• Transactions of the Korean Society of Mechanical Engineers A
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• 제29권8호
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• pp.1093-1101
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• 2005

Hybrid mass damper systems have recently been introduced as a dynamic vibration absorber to exploit the benefits of both the conventional tuned mass damper system and the active control system. A hybrid system is programmed to function as either a conventional TMD or as an active system according to the wind conditions and the resultant building and damper mass vibration characteristics. This paper deals with the design of the robust controller for the control of the flexible box structure. The control algorithm was devised based on $H_2$(LQG) robust control logic with acceleration feedback and to improve the capability of the controller Kalman Filter was accepted for the system. To test the ability of the robust controller using the linear motor damper system, performance tests and simulations were carried out on the full-scale steel frame structure. Through the performance tests, it was confirmed that acceleration levels are reduced down.

• International Journal of Highway Engineering
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• 제20권4호
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• pp.27-34
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• 2018

PURPOSES : The objective of this study is to evaluate the physical properties of recycled asphalt mixtures reinforced with glass fiber. METHODS : Firstly, mixing design was conducted on recycled asphalt mixture for use of 50% recycled aggregate. Various laboratory tests were performed on four types of recycled asphalt mixtures with different glass fiber content to evaluate the physical properties. The laboratory tests include indirect tensile strength test, dynamic modulus test, Hamburg wheel tracking test and tensile-strength ratio to evaluate cracks, rutting and moisture resistance of mixtures. RESULTS : The indirect tensile strength of fiber reinforced glass increased about 139.4%. As a result of comparing the master curves obtained by the dynamic modulus test, the elasticity was low in the low temperature region and high in the high temperature region when the glass fiber was reinforced. The glass fiber contents of PEGS 0.3%, Micro PPGF 0.1% and Macro PPGF 0.3% showed the highest moisture resistance and rutting resistance. CONCLUSIONS : The test results show that use of glass fiber reinforcement can increase the resistance to cracking, rutting, and moisture damage of asphalt mixtures. It is also necessary to validate the long-term performance of recycled asphalt mixtures with glass fiber using full scale pavement testing and field trial construction.

• Journal of the Korean Society of Clothing and Textiles
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• 제35권2호
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• pp.136-145
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• 2011

This study identifies methods to design patterns for jeans that are suitable for women in their twenties. Five patterns suggested by previous researchers were used to draw the same size of jeans (waist 67 and hip 91). The author compared and analyzed the measurements and shapes of the patterns, ranging from waist to crotch. Samples were produced based on these patterns and then tests were conducted to observe the dynamic functions and exteriors of the samples. The dynamic functions observed in this study include walking, ascending stairs, descending stairs and sitting on chairs. The results of the current study are as follow. The best evaluated pattern in terms of exteriors is the one where the hips and thighs are tightest compared to other patterns and where the back part is wider than the front part. This pattern also received high evaluations in dynamic functions due to comfort when walking. Regarding ascending or descending stairs, the tests found that all its parts (except the front crotch) are more comfortable than those of any other patterns. All these results show that a comfortable fit and easy movement is possible when the crotch width of the back is broader than the hip width so that the hips are comfortably supported.

• Transactions of Materials Processing
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• 제20권4호
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• pp.309-315
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• 2011

The behavior of metallic materials at high strain rates shows different characteristics from those in quasi-static deformation. Therefore, the strain rate should be considered when simulating crash events. The objective of this paper is to evaluate the dynamic tensile characteristics of SPRC440 as a function of the volume fraction of phases. As-received SPRC440 is composed of ferrite and pearlite phases. However, ferrite and martensite phases were observed after heat treatment at $730^{\circ}C$ and $780^{\circ}C$ for 5 minutes, as expected by calculations based on the curves from dilatometry tests. High cross-head speed tensile tests were performed to acquire strain-stress curves at various strain rates ranging from 0.001 to $300\;s^{-1}$, which are typical in real vehicle crashes. It was observed that the flow stress increases with the strain rate and this trend was more pronounced in the as-received specimens consisting of ferrite and pearlite phases. It is speculated that the dislocation density in each phase has an influence on the strain rate sensitivity.

• Journal of the Earthquake Engineering Society of Korea
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• 제17권2호
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• pp.79-88
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• 2013

Steel plate concrete (SC) composite structure is now being recognized as a promising technology applicable to nuclear power plants as it is faster and suitable for modular construction. It is required to identify its dynamic characteristics prior to perform the seismic design of the SC structure. Particularly, the damping ratio of the structure is one of the critical design factors to control the dynamic response of structure. This paper compares the criteria for the damping ratios of each type of structures which are prescribed in the regulatory guide for the nuclear power plant. In order to identify the damping ratio of SC shear wall, this study made SC wall specimens and conducted experiments by cyclic lateral load tests and vibration tests with impact hammer. During the lateral loading test, SC wall specimens exhibited large ductile capacities with increasing amplitude of loading due to the confinement effects by the steel plate and the damping ratios increased until failure. The experimental results show that the damping ratios increased from about 6% to about 20% by increasing the load from the safe shutdown earthquake level to the ultimate strength level.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 한국추진공학회 2010년도 제34회 춘계학술대회논문집
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• pp.5-9
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• 2010

In the paper, the dynamic characteristics obtained from hot-firing tests of 1/2.5-scale thrust chamber for 75 tonf-class liquid rocket engine were described. To investigate the dynamic characteristics by engine start transient period and chamber pressure variation, hot-firing tests were performed in the chamber pressures of 30 bar and 60 bar. According to these variations, combustion stability in the combustion chamber was examined.

• Transactions of Materials Processing
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• 제11권6호
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• pp.529-537
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• 2002

A series of load-relaxation tests and tensile tests were conducted to study the high temperature deformation mechanism of fine duplex gamma TiAl alloy at temperatures ranging from 800 to 105$0^{\circ}C$. Results of load relaxation test showed that deformation behavior at a small imposed strain ($\varepsilon$≒0.05) was dominated by dislocation glide and dislocation climb. To investigate the deformation behavior at a large amount of strain, the processing map was constructed using a dynamic materials model. Two domains were characterized in the processing map obtained at a strain level of 0.6. One domain was found at the region of 98$0^{\circ}C$ and $10^{-3}/sec$ with a peak efficiency of 48%, which was identified as a domain of dynamic recrystallization from the microstructural observation. The order was observed at the region of 125$0^{\circ}C$ and $10^{-4}/sec$ with a peak efficiency of 64%. The strain rate sensitivity measured indicates that the material was deformed by the superplasticity in the region.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 한국소성가공학회 2008년도 춘계학술대회 논문집
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• pp.427-430
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• 2008

The influence of subsequent annealing treatment on the dynamic deformation and the fracture behavior of submicrocrystalline Al-4.4%Mg alloy is investigated in this study. After inducing an effective strain of 8 via equal-channel angular pressing at $200^{\circ}C$, most of the grains are considerably reduced to nearly equiaxed grains of $0.3{\mu}m$ in size. With an increment of various subsequent heat treatments for 1 hour, resultant microstructures are found to be fairly stable at temperatures up to $200^{\circ}C$, suggesting that static recovery will be dominantly operative, whereas grain growth is pronounced above $250^{\circ}C$. The results of tensile tests show that yield and ultimate tensile strength decrease, but elongation-to-failure and strain hardening rate increase with an increase in annealing temperatures. The dynamic deformation and the fracture behavior retrieved with a series of torsional tests are explored with respect to annealed microstructures. Such mechanical response is analyzed in relation to resultant microstructure and fracture mode.

• Nuclear Engineering and Technology
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• 제53권3호
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• pp.974-987
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• 2021

This paper presents ductile fracture simulation of full-scale cracked pipe for nuclear piping materials using the cohesive zone model (CZM). The main objective of this study is to investigate the applicability of CZM to predict ductile fracture of cracked pipes with various crack shapes and under quasi-static/dynamic loadings. The transferability of the traction-separation (T-S) curve from a small-scale specimen to a full-scale pipe is demonstrated by simulating small- and full-scale tests. T-S curves are calibrated by comparing experimental data of compact tension specimens with finite element analysis results. The calibrated T-S curves are utilized to predict the fracture behavior of cracked pipes. Three types of full-scale pipe tests are considered: pipe with circumferential through-wall crack under quasistatic/dynamic loadings, and with 360° internal surface crack under quasi-static loading. Computational results using the calibrated T-S curves show a good agreement with experimental data, demonstrating the transferability of the T-S curves from small-scale specimen.

• Earthquakes and Structures
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• 제17권4호
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• pp.399-409
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• 2019

This paper presents the experimental investigations on the seismic performance of a peculiar steel-concrete vertical hybrid structural system referred to as steel truss-RC tubular column hybrid structure. It is typically applied as the supporting structural system to house air-cooled condensers in thermal power plants (TPPs). Firstly, pseudo-dynamic tests (PDTs) are performed on a scaled substructure to investigate the seismic performance of this hybrid structure under different hazard levels. The deformation performance, deterioration behavior and energy dissipation characteristics are analyzed. Then, a cyclic loading test is conducted after the final loading case of PDTs to verify the ultimate seismic resistant capacity of this hybrid structure. Finally, the failure mechanism is discussed through mechanical analysis based on the test results. The research results indicate that the steel truss-RC tubular column hybrid structure is an anti-seismic structural system with single-fortification line. RC tubular columns are the main energy dissipated components. The truss-to-column connections are the structural weak parts. In general, it has good ductile performance to satisfy the seismic design requirements in high-intensity earthquake regions.