO2 membranes for microfiltration were prepared on $\alpha$-alumina support tube by slurry coating. The coating layer was obtained by flowing TiO2 slip on the inner surface of the alumina support. TiO2 membranes were heat-treated at 9$25^{\circ}C$ for 2 hrs. The thickness of the unsupported membrane was about 10${\mu}{\textrm}{m}$. The mean pore diameter of the membranes were 0.09 and 0.15${\mu}{\textrm}{m}$ respectively and the pure water flux was 900~1,200ι/m2.hr at room temperature and 1 bar. For a possible application of oily wastewater treatement an kerosene/wa-ter emulsion was separated in terms of flux and removal efficiency. In 60 min of operating time the flux of TiO2 membranes was 50~100 ι/m2.hr and removal efficiency was over 97% at 3kgf/cm2 of operating pres-sure and 600 ml/min of flow rate. TiO2 membranes could be recycled by reheat treatments at $600^{\circ}C$ for 2 hrs.

• 한국지반신소재학회논문집
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• 제15권1호
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• pp.71-81
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• 2016

준설토 이송 시 윤활층에 전자기장을 인가하여 이송 동력을 절감하고, 송토량을 증가시키는 연구의 일환으로, 이런 전자기장 장치의 실제 적용성을 검증하고자 실현장 8.5km의 이송거리의 준설현장에 전자기장 장치를 설치하여 그 효과를 검증하였다. 이송 유속에 관계되는 운전 조건 및 토질상태와 유동상태를 모니터링하고, 획득한 데이터를 송토량과 동력 사이의 관계로 정리하여 전자기장 인가 후 약 30%의 동력대비 이송량 증가가 있음을 확인하였고, 이를 통해 전자기장 인가가 준설토 이송 시 동력절감에 효과가 있음을 확인하였다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2005년도 춘계 학술발표회 논문집
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• pp.49-56
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• 2005

The negative skin friction on piles, which are installed in currently consolidating soft deposits, creates significant problems on the stability of pile foundations. This study investigated whether or not the pile foundation designs were appropriate in soft deposits with large amount of consolidation settlement. The final settlements of the grounds along the pile depth were estimated by the soil parameters obtained from the laboratory tests and by the field-measured settlement curves, if they were available. The displacement of the piles along the pile depth was estimated by both the load transfer method and the numerical method. Both methods gave similar locations of neutral points and magnitudes of the maximum axial forces. The movements of the ground and the piles were compared to calculate the down drag acting on piles. For the piles whose bearing capacities were less than the design loads including the down drag, slip layer coatings and/or incrementing of the penetration depth into the bearing stratum were proposed to improve the piles capacities.