• 접착 및 계면
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• 제4권1호
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• pp.18-27
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• 2003

Micromechanical 시험법과 표면 젖음성 측정을 이용하여 플라즈마 처리된 생분해성 poly(p-dioxanone) (PPDO) 섬유강화 poly(L-lactide) (PLLA) 복합재료의 계면물성과 미세파괴 분해메카니즘을 연구하였다. PPDO 섬유강화 PLLA 복합재료는 장기간의 사용기간 동안 우수한 기계적 물성을 제공할 수 있다. PPDO 섬유와 PLLA 기지재료의 분해정도는 열분석과 광학적인 관찰을 통해서 확인하였다. PPDO 섬유와 PLLA 기지재료 사이의 계면전단강도와 접착일은 플라즈마 처리 시간이 60초 일때 가장 컸으며, 접착일과 polar 표면자유에너지는 계면전단강도와 비례하였다. 초기상태의 PPDO 섬유는 연성파단 형상이 나타났으나, 분해시간이 진행됨에 따라 분자량 감소로 인해 점차적으로 취성 파단 형상으로 변하였다. 계면물성과 미세파괴 분해메카니즘은 분해가 진행됨에 따라 변하기 때문에 섬유강화 생분해성 복합재료의 성능을 조절하는데 중요한 요인들이다.

• 전기전자학회논문지
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• 제25권3호
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• pp.430-436
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• 2021

비접촉형 체온 측정 시스템은 광학 및 열화상 카메라를 활용하여 집단시설의 발열성 질병을 관리하는 핵심 요소 중 하나이다. 기존 체온 측정 시스템은 딥러닝 기반 얼굴검출 알고리즘이 사용되어 얼굴영역의 단순 체온 측정에는 활용할 수 있지만, 의사표현이 어려운 영유아의 이상 징후를 인지하는데 한계가 있다. 본 논문에서는 기존의 체온 측정 시스템에서 영유아의 이상징후 감지를 위해 표정인식 알고리즘을 개선한다. 제안된 방법은 객체탐지 모델을 사용하여 영상에서 영유아를 검출한 후 얼굴영역을 추출하고 표정인식의 핵심 요소인 눈, 코, 입의 좌표를 획득한다. 이후 획득된 좌표를 기반으로 선택적 샤프닝 필터를 적용하여 표정인식을 진행한다. 실험결과에 따르면 제안된 알고리즘은 UTK 데이터셋에서 무표정, 웃음, 슬픔 3가지 표정에 대해 각각 2.52%, 1.12%, 2.29%가 향상되었다.

• Tribology and Lubricants
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• 제35권4호
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• pp.222-228
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• 2019

As rubber products such as O-rings, which are also known as packings or toric joints, come in regular, long term contact with liquid fuel, they can eventually swell, become mechanically weakened, and occasionally crack; this diminishes both their usefulness and intrinsic lifetime and could cause leaks during the steady-state flow condition of the fuel. In this study, we evaluate the lifetime of such products through compression set tests of FKM, a family of fluorocarbon elastomer materials defined by the ASTM international standard D141; these materials have great compression, sunlight, and ozone resistance as well as a low gas absorption rate. In this process, O-rings are immersed in the liquid fuel of airtight containers that can be expressed as a compression set, and the liquid fuel leakage in a flow rig tester at variable temperatures over 12 months is investigated. Using the Power Law model, our study determined a theoretical O-ring lifetime of 2,647 years, i.e. a semi-permanent lifespan, by confirming the absence of liquid fuel leakage around the O-ring assembled fittings. These results indicate that the FKM O-rings are significantly compatible for fuel tests to evaluate long-term sealing conditions.

• 한국항공우주학회지
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• 제47권9호
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• pp.629-641
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• 2019

고온, 고압의 연소가스에 의해 유입되는 많은 열을 효과적으로 차단하여 고체 로켓 노즐의 공력형상을 최대한 유지하면서 구조물의 온도 상승을 일정수준 이하로 제한하기 위해 연소가스와 접하는 위치에 내삭마성이 우수한 C/C 복합재 등의 내열재를, 그 배면에는 열확산계수가 낮은 단열재를 적용한다. 내산화성이 우수한 SiC/SiC 복합재는 가스터빈 엔진에 적용되고 있으며, 경량화와 내열성 향상으로 인해 엔진 성능 증가에 기여하고 있다. 극초음속으로 비행하는 스크램제트는 흡입 공기 온도가 매우 높아서 흡열 연료를 냉각제로 사용하는 C/SiC 구조물 개발 연구가 수행되고 있다. 본 논문에서는 고체 로켓 노즐, 가스터빈 엔진 및 램제트/스크램제트 추진기관에 사용되는 다양한 내열 복합재의 특성, 적용사례 및 개발 동향을 고찰하였다.

• Korean Journal of Chemical Engineering
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• 제35권11호
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• pp.2207-2219
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• 2018

Activated carbon (AC) was synthesized from Phoenix dactylifera stones and then modified by $CoFe_2O_4$ magnetic nanocomposite for use as a Cr(VI) adsorbent. Both $AC/CoFe_2O_4$ composite and AC were fully characterized by FTIR, SEM, XRD, TEM, TGA, and VSM techniques. Based on the surface analyses, the addition of $CoFe_2O_4$ nanoparticles had a significant effect on the thermal stability and crystalline structure of AC. Factors affecting chromium removal efficiency like pH, dosage, contact time, temperature, and initial Cr(VI) concentration were investigated. The best pH was found 2 and 3 for Cr adsorption by AC and $AC/CoFe_2O_4$ composite, respectively. The presence of ion sulfate had a greater effect on the chromium sorption efficiency than nitrate and chlorine ions. The results illustrated that both adsorbents can be used up to seven times to adsorb chromium. The adsorption process was examined by three isothermal models, and Freundlich was chosen as the best one. The experimental data were well fitted by pseudo-second-order kinetic model. The half-life ($t_{1/2}$) of hexavalent chromium using AC and $AC/CoFe_2O_4$ magnetic composite was obtained as 5.18 min and 1.52 min, respectively. Cr(VI) adsorption by AC and $AC/CoFe_2O_4$ magnetic composite was spontaneous and exothermic. In general, our study showed that the composition of $CoFe_2O_4$ magnetic nanoparticles with AC can increase the adsorption capacity of AC from 36 mg/L to 70 mg/L.

• Design & Manufacturing
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• 제14권4호
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• pp.71-77
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• 2020

Various manufacturing technologies, including over-molding and insert-injection molding, are used to produce hybrid plastics and metals. However, there are disadvantages to these technologies, as they require several steps in manufacturing and are limited to what can be reasonably achieved within the complexities of part geometry. This study aims to determine a practical approach for producing metal/plastic hybrid components by combining plastic injection molding and metal die casting to create a new hybrid metal/plastic molding process. The integrated metal/plastic hybrid injection molding process developed in this study uses the proven method of multi-component technology as a basis to combine plastic injection molding with metal die casting into one integrated process. In this study, the electrical conductivity and ampacity were verified to qualify the new process for the production of parts used in electronic devices. The electrical conductivity was measured, contacting both sides of the test sample with constant pressure, and the resistivity was measured using a micro ohmmeter. Also, the specific conductivity was subsequently calculated from the resistivity and contact surface of the conductor path. The ampacity defines the maximum amount of current a conductive path can carry before sustaining immediate or progressive deterioration. The manufactured hybrid multi-components were loaded with increasing currents, while the temperature was recorded with an infrared camera. To compare the measured infrared images, an electro-thermal simulation was conducted using commercial CAE software to predict the maximum temperature of the power loaded parts. Overall, during the injection molding process, it was demonstrated that multifunctional parts can be produced for electric and electronic applications.

• Korean Chemical Engineering Research
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• 제60권2호
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• pp.255-259
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• 2022

태양광을 이용한 증기 발생 방법은 순수한 물이 고갈되는 현재 사회에서 해수나 폐수에서 물을 수확할 수 있는 매우 유망한 기술이다. 태양광을 이용한 증기 발생 중에서 멤브레인을 이용한 증류법은 현재 개발 중에 있지만 멤브레인이 물과 직접 접촉하여 효율적인 증발량을 늘리기가 어려웠다. 본 연구에서는 PDMS (polydimethylsiloxane)와 산화 그래핀(GO)으로 구성된 태양열 멤브레인 증기 발생기와 부분적으로 멤브레인 전체에 절친 젖음성 제어를 통해 증발량을 개선하는 것을 제안하여 실험적 연구를 수행했다. 국부적인 젖음성 제어로 태양광과의 열교환 영역에서 열 국지화 및 온도 상승에서 상당한 개선을 보여주었다. 1sun(=1000 W/m)의 조사에서 1.54 kg m^-2 h^-1의 증발 능력을 갖습니다. 그 결과, 태양열 멤브레인 증기 발생 시스템은 국부적인 물 회수 성능 메커니즘을 이해 및 실험적 확인을 수행할 수 있었다.

• Journal of Periodontal and Implant Science
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• 제52권5호
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• pp.411-421
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• 2022

Purpose: In this study, we aimed to evaluate the degree of heat generation when a novel drill design with an irrigation slot was used with metal sleeve-free (MF) and metal sleeve-incorporated (MI) surgical guides in an environment similar to that of the actual oral cavity. Methods: A typodont with a missing mandibular right first molar and 21 bovine rib blocks were used. Three-dimensional-printed MF and MI surgical guides, designed for the placement of internal tapered implant fixtures, were used with slot and non-slot drills. The following groups were compared: group 1, MI surgical guide with slot drill; group 2, MI surgical guide with a non-slot drill; and group 3, MF surgical guide with a slot drill. A constant-temperature water bath at 36℃ was used. The drilling was performed in 6 stages, and the initial, highest, and lowest temperatures of the cortical bone were measured at each stage using a non-contact infrared thermometer. Results: There were no temperature increases above the initial temperature in any drilling procedure. The only significant difference between the non-slot and slot groups was observed with the use of the first drill in the MI group, with a higher temperature in the non-slot group (P=0.012). When the heat generation during the first and the second drilling was compared in the non-slot group, the heat generation during the first drilling was significantly higher (P<0.001), and there was no significant difference in heat generation between the drills in the slot group. Conclusions: Within the limitations of this study, implant-site preparation with the surgical guide showed no critical increase in the temperature of the cortical bone, regardless of whether there was a slot in the drill. In particular, the slotted drill had a cooling effect during the initial drilling.

• 한국초전도ㆍ저온공학회논문지
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• 제24권3호
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• pp.47-51
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• 2022

With the innovative development of bio, pharmaceutical, and semiconductor technologies, it is essential to demand a next-generation transfer system that minimizes dust and vibrations generated during the manufacturing process. In order to develop dust-free and non-contact transfer systems, the high temperature superconductor (HTS) bulks have been applied as a magnet for levitation. However, sintered HTS bulk magnets are limited in their applications due to their relatively low critical current density (J_c) of several kA/cm² and low mechanical properties as a ceramic material. In addition, during cooling to cryogenic temperatures repeatedly, cracks and damage may occur by thermal shock. On the other hand, the bulk magnets made by stacked HTS tapes have various advantages, such as relatively high mechanical properties by alternate stacking of the metal and ceramic layer, high magnetic levitation performance by using coated conductors with high J_c of several MA/cm², consistent superconducting properties, miniaturization, light-weight, etc. In this study, we tried to fabricate HTS tapes stacked bulk magnets with 60 mm × 60 mm area and various numbers of HTS tape stacked layers for magnetic levitation. In order to examine the levitation forces of bulk magnets stacked with HTS tapes from 1 to 16 layers, specialized force measurement apparatus was made and adapted to measure the levitation force. By increasing the number of HTS tapes stacked layers, the levitation force of bulk magnet become larger. 16 HTS tapes stacked bulk magnets show promising levitation force of about 23.5 N, 6.538 kPa at 10 mm of levitated distance from NdFeB permanent magnet.

• Medical Lasers
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• 제9권1호
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• pp.51-57
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• 2020

Background and Objectives For experiments on simulated burn, the preparation of an animal model is a very important step. The purpose of the current experiment is to design a simple and controllable method for the preparation of third-degree scald in a mouse model using the boiling water method. Materials and Methods A total of 18 Swiss mice were used. After the anesthetization, the mice were scalded by boiling water (100℃) using a mold with a 1 cm² circle area on the dorsum at contact times of 3s, 5s, and 8s. After confirming that 8 seconds of scald can cause a third-degree scald, the skin samples were collected at day 2, 4, 6, 8, 10, and 12, and analyzed by histopathological examinations. The wound retraction index (WRI) was also measured. Results Third-degree scald involving full-thickness skin was observed in the 8-second scald group, while a 3-second scald caused a superficial second-degree scald and a 5-second scald caused a deep second-degree scald. After third-degree scald, the burn wound continued to contract until day 14. Conclusion The scalding model of mice can be successfully established by the boiling water method. This method is easy to operate, it has a low cost, and it can control the scald depth by controlling the scald time. This is adequate to study skin thermal injury in the future. The scald model established by this method can last for 14 days.