• Composites Research
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• 제22권3호
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• pp.44-54
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• 2009

본 논문에서는 퍼콜레이션 이론적 관점에 기초한 복소 유전율의 수치모델을 제시하고, 전기 전도성이 뛰어난 카본 블랙을 혼합한 유리섬유/에폭시 복합재료 적층판의 복소 유전율을 이용하여 이 깃을 검증하였다. 제시된 모델은 카본 블랙의 함유율이 퍼콜레이션 임계함유율 보다 높고, 주파수가 충분히 높아서 복합재료의 교류 전기전도도가 주파수에 비례하는 구간에서의 복소 유전율을 모사한다. 복합재료의 복소 유전율은 벡터회로망분석기와 7 mm 동축관을 이용하여 $0.5\;GHz\;{\sim}18\;GHz$ 대역에서 측정되었다. 제시된 모델은 퍼콜레이션 이론에서 유용하게 사용되는 축척(눈금잡이) 법칙의 함수형태와 실험을 통하여 구한 상수들로 구성되어 있으며, 복소 유전율을 주파수와 가본 블랙의 함유율의 함수로 나타내었다. 제시된 모델은 복소 유전율을 측정결과와의 비교를 통하여 검증되었다.

• 대한기계학회논문집A
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• 제21권11호
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• pp.1786-1795
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• 1997

In order to perform leak-before-break design of nuclear piping systems and integrity evaluation of reactor vessels, full stress-strain curves and fracture resistance (J-R) curves are required. However it is time-consuming and expensive to obtain J-R curves experimentally. The objective of this paper is to modify two J-R curve prediction methods previously proposed by the authors and to propose an additional J-R curve prediction method for nuclear piping materials. In the first method which is based on the elastic-plastic finite element analysis, a blunting region handling procedure is added to the existing method. In the second method which is based on the empirical equation, a revised general equation is proposed to apply to both carbon steel and stainless steel. Finally, in the third method, both full stress-strain curve and finite element analysis results are used for J-R curve prediction. A good agreement between the predicted results based on the proposed methods and the experimental ones is obtained.

• 한국안전학회지
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• 제17권4호
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• pp.19-24
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• 2002

User-friendly-web-based database system for searching creep property data was developed. This system includes about 38000 creep data for 270 different materials including low carbon steel, stainless steel and alloy steel. Data on creep rupture, creep deformation, creep crack growth and creeping materials can be searched through this system. Retrieved data is displayed in numeric form and also presented in graphical form for visualizing the data. Furthermore, the creep rupture data is designed to be fitted to a regression equation of logarithmic stress using time-temperature parameter(TTP). The degree of the regression equation, orthogonal polynomials, was determined using analysis of variance.

• Advances in materials Research
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• 제13권1호
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• pp.1-18
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• 2024

The present experimental investigation focuses on finding optimal parametric data-set of laser micro-drilling operation with minimum taper and Heat-affected zone during laser micro-drilling of Carbon Nanotube/Epoxy-based composite materials. Experiments have been conducted as per Box-Behnken design (BBD) techniques considering cutting speed, lamp current, pulse frequency and air pressure as input process parameters. Then, the relationship between control parameters and output responses is developed using second-order nonlinear regression models. The analysis of variance test has also been performed to check the adequacy of the developed mathematical model. Using the Response Surface Methodology (RSM) and an Accelerated particle swarm optimization (APSO) technique, optimum process parameters are evaluated and compared. Moreover, confirmation tests are conducted with the optimal parameter settings obtained from RSM and APSO and improvement in performance parameter is noticed in each case. The optimal process parameter setting obtained from predictive RSM based APSO techniques are speed=150 (m/s), current=22 (amp), pulse frequency (3 kHz), Air pressure (1 kg/cm²) for Taper and speed=150 (m/s), current=22 (amp), pulse frequency (3 kHz), air pressure (3 kg/cm²) for HAZ. From the confirmatory experimental result, it is observed that the APSO metaheuristic algorithm performs efficiently for optimizing the responses during laser micro-drilling process of nanocomposites both in individual and multi-objective optimization.

• Steel and Composite Structures
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• 제34권4호
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• pp.599-613
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• 2020

In this article, free vibration attributes of double-walled carbon nanotubes based on nonlocal elastic shell model have been investigated. For this purpose, a nonlocal Flügge shell model is established to observe the small scale effect. The wave propagation is employed to frame the governing equations as eigenvalue system. The influence of nonlocal parameter subjected to different end supports has been overtly examined. A suitable choice of material properties and nonlocal parameter been focused to analyze the vibration characteristics. The new set of inner and outer tubes radii investigated in detail against aspect ratio and length. The dominance of boundary conditions via nonlocal parameter is shown graphically. The results generated furnish the evidence regarding applicability of nonlocal shell model and also verified by earlier published literature.

• Corrosion Science and Technology
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• 제9권5호
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• pp.201-208
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• 2010

Epoxy coatings cured by different amine based curing agents have been prepared. Atomic force microscopy (AFM) has been used to monitor the surface topology changes of epoxy coatings before and after hygrothermal cyclic test. The glass transition temperature ($T_g$) and coefficient of thermal expansion (CTE) of the epoxy coating were measured by Thermo-mechanical Analysis (TMA). The Electrochemical impedance spectroscopy (EIS) with hygrothermal cyclic test has been introduced to evaluate the corrosion protection of the epoxy coatings. In conclusion, thermal properties of epoxy coatings were in good agreement with the results of corrosion protection of epoxy coated carbon steel obtained result by EIS with hygrothermal cyclic test. The relationship between thermal properties, surface roughness changes and corrosion protection of epoxy coatings are discussed in this study.

• 비파괴검사학회지
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• 제30권3호
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• pp.244-256
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• 2010

Radio frequency identification(RFID) combined with wireless technology has good potential for structural health monitoring(SHM). We describe several advantages of RFID and wireless technologies for SHM, and review SHM examples with working principles, design and technical details for damage detection, heat exposure monitoring, force/strain sensing, and corrosion detection in concrete, steel, carbon fiber reinforced polymer(CFRP), and other materials. Various sensors combined with wireless communication are also discussed. These methodologies can be readily developed, implemented, and customized. There are some technical difficulties, but solutions are being addressed. Lastly, a surface acoustic wave-based RFID system is presented, and possible future trends of SHM based on RFID and wireless technology are presented.

• 한국건설순환자원학회논문집
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• 제12권2호
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• pp.229-238
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• 2024

이 연구에서는 박테리아 기반 악취저감 키트의 악취제거 성능을 평가하였다. 박테리아는 악취오염원인 암모니아(NH₃), 황화수소(H₂S), 총질소(T-P) 및 총인(T-N)을 제거할 수 있는 Rhodobacter capsulatus, Paracoccus limosus 및 Brevibacterium hankyongi를 사용하였다. 사용된 소재들은 박테리아와 다공성골재(팽창질석, 제올라이트 비드, 활성탄)이며, 제거 메커니즘에 따라 소재들의 융합을 달리하였다. 물리적 흡착 메커니즘을 갖는 소재들(제올라이트 비드 및 활성탄)은 악취오염원(NH₃, H₂S, T-P 및 T-N)의 농도 저감율이 점차 둔화되어 48시간 이후부터 더 이상의 악취오염원의 농도의 저감 효과가 없었다. 생물학적 흡착 메커니즘으로 악취를 제거하는 박테리아가 고정화된 팽창질석은 지속적인 농도 저감으로 108시간 이후에 악취오염원의 농도가 0 ppm에 도달하였다. 결과적으로 실제 하천수에서 물리적 흡착 메커니즘을 갖는 소재들의 악취제거 성능은 환경부에서 제시하고 있는 악취 배출허용 기준을 만족하지 못한 반면, 박테리아가 고정화된 팽창질석은 악취 배출허용 기준을 만족하였으며, 수질도 1등급으로 평가되었다.

• Tribology and Lubricants
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• 제23권6호
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• pp.266-271
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• 2007

The brake performance of sintered friction materials for the high speed train was studied. In this study, newly developed sintered materials based on copper were compared with the commercial products for high speed trains. They were tested on a 1/5 scale dynamometer using low carbon steel disks. Effectiveness, fade, and recovery tests were carried out to examine friction performance and the change of disk thickness variation (DTV) during brake applications and noise propensity were also evaluated. Results showed that the two sintered friction materials exhibit similar friction coefficients and braking performance, whereas the newly developed friction material was superior in terms of DTV generation and noise propensity to the commercial friction material. The improvement of the newly developed friction material was attributed to the high graphite content which reduced the stick-slip phenomena and prevented uneven disk wear by producing friction films on the counter disk.

• 분석과학
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• 제5권1호
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• pp.25-31
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• 1992

벤젠합성장치를 제작하여 액체섬광계수법을 이용한 방사성탄소 연대측정 시료인 목재, 목탄, 패류, 토양 등의 시료의 처리에 이용하였다. 이산화탄소, 아세틸렌의 생성 및 최종적으로 얻어지는 벤젠으로 이어지는 합성과정별 실험조건을 최적화하였다. 본 벤젠합성기를 이용함으로써 유기시료의 경우, 15시간의 합성을 통하여 탄산칼슘 기준으로 85% 이상의 합성수율을 얻을 수 있었다. 합성된 벤젠의 순도는 GC/MS 측정결과 99.9% 이상이었다.