• Applied Microscopy
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• 제45권3호
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• pp.170-176
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• 2015

In this work, various electron microscopy and analysis techniques were used to investigate the microstructural evolution of a 9% Cr tempered martensite ferritic (TMF) steel T91 upon ultrasonic nanocrystalline surface modification (UNSM) treatment. The micro-dimpled surface was analyzed by scanning electron microscopy. The characteristics of plastic deformation and gradient microstructure of the UNSM treated specimens were clearly revealed by crystal orientation mapping of electron backscatter diffraction (EBSD), with flexible use of the inverse pole figure, image quality, and grain boundary misorientation images. Transmission electron microscope (TEM) observation of the specimens at different depths showed the formation of dislocations, dense dislocation walls, subgrains, and grains in the lower, middle, upper, and top layers of the treated specimens. Refinement of the $M_{23}C_6$ precipitates was also observed, the size and the number density of which were found to decrease as depth from the top surface decreased. The complex microstructure and microstructural evolution of the TMF steel samples upon the UNSM treatment were well-characterized by combined use of EBSD and TEM techniques.

• Tribology and Lubricants
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• 제31권6호
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• pp.287-293
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• 2015

Laser surface texturing (LST), a surface engineering modification, has been considered as one of the new processes used to improve tribological characteristics of materials by creating artificially patterned microstructure on the contact surface of mechanical components. In LST technology, the laser is optimized to obtain or manufacture the dimples with maximum precision. The micro-dimples reduce the coefficients of friction and also improve the wear resistance of materials. This study investigates the effect of dimple density is investigated. For this purpose, a ball-on-disc type tester is used with AISI 52100 bearing steel as the test material. Discs are textured with a 5% and 10% dimple density. Experimental work is performed with normal loads of 5 N, 10 N, and 15 N under a fixed speed of 150 rpm at room temperature. The effect of the textured surface is compared to that of the untextured one. Experimental results show that the textured surface yields lower friction coefficients compared to those of untextured surfaces. Specifically, the 10% dimple density textured surface shows better friction reduction behavior than the 5% dimple density textured sample, and has an 18% improvement in friction reduction compared with the untextured samples. Microscopic observation using a scanning electron microscope (SEM) shows that the major friction mechanisms of the AISI 52100 bearing steel are adhesion, plastic deformation, and ploughing.

• 한국정밀공학회지
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• 제33권5호
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• pp.377-383
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• 2016

Recently, research on bone fracture and osteoplasty using ultrasonic bone surgery unit has been ongoing in the fields of dentistry, plastic surgery, and otorhinolaryngology. However, detailed data evaluation with ultrasonic bone surgery unit has not been conducted to date. In this study, we developed handpiece moving system (HMS) for cutting performance evaluation. In the experimental setup of HMS, a handpiece was immobilized, and bone samples from cortical bone of bovine leg were prepared. Also, the experimental process was described in detail, and a basic experiment was carried out to evaluate the cutting performance. Future study is required on all experimental process conditions by HMS.

• 열처리공학회지
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• 제36권4호
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• pp.230-236
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• 2023

The current study deals with the effect of cooling rate and temperature for annealing on medium-carbon Cr-Mo alloy steel, especially for cold heading quality wire rod, to derive the optimum micro-structures for plastic deformation. This is to optimize the spheroidization heat treatment conditions for softening the material. Heat treatment was performed under seven different conditions at a temperature between A_c1 and A_c3, mostly within 720℃ to 760℃, and the main variables at this time were temperature, retention time and cooling rate. Microstructure and phase changes were observed for each test condition, and it was confirmed that they were greatly affected by the cooling rate. It was also confirmed that the cooling rate was changed in the range of 0.1℃/min to 5℃/min and affected by phase deformation and spheroidization fraction. The larger the spheroidization fraction, the lower the hardness, which is associated with the increasing connection of ferrite phases.

• 한국전기전자재료학회논문지
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• 제35권2호
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• pp.149-154
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• 2022

In this paper, laser-induced fluorescence properties of four plastics were characterized through spectrometer analysis for real-time microplastic counting. Recently, environmental problems related to microplastics have emerged. In order to detect microplastics, analysis methods such as FT-IR and Raman are used. However, they have the disadvantages of being time-consuming and requiring a pretreatment process. In most plastic products on the market, 10% to 30% of plasticizers and reinforcing agents are added. Therefore, most microplastics present in seawater and freshwater emit fluorescence signals by 270 nm UV light source regardless of their type due to their molecular structure due to additives. Real-time microplastics counting is possible more easily by using the proposed laser-induced fluorescence detection method because of the fluorescence expression characteristic of 340 nm that appears due to the plasticizer of plastics.

• 한국해양환경ㆍ에너지학회지
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• 제17권2호
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• pp.104-115
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• 2014

2013년 가을, 한국 통영의 13개 해변에서 해양쓰레기의 풍도와 조성을 조사하였다. 대형쓰레기(25 mm 이상)의 풍도는 평균 약 30개/$m^2$, 소형쓰레기(1 mm-25 mm)의 풍도는 평균 26,971개/$m^2$로서 한국의 다른 지역이나 전세계 다른 지역에 비해 매우 높은 편이었다. 스티로폼, 경질플라스틱, 섬유, 금속, 유리, 목재, 기타 등 7개 재질로 구분했을 때 대형쓰레기 중 스티로폼의 갯수가 차지하는 비율은 약 75%, 소형 쓰레기에서는 약 98%였다. 대형 스티로폼 쓰레기 중 원래 부피의 50% 이상이 남아 있는 '완제품' 쓰레기들을 양식용 부자와 기타 완제품 쓰레기로 구분했을 때 양식용 부자가 차지하는 비율은 갯수로 93%였다. 결국 조사된 해변들에서 쓰레기로 인한 해변 오염은 매우 심각한 수준이며, 쓰레기의 발생 원인의 대부분은 양식장에서 사용되는 스티로폼 부자인 것으로 밝혀졌다. 통영 지역은 한국에서 굴 양식장이 가장 많은 곳이므로 굴 양식장의 스티로폼 부자 쓰레기 관리를 개선하는 것은 통영뿐만 아니라, 다른 지역의 해변 오염을 예방하는 데도 중요한 것으로 보인다.

• 한국산학기술학회논문지
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• 제9권6호
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• pp.1754-1759
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• 2008

일반사출성형에서는 수지가 캐비티 내를 흐르면서 냉각으로 인한 점도의 상승으로 전사성이 급격히 나빠지기 때문에 미세패턴을 가진 성형품을 제작하는데 많은 어려움이 따른다. 이를 해결하는 방법으로 금형온도를 용융된 수지온도 수준까지 순간적으로 표면만을 가열하여 성형시킨 후 급속히 냉각하는 다양한 순간금형가열방식이 있고, 그 중 본 연구에서는 전열가열방식인 E-Mold을 채택하였다. 특히, 마이크/나노 부품 성형에 필수적인 E-Mold 금형설계에 있어 heating line의 배치는 금형의 온도 제어 및 균일한 온도 분포에 절대적인 영향을 미치므로 최적화된 heating line의 배치가 필수적이다. 본 연구에서는 사출공정의 사이클 타임을 최소화하면서 다양한 해석 프로그램을 사용하여 E-Mold의 최적화 설계를 전산모사 하였고, 이를 실험결과와 비교하였다. 먼저, 3D CAD 프로그램인 Pro-Engineer Wildfire 2.0 을 사용하여 E-Mold 금형을 설계하고, ANSYS사의 ICEMCFD 프로그램을 사용하여 MESH 생성하고, ANSYS사의 FLUENT 프로그램을 사용하여 금형의 초기온도 $60^{\circ}C$에서 $120^{\circ}C$와 $180^{\circ}C$까지 가열하는데 걸리는 시간과 냉각시키는데 걸리는 시간 등을 전산모사 하였다. 그리고 Polycarbonate를 이용하여 LGP 도광판을 실제 사출성형하여 얻은 데이터와 비교 분석을 하였다. 전산모사와 실제 사출결과에서 $3{\sim}4$초가량의 차이가 나타났지만 실제 사출시 고온의 용융된 플라스틱 수지에 따른 냉각시간의 오차를 생각한다면, 전산모사와 실힘결과는 거의 일치한다고 볼 수 있다. 따라서 본 체계적인 전산모사방법을 통해 E-Mold의 Heating Line 최적화 설계가 가능하다는 것을 확인하였다.

• 센서학회지
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• 제14권2호
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• pp.69-77
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• 2005

The electronic nose (e-nose) has been used in food industry and quality controls in plastic packaging. Recently it finds its applications in medical diagnosis, specifically on detection of diabetes, pulmonary or gastrointestinal problem, or infections by examining odors in the breath or tissues with its odor characterizing ability. Moreover, the use of portable e-nose enables the on-site measurements and analysis of vapors without extra gas-sampling units. This is expected to widen the application of the e-nose in various fields including point-of-care-test or e-health. In this study, a PDA-based portable e-nose was developed using micro-machined gas sensor array and miniaturized electronic interfaces. The rich capacities of the PDA in its computing power and various interfaces are expected to provide the rapid and application specific development of the diagnostic devices, and easy connection to other facilities through information technology (IT) infra. For performance verification of the developed portable e-nose system, Six different vapors were measured using the system. Seven different carbon-black polymer composites were used for the sensor array. The results showed the reproducibility of the measured data and the distinguishable patterns between the vapor species. Additionally, the application of two typical pattern recognition algorithms verified the possibility of the automatic vapor recognition from the portable measurements. These validated the portable e-nose based on PDA developed in this study.

• 대한금속재료학회지
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• 제50권4호
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• pp.316-323
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• 2012

The aim of this study is to investigate the effect of post heat treatment on bonding properties of roll cladded Ti/MS/Ti materials. First grade Ti sheets and SPCC mild steel sheets were prepared and then Ti/MS/Ti clad materials were fabricated by a cold rolling and post heat treatment process. Microstructure and point analysis of the Ti/MS interfaces were performed using the SEM and EDX Analyser. Diffusion bonding was observed at the interfaces of Ti/MS. The thickness of the diffusion layer increased with post heat treatment temperature and the diffusion layer was verified as having $({\epsilon}+{\zeta})+({\zeta}+{\beta}-Ti)$ intermetallic compounds at $700^{\circ}C$ and an $({\zeta}+{\beta}-Ti)$ intermetallic compound at $800^{\circ}C$, respectively. The micro Knoop hardness of mild steel decreased with post heat treatment temperature; however, those of Ti decreased at a range of $500{\sim}600^{\circ}C$ and showed a uniform value until $800^{\circ}C$ and then increased rapidly up to $900^{\circ}C$. The micro Knoop hardness value of the diffusion layer increased up to $700^{\circ}C$ and then saturated with post heat treatment. A T-type peel test was used to estimate the bonding forces of Ti/Mild steel interfaces. The bonding forces decreased up to $800^{\circ}C$ and then increased slightly with post heat treatment. The optimized temperature ranges for post heat treatment were $500{\sim}600^{\circ}C$ to obtain the proper formability for an additional plastic deformation process.

• 한국건설순환자원학회논문집
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• 제10권3호
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• pp.293-299
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• 2022

본 연구에서는 도로변 미세먼지 내 타이어와 도로 마모입자의 정량화 분석과 타이어와 도로 마모입자 내 타이어 및 도로 성분 비율을 확인하기 위한 연구를 수행하였다. 이에 시간당 1,300여대 교통량을 갖는 충청남도 지자체중에서 C도시의 종합버스터미널 부근 정류장의 경계석 6곳에서 먼지 샘플을 채집하였다. 채집된 먼지 샘플 1,000 g에 대해 크기와 밀도 분리 수행한 결과 미세먼지 샘플 24 g과 타이어와 도로 마모입자 약 0.05 g이 분리되었다. 즉, 도로변 미세먼지에는 타이어와 도로 마모입자가 약 0.21 % 존재하는 것으로 분석되었다. 분리된 타이어와 도로 마모입자에 대해 주사전자현미경(SEM)을 이용하여 형상을 분석한 결과 지우개가루 형상이 관찰되었다. 또한, 도로변 미세먼지 내 존재하는 타이어와 도로 마모입자는 자동차 주행 중 타이어와 도로간 마찰에 의해 생성되어 도로변으로 분산되었기 때문에 열중량분석기(TGA)와 가스크로마토 질량분석기(GC/MS)를 이용하여 성분 분석을 수행하였다. 정량화 계산식을 통해 성분에 대한 타이어 및 도로 성분 비율을 도출한 결과 약 3:7로 분석되었다. 본 연구는 도로변 미세먼지 발생원의 구성원과 함량 분석을 위해 객관적이고 신뢰도 높은 분석 기법을 제시하였다. 추후, 도로건설과 타이어 소재의 미세먼지 저감 기술 확보와 개선 방안 확보를 위한 선행적 기초 연구로써 활용되기를 기대하고 지속적으로 더 많은 지역과 샘플 분석에 대한 통계 데이터를 확보하여 신뢰도 높은 연구를 수행하고자 한다.