• 한국마린엔지니어링학회:학술대회논문집
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• 한국마린엔지니어링학회 2001년도 추계학술대회 논문집(Proceeding of the KOSME 2001 Autumn Annual Meeting)
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• pp.80-87
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• 2001

The fatigue crack growth behavior of the SA516/60 steel which is used for pressure vessels was examined experimentally at room temperature $25^{\circ}C, -30^{\circ}C, -60^{\circ}C, -80^{\circ}C, -100^{\circ}C$ and -l2$0^{\circ}C$ with stress ratio of R=0.05, 0.1 and 0.3. Fatigue crack propagation rate da/dN related with stress intensity factor range ΔK was influenced by stress ratio in stable of fatigue crack growth (Region II) with an increase in ΔK. The resistance of fatigue crack growth at low temperature is higher compared with that at room temperature, which is attributed to the extent of plasticity-induced by compressive residual stress according to the cyclic loads. Fractographic examinations reveal that the differences of the fatigue crack growth characteristics between room and low temperatures are mainly explained by the crack closure and the strengthening due to the plasticity induced and roughness induced.

• 동력기계공학회지
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• 제4권4호
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• pp.41-47
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• 2000

Fatigue crack propagation rate and threshold characteristics of the SA516/70 steel which is used for the low temperature pressure vessels, were studied in the room temperature of $25^{\circ}C$ and low temperature ranges of $-10^{\circ}C,\;-30^{\circ}C,\;-60^{\circ}C\;and\;-80^{\circ}C$ with stress ratio of R=0.1. In the logarithmic relationship between the fatigue crack propagation rate($d{\alpha}/dN$) and stress intensity factor range ${\Delta}K$, the linear relationship was obtained up to $d{\alpha}/dN=4.425{\times}10^4mm/cycle$ in the same of room temperature, but in low temperature case, the relationship was extended to the range of low crack propagation rate. The fractured specimens were examined by SEM. Tested results showed that specimen failed at low temperature exhibit the quasi-cleavage fracture formation however considerable ductility proceed final fracture.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2002년도 추계학술대회 논문집
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• pp.359-365
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• 2002

The fatigue crack growth behavior of the SA516/60 steel which is used for pressure vessels was examined experimentally at room temperature $25^{\circ}C,\;-30^{\circ}C,\;-60^{\circ}C,\;-80^{\circ}C,\;-100^{\circ}C$ and $-120^{\circ}C$ with stress ratio of R=0.05, 0.1 and 0.3. Fatigue crack propagation rate da/dN related with stress intensity factor range ${\Delta}K$ was influenced by stress ratio in stable of fatigue crack growth (Region II) with an increase in ${\Delta}K$. The resistance of fatigue crack growth at low temperature is higher compared with that at room temperature, which is attributed to tile extent of plasticity-induced by compressive residual stress according to the cyclic loads. Fractographic examinations reveal that the differences of the fatigue crack growth characteristics between room and low temperatures are mainly explained by the crack closure and the strengthening due to the plasticity induced and roughness induced.

• 한국세라믹학회지
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• 제36권8호
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• pp.813-819
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• 1999

Ion implantation, photo-lithography, Ar ion milling과 hot press 법을 이용한 micro-fabrication techrique을 사용하여 고순도 알루미나 단결정인 사파이어의 내부에, 조절된 Ca의 첨가량을 갖고 있는, crack과 비슷한 형태의 기공들을 형성시켰다. 이 bi-cryslal을 각각의 온도에서 열처리하여 Ca 이온이 고온에서 알루미나의 morphology와 hcaling에 미치는 영향을 관찰하였다. 열처리 온도가 올라감에 따라서 crack-like pore의 내부에 hcxagonal bridging ligaments가 생성되었는데, 열처리 온도와 Ca의 첨가량이 증가할수록 크기가 커지는 것을 관찰할 수 있었고, 생성된 hexagonal bndgmg ligaments는 열처리가 진행됨에 따라 서서히 커지면서 모서리가 둥글어지는 현상을 관찰할 수 있었다. Bicrystal 내부에 형성된 crack-like pore는 열처리가 진행되면서 edge regression. ligamcnt growth 및 flow의 3가지의 특징적인 형태로 진행되었다. 이때 edge regression은 상대적으로 저온에서부터 전체 crack-like pore에서 서서히 일어나기 시작하였으며, ligament growth는 일부 crack-like pore에서 진행되있으며, 대단히 빠른 속도로 crack healing이 진행됨을 추정할 수 있었다. Flow는 $1800^{\circ}C$ 이상의 고온에서 모든 crack-like pore에 걸쳐서 느리게 일어남을 알 수 있었다.

• Nuclear Engineering and Technology
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• 제33권5호
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• pp.526-538
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• 2001

Fatigue tests in air and in room temperature water were performed to obtain comparable data and stable crack measuring conditions. In air environment, fatigue crack growth rate was increased with increasing temperature due to an increase in crack tip oxidation rate. In room temperature water, the fatigue crack growth rate was faster than in air and crack path varied on loading conditions. In simulated light water reactor (LWR) conditions, there was little environmental effect on the fatigue crack growth rate (FCGR) at low dissolved oxygen or at high loading frequency conditions. While the FCGR was enhanced at high oxygen condition, and the enhancement of crack growth rate increased as loading frequency decreased to a critical value. In fractography, environmentally assisted cracks, such as semi-cleavage and secondary intergranular crack, were found near sulfide inclusions only at high dissolved oxygen and low loading frequency condition. The high crack growth rate was related to environmentally assisted crack. These results indicated that environmentally assisted crack could be formed by the Electrochemical effect in specific loading condition.

• 한국도로학회논문집
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• 제18권2호
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• pp.43-49
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• 2016

PURPOSES : The field application and performance of continuously reinforced concrete pavement (CRCP), constructed by using the mechanical tube-feeding method, are evaluated in this study. METHODS: The location of the rebar was evaluated by using the MIRA system. The early-age CRCP performance was evaluated via visual survey, in which the crack spacing and crack width were examined. RESULTS: The location of longitudinal reinforcing bars was evaluated via MIRA testing and the results showed that the longitudinal rebars all lie within a given tolerance limit (${\pm}2.5cm$) of the target elevation. In addition, owing to the low temperature when the concrete was pured, the crack spacing in the Dae-Gu direction is slightly wider than that of the Gwang-Ju direction. Almost all of the crack spacings lay within the range of 1.0 m~3.0 m. A crack width of <0.3 mm was measured at the pavement surface. However, as revealed by the field survey, the crack spacing was not correlated with the crack width. CONCLUSIONS : In CRCP constructed by using the mechanical tube-feeding method, almost all of the longitudinal reinforcing bars lay within the tolerance limit (2.5 cm) of the target elevation. The concrete-placing temperature affects the crack spacing, owing to variations in the zero-stress temperature. Crack survey results show that there is no correlation between the crack spacing and crack width in CRCP.

• 한국자동차공학회논문집
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• 제11권5호
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• pp.219-226
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• 2003

The fatigue crack growth behavior of the SA516/60 steel used for pressure vessels was examined experimentally at room temperatures $25^{\circ}C$,$-30^{\circ}C$, $-60^{\circ}C$, $-80^{\circ}C$, $-100^{\circ}C$ and $-120^{\circ}C$ with stress ratio of R=0.05, 0.1 and 0.3. fatigue crack propagation rate da/dN related with stress intensity factor range $\Delta$K was influenced by stress ratio in stable than fatigue crack growth (Region II) with an increase in $\Delta$K. The resistance of fatigue crack growth at low temperature is higher compared with that at room temperature, which is attributed to the extent of plasticity-induced by compressive residual stress according to the cyclic loads. Fractographic examinations reveal that the differences of the fatigue crack growth characteristics between room and low temperatures are explained mainly by the crack closure and the strengthening due to the plasticity near the crack tip and roughness of the crack faces induced.

• 한국정밀공학회지
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• 제14권11호
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• pp.69-76
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• 1997

The rotating bending fatigue tests were performed using the specimens taken from Cr-Mo-V steel, widely sued in thermal power plant turbines, at various temperatures such as room temperature, 300 .deg. C, 425 .deg. C and 550 .deg. C. The characteristics of fatigue crack propagation were examined and analyzed by using fracture mechanics parameter. The plastic replica method was also applied in order to measure the crack length on the basis of serial observation of fatigue crack propagation behavior on the defected specimen surface. The fatigue crack propagation behavior of Cr-Mo-V steel was investigated within the frame work of elastic-plastic fracture mechanics. The propagation law of fatigue crack is obtained uniquely by using the term .sigma. $^{n}$ sub a/where .sigma. $_{a}$ is the service stress, a is the crack length and n is a constant. The values of constant n are nearly equal to 2.48, 2.60 and 8.61 at room temperature, 300 .deg. C and 425 .deg. C.

• 한국재료학회지
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• 제25권4호
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• pp.183-190
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• 2015

Fatigue crack growth rate tests were conducted as a function of temperature, dissolved hydrogen (DH) level, and frequency in a simulated PWR environment. Fatigue crack growth rates increased slightly with increasing temperature in air. However, the fatigue crack growth rate did not change with increasing temperature in PWR water conditions. The DH levels did not affect the measured crack growth rate under the given test conditions. At $316^{\circ}C$, oxides were observed on the fatigue crack surface, where the size of the oxide particles was about $0.2{\mu}m$ at 5 ppb. Fatigue crack growth rate increased slightly with decreasing frequency within the frequency range of 0.1 Hz and 10 Hz in PWR water conditions; however, crack growth rate increased considerably at 0.01 Hz. The decrease of the fatigue crack growth rate in PWR water condition is attributed to crack closure resulting from the formation of oxides near the crack tips at a rather fast loading frequency of 10 Hz.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회A
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• pp.264-268
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• 2008

An assessment of creep-fatigue crack behavior is required to ensure the structural integrity for high temperature components such as fast breeder reactor structures or thermal power plant components operating at an elevated temperature. In this study, an evaluation of creep-fatigue crack growth has been carried out according to the French assessment guide of the RCC-MR A16 for austenitic stainless steel structures. The assessment procedures for creep-fatigue crack growth in the recent version of the A16 (2007 edition) have been changed considerably from the previous version (2002 edition) and the material properties (RCC-MR Appendix A3) have been changed as well. The impacts of those changes on creep-fatigue crack growth behavior are quantified from the assessments with a structural model. Finally the assessment results were compared with the observed images obtained from the structural tests of the same structural specimen.