• Restorative Dentistry and Endodontics
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• 제15권2호
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• pp.17-33
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• 1990

The purpose of this study was to evaluate the fracture toughness of dental composite resins and to investigate the filler factor affecting the fracture behaviour on which the degree of fracture toughness depends. Six kinds of commercially available composite resin;, including two of each macrofilled, microfilled, and hybrid type were used for this study, The plane strain fracture toughness ($K_{10}$) was determined by three-point bending test using the single edge notch specimen according to the ASTM-E399. The specimens were fabricated with visible light curing or self curing of each composite resin previously inserted into a metal mold, and three-point bending test was conducted with cross-head speed of 0.1mm/min following a day's storage of the specimens in $37^{\circ}C$ distilled water. The filler volume fractions were determined by the standard ashing test according to the ISO-4049. Acoustic Emission(AE), a nondestructive testing method detecting the elastic wave released from the localized sources In material under a certain stress, was detected during three-point bending test and its analyzed data was compared with, canning electron fractographs of each specimen. The results were as follows : 1. The filler content of composite resin material was found to be highest in the hybrid type followed by the macrofilled type, and the microfilled type. 2. It was found that the value of plane strain fracture toughness of composite resin material was in the range from 0.69 MPa$\sqrt{m}$ to 1 46 MPa$\sqrt{m}$ and highest In the macrofilled type followed by the hybrid type, and the microfilled type. 3. The consequence of Acoustic Emission analysis revealed that the plane strain fracture toughness increased according as the count of Acoustic Emission events increased. 4. The higher the plane strain fracture toughness became, the higher degree of surface roughness and irregularity the fractographs demonstrated.

• 한국세라믹학회지
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• 제36권1호
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• pp.61-68
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• 1999

층상구조를 이루는 재료의 소결시 형성되는 다양한 결함 및 잔류응력을 고찰하기 위해 TZP-SUS계 및 ZT/SUS계다층재료와 porcelain/alumina 및 porcelain/Y-TZP 이층재료를 소결법으로 제조하였다. 상압소결로 제조한 다층재료에서는 층간의 소결수축율 차이에 의해 warping, splitting, 균열 등의 소결결함이 관찰되었으며, 중간층수 및 두께의 조절과 출발물질의 제어를 통해 이러한 소결결함이 완화됨을 알 수 있었다. Tape casting법으로 제조한 다층재료에서는 소결시 가한 압력에 의해 소결결함, 특히 warping이 제어됨을 확인할 수 있었다. 이층재료에서 형성되는 잔류응력은 vickers 압입법으로 관찰하였다. Porcelain/alumina에서는 porcelain 측의 계면에 작은 인장응력이, porcelain/Y-TZP에서는 압축응력이 형성됨을 확인할 수 있었으며, 이러한 잔류응력은 이층재료의 강도에도 영향을 미침을 알수 있었다. 결국 다층재료의 소결결함 및 잔류응력은 재료설계와 출발물질 상수에 영향을 받는다는 것을 알 수 있었다.

• 한국재료학회지
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• 제31권10호
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• pp.562-568
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• 2021

(Bi_1/2Na_1/2)TiO₃ (BNT)-based ceramics are considered promising candidates for actuator application owing to their excellent electromechanical strain properties However, to obtain large strain properties, there remain several issues such as thermal stability and high operating fields. Therefore, this study investigates a reduction of operating field in (0.98-x)Bi_1/2Na_1/2TiO₃-0.02 BiAlO₃-xSrTiO₃ (BNT-2BA-100xST, x = 0.20, 0.21, 0.22, 0.23, and 0.24) via analyses of the microstructure, crystal structure, dielectric, polarization, ferroelectric and electromechanical strain properties. The average grain size of BNT-${\underline{2}}$BA-100xST ceramics decreases with increasing ST content. Results of polarization and electromechanical strain properties indicate that a ferroelectric to relaxor state transition is induced by ST modification. As a consequence, a large electromechanical strain of 592 pm/V is obtained at a relatively low electric field of 4 kV/mm in 22 mol% ST-modified BNT-2BA ceramics. We believe that the materials synthesized in this study are promising candidates for actuator applications.

• 한국마이크로전자및패키징학회:학술대회논문집
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• 한국마이크로전자및패키징학회 2004년도 ISMP Pb-free solders and the PCB technologies related to Pb-free solders
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• pp.93-99
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• 2004

At present, LG Electronics pushes ahead to eliminate the Pb(Lead) -a hazardous material- from all products. Especially, we have performed to select the optimum standard composition of lead free alloy for the application to products for about 3 years from 2000. These days, we have the chance for applying to the mass-production. This project constructed the system for applying the lead free solders on consumer electronic products, which is one of the major products of the LG Electronics. To select the lead free solders with corresponding to the product features, we have passed through the test and applied with Sn-3.0Ag-0.5Cu alloy system to our products, and for the application to the high melting temperature composition, we secured the thermal resistance of the many parts and substrate and optimized the processing conditions. We have operated the temperature cycling test and the high temperature storage test under the standards to confirm the reliability of the products. On these samples, we considered the consequence of our decision by the operating test. For the long life time of the product, we have operated the temperature cycling test at $-45^{\circ}C-+125^{\circ}C$, 1 cycle/hour, 1000 cycles. Also we have tested the tin whisker growth about lead free plating on lead finish. We have analyzed with the SEM, EDS and any other equipment for confirming the failure mode at the joint and the tin whisker growth on lead free finish.

• 대한기계학회논문집A
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• 제21권9호
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• pp.1364-1372
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• 1997

In this paper, the forging of helical gears has been investigated. Punch is tooth-shaped as is the die insert. The punch compresses a cylindrical billet placed in a die insert. As a consequence the material of billet flows into the tooth region. The forging has been analysed by using the upper-bound method. A kinematically admissible velocity field has been developed, wherein, an involute curve has been introduced to represent tooth profile of the gear. Numerical calculations have been carried out to investigate the effects of various parameters, such as module, number of teeth, helix angle and friction factor on the forging of helical gears. Some forging experimentswere carried out with aluminum alloy to show the validity of the analysis. Good agreement was found between the predicted values of the forging load and obtained from the experimental results.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제43회 하계 정기 학술대회 초록집
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• pp.230-230
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• 2012

Graphene have showed promising performance as electrodes of organic devices such as organic transistors, light-emitting diodes, and photovoltaic solar cells. In particular, among various organic materials of graphene-based organic devices, pentacene has been regarded as one of the promising organic material because of its high mobility, chemical stability. In the bottom-contact device configuration generally used as graphene based pentacene devices, the morphology of the organic semiconductors at the interface between a channel and electrode is crucial to efficient charge transport from the electrode to the channel. For the high quality morphology, understanding of initial stages of pentacene growth is essential. In this study, we investigate self-assembly of pentacene molecules on graphene formed on a 6H-SiC (0001) substrate by scanning tunneling microscopy. At sub-monolayer coverage, adsorption of pentacene molecules on epitaxial graphene is affected by $6{\times}6$ pattern originates from the underlying buffer layer. And the orientation of pentacene in the ordered structure is aligned with the zigzag direction of the edge structure of single layer graphene. As coverage increased, intermolecular interactions become stronger than molecule-substrate interaction. As a result, herringbone structures the consequence of higher intermolecular interaction are observed.

• 한국세라믹학회지
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• 제45권9호
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• pp.507-511
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• 2008

A "C-sphere" specimen geometry was used to determine the failure strength distributions of a commercially-available bearing-grade silicon nitride ($Si_3N_4$) with ball diameters of 12.7 and 25.4 mm. Strengths for both diameters were determined using the combination of failure load, C-sphere geometry, and finite element analysis and fitted using two-parameter Weibull distributions. Effective areas of both diameters were estimated as a function of Weibull modulus and used to explore whether the strength distributions predictably scaled between each size. They did not. That statistical observation suggested that the same flaw type did not limit the strength of both ball diameters indicating a lack of material homogeneity between the two sizes. Optical fractography confirmed that. It showed there were two distinct strength-limiting flaw types common to both ball diameters, that one flaw type was always associated with lower strength specimens, and that a significantly higher fraction of the 25.4-mm-diameter C-sphere specimens failed from it. Predictable strength-size-scaling would therefore not result as a consequence of this because these flaw types were not homogenously distributed and sampled in both C-sphere geometries.

• 소성∙가공
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• 제18권2호
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• pp.160-165
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• 2009

A Study on Effects of the Runner and the Gate of double shot injection molded Parts using CAE Double shot injection molding can inject two different materials or two different colors in the same mold in a injection molding process. Double shot injection molded parts can be characterized that the base part maintains strength and specified part can inject soft-material. It can reduce the production cost by single automatic operations. In this paper, we designed double shot injection mold for automobile emote control To inject secondary part, this part is used as an insert after external appearance of product is injected. CAE analysis was progressed gate location and runner size as variables. The analysis result is reflected in mold design process. As a result, it could solve problems which are generated in the conventional mold. Additionally, cost can be downed by reducing runner weight. As well as it could omit painting process because the surface of finished product is improved through new mold.

• Carbon letters
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• 제14권1호
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• pp.40-44
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• 2013

The bipolar plate is the most important and most costly component of proton exchange membrane fuel cells. The development of a suitable low density bipolar plate is scientifically and technically challenging due to the need to maintain high electrical conductivity and mechanical properties. Here, bipolar plates were developed from different particle sizes of natural and expanded graphite with phenolic resin as a polymeric matrix. It was observed that the particle size of the reinforcement significantly influences the mechanical and electrical properties of a composite bipolar plate. The composite bipolar plate based on expanded graphite gives the desired mechanical and electrical properties as per the US Department of Energy target, with a bulk density of 1.55 $g.cm^{-3}$ as compared to that of ~1.87 $g.cm^{-3}$ for a composite plate based on natural graphite (NG). Although the bulk density of the expanded-graphite-based composite plate is ~20% less than that of the NG-based plate, the I-V performance of the expanded graphite plate is superior to that of the NG plate as a consequence of the higher conductivity. The expanded graphite plate can thus be used as an electromagnetic interference shielding material.

• 한국근적외분광분석학회:학술대회논문집
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• 한국근적외분광분석학회 2001년도 NIR-2001
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• pp.1285-1285
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• 2001

For NIR measurements of papers normally diffuse reflectance accessories are used which can provide a large sampling area. The in-line process control FT-NIR spectrometer MATRIX-E enables the contactless measurement of paper samples of low silicone coat weights on label-stocks in a paper converting factory. For this study concentrations of silicone between 0 and 2 g/$m^2$ on various paper substrates were included in a quantitative method. The aim was to achieve an absolute value for the deviation from the target value of 1 g/$m^2$ during continuous movement of the paper with velocities around 400 numinute. Influences from the uncoated paper type due to supplier, color, opacity, area densities, pre-coating as well as different compounds of the agent silicone were investigated and it was found that all these papers can be represented in one PLS-model. Especially the fact that silicone as an element is present in clay coated papers is of no consequence to the measurements with MATRIX-E. Moreover during in-line installations the variation of the moisture contents in the moving paper due to variable machine velocities as well as the reflecting material of the cylinder have to be considered. It is shown that the result of the in-line calibration has the same prediction ability compared to lab scale results(Root Mean Square Error of Cross-Validation RMSECV = 0.034 g/$m^2$).