• Journal of the Korea Concrete Institute
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• v.20 no.5
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• pp.583-592
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• 2008

Recently, the effects of high temperature on compressive strength, elastic modulus and strain at peak stress of high strength concrete were experimentally investigated. The present study is aimed to study the effect of elevated temperatures ranging from 20 to 700 on the material mechanical properties of high strength concrete of 40, 60, 80 MPa grade. In this study, the types of test were the stressed test and stressed residual test that the specimens are subjected to a 25% of ultimate compressive strength at room temperature and sustained during heating and when target temperature is reached, the specimens are loaded to failure. And another specimens are loaded to failure after 24 hour cooling time. Tests were conducted at various temperatures ($20{\sim}700^{\circ}C$) for concretes made with W/B ratios 46%, 32% and 25%. Test results showed that the relative values of compressive strength and elastic modulus decreased with increasing compressive strength grade of specimen and the axial strain at peak stress were influenced by the load before heating. Thermal strain of concrete at high temperature was affected by the preload level as well as the compressive strength. Finally, model equation for compressive strength and elastic modulus of heated high strength concrete proposed by result of this study.

• Nuclear Engineering and Technology
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• v.26 no.4
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• pp.471-483
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• 1994

A sodium fire facility with a test chamber of 1.7㎥ volume was constructed and operated to carry out experiments of sodium fires such as pool, spray, and columnar fires which might take place in sodium-related facilities. The experimental results of pool fires showed that the increase of temperature and pressure in the test chamber was much smaller than that of spray and columnar fires even though their amount of sodium injection in the chamber was much larger compared to other types of fires. And it was found in pool fires that the temperatures of sodium pool and the gas temperature in the test chamber had been maintained much longer than other types of fires, and that the chamber pressure had come to vacuum due to depletion of the oxygen for a large amount of sodium injection in the chamber. The experimental results of spray fires showed that sprayed sodium of small particles instantly reacted with oxygen, and that its reaction heat increased gas temperature and pressure of the test chamber rapidly and decreased them shortly. And the maximum gas temperature and pressure of the test chamber in spray fires ore greatly changed according to the inlet sodium temperature in the test chamber. The characteristics of the columnar fires were almost similar to those of spray fires, but the maximum temperature and pressure of the test chamber were much smaller even for a large amount of sodium injection. And it was shown in spray and columnar fires that the temperatures at each measurement position in the test chamber were quite different due to the instantaneous sodium oxidation in comparision with pool fires. Finally, the graphex powder was proved to be a very effective extinguisher against sodium pool fires.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.3
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• pp.479-486
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• 2002

In this study, the progressive inelastic deformation, so called, thermal ratchet phenomenon which can occur in high temperature structures of liquid metal reactor was simulated with thermal ratchet structural test facility and 316L stainless steel test cylinder. The thermal ratchet deformation at the reactor baffle cylinder of the liquid metal reactor can occur due to the moving temperature distribution along the axial direction as the sodium free surface moves up and down under the cyclic heat-up and cool-down transients. The ratchet deformation was measured with the laser displacement sensor and LVDTs after cooling the structural specimen which is heated up to 55$0^{\circ}C$ with steep temperature gradients along the axial direction. The temperature distribution of the test cylinder along the axial direction was measured with 28 channels of thermocouples and was used for the ratchet analysis. The thermal ratchet deformation was analyzed with the constitutive equation of nonlinear combined hardening model which was implemented as ABAQUS user subroutine and the analysis results were compared with those of the test. Thermal ratchet load was applied 9 times and the residual displacement after 9 cycles of thermal load was measured to be 1.79mm. The ratcheting deformation shapes obtained by the analysis with the combined hardening model were in reasonable agreement with those of the structural tests.

• Transactions of the Korean Society of Automotive Engineers
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• v.19 no.4
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• pp.121-129
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• 2011

Hydrocarbons which are the main sources of VOCs from motor vehicles are emitted not only from the engine exhaust gas but also from evaporation of the fuel in storage and supplying systems. Evaporative emissions from gasoline fuel systems could be classified by diurnal, hotsoak and running loss. Diurnal loss test procedures are different as countries. Korea introduced new evaporative regulation in 2009 with 24hour VT-shed test procedure and relaxed emission standards. The estimations on different test procedures in this study show that the new Korean regulation get a little more severe than before and the 2 day diurnal loss test of U.S. is the most severe. So the test procedures as well as the stronger standards should be considered in the next evaporative emission regulation to reduce VOCs from motor vehicles. The important parameters to affect evaporative emissions are air and fuel temperature and fuel vapor pressure. Diurnal loss increases exponentially as rising air temperature and vapor pressure. The effects of vapor pressure on running loss are different as the capacities of canisters. Tests with simulating real temperature and driving conditions show that hydrocarbons in evaporative emissions could be more than those in exhaust gas in summer season because of the higher air temperature.

• Nuclear Engineering and Technology
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• v.38 no.3
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• pp.293-300
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• 2006

A liquid metal reactor (LMR) operated at high temperatures is subjected to both cyclic mechanical loading and thermal loading; thus, creep-fatigue is a major concern to be addressed with regard to maintaining structural integrity. The Korea Advanced Liquid Metal Reactor (KALIMER), which has a normal operating temperature of $545^{\circ}C$ and a total service life time of 60 years, is composed of various cylindrical structures, such as the reactor vessel and the reactor baffle. This study focuses on the creepfatigue crack initiation for a cylindrical Y-junction structure made of 316 stainless steel (SS), which is subjected to cyclic axial tensile loading and thermal loading at a high-temperature hold time of $545^{\circ}C$. The evaluation of the considered creep-fatigue crack initiation was carried out utilizing the ${\sigma}_d$ approach of the RCC-MR A16 guide, which is the high-temperature defect assessment procedure. This procedure is based on the total accumulated strain during the service time. To confirm the evaluated result, a high-temperature creep-fatigue structural test was performed. The test model had a circumferential through wall defect at the center of the model. The defect front of the test model was investigated after the $100^{th}$ cycle of the testing by utilizing a metallurgical inspection technique with an optical microscope, after which the test result was compared with the evaluation result. This study shows how creep-fatigue crack initiation for a high-temperature structure can be predicted with conservatism per the RCC-MR A16 guide.

• Journal of the Korean Ceramic Society
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• v.52 no.6
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• pp.441-448
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• 2015

Silicon carbide (SiC) coatings for tri-isotropic (TRISO) nuclear fuel particles were fabricated using a chemical vapor deposition (CVD) process onto graphite. A micro-tensile-testing system was developed for the mechanical characterization of SiC coatings at high temperatures. The fracture strength of the SiC coatings was characterized by the developed micro-tensile test in the range of $25^{\circ}C$ to $1000^{\circ}C$. Two types of CVD-SiC films were prepared for the micro-tensile test. SiC-A exhibited a large grain size (0.4 ~ 0.6 m) and the [111] preferred orientation, while SiC-B had a small grain size (0.2 ~ 0.3 mm) and the [220] preferred orientation. Free silicon (Si) was co-deposited onto SiC-B, and stacking faults also existed in the SiC-B structure. The fracture strengths of the CVD-SiC coatings, as measured by the high-temperature micro-tensile test, decreased with the testing temperature. The high-temperature fracture strengths of CVD-SiC coatings were related to the microstructure and defects of the CVD-SiC coatings.

• Journal of Korean Society of Forest Science
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• v.94 no.2 s.159
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• pp.73-81
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• 2005

This study was conducted to examine the geographic variation among provenances of Pinus densiflora in survival rate and height growth at four test plantations (Jungsun, Chungju, Naju, and Jeju). The plantations were parts of the eleven provenance trials of Pinus densiflora established by Korea Forest Research Institute in 1996. The survival rate and height growth were significantly different among test plantations at $p{\leq}0.01$. Latitude and longitude of test plantation were negatively correlated with survival rate and height growth. On the other hand, annual mean temperature, mean temperature (Nov.~Feb.), extremely low temperature (Dec.~Feb.), and annual mean growing days of test plantation were positively correlated with these two. The relationships between growth variables and geographic variables were analysed with canonical correlation analysis. A considerable amount of variation in survival rate and height growth was explained by latitude, annual mean growing days, extremely low temperature (Dec.~Feb.) and extremely high temperature (Nov.~Feb.) of provenances. It is estimated that up to 47.1% and 67.4% of the genetic variability in survival rate and height growth was attributable to the environmental variability of the provenances, respectively. The response surface curve of survival rate and height growth was plotted against latitude and longitude to examine growth performance of provenances for each test site. Generally, the local provenances showed better survival rate and height growth.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.14 no.5
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• pp.120-125
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• 2015

This research aims to increase the reliability and reproducibility of the ambient cycling test by properly making corrections to the test procedure. The vessel (106 L) is initially filled with 70 L of water and horizontally placed on a balance. The pressure range inside the vessel varies from 2.5 to 25.9 MPa at the frequency of 6 cycles per minute. After reviewing the results, there was a temperature difference of approximately $10^{\circ}C$ between the air pocket and the water, and the upper part of the liner faced a repeated temperature change of $40^{\circ}C$. It is possible for the aluminum liner of the composite vessel to be damaged by such a sharp change in temperature. Additionally, as a result, no pass having anything to do with the purpose of the test would occur. Therefore, it is suggested that the air pocket be completely removed.

• Journal of Sensor Science and Technology
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• v.4 no.1
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• pp.43-50
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• 1995

We measured the traceability error for nine high temperature calibration service centers including KRISS through the round-robin test. In this test the type S thermocouple, which used as a calibration standard thermometer commonly, was accommodated as a test thermocouple. Intercomparison data of three institutions were coincident with KRISS's data within ${\pm}0.5^{\circ}C$, which was the calibration uncertainty of the type S thermocouple, but the remaining six institution's data were deviated from the assigned uncertainty level. Deviation of the intercomparison data increased gradually according to the increase of the test temperature. and the maximum difference was so large as about $2.0^{\circ}C$ at the highest test temperature, gold point. In this study we found the traceability error of high temperature calibration service center for a high temperature standard was within $2.0^{\circ}C$.

• The Korean Journal of Applied Statistics
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• v.34 no.3
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• pp.439-447
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• 2021

Due to the frequent emergence of global abnormal climates, related studies on meteorological change is being actively proceed. However, the research on trend analysis using weather data accumulated over a long period of time was insufficient. In this study, the trend of temperature time series data accumulated from automated surface observing system (ASOS) for 40 years was analyzed by using a non-parametric analysis method. As a result of the Mann-Kendall test on the annual average temperature and seasonal average temperature time series data in South Korea, it has shown that an upward trend exists. In addition, the result of calculating the Sen's slope, which can determine the degree of tendency before and after the searched change point by applying the Pettitt test, recent data after the fluctuation point confirmed that the tendency of temperature rise was even greater.