• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제51권12호
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• pp.601-607
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• 2002

IPMC(Ionic Polymer Metal Composite)actuators were optimized for producing improved forces by changing multiple parameters including repetition of number of plating, surface electroding and additive(PVP)-treatment on reduction. The platinum electrode is deposited on the surface of the material where platinum particle stay in a dense form that appears to introduce a significant level of surface electrode resistance. Actuation tests were performed for such IPMC actuators under a low voltage. The test results show that the lower surface-electrode resistance generates higher actuation capability in the IPMC actuators. In order to investigate relaxation behavior of bending and repeatability in dry condition, the IPMC was coated by$rubber(KRATON^{TM})$to minimize the effect of water evaporation from IPMC. This actuator can be used in air with surface coating to avoid membrane drying.

• Computers and Concrete
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• 제24권2호
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• pp.173-183
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• 2019

This study presents experimental and numerical results of prestressed concrete composite beams with different casting and stressing sequence. The beams were tested under three-point bending and it was found that prestressed concrete composite beams could not achieve monolith behavior due to interface slippage between two layers. The initial stress distribution due to different construction sequence has little effect on the maximum load of composite beams. The multi-step FE analyses could simulate different casting and stressing sequence thus correctly capturing the initial stress distribution induced by staged construction. Three contact algorithms were considered for interaction between concrete layers in the FE models namely tie constraint, cohesive contact and surface-to-surface contact. It was found that both cohesive contact and surface-to-surface contact could simulate the interface slip even though each algorithm considers different shear transfer mechanism. The use of surface-to-surface contact for beams with more than 2 layers of concrete is not recommended as it underestimates the maximum load in this study.

• Composites Research
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• 제27권2호
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• pp.47-51
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• 2014

본 논문은 기존의 유/공압 및 전기식 모터를 대체할 수 있는 경량, 고성능 지능소자 구동기를 설계/제작하고 이를 소형 무인비행체의 조종익 시스템에 적용 가능성을 연구한 것이다. 또한 압전 복합재료 작동기에 대한 성능평가를 수행하였으며, 유니모프 및 바이모프 형태의 작동기를 제작하여 각각의 작동 특성을 확인하였다. 이와 같은 성능시험 평과 결과를 통해 바이모프 형태의 작동기가 하중 유무와 무관하게 선형적인 받음각 변화를 가짐을 알 수 있었다. 이러한 지능소자 구동 시스템은 소형 로봇, 유도무기 및 MAV, UAV의 조종익 제어 시스템으로 사용될 수 있는 가능성을 확인하였다.

• Composites Research
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• 제25권5호
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• pp.154-158
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• 2012

복합시트의 구조를 변화시켜 흡 차음성에 미치는 영향을 연구하였다. 폴리프로필렌 보드의 표면과 배면에 폴리에틸렌테레프탈레이트 부직포를 핫 프레스로 융착하여 복합시트를 제조하였다. 면밀도가 $0.64kg/m^2$인 부직포를 사용하여 제조한 복합시트의 흡음률은 0.1-0.2의 값을 나타내어 폴리프로필렌 보드의 흡음률에 비해 약 100~400%의 증가를 나타내었다. 폴리프로필렌 보드의 면밀도를 증가시키거나 복합시트 위에 반구형의 홈을 포함하는 경우에 복합시트의 투과손실이 증가하였다. 평판 복합시트와 사인 파형을 가지는 복합시트의 구조를 변화시켜 만든 2가지 복합시트 구조에 따른 흡음률과 차음도의 변화를 조사하였다.

• Corrosion Science and Technology
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• 제18권1호
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• pp.16-23
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• 2019

Steels for automotive fuel tank require unique properties such as corrosion resistance for fuel, welding for joining, forming for press, and painting for exterior. Recently, automakers have been requiring excellent seam weldable steels to enhance manufacturing productivity of fuel tank. Thus, POSCO developed a new type of functional steels coated with nano-composite thin layer on Zn-Ni plating steels. The nano-composite coating solution was prepared by mechanical fine dispersion of solutions consisting of polymeric resin and nano-composite materials in aqueous media. The composite solution was coated on the plating steel surface by using roll coater and cured through induction furnace. These new developed plating steels were evaluated for quality performances such as seam and spot weldability, press formability, and corrosion resistance. These new functional steels coated with nano-composite layer exhibited excellent seam weldability and press formability. Detailed discussion of coating solution and experimental results suggest that nano-sized composite dispersion as coating layer plays a key role in enhancing the quality performance.

• Structural Engineering and Mechanics
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• 제72권2호
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• pp.203-216
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• 2019

Reliability analysis of composite structures considering random variation of involved parameters is quite important as composite materials revealed large statistical variations in their mechanical properties. The reliability analysis of such structures by the first order reliability method (FORM) and Monte Carlo Simulation (MCS) based approach involves repetitive evaluations of performance function. The response surface method (RSM) based metamodeling technique has emerged as an effective solution to such problems. In the application of metamodeling for uncertainty quantification and reliability analysis of composite structures; the finite element model is usually formulated by either classical laminate theory or first order shear deformation theory. But such theories show significant error in calculating the structural responses of composite structures. The present study attempted to apply the RSM based MCS for reliability analysis of composite shell structures where the surrogate model is constructed using higher order shear deformation theory (HSDT) of composite structures considering the uncertainties in the material properties, load, ply thickness and radius of curvature of the shell structure. The sensitivity of responses of the shell is also obtained by RSM and finite element method based direct approach to elucidate the advantages of RSM for response sensitivity analysis. The reliability results obtained by the proposed RSM based MCS and FORM are compared with the accurate reliability analysis results obtained by the direct MCS by considering two numerical examples.

• The Journal of Advanced Prosthodontics
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• 제4권2호
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• pp.103-108
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• 2012

PURPOSE. Debonding of a composite resin core of the fiber post often occurs at the interface between these two materials. The aim of this study was to evaluate the effects of different surface treatment methods on bond strength between fiber posts and composite core. MATERIALS AND METHODS. Sixty-four fiber posts were picked in two groups (Hetco and Exacto). Each group was further divided into four subgroups using different surface treatments: 1) silanization; 2) sandblasting; 3) Treatment with 24% $H_2O_2$, and 4) no treatment (control group). A cylindrical plexiglass matrix was placed around the post and filled with the core resin composite. Specimens were stored in 5000 thermal cycles between $5^{\circ}C$ and $55^{\circ}C$. Tensile bond strength (TBS) test and evaluation using stereomicroscope were performed on the specimen and the data were analyzed using two-way ANOVA, Post Hoc Scheffe tests and Fisher's Exact Test (${\alpha}$=.05). RESULTS. There was a significant difference between the effect of different surface treatments on TBS ($P$ <.001) but different brands of post ($P$=.743) and interaction between the brand of post and surface treatment ($P$=.922) had no significant effect on TBS. Both silanization and sandblasting improved the bonding strength of fiber posts to composite resin core, but there were not any significant differences between these groups and control group. CONCLUSION. There was not any significant difference between two brands of fiber posts that had been used in this study. Although silanization and sandblasting can improve the TBS, there was not any significant differences between surface treatments used.

• The Journal of Advanced Prosthodontics
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• 제12권5호
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• pp.322-328
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• 2020

PURPOSE. This study evaluated the shear bond strength between 3D printed provisional resin and conventional provisional resin depending on type of conventional provisional resin and different surface treatments of 3D printed resin. MATERIALS AND METHODS. Ninety-six disc-shaped specimens (Ø14 mm × 20 mm thickness) were printed with resin for 3D printing (Nextdent C&B, Vertex-Dental B. V., Soesterberg, Netherlands). After post-processing, the specimens were randomly divided into 8 groups (n=12) according to two types of conventional repair resin (methylmethacrylate and bis-acryl composite) and four different surface treatments: no additional treatment, air abrasion, soaking in methylmethacrylate (MMA) monomer, and soaking in MMA monomer after air abrasion. After surface treatment, each repair resin was bonded in cylindrical shape using a silicone mold. Specimens were stored in 37℃ distilled water for 24 hours. The shear bond strength was measured using a universal testing machine at a crosshead speed of 0.5 mm/min. Failure modes were analyzed by scanning electron microscope. Statistical analysis was done using one-way ANOVA test and Kruskal-Wallis test (α=.05). RESULTS. The group repaired with bis-acryl composite without additional surface treatment showed the highest mean shear bond strength. It was significantly higher than all four groups repaired with methylmethacrylate (P<.05). Additional surface treatments, neither mechanical nor chemical, increased the shear bond strength within methylmethacrylate groups and bis-acryl composite groups (P>.05). Failure mode analysis showed that cohesive failure was most frequent in both methylmethacrylate and bis-acryl composite groups. CONCLUSION. Our results suggest that when repairing 3D printed provisional restoration with conventional provisional resin, repair with bis-acryl composite without additional surface treatment is recommended.

• Restorative Dentistry and Endodontics
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• 제23권1호
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• pp.413-423
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• 1998

Dental ceramics exhibit excellent esthetic property, compressive strength, chemical durability, biocompatibility and translucency. This study evaluated the shear bond strength of composite resin to the new heat-pressed ceramic material (IPS-Empress System) depending on the surface treatments and bonding agents. The surface treatments were etching with 4.0% hydrofluoric acid, application of silane, and the combination of the two methods. Composite resin was bonded to ceramic with four kinds of dentin bonding agents(All-Bond 2, Heliobond, Scotch bond Multi-purpose and Tenure bonding agents). The ceramic specimen bonded with composite resin was mounted in the testing jig, and the universal testing machine(Zwick 020, Germany) was used to measure the shear bond strength with the cross head speed of 0.5 mm/min. The results obtained were as follows 1. The mean shear bond strength of the specimens of which the ceramic surface was treated with the combination of hydrofluoric acid and silane before bonding composite resin was significantly higher than those of the other surface treatment groups(p<0.05). 2. In the case of All-Bond 2 and Scotchbond Multi-purpose bonding agent group, the surface treatment methods did not influenced significantly on the shear bond(p>0.05). 3. Of the four bonding agents tested, the shear bond strength of Heliobond was significantly lower than those of other bonding agents regardless of the surface treatment methods(p<0.05). 4. The highest shear bond strength($12.55{\pm}1.92$ MPa) was obtained with Scotchbond Multipurpose preceded by the ceramic surface treatment with the combination of 4% hydrofluoric acid and silane.

• 대한치과보철학회지
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• 제32권1호
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• pp.23-36
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• 1994

Most investigators recommended that porcelain surface should be roughened with abrasives and/or be etched with acid in repairing the fractured porcelain with composite resin. This study was designed to evaluate the effect of porcelain surface treatments on the bond strength between porcelain and composite resin by measuring the shear bond strength and observing the porcelain surface with SEM. 48 porcelain disc were fabricated with Vintage porcelain and embedded in epoxy resin with the test surface exposed. The specimens were divided four groups at random and the test surfaces of the four groups were prepared as follows : Group 1 : Porcelain surface was roughened with a fine diamond and treated with 32% phosphoric acid gel for 10 seconds. Group 2 : Porcelain surface was roughened with a fine diamond and etched with 8% hydrofluoric acid gel for 5 minutes. Group 3 : Porcelain surface was roughened with a coarse diamond and treated with 32% phosphoric acid gel for 10 seconds. Group 4 : Porcelain surface was roughened with a coarse diamond and etched with 8% hydrofluoric acid gel for 5 minutes. All specimens were washed for 30 seconds. A representative specimen of each group was selected and the porcelain surface was observed with SEM at 1000 magnification. Remaining specimens were silanated, bonded with composite resin, thermocycled, and shear-tested on specially designed zig connected to Instron machine. The results were as follows : 1. The shear bond strength of the group etched with hydrofluoric acid was significantly higher than that of group treated with phosphoric acid(p<0.01). 2. The shear bond strength of the group roughened with a fine diamond was not significantly different from that of the group roughened with a coarse diamond(p>0.01). 3. SEM examination of prepared porcelain surfaces revealed that the surface etched with hydrofluoric acid showed numerous microporosities, undercut, and rougher surface than the surface treated with phosphoric acid. 4. All specimens etched with hydrofluoric acid showed cohesive failure within porcelain, but specimens treated with phosphoric acid mainly showed adhesive failure between porcelain and composite resin.