• Journal of the Korean Crystal Growth and Crystal Technology
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• v.32 no.5
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• pp.212-217
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• 2022

Large thermal stress due to the difference between silicon carbide and graphite's coefficients of thermal expansion could be formed during crystal growing process of silicon carbide (SiC) at high temperature. The large thermal stress could separate the SiC seed crystals from graphite components, which bring about the drop of the seed crystal during crystal growth. However, the bonding properties of SiC seed crystal module has hardly reported so far. In this study, SiC and graphite were bonded using 3 types of bonding agents and a three-point bending tests using a mixed-mode flexure test were conducted for the bonded samples to evaluate the bonding characteristics between SiC and graphite. Raman spectroscopy, X-ray Photoelectron Spectroscopy, and X-ray Computed Tomography were used to analyze the bonding characteristics and the microstructures of the SiC-graphite interfaces bonded with the bonding agents. As results, an excellent bonding agent was chosen to fabricate SiC seed crystal module with 50 mm in diameter. An SiC single crystal with 50 mm in diameter was successfully grown without falling out during top seeded solution growth of SiC at high temperature.

• Journal of Dental Rehabilitation and Applied Science
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• v.27 no.2
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• pp.197-207
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• 2011

The study aimed at examining how different reline resins affect flexural strength and flexural modulus of denture base. A total of 80 specimens ($64{\times}10{\times}3.3$ mm, according to ISO 1567:1999) of heat-polymerized resin, 40 specimens for (Lucitone199(Dentsply Int., NewYork, USA), SR Ivocap(Ivoclar AG, Schaan, Liechtenstein)) respectively, were polymerized according to the manufacturer's instructions and divided into eight groups(n = 10). Control group specimens remained intact. Specimens in the other groups were abraded on both sides to 2 mm thickness, and were relined in 1.3 mm thickness with 3 types of resins (Lucitone199(Dentsply), SR Ivocap(Ivoclar), and Rebase II(Tokuyama Co., Ltd, Tokyo, Japan)). All specimens were preserved in distilled water at $37^{\circ}C$ for 50 hours, and then were subjected to flexural strength testing in a universal testing machine using 3-point loading. A crosshead speed of 5 mm/min was used, and the distance between the supports was 50 mm. Data analyses included one-way analysis of variance(ANOVA) and the Tukey Honestly Significant Difference test (p=.05). Both heat-polymerized resin groups and auto-polymerized resin groups showed statistically low flexural strength and flexural modulus than control groups. Specimens relined with Lucitone 199 showed significantly higher flexural strength and flexural modulus than those relined with SR-Ivocap. Specimens relined with auto-polymerized resin showed significantly lower flexural strength and flexural modulus than those relined with heat-polymerized resin. Relining with heat-polymerized resins showed superior mechanical properties to relining with an auto-polymerized resin. Relining with the same heat-polymerized resin as the denture base does not affect mechanical properties of a denture. Lucitone199 using a compression-mould technique resulted in the highest flexural strength.

• Journal of the Korean Ceramic Society
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• v.40 no.9
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• pp.874-880
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• 2003

The effect of h-BN content on microstructure, mechanical properties, and machinability of AlN-BN based machinable ceramics were investigated. The relative density of sintered compact decreased with increasing h-BN content. The four-point flexural strength also decreased from 238 MPa of monolith up to 182 MPa by the addition of 30 vol％ h-BN. Both low Young's modulus and residual tensile stress, formed by the thermal expansion coefficient difference between AIN and h-BN, might cause the strength drop in AlN-BN composite. The crack deflection, and pull-out phenomena increased by the plate-like h-BN. However, the fracture toughness decreased with h-BN content. The second phases, consisted of YAG and ${\gamma}$-Al$_2$O$_3$, were formed by the reaction between Al$_2$O$_3$ and Y$_2$O$_3$. During end-milling process, feed and thrust forces measured for AlN-(10～30) vol％ BN composites decreased with increasing h-BN particles, showing excellent machinability. Also, irrespective of h-BN content, relatively good surfaces with roughness less than 0.5 m (Ra) could be achieved within short lapping time.

• Tunnel and Underground Space
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• v.30 no.3
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• pp.256-269
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• 2020

The objective of this study is to evaluate the stress thresholds in crack development and the corrected fracture toughness of KURT granite under dry and saturated conditions. The stress thresholds were identified by calculation of inelastic volumetric strain from an uniaxial compression test. The corrected fracture toughness was estimated by using the Level II method (Chevron Bend specimen), suggested by ISRM (1988), in which non-linear behaviors of rock was taken into account. Average crack initiation stress(σ_ci) and crack damage stress(σ_cd) under a dry condition were 91.1 MPa and 128.7 MPa. While, average crack initiation stress(σ_ci) and crack damage stress(σ_cd) under a saturated condition were 58.2 MPa and 68.2 MPa. The crack initiation stress and crack damage stress of saturated ones decreased 36% and 47% respectively compared to those of dry specimens. A decrease in crack damage stress is relatively larger than that of crack initiation stress under a saturated condition. This indicates that the unstable crack growth can be more easily generated because of the saturation effect of water compared to the dry condition. The average corrected fracture toughness of KURT granite was 0.811 MPa·m^0.5. While, the fracture toughness of saturated KURT granite(K_CB) was 0.620 MPa·m^0.5. The corrected fracture toughness of rock in saturated condition decreases by 23.5% compared to that in dry condition. It is found that the resistance to crack propagation decreases under the saturated geological condition.

• Journal of the Microelectronics and Packaging Society
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• v.30 no.2
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• pp.52-59
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• 2023

The effects of dielectric curing temperature and temperature/humidity treatment conditions on the interfacial adhesion energies between Ti diffusion barrier/polybenzoxazole (PBO) dielectric layers were systematically investigated for Cu redistribution layer applications of fan-out wafer level package. The initial interfacial adhesion energies were 16.63, 25.95, 16.58 J/m² for PBO curing temperatures at 175, 200, and 225 ℃, respectively. X-ray photoelectron spectroscopy analysis showed that there exists a good correlation between the interfacial adhesion energy and the C-O peak area fractions at PBO delaminated surfaces. And the interfacial adhesion energies of samples cured at 200 ℃ decreased to 3.99 J/m² after 500 h at 85 ℃/85 % relative humidity, possibly due to the weak boundary layer formation inside PBO near Ti/PBO interface.

• Korean Chemical Engineering Research
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• v.45 no.5
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• pp.466-472
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• 2007

A technology platform for wafer-level three-dimensional integration circuits (3D-ICs) is presented, and that uses wafer bonding with low-k polymeric adhesives and Cu damascene inter-wafer interconnects. In this work, one of such technical platforms is explained and characterized using a test vehicle of inter-wafer 3D via-chain structures. Electrical and mechanical characterizations of the structure are performed using continuously connected 3D via-chains. Evaluation results of the wafer bonding, which is a necessary process for stacking the wafers and uses low-k dielectrics as polymeric adhesive, are also presented through the wafer bonding between a glass wafer and a silicon wafer. After wafer bonding, three evaluations are conducted; (1) the fraction of bonded area is measured through the optical inspection, (2) the qualitative bond strength test to inspect the separation of the bonded wafers is taken by a razor blade, and (3) the quantitative bond strength is measured by a four point bending. To date, benzocyclobutene (BCB), $Flare^{TM}$, methylsilsesquioxane (MSSQ) and parylene-N were considered as bonding adhesives. Of the candidates, BCB and $Flare^{TM}$ were determined as adhesives after screening tests. By comparing BCB and $Flare^{TM}$, it was deduced that BCB is better as a baseline adhesive. It was because although wafer pairs bonded using $Flare^{TM}$ has a higher bond strength than those using BCB, wafer pairs bonded using BCB is still higher than that at the interface between Cu and porous low-k interlevel dielectrics (ILD), indicating almost 100% of bonded area routinely.

• Journal of the Korean Society for Nondestructive Testing
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• v.34 no.4
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• pp.277-282
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• 2014

Recently, much attention has been paid to nonlinear ultrasonic technology as a potential tool to assess hidden damages that cannot be detected by conventional ultrasonic testing. One nonlinear ultrasonic technique is measurement of the resonance frequency shift, which is based on the hysteresis of the material elasticity. Sophisticated measurement of resonance frequency is required, because the change in resonance frequency is usually quite small. In this investigation, the nonlinear electromagnetic acoustic resonance (NEMAR) method was employed. The NEMAR method uses noncontact electromagnetic acoustic transducers (EMATs) in order to minimize the effect of the transducer on the frequency response of the object. Aluminum plate specimens that underwent three point bending fatigue were tested with a shear wave EMAT. The hysteretic nonlinear parameter ${\alpha}$, a key indicator of damage, was calculated from the resonance frequency shift at several levels of input voltage. The hysteretic nonlinear parameter of a damaged sample was compared to that of an intact one, showing a difference in the values.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.10
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• pp.1093-1100
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• 2014

The purpose of this paper is to suggest a weight-reduction design method for the hybrid carbody of a high-speed maglev train that uses aluminum extrusion profiles and sandwich composites. A sandwich composite was used on the roof as a secondary member to minimize the weight. In order to assemble the sandwich composite roof and aluminum extrusion side frame of the carbody using welding, a guide aluminum frame located at the four sides of the sandwich composite roof was introduced in this study. The clamping force of this guide aluminum frame was verified by three-point bending test. The structural integrity and crashworthiness of the hybrid carbody of a high-speed maglev train were evaluated and verified according to the Korean Railway Safety Law using a commercial finite element analysis program. The results showed that the hybrid carbody composed of aluminum extrusion frames and a sandwich composite roof was lighter in weight than a carbody made only of aluminum extrusion profiles and had better structural performance.

• The Journal of Korean Academy of Prosthodontics
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• v.47 no.2
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• pp.191-198
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• 2009

Statement of problem: Ceramics have been important materials for the restoration of teeth. The demands of patients for tooth-colored restorations and the availability of various dental ceramics has driven the increased use of new types of dental ceramic materials. Improved physical properties of theses materials have expanded its use even in posterior crowns and fixed partial dentures. However, ceramic still has limitation such as low loading capability. This is critical for long-span bridge, because bridge is more subject to tensile force. Purpose: The wire reinforced ceramic was designed to increase the fracture resistance of ceramic restoration. The purpose of this study was to evaluate the fracture resistance of wire reinforced ceramic. Material and methods: Heat pressed ceramic(ingot No.200 : IPS Empress 2, Ivoclar Vivadent, Liechtenstein) and Ni-Cr wire(Alfa Aesar, Johnson Matthey Company, USA) of 0.41 mm diameter were used in this study. Five groups of twelve uniform sized ceramic specimens(width 4 mm, thickness 2 mm, length 15 mm) were fabricated. Each group had different wire arrangement. Wireless ceramic was used as control group. The experimental groups were divided according to wire number and position. One, two and three strands of wires were positioned on the longitudinal axis of specimen. In another experimental group, three strands of wires positioned on the longitudinal axis and five strands of wires positioned on the transverse axis. Three-point bending test was done with universal testing machine(Z020, Zwick, Germany) to compare the flexural modulus, flexural strength, strain at fracture and fracture toughness of each group. Fractured ceramic specimens were cross-sectioned with caborundum disc and grinded with sandpaper to observe interface between ceramic and Ni-Cr wire. The interface between ceramic and Ni-Cr wire was analyzed with scanning electron microscope(JSM-6360, JEOL, Japan) under platinum coating. Results: The results obtained were as follows: 1. The average and standard deviation in flexural modulus, flexural strength and fracture toughness showed no statistical differences between control and experimental groups. However, strain was significantly increased in wire inserted ceramics(P<.001). 2. Control group showed wedge fracture aspects across specimen, while experimental groups showed cracks across specimen. 3. Scanning electron microscopic image of cross-sectioned and longitudinally-sectioned specimens showed no gap at the interface between ceramic and Ni-Cr wire. Conclusion: The results of this study showed that wire inserted ceramics have a high strain characteristic. However, wire inserted ceramics was not enough to use at posterior area of mouth in relation to flexural modulus and flexural strength. Therefore, we need further studies.

• Journal of Dental Rehabilitation and Applied Science
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• v.36 no.3
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• pp.183-195
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• 2020

Purpose: The purpose of this study is to compare the flexural strength of CAD/CAM denture base resins with conventional denture base resins based on their thicknesses. Materials and Methods: For the conventional denture base resins, Lucitone 199^® (C-LC) was used. DIOnavi - Denture (P-DO) and DENTCA Denture Base II (P-DC) were taken for the 3D printing denture base resins. For the prepolymerized PMMA resins, Vipi Block Gum (M-VP) and M-IVoBase^® CAD (M-IV) were used. The final dimensions of the specimens were 65.0 mm x 12.7 mm x 1.6 mm / 2.0 mm / 2.5 mm. The 3-point bend test was implemented to measure the flexural strength and flexural modulus. Microscopic evaluation of surface of fractured specimen was conducted by using a scanning electron microscope (SEM). After testing the normality of the data, one-way ANOVA was adopted to evaluate the differences among sample groups with a significance level of P = 0.05. The Tukey HSD test was performed for post hoc analysis. Results: Under the same thicknesses, there are significant differences in flexural strength between CAD/CAM denture base resins and conventional denture base resins except for P-DO and C-LC. M-VP showed higher flexural strength than conventional denture base resins, P-DC and M-IV displayed lower flexural strength than conventional denture base resins. Flexural modulus was highest in M-VP, followed by C-LC, P-DO, P-DC, M-IV, significant differences were found between all materials. In the comparison of flexural strength according to thickness, flexural strength of 2.5 mm was significantly higher than that of 1.6 mm in C-LC. Flexural strength of 2.5 mm and 2.0 mm was significantly higher than that of 1.6 mm in P-DC and M-VP. In M-IV, as the thickness increases, significant increase in flexural strength appeared. SEM analysis illustrates different fracture surfaces of the specimens. Conclusion: The flexural strength of different CAD/CAM denture base resins used in this study varied according to the composition and properties of each material. The flexural strength of CAD/CAM denture base resins was higher than the standard suggested by ISO 20795-1:2013 at a thickness of 1.6 mm or more though the thickness decreased. However, for clinical use of dentures with lower thickness, further researches should be done regarding other properties at lower thickness of denture base resins.