• The Journal of Advanced Prosthodontics
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• v.11 no.2
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• pp.128-137
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• 2019

PURPOSE. The aim of this study was to compare the effect of different finishing and polishing techniques on water absorption, water solubility, and microhardness of ceramic or glass-polymer based computer-aided design and computer-aided manufacturing (CAD/CAM) materials following thermocycling. MATERIALS AND METHODS. 150 disc-shaped specimens were prepared from three different hybrid materials and divided into five subgroups according to the applied surface polishing techniques. All specimens were subjected up to #4000 grit SiC paper grinding. No additional polishing has been done to the control group (Group I). Other polishing procedures were as follows: Group II: two-stage diamond impregnated polishing discs; Group III: yellow colored rubber based silicone discs; Group IV: diamond polishing paste; and Group V: Aluminum oxide polishing discs. Subsequently, 5000-cycles of thermocycling were applied. The analyses were conducted after 24 hours, 7 days, and 30 days of water immersion. Water absorption and water solubility results were analyzed by two-way ANOVA and Tukey post-hoc tests. Besides, microhardness data were compared by Kruskal-Wallis and MannWhitney U tests (P<.05). RESULTS. Surface polishing procedures had significant effects on water absorption and solubility and surface microhardness of resin ceramics (P<.05). Group IV exhibited the lowest water absorption and the highest microhardness values (P<.05). Immersion periods had no effect on the microhardness of hybrid ceramic materials (P>.05). CONCLUSION. Surface finishing and polishing procedures might negatively affect physical properties of hybrid ceramic materials. Nevertheless, immersion periods do not affect the microhardness of the materials. Final polishing by using diamond polishing paste can be recommended for all CAD/CAM materials.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2000.04a
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• pp.116-119
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• 2000

본 연구에서는 온도의 상승에 의하여 부피가 팽창하는 열팽창 고무 치공구의 팽창 특성을 이용하여 열경화성 복합재료를 경화하고 압축하는 과정을 실험과 모델링을 통하여 해석하였으며, 열가소성 복합재료의 함침공정을 연구하였다. 열팽창 고무치공구가 사용되는 닫힌계와 열린계에서 예상되는 압력을 이론적으로 유도하였고, 경화가 수반되는 과정에 있어서는 실험을 통하여 열팽창치공구와 프리프레그가 나타내는 압력을 측정하였다. 온도가 상승하고 경화가 수반되는 경우에 등속도 압축실험에 의하여 얻어지는 응력-변형율 곡선은 비선형점탄성 특성을 보여주었는데, 본 연구에서는 Maxwell모델을 KWW(Kohlrausch-Williame-Watts)식으로 변형시킨 모델식을 이용하여 이를 매우 정확하게 표현할 수 있었다. 또한 고무치공구를 이용하여 열가소성 수지의 복합재료 성형공정을 실험하였고, 중성자 레디오그래피 촬영을 통하여 기공의 분포를 관찰하였다.

• Proceedings of the Korean Society of Dyers and Finishers Conference
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• 2011.03a
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• pp.69-69
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• 2011

폴리케톤 섬유는 제조 원료로 에틸렌과 일산화탄소를 사용하여 합성한 공중합체 물질로 생산에 필요한 비용을 크게 절약할 수 있다. 폴리케톤 섬유는 p-아라미드 섬유에 근접하는 고강도 고탄성을 가진 섬유로 우수한 내화학성을 가지며, 고무와의 계면접착이 우수하다는 특성을 가지고 있어 MRG(Mechanical Rubber Goods)용 보강재 및 타이어코드로의 사용에 대한 관심이 증대하고 있다. 그러나 폴리케톤 섬유의 생산 및 산업현장에서의 활용은 아직 적은 상태로 그 특성에 대한 연구가 미흡한 상태이다. 따라서 본 연구에서는 폴리케톤 섬유의 기본적인 특성 분석을 하고, 폴리케톤 소재의 표면을 UV 조사와 인산을 이용한 산처리 방법을 이용하여 처리하고 표면처리에 따른 폴리케톤 섬유의 표면특성 및 물성특성을 분석하였다. UV 조사 처리시 에너지 변화와 산처리시의 pH조건 및 처리시간의 변화에 따른 표면의 미세구조를 SEM과 AFM 등을 이용하여 관찰한 결과, UV 에너지와 산처리 조건의 증가에 따라 표면요철이 증가를 보이다가 과도한 처리에 의하여 표면에 degradation이 발생하였다. 또한 UV 에너지 및 산처리 조건에 따른 열적, 화학적 그리고 물리적 특성의 변화를 분석하였다.

• Elastomers and Composites
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• v.49 no.1
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• pp.53-58
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• 2014

In this study, characteristics of visible-light responsive photocatalyst Weltouch, especially VOCs reduction of visible-light responsive photocatalyst coated nylon/polyester composite fiber for vehicle interior parts and materials were evaluated. Visible-light responsive photocatalyst Weltouch was observed for both anatase phase and rutile phase. It is activated by light longer than 420nm. VOCs and formaldehyde generated from visible-light responsive photocatalyst treated nylon/polyester composite fiber were reduced confirmly. Visible-light responsive photocatalyst was firmly attached to the surface of nylon/polyester composite fiber without elimination even after 25 times repeated washing. And washing durability of nylon/polyester composite fiber confirmed the excellence that reduction effects of VOCs after repeated washing has appeared as much as before washing.

• Progress in Superconductivity
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• v.7 no.1
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• pp.64-68
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• 2005

We fabricated Ni-based alloy substrates for YBCO coated conductor using powder metallurgy. Tungsten and copper were selected as alloy elements due to their mutual solubility to the base element of nickel. The alloying elements were mixed with nickel using ball milling and dried in air. The powder mixtures were packed in a rubber mold, cold isostatic pressed 200 MPa and made into rods. The compacted rods were sintered at $1150^{\circ}C$ for 6 hours for densification. It was confirmed by neutron diffraction experiment that W and Cu atoms made complete solid solution with Ni. Lattice constant of nickel alloy increased by $0.004{\AA}$ for 1at. $\%$ W in Ni-W alloy, $0.0006{\AA}$ for 1 at. $\%$ Cu in Ni-W-Cu alloy.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.16 no.4 s.109
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• pp.372-379
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• 2006

Little attention has been paid to static-strain-dependence of dynamic complex modulus of viscolelastic materials in computational analysisso far. Current commercial Finite Element Method (FEM) codes do not take such characteristics into consideration in constitutive equations of viscoelastic materials. Recent experimental observations that static-strain-dependence of dynamic complex modulus of viscolelastic materials, especially filled rubbers, are significant, however, require that solutions somehow are necessary. In this study, a simple technique of using a commercial FEM code, ABAQUS, is introduced, which seems to be far more cost/time saving than development of a new software with such capabilities. A static-strain-dependent correction factor is used to reflect the influence of static-strains in Merman model, which is currently the base of the ABAQUS. The proposed technique is applied to viscoelastic components of rather complicated shape to predict the dynamic stiffness under static-strain and the predictions are compared with experimental results.

• Journal of Energy Engineering
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• v.26 no.4
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• pp.1-6
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• 2017

This study evaluated hydrogen effect of metal and non-metallic materials used in the hydrogen blended natural gas vehicle. Hydrogen penetrated concentration of 34Cr-Mo steel(850MPa tensile strength) for winter driving conditions was measured 0.0018ppm and summer driving conditions was 5.3ppm. The critical hydrogen concentration of high strength metal used in this study was measured 1.03ppm by CLT. Therefore, 34CrMo steel cas cause problems in the 30% HCNG(25MPa) environment. In case of the test for non-metallic materials, all materials met the criteria of the gas resistance test, but Fluorocarbon Rubber material had a significant change in the volume. So if it is used, extra care is needed.

• Elastomers and Composites
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• v.44 no.3
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• pp.244-251
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• 2009

Recently, there are a lot of studies on the engineering application of biomimetic functional surface in the world. The nature-inspired functional surfaces offer many solutions for copying with problems which are faced with human such as environmental contamination, energy depletion, exhaustion of water, and food shortage by giving the high quality function to industrial products. In this paper, we introduce the superhydrophobicity of nature surface and review the research on theoretical modeling and fabrication of superhydrophobic surface with micro/nanostructure.

• Elastomers and Composites
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• v.45 no.3
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• pp.188-198
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• 2010

The term 'shape memory polymers (SMPs)' describes a class of polymers which can remember the original shape and recover from deformed to its original shape by the applied stimuli, e.g., heat, electricity, magnetic field, light, etc. SMPs are classified as one of the 'smart polymers' and have great potentials as high-value-added materials. Especially, low thermal, electrical, and mechanical properties of SMPs can be improved by incorporating the various fillers. This paper aims to review the SMPs and their basic principles, and the trends of the development of SMPs nanocomposites.

• Elastomers and Composites
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• v.55 no.1
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• pp.13-19
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• 2020

4,4'-Methylenebis(2-chlorobenzenamine) (MOCA)-free fast curing polyurethanes were prepared. In this study, the processibility of a fast curing polyurethane system was characterized by assessing the pot life. The obtained pot life of the polyurethane was 6-8 s, indicating that this prepolymer-curative system is appropriate for ribbon flow casting. The influence of the NCO index on the viscosity and mechanical properties was evaluated. The viscosity, tensile strength, tear strength, and hardness of the as-prepared polyurethanes showed an increasing trend, with an increase in the NCO index, whereas the elongation at break increased initially and then decreased with an increase in the NCO index. The gel fraction and crosslink density showed a direct correlation with the NCO index, which substantiated the improved mechanical properties at the higher NCO index. The coefficients of friction and abrasion deteriorated with an increase in the NCO index.