• 한국안전학회지
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• 제30권4호
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• pp.168-173
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• 2015

A steam generator tubing is one of the main pressure boundary of the reactor coolant system in the nuclear power plants. Structural integrity refers to maintaining adequate margins against failure of the tubing. Burst pressure of a tube at tube support plate can be higher than that for a free-span tube because failure behaviors could be interfered from the tube support plate. Alternative repair criteria for out-diameter stress corrosion cracking indications in tubes to the drilled type tube support plate were developed, however, there are very limited information to the eggcrate type tube support plate. This paper discussed reinforcement effect of steam generator tube burst pressure with axial out-diameter stress corrosion cracking within an eggcrate type tube support plate. A series of tube burst tests were performed under the room temperature and it was found out that there is no significant but marginal effects.

• Tribology and Lubricants
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• 제21권2호
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• pp.63-70
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• 2005

This study presents the thermal cracking on a commercial vehicle ventilated brake disk. Distributions of temperature and thermal stress of the disk were analysed, using FEM analysis, under the several driving conditions with actual vehicle specifications. The results from the fatigue tests on the disk material were compared with those from FEM analysis. In case of deceleration of 0.6 g with initial vehicle speed of 97, 140, and 160 km/h, the maximum compressive stress at the disk surface of disk due to braking was 224, 318, and 362 MPa, respectively. It was estimated that each damage fraction of 0.00005, 0.00050, 0.00136 per full stop was imposed on the brake disk in case of deceleration of 0.6 g with initial vehicle speed of 97, 140, and 160 km/h, respectively.

• Corrosion Science and Technology
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• 제2권2호
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• pp.82-87
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• 2003

Stress corrosion cracking of Alloy 600 and Alloy 690 has been studied with a C-ring specimen in 1%, 10% and 40% NaOH at $315^{\circ}C$. SCC test was performed at 200 mV above corrosion potential. Initial stress on the apex of C-ring specimen was varied from 300 MPa to 565 MPa. Materials were heat treated at various temperatures. SCC resistance of Ni-$_\chi$Cr-10Fe alloy increased as the Cr content of the alloy increased if the density of an intergranular carbide were comparable. SCC resistance of Alloy 600 increased in caustic solution as the product of coverage of an intergranular carbide in grain boundary, intergranular carbide thickness and Cr concentration at grain boundary increased. Low temperature mill annealed Alloy 600 with small grain size and without intergranular carbide was most susceptible to SCC. TT Alloy 690 was most resistant to SCC due to the high value of the product of coverage of an intergranular carbide in grain boundary, intergranular carbide thickness and Cr concentration at grain boundary. Dependency of SCC rate on stress and NaOH concentration was obtained.

• Corrosion Science and Technology
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• 제22권2호
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• pp.131-136
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• 2023

The aim of this study was to investigate effects of microstructure control on hydrogen diffusivity, trap activation energy, and cracking behaviors of high-strength steel using a range of experimental techniques. Results of this study showed that susceptibility to hydrogen induced cracking (HIC) was significantly associated with hydrogen diffusivity and trap activation energy, which were primarily influenced by the microstructure. On the other hand, microstructural modifications had no significant impact on electrochemical polarization behavior on the surface at an early corrosion stage. To ensure high resistance to HIC of the steel, it is recommended to increase the cooling rate during normalizing to avoid formation of banded pearlite in the microstructure. However, it is also essential to establish optimal heat treatment conditions to ensure that proportions of bainite, retained austenite (RA), and martensite-austenite (MA) constituents are not too high. Additionally, post-heat treatment at below A₁ temperature is desired to decompose locally distributed RA and MA constituents.

• 한국도로학회논문집
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• 제19권3호
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• pp.31-43
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• 2017

PURPOSES : The objective of this study is to verify the effect of fiber grid reinforcement on the long-term performance of asphalt pavement overlaid on old concrete pavement by performing field investigation, laboratory test, and finite element analysis. METHODS : The reflection cracking, roughness, and rutting of fiber grid reinforced overlay sections and ordinary overlay sections were compared. Cores were obtained from both the fiber grid reinforced and ordinary sections to measure bonding shear strength between the asphalt intermediate and asphalt overlay layers. Fracture energy, displacement after yield, shear stiffnesses of the cores were also obtained by analyzing the test results. Finite element analysis was performed using the test results to validate the effect of the fiber grid reinforcement on long-term performance of asphalt pavement overlaid on the old concrete pavement. The fatigue cracking and reflection-cracking were predicted for three cases: 1) fiber grid was not used; 2) glass fiber grid was used; 3) carbon fiber grid was used. RESULTS : The reflection-cracking ratio of fiber grid reinforced sections was much smaller than that of ordinary sections. The fiber grid reinforcement also showed reduction effect on rutting while that on roughness was not clear. The reflection-cracking was not affected by traffic volume but by slab deformation and joint movement caused by temperature variation. The bonding shear strength of the fiber grid reinforced sections was larger than that of the ordinary sections. The fracture energy, displacement after yield, and shear stiffnesses of the cores of the fiber grid reinforced sections were also larger than those of the ordinary sections. Finite element analysis results showed that fatigue cracking of glass or carbon fiber grid reinforced pavement was much smaller than that of ordinary pavement. Carbon fiber grid reinforcement showed larger effect in elongating the fatigue life of the ordinary overlay pavement compared to glass fiber grid reinforcement. The binder type of the overlay layer also affected the fatigue life. The fiber grid reinforcement resisted reflection-cracking and the carbon fiber grid showed the greater effect. CONCLUSIONS :The results of field investigation, laboratory test, and finite element analysis showed that the fiber grid reinforcement had a better effect on improving long-term performance of asphalt pavement overlaid on the old concrete pavement.

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 2001년도 추계학술발표회요약집
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• pp.215-215
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• 2001

• 한국도로학회:학술대회논문집
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• 한국도로학회 2003년도 학술발표회 논문집
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• pp.205-211
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• 2003

• 한국자원리싸이클링학회:학술대회논문집
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• 한국자원리싸이클링학회 2006년도 고분자리싸이클링 심포지엄
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• pp.39-54
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• 2006

폐플라스틱으로부터 만든 재생연료유의 연료특성 향상을 위하여 수첨 열분해 실험을 수행하였다. 주요 실험인자로 반응온도($300^{\circ}C{\sim}700^{\circ}C$), 촉매(알루미나-실리카, 활성탄, 제올라이트)를 선정하였고 이들이 액상 생성물의 인화점, 동점도, 고형물 함량에 미치는 영향을 조사하였다. $300^{\circ}C{\sim}400^{\circ}C$ 온도에서 수첨 열분해는 재생연료유의 연료특성을 개선하는 효과가 있었다. $500^{\circ}C$ 이상 온도에서는 열분해반응이 활발하게 진행되어 생성물의 인화점이 급격히 낮아졌다. 촉매를 도입하여 생성물의 인화점을 높일 수 있었는데 이는 촉매가 수첨반응을 활성화하였기 때문으로 사료된다. 동점도는 무촉매 반응에서 가장 낮은 값을, 제올라이트 촉매 반응에서 가장 높은 값을 보였다. 고형물 제거율은 모든 반응조건에서 70 % 이상이었다. 조사한 촉매들 중에서 활성탄이 재생연료유의 수첨 열분해 반응에 가장 안정적이며 높은 활성을 보였다.

• 한국주조공학회지
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• 제37권5호
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• pp.148-156
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• 2017

The effects of minor additives on the casting properties of AC4A aluminum alloys were investigated. Measurements of the cooling curve and microstructure observations were conducted to analyze the effects of Ti-B and Sr minor elements during the solidification process. A fine grain size and an increase in the crystallization temperature for the ${\alpha}-Al$ solution were evident after the addition of 0.1wt% Al-5%Ti-1%B additive. The modification effect of the eutectic $Mg_2Si$ phase with the addition of 0.05% Al-10%Sr additive was prominent. A fine eutectic $Mg_2Si$ phase and a decrease in the growth temperature of the eutectic $Mg_2Si$ phase were evident. Fluidity, shrinkage and solidification-cracking tests were conducted to evaluate the castability of the alloy. The combined addition of Al-5%Ti-1%B and Al-10%Sr additives showed the maximum filling length owing to the effect of the fine ${\alpha}-Al$ grains. The macro-shrinkage ratio increased, while the micro-shrinkage ratio decreased with the combined addition of Al-5%Ti-1%B and Al-10%Sr additives. The macro-shrinkage ratio was nearly identical, while the micro-shrinkage ratio increased with the addition of the Al-10%Sr additive. The tendency of the occurrence of solidification cracking decreased owing to the effect of the fine ${\alpha}-Al$ grains and the modification of the $Mg_2Si$ phase with the combined addition of Al-5%Ti-1%B and Al-10%Sr additives.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2000년도 봄 학술발표회논문집
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• pp.111-118
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• 2000

Concrete cracking due to the temperature gradient across the wall, caused by the difference in temperature between cryogenic liquid natural gas stored and surrounding environment of in-ground LNG storage tank, is investigated in this study. Crack propagation of concrete LNG tank is effectively simulated by using a layered degenerated shell element. In addition, material nonlinearity is taken into consideration on the basis of the nonlinear elastic-orthotropic model. Finally, numerical analysis for a real LNG storage tank is conducted with the objective to verify the efficiency of the introduced model.