• Proceedings of the Korean Vacuum Society Conference
• /
• 2011.02a
• /
• pp.45-45
• /
• 2011

알루미늄과 그 합금은 내부식성(corrosion resistance)이 좋고, 밀도가 낮아 높은 연료소비 효율을 필요로 하는 항공기와 자동차 같은 운송수단의 내-외장 소재로 사용되고 있다. 또한 알루미늄의 높은 내부식성을 이용하여 철강소재의 부식을 방지하는 보호막으로도 폭 넓게 사용된다. 물리기상증착(physical vapor deposition)으로 알루미늄을 코팅하면 박막 성장 초기단계에서 핵(nucleus)을 형성하고, 형성된 핵을 중심으로 주상 구조(columnar structure)로 박막이 성장하는 것이 일반적으로 알려진 방식이다. 주상 구조의 알루미늄 박막은 주상정과 주상정 사이에 필연적으로 공극(pore)이 존재하게 되어 부식을 일으키는 물질이 박막으로 침투하게 되고, 부식 물질과 모재가 반응하여 공식(pitting corrosion)이 발생한다. 본 연구에서는 스퍼터링(magnetron sputtering)을 이용하여 치밀한 조직을 갖는 알루미늄 박막을 코팅할 수 있는 공정을 개발하고, 치밀한 알루미늄 조직이 내부식성에 어떠한 영향을 미치는지 평가하였다. 기판은 냉연강판(cold rolled steel sheet)이 사용되었으며, 알루미늄 타겟의 순도는 99.999%, 크기는 직경 4"이었다. 냉연강판은 진공용기(vacuum chamber)에 장착하기 전에 계면활성제를 이용하여 표면에 존재하는 기름성분을 제거하였으며, 진공용기에 장착한 후에는 아르곤 가스를 이용하여 발생시킨 글로우 방전으로 표면에 존재하는 산화물을 제거하였다. 알루미늄 박막의 조직에 영향을 미치는 공정변수를 확인하기 위해서 스퍼터링 파워, 공정 온도, 공정 압력, 외부 자기장 세기 등의 공정 조건을 변화시켜 코팅을 실시하였다. 실험을 통해서 얻어진 최적 조건으로 알루미늄을 코팅할 경우, 알루미늄 bulk의 밀도와 비교하여 약 94.7%의 밀도를 갖는 알루미늄 박막을 코팅할 수 있었다. 알루미늄 박막이 약 3 ${\mu}$m의 두께로 코팅된 냉연강판의 내부식성 평가(salt spray test, 5% NaCl) 결과, 평가를 시작한 후 72시간 후에도 적청이 발생하지 않았다.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2015.10a
• /
• pp.1109-1112
• /
• 2015

A milatary ship without degaussing coil has a vertical magnetization to compensate magnetization induced by the vertical magnetic field component of earth magnetic field during demagnetization process. Flash D is very useful to acquire vertical magnetization. However this is hard to predict vertical magnetization. This experiment was investicated on another method, which used the only vertical bias magentic field. The specimens were prepared by thin Zn coated steel sheet with a thickness of 0.15mm. The shapes of 3 specimes was rectangular, triangular and circular cylinders. These shapes were corresponded to the shapes of bow, mid and stern of a vessel. Through FEM analysis, the difference of magnetic signatures for these specimens was recognized and the residual magnetization curve was measured. magnetic field was generated by a solenoid coil and magnetic signature was measured by a magnetic field sensor. A linearity between a vertical bias magnetic field and a vertical manetzation existed and the vertical magnetization of a miltary vessel was predicted by the linearity.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2009.05a
• /
• pp.266-269
• /
• 2009

Iron-based soft magnetic materials are widely used as cores, such as transformer transformers, motors, and generators. Reducing losses generated from soft magnetic materials of these applications results in improving energy conversion efficiency. Recently, the new P/M soft magnetic material realized an energy loss of 68 W/kg with a drive magnetic flux of 1 T, at a frequency of 1 kHz, rivaling general-purpose electromagnetic steel sheet in the low frequency range of 200 Hz to 1 kHz. In this research, the effect of rolling parameters on soft magnetic properties of Fe-based powder cores was investigated. The Fe-based soft magnetic plates were produced by the hot powder rolling process after both pure Fe and Fe-4%Si powders were canned, evacuated, and sealed in Cu can. The soft magnetic properties such as energy loss and coercive power were measured by B-H curve analyzer. The soft magnetic properties of rolled sheets were measured under conditions of a magnetic flux density of 1 T at a frequency of 200 kHz. It was found that rolling reduction ratio is the most effective parameter on reducing both energy loss and coercivity because of increasing aspect ratio with reduction ratio. By increasing aspect ratio from 1 to 9 through hot rolling of pure Fe powder, a significant loss reduction of one-third that of SPS sample was achieved.

• Journal of the Korea Concrete Institute
• /
• v.23 no.3
• /
• pp.385-392
• /
• 2011

In this study, experimental research was carried out to evaluate and improve the seismic performance of reinforced concrete beam-column joint regions using strengthening materials (steel plate, carbon fiber sheet, and embedded carbon fiber rod) in existing reinforced concrete buildings. Six specimens of retrofitted beam-column joints are constructed using various retrofitting materials and tested for their retrofit performances. Specimens designed by retrofitting the beam-column joint regions (LBCJ series) of existing reinforced concrete building showed a stable mode of failure and an increase in load-carrying capacity due to the effect of crack control at the time of initial loading and confinement from retrofitting materials during testing. Specimens of LBCJ series, designed by the retrofitting of FRP in reinforecd beam-column joint regions increased its maximum load carrying capacity by 26~50% and its energy dissipation capacity by 13.0~14.4% when compared to standard specimen of LBCJC with a displacement ductility of 4.

• Structural Engineering and Mechanics
• /
• v.44 no.6
• /
• pp.839-856
• /
• 2012

To enable remodeling of the exterior of buildings more convenient, such finishing materials as curtain walls, metal panels, concrete panels or dry stones need to be easily detached. In this respect, this study proposed a new design of the slab for the purposes. In the new design, the sides of the slab were properly modified, and the capabilities of anchors fixed in the modified slab were experimentally tested. In details, a number of concrete specimens with different sizes and compressive strengths were prepared, and the effect of anchors with different diameters and embedment depths applied in the concrete specimens were tested. The test results of the maximum capacities of the anchors were compared with the number of current design codes and the stress distribution was identified. This study found that the embedment depth specified in the current design code (ACI318-08) should be revised to be more than 1.5 times the edge distance. However, with the steel sheet reinforcement, the experiment acquired higher tensile strength than the design code proposed. In addition, for two types of specimens in the tensile strength experiment, the current design code (ACI 318-08) is overestimated for the anchor depth of 75 mm. This study demonstrated that the ideal breakout failure was attainable for the side slot details of a slab with more than 180 mm of a slab thickness and less than 75 mm of an anchor embedment depth. It is expected that these details of the modified slab can be specified in the upgraded construction design codes.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
• /
• v.22 no.12
• /
• pp.47-55
• /
• 2008

According to the increase of power demand and expansion of downtown, it is necessary to install transformers additionally in operating substations and construct substations in residential area. But the public complaint has been increased due to the transformer noise of the substation. KEPCO has used a vibration preventing pad, various soundproof walls and an enclosure to transformers in outdoor substations, and a soundproof door, shutter and wind-path soundproof equipment in indoor substations to block the sound propagation from the transformers. But these noise reduction methods are not satisfied. It should be considered to reduce transformer noise itself. To shut out sound emitted from transformers, we developed a soundproof technology that wall up reinforcing bar by steel sheet. For the practical application of it, we analyzed the vibration characteristics of a transformer tank and reduction of noise according to soundproof plate. As a result, it is confirmed that the technology can reduce 11 [dB] of transformer noise.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.1 no.1
• /
• pp.23-26
• /
• 2000

In spot welded joint. Electronic Speckle Pattern Interferometry(ESPI) method using the Model 95 Ar laser a video system and an image processor was applied to measure the stress Unlike traditional strain gauges or Moire method, ESPI method has no special surface preparation or attachments and can be measured in-plane displacement with non-contact and real time. In this experiment, specimens are loaded in parallel with a load cell. The specimens are made of the cold rolled steel sheet with 1mm thickness, are attached strain. gauges. This study Provides an example of how ESPI has been used to measure stress and strain inspecimen. The results measured by ESPI are compared with the data which was measured by strain gauge method under tensile testing.

• Journal of the Korean Vacuum Society
• /
• v.9 no.3
• /
• pp.207-215
• /
• 2000

Al films on cold-rolled steel sheet have been prepared by vacuum evaporation and arc-induced ion plating, respectively, and the evaporation rate and vapor distribution (thickness distribution over the substrate) have been investigated according to deposition conditions. The arc-induced ion plating (AIIP) method have been employed, which makes use of arc-like discharge current induced by ionization electrode located near the evaporation source. The AIIP takes advantage of high ionization rate compared with conventional ion plating, and can be carried out at low pressure of less than $10^{-4}$ torr. Very high evaporation rate of more than 2.0 mu\textrm{m}$/min could be achieved for Al evaporation using alumina liner by electron beam evaporation. The geometry factor n for the $cos^{n/\phi}$ vapor distribution, which affects the thickness distribution of films at the substrate turned out to be around 1 for vacuum evaporation, while it features around 2 or higher for ion plating. For the ion plated films, it has been found that the ionization condition and substrate bias are the main parameters to affect the thickness distribution of the films.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.36 no.9
• /
• pp.1081-1086
• /
• 2012

This study deals with hardness evaluation for spot welding by using an instrumented indentation technique to improve the quality of the inspection methodology. First, an instrumented indentation test and a Rockwell hardness test were performed for normal and abnormal spot welding. The hardness to indentation force-displacement curve obtained using each of the tests was compared. Furthermore, an analysis was conducted using the hardness obtained by the instrumented indentation technique. A quality control standard based on reliability was this evaluated for spot welding.

• Journal of the Korean Institute of Gas
• /
• v.8 no.2 s.23
• /
• pp.54-60
• /
• 2004

In this paper, the maximum von Mises stress and maximum displacement of the corner protection and secondary bottom structures have been analyzed using a finite element analysis technique. The design criterion of the comer protection is 1,500Pa for a normal nitrogen gas purging process at the beginning stage of start-up procedure. This pressure is very safe for the structure safety of the comer protection and secondary bottom plates. The corner protection and secondary bottom plates fabricated by $9\%$ nickel steel sheet may plastically be distorted and fractured for the increased gas pressure of 8,475Pa, which produces the maximum von Mises stress of 833MPa and maximum displacement of 1.9m at the center of secondary bottom plate.