• 한국건축시공학회:학술대회논문집
• /
• 한국건축시공학회 2016년도 춘계 학술논문 발표대회
• /
• pp.201-202
• /
• 2016

Energetically-modified material using reject fly ash was manufactured to investigate the effect of the material on strength characteristic of cement mortar. In order to modify reject fly ash, a vibration mill was used. after grinding process, the defects in the alignment of atom was checked using transmission electron microscope. It was found that the compressive strength values of 28 days-cured specimens using energetically-modified reject fly ash (ERFA) were higher than that of mortar with non-ground reject fly ash.

• 한국레이저가공학회:학술대회논문집
• /
• 한국레이저가공학회 2006년도 추계학술발표대회 논문집
• /
• pp.103-107
• /
• 2006

Decapsulation of EMC(Epoxy Molding Compound) in package device is a method used to inspect inside of device by removing plastic molding. So far, chemical etching and mechanical grinding methods have been used widely. Recently, several works using laser have been carried out. This method has advantages with fast process time and precision than conventional methods because of noncontact process. Also, laser process is a clean process because of removing EMC directly without using toxic chemicals. The wavelength of laser used in this study is 355nm. Key parameters of removing EMC are laser power, scan speed, and number of scans of laser. It if confirmed that laser decapsulation is a useful process to inspect inside a device with a small thermal damage to chip surface.

• 한국건축시공학회:학술대회논문집
• /
• 한국건축시공학회 2001년도 학술논문발표회
• /
• pp.82-87
• /
• 2001

The purpose of this study is for the active use of the fly ash, which is a by-product of the combustion pulverizes coal thermal power plants, to compensate for the lack of landfill and for conservation of energy, by using fly ash as the supplementary cementitious material, and to prove its possibility as the related products of the cement. First of all, the ordinary fly ash is grinded in a special method and its fineness is controlled from 6000$\textrm{cm}^2$/g to 8000$\textrm{cm}^2$/g, then replaced it with the 10% to 80% of the cement mortar in order to test physics characteristics. The first experiment conducts on the strength development in fly ash replacing content and fineness. and the changes of the flow values, incorporating fly ash into cement. The second one is about the slow development of the strength of the fly ash mortar in early ages, and improves its strength with the activator $Na_{2}SO_{4}$, using high volume fly ash.

• 마이크로전자및패키징학회지
• /
• 제17권2호
• /
• pp.49-54
• /
• 2010

n형 $Bi_2(Te,Se)_3$ 분말을 용해/분쇄법으로 제조하여 가압소결 후, 가압소결체의 열전특성을 $Bi_2(Te,Se)_3$ 잉곳과 비교하였으며, $Bi_2(Te,Se)_3$ 열전분말의 기계적 밀링처리가 가압소결체의 열전특성에 미치는 영향을 분석하였다. $Bi_2(Te,Se)_3$ 잉곳은 $24.2{\times}10^{-4}W/m-K^2$의 power factor를 나타내었으며, 이를 가압소결함으로써 power factor가 $27.3{\sim}32.3{\times}10^{-4}W/m-K^2$로 향상되었다. 기계적 밀링처리한 분말로 제조한 $Bi_2(Te,Se)_3$ 가압소결체는 $100^{\circ}C$에서 1.02의 무차원 성능지수를 나타내었으며, $130^{\circ}C$에서 외인성-내인성 천이거동을 나타내었다.

• 대한용접접합학회:학술대회논문집
• /
• 대한용접접합학회 2009년 추계학술발표대회
• /
• pp.100-100
• /
• 2009

본 논문에서는 원자력발전소 1차 계통의 스테인리스강 저합금강 이종금속용접부 및 스테인리스강 동종용접부의 잔류응력을 평가하고 스테인리스강 용접부의 응력부식균열 민감성에 대해 고찰하였다. 노즐 안전단의 이종금속용접부 및 안전단 배관의 동종용접부 제작 및 소재가공에 의행 생성되는 잔류응력을 예측하기 위해 열 탄소성 유한요소법 수치해석을 수행하였으며, 용접공정과 함께 표면의 잔류응력에 기여하는 절삭 및 연삭가공과 소재의 담금질 공정을 열 탄소성적으로 모사하였다. 전산해석 결과, 스테인리스주강의 담금질 잔류응력은 무시할 수 없는 상당한 크기이므로 배관 용접잔류응력 평가 시 소재의 담금질 효과를 고려해야 할 것으로 판단된다. 이종금속 용접과 동종금속 용접공정이 보수용접 없이 정상적인 절차(내면에서 외면으로 적층)로 완성된다면, 냉각재 환경에 노출되는 용접부 내면의 잔류응력은 재료의 응력부식균열 민감성에 영향을 주지 않을 것으로 판단된다. 한편, 안전단 배관 동종용접부의 연삭가공에 의해 내면의 잔류응력이 크게 상승하는 것으로 예측되었으므로, 내면의 연삭가공 이후 표면잔류응력 완화처리(예, 버핑)가 필요하다.

• 대한기계학회논문집A
• /
• 제35권5호
• /
• pp.453-458
• /
• 2011

본 논문은 TP316L 스테인리스강 재료에 대한 표면 기계가공 및 열처리에 의한 잔류응력의 생성 및 변화에 대해 연구한 것이다. 연구를 위해서 TP316L 시편에 대해 방전가공, 밀링, 연마의 3 가지 기계가공을 수행하고 표면의 잔류응력을 측정하였다. 동일한 방법으로 기계가공한 다른 시편은 열처리를 수행한 후에 표면잔류응력을 측정하여 열처리를 수행하지 않은 시편과의 차이를 비교하였다. 잔류응력측정은 엑스선회절법을 사용하였다. 또한 각 시편에 대해 비커스경도를 측정하여 열처리 수행전과 수행후의 경도를 비교하였다. 본 연구를 통해서 기계가공 방법에 따라 잔류응력의 형태가 달라지며 열처리에 의해서 대부분의 잔류응력이 제거됨이 확인되었다. 경도는 잔류응력의 인장 또는 압축의 방향에는 관계없이 크기에만 관련성이 있는 것으로 관찰되었다.

• Nuclear Engineering and Technology
• /
• 제45권4호
• /
• pp.513-522
• /
• 2013

The ODSCC detected in the TSP position of Ulchin 3&4 SGs are typical ODSCC of Alloy 600MA tubes. The causative chemical environment is formed by concentration of impurities inside the occluded region formed by the tube surface, egg crate strips, and sludge deposit there. Most cracks are detected at or near the line contacts between the tube surface and the egg crate strips. The region of dense crack population, as defined as between $4^{th}$ and $9^{th}$ TSPs, and near the center of hot leg hemisphere plane, coincided well with the region of preferential sludge deposition as defined by thermal hydraulics calculation using SGAP computer code. The cracks developed homogeneously in a wide range of SGs, so that the number of cracks detected each outage increased very rapidly since the first detection in the $8^{th}$ refueling outage. The root cause assessment focused on investigation of the difference in microstructure and manufacturing residual stress in order to reveal the cause of different susceptibilities to ODSCC among identical six units. The manufacturing residual stress as measured by XRD on OD surface and by split tube method indicated that the high residual stress of Alloy 600MA tube played a critical role in developing ODSCC. The level of residual stress showed substantial variations among the six units depending on details of straightening and OD grinding processes. Youngwang 3&4 tubes are less susceptible to ODSCC than U3 and U4 tubes because semi-continuous coarse chromium carbides are formed along the grain boundary of Y3&4 tubes, while there are finer less continuous chromium carbides in U3 and U4. The different carbide morphology is caused by the difference in cooling rate after mill anneal. There is a possibility that high chromium content in the Y3&4 tubes, still within the allowable range of Alloy 600, has made some contribution to the improved resistance to ODSCC. It is anticipated that ODSCC in Y5&6 SGs will be retarded more considerably than U3 SGs since the manufacturing residual stress in Y5&6 tubes is substantially lower than in U3 tubes, while the microstructure is similar with each other.

• 한국세라믹학회지
• /
• 제53권4호
• /
• pp.435-443
• /
• 2016

Coal ash, a material generated from coal-fired power plants, can be classified as fly ash and bottom ash. The amount of domestic fly ash generation is almost 6.84 million tons per year, while the amount of bottom ash generation is 1.51 million tons. The fly ash is commonly used as a concrete admixture and a subsidiary raw material in cement fabrication process. And some amount of bottom ash is used as a material for embankment and block. However, the recyclable amount of the ash is limited since it could cause deterioration of physical properties. In Korea, the ashes are simply mixed and used as a replacement material for cement. In this study, an attempt was made to mechanically activate the ash by grinding process in order to increase recycling rates of the fly ash. Activated fly ash was prepared by controlling the mill types and the milling times and characteristics of the mortar containing the activated fly ash was analyzed. When the ash was ground by using a vibratory mill, physical properties of the mortar mixed with such fly ash were higher than the mortar mixed with fly ash ground by a planetary mill.

• 한국기계가공학회지
• /
• 제2권1호
• /
• pp.15-21
• /
• 2003

The ultrasonic polishing machine was developed to get super finishing that consist of machine part that can rotate and travel the main shaft with power 1.5kW, ultrasonic generator with frequency 20kHz. By using this machine we were investigated the characteristics of ultrasonic polishing for three different ceramics, and so could be obtained following results. First, we could be obtained the excellent surface for hard-ta-difficult cutting materials. Second, the effect of surface roughness for the feed rate could be shown that the more the feed rate Increases, the more the value of surface roughness increases. Third, owing to the characteristics being progressed brittle fracture in $Al_2O_3$ polishing with this machine, the value of surface roughness is larger than other ceramics. Forth, because the ultrasonic polishing can be smoother than the existing grinding in discharging the chips, it could be possible to improve the surface roughness about up to 15%.

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 1997년도 추계학술대회 논문집
• /
• pp.947-952
• /
• 1997

The magnetic polishing is the useful method to finish using magnetic power of a magnet. The time hasn't been that long since the magnetic polishing method was introduced to korea as one of precision polishing techniques. However, the reasons for not being spreaded widely are the magnetic polishing method don't have mediocrity for machine, the efficiency of magnet-abrasive is confined as a bad polishing, and there are not many researchers in this field. The mechanism of this R&D is dealing with the dynamic state of magnet-abrasive. This paper deals with mediocritizing magnetic polishing device into regular lathe and this experiment was conducted in order to get a best surface roughness with low cost. Beside the subsidiary experiment was performed using the mixed magnet-abrasive with general alumina, barium. This paper introduced the main reason for difficulty using this method in industrial field. It needs more continues research on it. This paper contains the result of experiment to acquire the best surface roughness, not using the high-cost polishing material in processing. The average diameters of magnet-abrasive are the particles of 150 $\mu\textrm{m}$, 250 $\mu\textrm{m}$.