• Journal of the Korean Institute of Gas
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• v.10 no.1 s.30
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• pp.43-47
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• 2006

This study attempted to examine how the hydrogen embrittlement susceptibility of the STS 444 stainless steel varies under different welding conditions and how its effect on hydrogen embrittlement differs by the impressed current density levels. For doing so, U bend test specimens was used to impress the current density at 5,10, 15, and 20 $mA/cm^2$ in the $0.5M\;H_2SO_4+0.001M\;As_2O_3$ solution with an electrochemical corrosion tester. The hydrogen embrittlement was assessed by observing the time to failure, and then the microphotographs of metal structures were compared to investigate the metal- related structural properties. The study findings suggest that the effect on hydrogen embrittlement for the STS 444 steel significantly depends on both the welding conditions, or variations in the amount of shield gas, and the levels of current density. In particular, as the impressed current density increases, the hydrogen embrittlement increases rapidly.

• Journal of Welding and Joining
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• v.13 no.3
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• pp.134-146
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• 1995

Aluminium nitride(AlN) is currently under investigation as potential candidate for replacing alumium oxide(Al$_{2}$ $O_{3}$) as a substrate material for for electronic circuit packaging. Brazing of aluminium nitride(AlN) to Cu with Ag base active alloy containing Ti has been investigated in vacuum. Binary Ag$_{98}$ $Ti_{2}$(AT) and ternary At-1wt.%Al(ATA), AT-1wt.%Ni(ATN), AT-1wt.% Mn(ATM) alloys showed good wettability to AlN and led to the development of strong bond between brate alloy and AlN ceramic. The reaction between AlN and the melted brazing alloys resulted in the formation of continuous TiN layers at the AlN side iterface. This reaction layer was found to increase by increase by increasing brazing time and temperature for all filler metals. The bond strength, measured by 4-point bend test, was increased with bonding temperature and showed maximum value and then decreased with temperature. It might be concluded that optimum thickness of the reaction layer was existed for maximum bond strength. The joint brazed at 900.deg.C for 1800sec using binary AT alloy fractured at the maximum load of 35kgf which is the highest value measured in this work. The failure of this joint was initiated at the interface between AlN and TiN layer and then proceeded alternately through the interior of the reaction layer and AlN ceramic itself.

• Magazine of the Korean Society of Agricultural Engineers
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• v.34 no.3
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• pp.53-63
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• 1992

To investgate the fracture behavior of the steel fiber reinforced concreate, the specimens with different steel fiber contents of 0.0%, 0.5%, 1.0%, 1.5%, were made and notched with differents notch depth ratios of 0.0,0.2, 0.4, 0.6, and the three point bend tests were followed. Test results of 16 different types of above combined specimens were summarized as follows. 1.The load line deflection contents were found to increase 5%, 16%, 19%, respectively, compared to the unnotched specimen with the increased of initial notch depth ratio to 0.2,0.4, 0.6, respectively. 2.The frexural strength were found to decrease 14%, 16%, 21 %, respectively, compared to the unnotched specimen with the increase of initial notch depth ratio to 0.2, 0.4, 0.6,respectively. 3.The stress intensity factors of the steel fiber reinforced concrete were found to increase 1.1 1.5 1.9 times, respectively, compared to the concrete with no steel fiber content with the increase of fiber content to 0.5%, 1.0%, 1.5%, respectively. 4.The influence of the mass of the steel fiber reinforced concrete to the whole fracture energy was found to be minor with 6~8 % contribution. 5.The fracture energy of the steel fiber reinforced concrete, considering the load-deflection curve and concrete mass was found to be approximately 350-380kg m/m$^2$. 6.The regression analysis through the relationship between the compressive(Oc)/tensile (OT) strength and fracture energy(Gf) showed that the fracture energy of the steel fiber reinforced concrete could be predicted as follows. Gf= 19.2662 Oc - 3940.4 Gf= 246.876 OT- 6008.8

• Korean Journal of Food Science and Technology
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• v.20 no.4
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• pp.613-617
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• 1988

This study was undertaken to observe the effects of partial replacement of acorn starch with dent, cross-linked, or acid modified corn starches, and of refrigeration on sensory characteristics of acorn mooks(starch gels). Triangle test was used to determine if there were noticeable differences among the monks. In order to find the source of differences, various sensory properties of the monks were evaluated with quantitative descriptive analysis on unstructured scale. The results indicated that added corn starches affected significantly most of the sensory characteristics evaluated. Control acorn monks had greater intensities in color, clarity, bend property, firmness and cohesiveness. Monks containing cross-liked corn starch were more similar to control than the other mixed starch monks, fresh or refrigerated.

• Transactions of the Korean hydrogen and new energy society
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• v.28 no.5
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• pp.521-530
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• 2017

Improving the microstructure of NiO/YSZ is one of several approaches used to enhance the electrical and mechanical properties of an anode support in Solid Oxide Fuel Cells (SOFCs). The aim of the work reported in this paper was to predict the relationship between these microstructural changes and the resulting properties. To this end, modification of the anode microstructure was carried out using different sizes of Poly (Methyl Methacrylate) (PMMA) beads as a pore former. The electrical conductivity and mechanical strength of these samples were measured using four-probe DC, and three-point bend-test methods, respectively. Thermal etching followed by high resolution SEM imaging was performed for sintered samples to distinguish between the three phases (NiO, YSZ, and pores). Recently developed image analysis techniques were modified and used to calculate the porosity and the contiguity of different phases of the anode support. Image analysis results were verified by comparison with the porosity values determined from mercury porosimetry measurements. Contiguity of the three phases was then compared with data from electrical and mechanical measurements. A linear relationship was obtained between the contiguity data determined from image analysis, and the electrical and mechanical properties found experimentally. Based upon these relationships we can predict the electrical and mechanical properties of SOFC support from the SEM images.

• Corrosion Science and Technology
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• v.16 no.6
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• pp.305-316
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• 2017

Austenitic stainless steels have been widely used for various systems of nuclear power plants. Among these stainless steels, small pipes with diameter less than 14 inch have been produced in the form of seamless pipe. Annealing and cooling process during the manufacturing process can affect corrosion properties of seamless stainless steels. Therefore, 12 inch-diameter of as-received 304L stainless steel pipe was annealed and aged in this study. Intergranular corrosion resistance was evaluated by ASTM A262 Practice A, C, and E methods. The degree of sensitization was determined using a DL-EPR test. U-bend method in an autoclave was used to evaluate the SCC resistance in 0.01 M $Na_2S_4O_6$ or 40% NaOH solution at $340^{\circ}C$. As-received specimen showed relatively high degree of sensitization and intergranular corrosion rate. Carbon segregation was also observed near grain boundaries. Annealing treatment could give the dissolution of segregated carbon into the matrix. Aging treatment could induce segregation of carbon and finally form carbides. Microstructural analysis confirmed that high intergranular corrosion rate of the as-received seamless pipe was due to micro-galvanic corrosion between carbon segregation and grains.

• Physical Therapy Korea
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• v.23 no.3
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• pp.48-56
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• 2016

Background: Recently, there has been an emphasis on the use of interventions with biofeedback information for the maintenance or correction of posture. Objects: This study assessed the change of trunk posture and trunk muscle activation when people exhibiting postural kyphosis performed visual display terminal work with or without a contact feedback device (CFD). Methods: Eighteen right-handed individuals were recruited. Thoracic angle and right thoracic erector spinae (TES) muscle amplitude were analyzed. There were two sessions in these experiments. The control session involved 16 minutes of typing without a CFD, and the CFD session involved 16 minutes of typing with a CFD. The visual analog scale score was analyzed with a paired t-test, and the kinematic and electromyography data were analyzed through two-way repeated analysis of variance. Results: The paired t-tests revealed that subjects had significantly less pain after the CFD sessions than after the control sessions (p<.05). Significant main effects by session and by time were observed in the thoracic kyphosis angle (p<.05). There was a significant session${\times}$time interaction for TES amplitude (p<.05), along with significant main effects by session and by time (p<.05). Conclusion: The CFD caused people with postural kyphosis to straighten and to activate their TES continuously, even though they were habituated to bend their bodies forward. Therefore, the CFD was a beneficial treatment tool.

• The Journal of the Korean dental association
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• v.57 no.11
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• pp.672-678
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• 2019

AIM: The purpose of this study was to evaluate and compare the torsional fracture resistances, cyclic fatigue resistance, and bending stiffness of two nickel-titanium (NiTi) rotary instruments made of different heat-treated alloy: Aurum Blue (heat-treated) and Aurum Pro (conventional). Methods: Forty-five Aurum Blue and Aurum Pro NiTi files were selected for the three mechanical tests (n=15). For the torsional resistance test, 3 mm file tip was fixed and the shaft was driven clockwise at 2 rpm until fracture occurred by using a customized device. Cyclic fatigue resistance was evaluated by rotating instruments in artificial canal with dynamic mode. Bending stiffness was tested by observation of the bending moment on attaining a 45° bend. The results were analyzed by student-t tests at a significance level of 95%. The fractured surface of each groups were examined under a scanning electron microscope (SEM). Results: Aurum Blue showed significantly higher toughness, ultimate strength, distortion angle, and number of cycles to failure than those of Aurum Pro (p < 0.05). However, Aurum Blue and Aurum Pro did not differ significantly in terms of bending stiffness. SEM showed typical topographic appearances of the cyclic fatigue and torsional fracture. Conclusions: Under the limitations of this study, heat-treated instruments showed higher flexibility and fracture resistances than conventional NiTi instruments.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.7 no.2
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• pp.59-68
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• 1987

Several series of fracture tests were conducted to explore the fracture characteristics and to determine the fracture energy of concrete. A stable three-point bend test was employed to generate the load-deflection curves. The fracture energy may then be calculated from the area under the complete load-deflection curve. The initial notch-to-beam depth ratio (${\alpha}_0$/H) was varied from zero to 0.6. The prediction formula for the fracture energy of concrete is also derived and is found to depend on the tensile strength and aggregate size. The proposed fracture energy formula can be used for the fracture analysis of concrete structures. The present study also devises an equivalent crack length concept to predict the maximum failure loads of concrete beams. A simple formula for the equivalent crack length is proposed.

• Korean Journal of Materials Research
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• v.11 no.3
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• pp.221-226
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• 2001

The basal slip (0001)1/3<1120 > dislocation velocity in sapphire ($\alpha$-$Al_2$$O_3$) single crystals was measured by four-point bending test. The bending experiment was carried out in the temperature range from 120$0^{\circ}C$ to $1400^{\circ}C$ at various engineering stresses 90MPa, 120MPa, and 150MPa. The velocity of such dislocations was estimated from the bending displacement rate of the four-point bend sample. The dependence of temperature and stress in dislocation velocity was investigated. The activation energy for dislocation velocity was determined to be about 2.2$\pm$0.4eV. In addition, the stress exponent (m) describing the stress dependence of dislocation velocities was in the range of 2.0$\pm$0.2.