• 센서학회지
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• 제29권3호
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• pp.201-204
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• 2020

In this study, we fabricated and evaluated graphene composite based 3D scaffolds and planar films. The hybrid composite was prepared by mixing a calculated amount of graphene nanopowder and polydimethylsiloxane in tetrahydrofuran solution. The hybrid composite is easy to manufacture into various forms using direct printing technology or a pressing method. A 3D scaffold structure was prepared at ambient temperature with a flow rate of 240 mm/min. The nozzle pressure was maintained at 350 kPa by adjusting the viscosity of the composite material. The planar film was prepared at different thicknesses using a roll-to-roll equipment. The prepared hybrid nanocomposites were evaluated to investigate their electrical properties according to temperature and mechanical deformation. The obtained results were consistent with each other. Therefore, it can be used effectively as sensors through shape definition.

• Steel and Composite Structures
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• 제30권4호
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• pp.327-336
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• 2019

This paper presents geometrically nonlinear behavior of cracked fiber reinforced composite beams by using finite element method with and the first shear beam theory. Total Lagrangian approach is used in the nonlinear kinematic relations. The crack model is considered as the rotational spring which separate into two parts of beams. In the nonlinear solution, the Newton-Raphson is used with incremental displacement. The effects of fibre orientation angles, the volume fraction, the crack depth and locations of the cracks on the geometrically nonlinear deflections of fiber reinforced composite are examined and discussed in numerical results. Also, the difference between geometrically linear and nonlinear solutions for the cracked fiber reinforced composite beams.

• Journal of Electrochemical Science and Technology
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• 제13권1호
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• pp.100-111
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• 2022

This paper presents a simple and inexpensive method to fabricate chemically and mechanically resistant hot electron-emitting composite electrodes on reusable substrates. In this study, the hot electron emitting composite electrodes were manufactured by doping a polymer, nylon 6,6, with few different brands of carbon particles (graphite, carbon black) and by coating metal substrates with the aforementioned composite ink layers with different carbon-polymer mass fractions. The optimal mass fractions in these composite layers allowed to fabricate composite electrodes that can inject hot electrons into aqueous electrolyte solutions and clearly generate hot electron- induced electrochemiluminescence (HECL). An aromatic terbium (III) chelate was used as a probe that is known not to be excited on the basis of traditional electrochemistry but to be efficiently electrically excited in the presence of hydrated electrons and during injection of hot electrons into aqueous solution. Thus, the presence of hot, pre-hydrated or hydrated electrons at the close vicinity of the composite electrode surface were monitored by HECL. The study shows that the extreme pH conditions could not damage the present composite electrodes. These low-cost, simplified and robust composite electrodes thus demonstrate that they can be used in HECL bioaffinity assays and other applications of hot electron electrochemistry.

• Composites Research
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• 제19권3호
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• pp.29-36
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• 2006

섬유강화 복합재료는 적층각도와 적층순서에 따라 이방성을 가지기 때문에, 복합재료가 튜브형 접합부의 피접착체로 사용될 경우 지금까지 많이 수행된 등방성 피접착체를 가지는 접합부에 대한 해석을 통하여 복합재료 접합부의 거동을 예측하는 것은 한계가 있다. 본 연구에서는 접착제의 비선형 거동을 고려하여 복합재료 피접착체를 가지는 튜브형 접합부에 대한 비선형 해석을 수행하였다. 먼저 적층 복합재료 튜브에 대한 해석을 수행하였고, 이를 바탕으로 튜브형 접합부에 대한 비선형 방정식을 유도하였으며, 접착층의 응력 분포 및 접합부의 토크전달능력을 계산하였다. 복합재료 튜브의 적층순서와 접착길이가 접착층의 응력 분포 및 토크전달능력에 어떤 영향을 미치는 지 살펴보았으며, 또한 비선형 해석과 선형해석의 차이점을 비교하고 분석하였다.

• 대한치과보철학회지
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• 제40권3호
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• pp.225-235
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• 2002

The color stability of current prosthetic composites is unknown, even though the quality of composite materials has been improving. This study examined the intrinsic color stability of various current prosthetic resins (ceramic-polymers) after an accelerated aging process and the extrinsic color stability after immersion in a coffee solution. By comparing the amount of discoloration after aging with that without aging, the effect of the accelerated aging process on external discoloration could be evaluated. Three current prosthetic composites (Artglass, Targis, Sculpture), one light polymerized direct composite (Z100) and one dental porcelain control (Ceramco) were assessed. The color changes (${\Delta}$E) of all the specimens were determined using the CIE $L^{*}a^{*}b^{*}$ color order system with a reflected spectrophotometer. The results were as follows: 1. The prosthetic composite materials subjected to the accelerated aging test showed no significant difference in color changes (p >.05). 2. In the coffee solution immersion test after the aging process, the color changes of the Targis and Artglass groups were not different from that of the Z100 group, which showed the highest color change. 3. In the immersion only test, a significantly high color change was observed in the sculpture glazing group. 4. The aging process influenced on the color changes more in the Targis, Artglass and Z100 groups than in the Sculpture and Ceramco groups.

• 한국재료학회지
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• 제24권4호
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• pp.201-206
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• 2014

TiC-21 mol% Mo solid solution (${\delta}$-phase) and TiC-99 mol% Mo solid solution (${\beta}$-phase), and TiC-(80~90) mol% Mo hypo-eutectic composite were deformed by compression in a temperature range from room to 2300 K and in a strain rate range from $4.9{\times}10^{-5}$ to $6.9{\times}10^{-3}/s$. The deformation behaviors of the composites were analyzed from the strengths of the ${\delta}$- and ${\beta}$-phases. It was found that the high strength of the eutectic composite is due primarily to solution hardening of TiC by Mo, and that the ${\delta}$-phase undergoes an appreciable plastic deformation at and above 1420 K even at 0.2% plastic strain of the composite. The yield strength of the three kinds of phase up to 1420 K is quantitatively explained by the rule of mixture, where internal stresses introduced by plastic deformation are taken into account. Above 1420 K, however, the calculated yield strength was considerably larger than the measured strength. The yield stress of ${\beta}$-phase was much larger than that of pure TiC. A good linear relationship was held between the yield stress and the plastic strain rate in a double-logarithmic plot. The deformation behavior in ${\delta}$-phase was different among the three temperature ranges tested, i.e., low, intermediate and high. At an intermediate temperature, no yield drop occurred, and from the beginning the work hardening level was high. At the tested temperature, a good linear relationship was held in the double logarithmic plot of the yield stress against the plastic strain rate. The strain rate dependence of the yield stress was very weak up to 1273 K in the hypo-eutectic composite, but it became stronger as the temperature rose.

• Carbon letters
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• 제14권4호
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• pp.251-254
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• 2013

In this study, poly(amic acid) was prepared via a polycondensation reaction of 3,3'-dihydroxybenzidine and pyromellitic dianhydride in an N-methyl-2-pyrrolidone solution; reduced graphene oxide/polybenzoxazole (r-GO/PBO) composite films, which significantly increased the electrical conductivity, were successfully fabricated. GO was prepared from graphite using Brodie's method. The GO was used as nanofillers for the preparation of r-GO/PBO composites through an in situ polymerization. The addition of 50 wt% GO led to a significant increase in the electrical conductivity of the composite films by more than sixteen orders of magnitude compared with that of pure PBO films as a result of the electrical percolation networks in the r-GO during the thermal treatment at various temperatures within the films.

• 한국정밀공학회지
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• 제29권9호
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• pp.1012-1019
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• 2012

In this study, CNG composite vessel is analyzed by using coupled model with liner and composite layer. For the coupled model, a method using theoretical analysis and FEA is suggested: elastic solution for laminated tube is used for theoretical analysis of the composite vessel, FEA is performed to the model of CNG composite vessel in actual conditions. On the basis of these results, optimal thickness and winding angle of the composite layer considering the material properties and thickness of the liner are determined. The results of theoretical analysis and FEA are compared with those carried out in previous studies for verifying the suggested analysis method.

• 한국강구조학회 논문집
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• 제10권3호통권36호
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• pp.437-449
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• 1998

합성형구조에서 콘크리트와 강재가 일체로 거동하기 위해서 전단연결재는 충분한 강성과 강도를 지니고 있어야 한다. 만약 콘크리트와 판형의 경계면에서 수직 또는, 수평방향으로 미끄러짐이 발생하지 않는다면 전단연결재는 무한강성으로 표현되어지고, 이상적으로 완전합성거동을 하게 된다. 그러나, 모든 전단연결재는 어느 정도의 범위내에서 유연성을 가지게 되며, 항상 불완전합성작용을 하게 된다. 본 논문에서는 3가지 방법에 의해서 불완전합성작용을 하는 합성형을 해석하는 실용적인 방법에 대하여 연구하였다. 미분방정식의 일반해로부터 유도된 강도매트릭스법과 경계부분의 스프링상수를 뼈대구조로 대체한 유한요소법, 가상일의 원리를 이용한 유한요소법의 3가지 방법에 의하여 합성형의 처짐특성을 고찰하였다. 또한, 불완전합성형에서 단면특성과 전단연결재의 스프링상수를 이용하여 합성형의 합성정도를 추정할수 있는 간이법을 제시하였다.

• 한국염색가공학회지
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• 제20권2호
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• pp.1-8
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• 2008

Regenerated composite fibers are prepared from solution(styela clava tunics /poly vinyl alchol) using N-methylmorpholine-N-oxide(NMMO)/water(87/13)(wt/wt) as a solvent by dry-wet spinning. The chemical cellulose (94%, ${\alpha}$-cellulose content) used for this study is extracted from styela clava tunics (SCT, Midduck), which are treated in chemical process and mechanical grinding. The structure and physical properties of regenerated composite fibers were investigated through IR-spetra, DSC, TGA and SEM. The optimal blend ratio of SCT/PVA for spinning solution was 70/30 and the total weight was 4% concentrations in NMMO/water solvent system. The fiber density, moisture contents and the degree of swelling were $1.5(g/cm^3)$ 10.2(%) and 365(%), respectively. The crystallinity index of composite fibers are decreased as the PVA contents increased. Thermal decomposition of composite fibers took place in two stages at around $250^{\circ}C$ and $550^{\circ}C$. The best thermal stability was obtained with 30% PVA contents.