• Restorative Dentistry and Endodontics
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• 제24권4호
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• pp.604-613
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• 1999

This study was performed to evaluate the effect of resin and filler type on the fracture toughness of light-activated composites. Experimental composites were prepared using urethane tetramethacrylate(UTMA) and bisphenol glycidylmethacrylate(Bis-GMA) monomers and five different types of silica fillers. Fracture toughness was measured by a single edge V-notched beam(SEVNB) method, which was discussed from ASTM E399-78. Rectangular bars of $2.5{\times}5{\times}26mm$ were prepared with experimental composites and a notch about 2.25mm deep was carved at the center of the long axis of the specimen using a dental diamond disk driven by a dental micro engine. The flexural test was carried out at a crosshead speed of 0.05mm/min and fracture surfaces were observed under scanning electron microscope. The results obtained were summarized as follows: 1. The fracture toughness values of UTMA-based composites were relatively higher than those of Bis-GMA-based composites. 2. The highest fracture toughness value was observed in the UTMA-based composite containing the $1.5{\mu}m$-spherical fillers. 3 Aging in the distilled water at $37^{\circ}C$ for 10 days showed the increase of fracture toughness, which was severer in the Bis-GMA-based composites than those of UTMA-based composites. 4. The AE amplitude occurring during the fracture toughness tests was the highest at the point of macroscopic fracture.

• 한국안전학회지
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• 제33권4호
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• pp.8-14
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• 2018

In the industrial chemical process involving combustible materials, reliable safety data are required for design prevention, protection and mitigation measures. The accurate combustion properties are necessary to safely treatment, transportation and handling of flammable substances. The combustion parameters necessary for process safety are lower flash point, upper flash point, fire point, lower explosion limit(LEL), upper explosion limit(UEL)and autoignition temperature(AIT) etc.. However, the combustion properties suggested in the Material Safety Data Sheet (MSDS) are presented differently according to the literatures. In the chemical industries, tetralin which is widely used as a raw material of intermediate products, coating substances and rubber chemicals was selected. For safe handling of tetralin, the lower and flash point, the fire point, and the AIT were measured. The LEL and UEL of tetralin were calculated using the lower and upper flash point obtained in the experiment. The flash points of tetralin by using the Setaflash and Pensky-Martens closed-cup testers measured $70^{\circ}C$ and $76^{\circ}C$, respectively. The flash points of tetralin using the Tag and Cleveland open cup testers are measured $78^{\circ}C$ and $81^{\circ}C$, respectively. The AIT of the measured tetralin by the ASTM E659 apparatus was measured at $380^{\circ}C$. The LEL and UEL of tetralin measured by Setaflash closed-cup tester at $70^{\circ}C$ and $109^{\circ}C$ were calculated to be 1.02 vol% and 5.03 vol%, respectively. In this study, it was possible to predict the LEL and the UEL by using the lower and upper flash point of tetralin measured by Setasflash closed-cup tester. A new prediction method for the ignition delay time by the ignition temperature has been developed. It is possible to predict the ignition delay time at different ignition temperatures by the proposed model.

• 자원리싸이클링
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• 제24권6호
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• pp.38-44
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• 2015

동해-삼척지역 석회석을 활용하여 습식배연탈황공정기술에 대한 적용성을 검토하기 위해 석회석의 물리화학적 특성이 탈황성능에 미치는 영향을 연구하였다. 실험은 ASTM 표준 시험방법인 염산적정법을 적용한 실험실 규모의 실험 장치를 이용하여 총중화능력을 측정하였다. 실험결과 총중화능력은 CaO 함량 등의 화학성분 보다 입자크기의 물리적 특성에 더 큰 영향이 있음을 알 수 있었으며, 입자크기가 미립화 될수록 총중화능력의 값은 높아지는 것으로 확인되었다.

• 한국결정성장학회지
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• 제25권5호
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• pp.212-217
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• 2015

본 연구는 해상 양식장 내에 유해 조류로 인해 발생하는 수산 동, 식물의 폐사를 막고, 양식장을 주기적으로 정화하는 폰툰 시스템 내의 멤브레인 층(Membrane Layer)의 생물오손(Biofouling)을 막고자, ML에 적용되는 인공경량골재 및 골재의 구조에 따른 미생물 흡착을 비교하고자 지오폴리머에 은 나노 입자를 코팅하여 생물오손 정도를 확인하고 그 능력을 평가하였다. 이후 코팅에 따른 미생물 기능 억제 능력을 확인하고자 항균 테스트를 실시하였으며, 한국해양과학기술원 남해연구소 앞바다에 설치하여 생물오손 정도와 무게변화율을 관찰하였다. 항균 테스트 결과 은 나노 입자를 코팅한 인공경량골재에서 99.99 %의 세균 감소율을 확인하였으며, 생물오손 정도를 관찰한 결과 2개월부터 은 나노 입자의 효과에 의해 생물오손 정도가 억제되는 것을 확인하였다. 은 나노 입자 코팅에 의한 생물오손 억제기간은 인공경량골재에서 5개월, 지오폴리머에서 3개월 미만으로 나타났으며, 따라서 은 나노 입자가 코팅된 인공경량골재가 효과적으로 생물오손을 감소시킬 수 있는 친환경적이며 효과적인 방법임을 알 수 있었다.

• Corrosion Science and Technology
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• 제19권4호
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• pp.163-173
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• 2020

Cavitation corrosion in many industrial plants has recently become a serious issue. Cavitation corrosion has generally been investigated using a vibratory method based on ASTM G32 standard, and the test can be divided into direct cavitation and indirect cavitation. Cavitation corrosion test uses the vibration frequency of the horn of 20 kHz with constant peak-to-peak displacement amplitude. In this work, the peak-to-peak amplitude was controlled from 15 ㎛ to 85 ㎛, and electrochemical measurements were obtained during indirect cavitation. The relationship between cavitation corrosion rate and electrochemical properties was discussed. Corrosion steps of carbon steel at the initial stage under cavitation condition in 3.5 % NaCl can be proposed. When the cavitation strength is relatively low, corrosion of the steel is more affected by the electrochemical process than by the mechanical process; but when the cavitation strength is relatively high, corrosion of the steel is affected more by the mechanical process than by the electrochemical process. This work confirmed that the critical ultrasonic amplitude of 0.42 %C carbon steel is 53.8 ㎛, and when the amplitude is less than 53.8 ㎛, the corrosion effect during the cavitation corrosion process is higher than the mechanical effect.

• 대한기계학회논문집
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• 제11권3호
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• pp.376-385
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• 1987

본 연구에서는 평면응력 파괴인성치의 거동에 관한 일련의 연구로서 위와 같 은 점을 고려하여 얇은 두께의 시험편을 이용하여 z의 변화에 대한 평면응력 파괴인성 치와 J저항곡선을 실험적으로 고찰하였으며 크랙성장을 고려한 J적분식도 검토하였다. 크랙길이는 하중제거 컴플라이언스법에 의하여 구하였고, ASTM E813의 방법으로J= .sigma.$_{f}$ .DELTA.(2ａ)인 크랙둔화선과 J저항곡선의 교점에서 구한 J적분값을 J$_{c}$로 정 의하였다. 또한, 재료를 변형경화재료로 가정하여 HRR응력변형율장의 특성을 이용 하여 J적분값을 구한 후 실험치와 상호 비교 검토하였다.이때 입력자료는 실험치의 그것과 동일하게 하였다. 동시에 z의 변화에 대한 T의 변화도 함께 고찰하였다.다.

• 한국해양공학회지
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• 제26권5호
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• pp.73-80
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• 2012

It is well known that a considerable amount of scatter is shown in experimental results relating to fatigue crack growth even under identical and constant amplitude cyclic loading conditions. Moreover, flux cored arc welding (FCAW) is a common method used to join thick plates such as the structural members of large scale offshore structures and very large container ships. The objective of this study was to investigate the macro- and microscopic observations of the fatigue crack growth (FCG) behavior of the FCAWed API 2W Gr. 50 steel joints typically applied for offshore structures. In order to clearly understand the randomness of the fatigue crack growth behavior in the materials of three different zones, the weld metal (WM), heat affected zone (HAZ), and base metal (BM), experimental fatigue crack growth tests for each of five specimens were performed on ASTM standard compact tension (CT) specimens under constant amplitude cyclic loading. Special focus was placed on the fatigued fracture surfaces. As a result, a different behavior was observed at the macro-level, depending on the type of material property: BM, HAZ, or WM. The variability in the fatigue crack growth rate for WM was higher than that of BM and HAZ.

• 한국의류학회지
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• 제35권12호
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• pp.1454-1465
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• 2011

Menswear body types are often labeled on garments (to indicate how the garments are designed to fit) with indicators of a size category such as regular, portly, and stout, athletic, or big and tall. A drop (relationships between the chest and waist girths) is related to the fit of a tailored suit. However, current standards are not designed for various drops or body types. There is not enough information of categorizing men's body shapes for the apparel sizing systems. In this article, a set of men's data from SizeUSA sizing survey was analyzed to investigate men's body shapes and drops. Factor analysis and a cluster analysis method were used to categorize men's body shapes. In the results, twenty-five variables were selected through the factor analysis and found four factors: girth factor, height factor, torso girth factor, and slope degree factor. According to the factor and cluster analysis, various body shapes were found: Slim Shape (SS - tall ectomorphy), Heavy Shape (HS - athletic, big & tall, endomorphy and mesomorphy), Slant Inverted Triangle Shape (SITS - regular, slight ectomorphy and slight mesomorphy weight range from normal to slightly overweight), Short Round Top Shape (SRTS - portly and stout, endomorphy). Body shapes were related to fitting categories. SS and HS were related to big & tall fitting category. SITS was related to regular. SRTS was related to portly and stout. Shape 1 (31%) and Shape 2 (26%) were related to current big & tall category. Shape 3 (34%) were related to regular. Shape 4 (9%) were in portly and stout category. ASTM D 6240 standard was the only available standard that presented a regular fitting category. Various drops were found within a same chest size group; however, this study revealed great variances of drops by body shape.

• Corrosion Science and Technology
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• 제17권6호
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• pp.279-286
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• 2018

Austenitic stainless steels used in nuclear power plants mainly use pipes made of seamless pipes, which depend on imports. The manufacturing process and high cost are some of the problems associated with seamless pipes. Therefore, in this study, the corrosion characteristics of the seamless pipe and the SAW pipe were assessed to determine the safety and reliability of the SAW pipe in a bid to replace the seamless pipe. Microstructure was analyzed using an optical microscope and the degree of hardness was measured using a Rockwell B scale. Intergranular corrosion resistance was evaluated by ASTM A262 Practice A, C, and E methods. The degree of sensitization was determined using a DL-EPR test. Anodic polarization test was performed in deaerated 1% NaCl solution at $30^{\circ}C$ and the U-bend method was used to evaluate the SCC resistance in 0.01 M $Na_2S_4O_6$ at $340^{\circ}C$ and 40% NaOH solution at $290^{\circ}C$. Weld metal of the SAW pipe specimen showed relatively high degree of sensitization and intergranular corrosion rate. However, annealing to SAW pipes improved the corrosion properties in comparison to that of the seamless pipe.

• 한국기계가공학회지
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• 제18권1호
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• pp.59-64
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• 2019

In recent years, the HP-CRTM method, which has the ability to produce carbon fiber-reinforce plastic composites at high speeds, has come into the spotlight in the automotive parts industry, which demands high productivity. Multi-axial carbon fabric, an intermediate material used in this HP-CRTM molding process, consists of layered fibers without crimp, which makes it better in terms of tensile and shear strength than the original woven fabrics. The NCF (non-crimp fabric) can form the layers of the carbon fiber, which have different longitudinal and lateral directions, and ${\pm}{\theta}$ degrees, depending on the product's properties. In this research, preforms were made with carbon fibers of ${\pm}45^{\circ}$ and $0/90^{\circ}$, which were lamination structures under seven different conditions, in order to create the optimal laminated structure for automobile reinforcement center floor tunnels. Carbon fiber composites were created using each of the seven differently laminated preforms, and polyurethane was used as the base material. The specimens were manufactured in accordance with the ASTM D3039 standards, and the effect of the NCF lamination structure on the mechanical properties was confirmed by a tensile test.