• Journal of the Korean institute of surface engineering
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• v.34 no.2
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• pp.125-134
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• 2001

($Ti_{1-x}$ $Cr_{x}$ )N coatings were deposited by an ion-plating method in a reactor with two separate metal sources, Ti and Cr. Ti was evaporated using an electron beam, while Cr evaporation was carried out by resistant heating. The Ti and Cr concentrations in the coatings were controlled by the Ti and Cr evaporation ratio. The coating hardness increased with increasing the Cr content(x) and showed a maximum value of 6,000 HK at around x=0.8. The critical load of the coatings, measured by the scratch test, was around 30 N. The wear resistance properties of the ($Ti_{1-x}$$Cr_{ x}$)N coatings were evaluated using a CSEM pin-on-disk type tribometer. A Cr-steel ball as well as a SiC ball, which had hardness values of 590 HK and 2,600 HK respectively, were used as the pin. After the wear test, the surface morphology, roughness and the concentration of the coatings were investigated, with the main focus being on the effect of wear debris and the transferred layer on the wear behavior.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.18 no.9
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• pp.815-820
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• 2005

ZnO varistor ceramics were fabricated with variation of addition of glass-frit amount and the sintering temperature was $1100^{\circ}C$. The average grain sizes were showed increased from $8.6{\mu}m\;to\;10{\mu}m$, and varistor voltages were decreased from 506V to 460V by added amount of glass-frit. Nonlinear coefficient $\alpha$, of all were with increasing the amount of glass-frit more than 70, in case of added on $0.03wt\%$ glass-frit was 83. And leakage current were less than $1{\mu}A$ with applied at $82\%$ of varistor voltage. The clamping voltage ratio of the specimens added $0.03wt\%$ glass-frit was 1.41 at applied 25A $[8/20\;{\mu}s]$. In the specimen added $0.03wt\%$ glass-frit, endurance of surge current and deviation of varistor voltage were $6200A/cm^2,\;\Delta-1.67\%$, respectively and clamping voltage ratio was 2.33. In the Specimen added $0.03wt\%$ glass-frit were superior to any other compositions on High Temperature Load Test(HTLT) for 1000 hr at $85^{\circ}C$, and deviation of the varistor voltage were $\Delta-1.29\%$.

• Proceedings of the Korean Geotechical Society Conference
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• 2006.03a
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• pp.1245-1250
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• 2006

The rapid growth of the economy recently gas led to increasing social needs for large scaled structures, such as high-rise buildings and long span bridges. In building these large-scaled structures the trend has been to construct foundations beating on or in rock masses in order to ensure stability and serviceability of the structure under several significant loads. However. when designing the drilled shaft foundation socketed in rock masses in Korea, the bearing capacity for the pier used to be determined by using the empirical expression, which depends on the compressive strength of the rock, or presumable bearing capacity recommended on foreign references or manuals. In this study, numerical analyses are used to trace rock-socketed pile behavior and are made alike with pile load test result in field. The result of this numerical analyses study have shown that following factors have a significant influence on the load capacity and settlement of the pier. Significant influence first factor of the geometry of the socket as defined by the length to diameter ratio. Second factor of the modulus of the rock both around the socket and below the base. third factor of the condition of the end of the pier with respect to the removal of drill cuttings and other loose material from the bottom of the socket.

• Journal of Korean Society of Steel Construction
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• v.18 no.5
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• pp.643-654
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• 2006

Thispaper presents the results of an experimental investigation into the fire performances ofsimply supported iTECH composite beams using an ISO834 standard fire. There are very few independent studies on the fire resistance of composite steel and concrete structures of various designs. The iTECH composite beam system has been used in construction, but nothing is known about its influence in a fire. To evaluate the fire resistance performanceof the iTECH beam, a test was conducted for 4.7m-span-length iTECH beams under given conditions in a laboratory. The fire resistance performance of unprotected coatings of the iTECH beam has been examined, and a longer period of fire resistance was achieved by increasing the beam coating's section size and decreasing its load ratio. Coatings for the fire protection of iTECH beams reduce the rate of temperature rise of the beam in case of fire, and the required thickness of spray-on fire protection coatings can be determined by means of tests.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.3
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• pp.237-243
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• 2018

In this study, the hub vibration load characteristic is evaluated for a rotor in high advance ratio conditions while investigating blade loads through the structural load prediction and harmonic analysis. Numerical studies are performed to validate the wind tunnel test data performed in NASA as the rotor advance ratios are varied from 0.40 to 0.71. A good correlation is obtained for rotor performance calculation at the range of advance ratios considered. It is observed that the hub vibration loads remain almost unchanged when the advance ratios are higher than 0.5, even though the amplitudes of blade structural loads become larger with increasing advance ratios. A harmonic analysis on blade moments is confirmed that the dominant structural mode is 3/rev component for flap bending moments and 4/rev for lag bending moments. The reason is due to the tendency of the second flap and lag mode frequencies which approach 3/rev and 4/rev, respectively, as the advance ratios are increased.

• Journal of the Korean Society for Railway
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• v.16 no.4
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• pp.305-310
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• 2013

In general, it is difficult to measure dynamic responses of a bridge with stepwise increasing speed of a train during commercial service on a high speed railroad. However, before opening the 2nd stage of the Gyeongbu high speed railroad, there was an opportunity for field tests and measurements of the bridge with stepwise increasing speed(from 170km/ h to 315km/h). The measured responses were compared with the results of a developed bridge/train interaction analysis. Although good agreement was found throughout almost the entire range of speeds, relatively large differences were found in the vicinity of the critical speed at which resonance behavior of the bridge occurs. To investigate the cause of this, reanalyses are performed with re-estimated damping ratios from field tests.

• Steel and Composite Structures
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• v.33 no.1
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• pp.111-122
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• 2019

This paper presents an experimental work on the post-fire behavior of two kinds of innovative composite stub columns under eccentric compression. The partially precast steel reinforced concrete (PPSRC) column is composed of a precast outer-part cast using steel fiber reinforced reactive powder concrete (RPC) and a cast-in-place inner-part cast using conventional concrete. Based on the PPSRC column, the hollow precast steel reinforced concrete (HPSRC) column has a hollow column core. With the aim to investigate the post-fire performance of these composite columns, six stub column specimens, including three HPSRC stub columns and three PPSRC stub columns, were exposed to the ISO834 standard fire. Then, the cooling specimens and a control specimen unexposed to fire were eccentrically loaded to explore the residual capacity. The test parameters include the section shape, concrete strength of inner-part, eccentricity ratio and heating time. The test results indicated that the precast RPC shell could effectively confine the steel shape and longitudinal reinforcements after fire, and the PPSRC stub columns experienced lower core temperature in fire and exhibited higher post-fire residual strength as compared with the HPSRC stub columns due to the insulating effect of core concrete. The residual capacity increased with the increasing of inner concrete strength and with the decreasing of heating time and load eccentricity. Based on the test results, a FEA model was established to simulate the temperature field of test specimens, and the predicted results agreed well with the test results.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.17 no.3
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• pp.87-92
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• 2018

As gas turbines for power generation become increasingly more important for high capacity and high efficiency, the technological development and investment of companies are increasing globally. Gas turbine manufacturing technology is only owned by a few companies such as GE, Siemens, and MHI, and our country currently depends on imports of processing technology and component parts. The core part of the gas turbine is curvic coupling tooth processing technology that improves turbine efficiency by smoothly transmitting power to the turbine rotor. Curvic coupling tooth machining and evaluation research is restricted overseas, and it is not underway in Korea. Therefore, in this study, roughing and finishing process technology for curvic coupling tooth machining is developed and a quantitative evaluation method is proposed. For the development of machining technology, the analysis of critical parameters was performed through C & E analysis. In the roughing process, the conditions considering the minimum machining time and tool load ratio were determined. Finishing process conditions were determined based on the contact ratio between the tooth surfaces. The image-processing method is presented for evaluation of the contact ratio and a verification test was performed.

• Journal of the Korean Geotechnical Society
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• v.19 no.4
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• pp.223-233
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• 2003

Sand compaction pile (SCP) is one of the ground improvement techniques which are being used for not only accelerating consolidation but also increasing bearing capacity of loose sands or soft clay grounds. In this study, laboratory model tests and 3-D finite element analyses were performed to investigate the interaction between sand compaction piles and surrounding soft soils. Based on the results obtained, as the area replacement ratio increases, the stress concentration ratio increases at the pile point, the settlement decreases, and the relative displacement between column and soil also decreases. It is also found that numerical study is illustrated by good comparison with model test results, and the numerical analysis revealed slip effects which could not be specifically identified in the model tests.

• Composites Research
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• v.14 no.1
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• pp.1-7
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• 2001

In this study, damage evaluation of glass fiber reinforced thermoplastic composites was investigated with acoustic emission method. Specimens of 1.7mm thickness laminate were made from PET and 7 layers o171ass fabrics. Notch and impact loading were added to the specimen and normal tensile test and tensile test with the dead load were carried out. AE signal was measured as the functions of notch ratio to the width0 and impact energy in order to find out the correlation between fracture mode and AE parameters. The result has shown that low amplitude of AE signal was due to the microcrack of matrix and its growth, whereas the amplitude in the mid range was the response to the delamination and interfacial separation. In the range of high amplitude above 90dB. the fracture of glass fabric was found. Tensile strength decreased with increasing notch ratio to the width and impact energy because of tile effect or delamination, the cracking of matrix and stress concentration. In proportion to the size of damaged area. AE signal showed its wider range of frequency and energy as well as increased number of hits.