• Journal of Korea Foundry Society
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• v.21 no.5
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• pp.296-303
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• 2001

The effects of the revolution speed on the mechanical properties and microstructure of Cr-Mo steel during vertical centrifugal casting using investment mold were investigated. The casting yield, tensile strength, hardness and absorbed energy during impact test were increased with increasing revolution speed. The effect of mass variation caused by the change in the revolution speed on the grain size was the most significant.

• Proceedings of the KWS Conference
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• 2006.10a
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• pp.123-124
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• 2006

This study aimed at exploiting low heat input characteristic of laser welding to effectively control grain coarsening in the fusion zone(FZ) and heat affected zone(HAZ) of 1.5mm thick 18wt% Cr ferritic stainless steel weld. The study demonstrated that as compared with gas tungsten arc welding(GTAW), laser welding brought about significant grain refinement in the FZ and HAZ. However, the impact absorbed energy of GTA weld was superior than that of laser weld because the strengthening effect during welding and cooling stage was higher In laser weld than that in GTA weld. The coarser grains in each weld than base metal resulted in an inferior toughness.

• Journal of the Korean Society for Railway
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• v.9 no.6 s.37
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• pp.695-700
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• 2006

This study investigates the effects of the material properties and the fatigue behavior in the SM490A material specimens due to the low-temperature atmosphere. In the fatigue behavior, the low-temperature affects the fatigue life. As the temperature get low, the fatigue limit increase, also As the yield strength and the tensile strength increase, the impact absorbed energy decrease. The difference of fatigue lift represents to normal distribution and it is larger between the room temperature and the low temperature, but in the result of the cumulative density function, the effect of temperature is not too large on it.

• Geomechanics and Engineering
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• v.30 no.5
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• pp.401-411
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• 2022

To obtain the dynamic mechanical properties, fracture modes, energy and brittleness characteristics of Furong Baijiao coal rock, the dynamic impact compression tests under 0, 4, 8 and 12 MPa confining pressure were carried out using the split Hopkinson pressure bar. The results show that failure mode of coal rock in uniaxial state is axial splitting failure, while it is mainly compression-shear failure with tensile failure in triaxial state. With strain rate and confining pressure increasing, compressive strength and peak strain increase, average fragmentation increases and fractal dimension decreases. Based on energy dissipation theory, the dissipated energy density of coal rock increases gradually with growing confining pressure, but it has little correlation with strain rate. Considering progressive destruction process of coal rock, damage variable was defined as the ratio of dissipated energy density to total absorbed energy density. The maximum damage rate was obtained by deriving damage variable to reflect its maximum failure severity, then a brittleness index BD was established based on the maximum damage rate. BD value declined gradually as confining pressure and strain rate increase, indicating the decrease of brittleness and destruction degree. When confining pressure rises to 12 MPa, brittleness index and average fragmentation gradually stabilize, which shows confining pressure growing cannot cause continuous damage. Finally, integrating dynamic deformation and destruction process of coal rock and according to its final failure characteristics under different confining pressures, BD value is used to classify the brittleness into four grades.

• Journal of the Korean Society for Heat Treatment
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• v.24 no.1
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• pp.10-15
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• 2011

Recently, renewable energy sources such as wind turbine, solar cell are interested in preventing global warming which is caused by the consumption of fossil fuel. SCM440(H) and SNCM439 have been used in the major components of the wind turbine gear because of excellent mechanical properties. In the present study, the heat treated mechanical properties of SCM440(H) and SNCM439 with 150 mm diameter were compared with those with 25 mm diameter which is generally accepted material for structural application. Heat treated SCM440(H) showed better mechanical properties such as tensile strength, hardness and impact absorbed energy compared with those in SNCM439. Hardenss value between as-quenched and as-quenched followed by tempering showed big difference in SNCM439, however the difference in SCM440(H) was relatively small. Heat treated mechanical properties of the alloys with 25 mm diameter were more uniform value than those with 150 mm diameter.

• Journal of the Korean Institute of Rural Architecture
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• v.17 no.2
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• pp.9-16
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• 2015

This study comparatively analyzed thermal characteristics of the green color, which is currently used the most, and other various colors of a rooftop urethane water proofing sheet. This study also analyzed the cooling performance by color of the water proofing sheet that fused cooling paints, and presented the effective water proofing sheet color for building energy savings. The experimental results are as follows: (1) The value of L (brightness) diminished, and brilliance also became lower from the white color to the black color, and thus, it was confirmed that relatively more heat was absorbed. In a and b chromaticity, which is the color attribute that ignores brightness, no special relationship was identified. (2) Considering that the cooling performance effect is bigger in summer than winter, due to heat reflection, the white water proofing sheet is more effective in building energy savings than the green water proofing sheet that is currently used the most. (3) The water proofing sheet's color has an impact more on cooling performance than the color of the background side of a structure on which water proofing sheet is installed. The experiment object of gray, of which background side is similar to cement mortar, was lower by $5.7^{\circ}C$ than the white background side.

• Clean Technology
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• v.6 no.2
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• pp.93-99
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• 2000

Effect of amount of red mud and processing method on the tensile and impact properties of polymers were investigated when the red mud was added as a filler to polypropylene (PP), low density polyethylene (LDPE) and PP/LDPE blend. Especially in case of PP, increase in the tensile strength, elongation at break and absorbed energy was observed when extrusion was carried out more than two times. Tensile strength showed a very remarkable increase when master batch was used in comparison with simple multiple extrusion. In case of LDPE, 10% addition of red mud resulted in the increase of tensile modulus and impact strength, while 20% addition caused a decrease in the same properties. Addition of 5% EVA could reverse this trend. Addition of 20% red mud to PP/LDPE blend gave a decrease in impact strength but 5% EPR compatibilizer could improve the impact properties. Above results showed that the processing method is a very important factor in the utilization of red mud as a plastic fillers and master batch is one of the very effective way of red mud addition.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.774-779
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• 2007

The crash energy absorbers used in the trains normally are classified into two types. The first is the structure type, which mainly used in not only the primary structure of train but also the crash energy absorbers at the critical accidents. The second is the module type, which just absorbs the crash energy independently and attached onto the structures of the trains. The expansion tube is widely used as the module type of the crash energy absorbers, especially in the trains that have a heavy mass. Since the crash energy is absorbed by means of expanding the tube in the radial direction, the features of the expansion tube have the uniform load during the compression. As the uniform load remains in sudden impact, the expansion tube is effective to decrease acceleration of passengers when the train accident occur. The buckling instability of the expansion tubes is affected by the boundary conditions, thickness and length of tube. In this study, the effects of the length and thickness of the expansion tubes under the arbitrary load on the buckling are studied using the ABAQUS/standard and ABAQUS/explicit, a commercial finite element analysis program, and then presents the guideline to design the expansion tubes. The analysis processes to compute the buckling load consist of the linear buckling analysis and the nonlinear post-buckling analysis. To analysis the nonlinear post-buckling analysis, the geometry imperfections are introduced by applying the linear buckling modes to nonlinear post-buckling analysis.

• Journal of Korean Society of Steel Construction
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• v.24 no.6
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• pp.693-700
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• 2012

In this study, the Charpy impact test along with metallurgical observation was conducted to evaluate low temperature impact toughness of structural steel welds with different welding processes to find out the optimal welding process to guarantee the required impact toughness at low temperatures. The welding processes employed are shield metal arc welding (SMAW) and flux cored arc welding(FCAW), which are commonly used welding methods in construction. The Charpy impact test is a commercial quality control test for steels and other alloys used in the construction of metallic structures. The test allows the material properties for service conditions to be determined experimentally in a simple manner with a very low cost. To investigate the impact toughness at low temperatures of the steel welds, specimens were extracted from the weld metal and the heat affected zone. Standard V-notch Charpy specimens were prepared and tested under dynamic loading condition. The low temperature impact performance was evaluated based on the correlation between the absorbed energy and the microstructure. Analysis of the results showed that the optimal welding process to ensure the higher low temperature impact toughness of the HAZ and the weld metal is SMAW process using the welding consumable for steels targeted to low temperature use.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.12
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• pp.1070-1079
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• 2012

The impact energy absorbing is a very important characteristic of an aircraft to enhance the survivability of occupants when an aircraft is under the survivable accident such as an emergency landing condition. The impact energy is generally transmitted into the occupant and absorbed through a landing gear, a subfloor (lower structure of fuselage), and a seat. The characteristic of crash energy absorbing of a subfloor depends on the type of an aircraft, a shape of structure, and an applied material. Therefore, the study of crashworthiness characteristics of a subfloor structure is very important work to improve the safety of an aircraft. In this study, a finite element model of a narrow body fuselage section for the 80~90 seats regional aircraft was developed and crash simulation was executed using an explicit finite element analysis. Through survey of the impact energy distribution of each structural part of a fuselage and floor-level acceleration response, the crashworthiness characteristics and performance was evaluated.