• Proceedings of the Materials Research Society of Korea Conference
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• 2009.11a
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• pp.35.2-35.2
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• 2009

최근 전세계적으로 저탄소, 녹색성장으로 인하여 원자력발전이 주목받고 있다. 또한 에너지의 고효율로 인한 발전소의 설비가 대형화가 됨에 따라 발전소의 수명평가와 건전성평가가 중요해지고 있다. 일반적으로 구조물 내에 존재하는 균열의 크기와 형상을 파악하여 피로균열전파속도를 평가함으로써 건전성평가를 확인하고 있다. 그리고 고온, 고압에서의 피로균열전파속도는직류전위차 (Direct Current Potential Drop : DCPD)법을 사용하고 있다. DCPD법은 균열의 정밀한 측정방법으로써 측정시 오차가 발생하기 때문에 ASTM에서 제시된 incremental polynomial 법을 권고하고 있다. 따라서 본 연구에서는 피로균열전파전파속도의통계적처리를 통해서 합리적인 곡선을 구하여 건전성평가에 활용하고자 한다. 실험에 사용된 시편은 두께 5mm, 폭 25.4mm CT시편을 사용하였으며, 1mm의 예비균열을 주었다. 그리고 실험온도는 상온에서 실시 하였으며, 주파수는 10Hz를 주었다. 그리고 DCPD 측정을 위해 5A의 전류를 주었으며, 이때 측정된 전압값을 ASTM에 제시된 관계식에넣어 균열길이로 환산하였으며, 데이터처리는 ASTM에 제시된 incremental polynomial법을 기본적으로 사용하였다. 또한 ASTM에 제시된 2n+1을 이용하여 데이터의 수 n을 1~7 까지 변화를 주어 3~15 point 까지 데이터를 처리하여곡선을 제시하였다. 분석결과 $R^2$값이 1을 기준으로 했을 때 3~7 point 까지는큰 차이를 보이지 않았지만 9-point 이후부터는 $R^2$ 감소함을 알 수 있었다. 또한 적용된 데이터의수에 따라 피로군열전파속도 곡선에서 측정된 Paris law의 n값과 C 값은 큰차이를 보이지 않았다.

• Journal of Ocean Engineering and Technology
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• v.9 no.2
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• pp.98-111
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• 1995

High temperature low cycle fatigue shows that cycle-dependent crack growth owing to cyclic plastic deformation occurred simultaneosly with time-dependent crack growth owing to intergranular deformation. Consequently, to estimate crack growth rate uniquely, many to investigators have proposed various kinds of parameters and theories but these could not produce satisfactory results. Therefore the goal of this study is focused on prediction of crack growth rate using predominant damage rule, linear cumulative damage rule and transitional parameter ${\Delta}J_c/{\Delta}J_f$. On the basis of these sinusoidal loading waveform at 600$^{\circ}C$ and 700$^{\circ}C$.

• Proceedings of the Korean Nuclear Society Conference
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• 1995.05b
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• pp.709-714
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• 1995

영광 3, 4호기에 사용되고 있는 원전 압력용기용 SA-508 IH 강의 미세구조 및 상온 피로균 열성장 특성을 고찰하였다. 본 강재의 미세구조, 석출물 분포 및 형상을 투과전자현미경을 통하여 관찰하였으며 임계영역에서의 거동 및 균열닫힘에 주목하여 피로균열성장 특성을 연구하였다. 다양한 형태의 (Fe, MR)$_3$C 세멘타이트 및 Mo$_2$C 석출물이 입계, 래스경계면 및 입내에 분포되고 있음을 확인하였다. Paris 영역에서의 피로균열성장 속도는 ASME 기준선과 유사하였으며, 임계 영역에서는 일반적인 저합금강의 경우보다 다소 낮게 나타났다. 파면조사 결과 입내 연성파괴현상이 전 $\Delta$K 영역에서 나타나고 있으며, $\Delta$K$_{th}$ 부터 $\Delta$K가 12 Mpa√m 영역에서는 입계파괴 및 입내 평활면이 관찰되었다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.5
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• pp.1097-1103
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• 1988

This paper deals with surface crack behavior and the fatigue life prediction of notched specimens using the relation between surface crack length, a, and the cycle ratio, $N/N_{f}$. From the $a-N\;/\;N_{f}$ curves, UC(the upper limit curve), LC(the lower limit curve) and MC(the middle limit curve) were assumed and utilized to predict the fatigue life and crack growth rate. The data computed from the three assumed curves were compared with the experimental data. It has been found that in the stable crack growth region ($N/N_{f}=0.3-0.8$) fatigue life can be predicted within 20% errors. Using the characteristics of $a-N\;/\;N_{f}$ curve, it is possible to predict the $da/dN-K_{max}$ curve, the $da/dN-{\Delta}K_{{\varepsilon}_t}$ curve, and the $S-N_{f}$ curve.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.1 s.173
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• pp.156-162
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• 2000

Sensitized STS 304 stainless steel crack growth rate(CGR) in high temperature water was investigated under trapezoidal wave loading test using fracture mechanics techniques. The CGR, due to stress corrosion cracking(SCC), were systematically measured as a function of the stress intensity factor and stress. holding time under trapezoidal wave loading. In high temperature water, CGR was enhanced by a synergistic effects in combination with an aggressive environment and mechanical damage. The CGR, $(da/dN)_{env}$ was basically described as a summation of the environmentally assisted crack growth rate $(da/dN)_{SCC}$, $(da/dN)_{CF}$ and fatigue crack growth rate in air $(da/dN)air,. The CGR, $(da/dN)_{env}$, increased linearly with increasing stress holding time. The CGR, $(da/dN)_{SCC}$ decreased linearly with increasing stress holding time. Fracture surface mode varied from trans-granular cracking to inter-granular cracking with increasing stress holding time.

• 한국해양학회지
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• v.29 no.3
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• pp.248-257
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• 1994

Growth rates of two manganese nodules collected in the Korea Deep Ocean Study (KODOS-89) site in the Clarion-Clipperton Fracture Zones in the central Equatorial Pacific have been estimated by employing uranium-series disequilibrium techniques to investigate the geochemical processes leading to the formation of deep-sea nodules. the growth rates estimated from the profiles of excess /SUP 230/Th activities and ratios of excess /SUP 230/Th to /SUP 232/Th to /SUP 232/Th are in the order of a few millimeters per million years. Growth rates at bottom-side of nodules are 2-3 times faster than those at top-sides. Diagenetic supply of manganese could explain the faster growth at the bottom-side of nodules.

• Rubber Technology
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• v.5 no.2
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• pp.81-93
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• 2004

• Economic and Environmental Geology
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• v.52 no.6
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• pp.587-593
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• 2019

This study were subjected to accelerated weathering test under freeze-thaw and pressure conditions to observe initiation and propagation of cracks using CLSM. Applied stress was set at 50 MPa, 55 MPa, 70 MPa for 3 samples each by using compressor and freeze-thaw experiment was conducted while samples maintained that condition. In freeze-thaw experiments, a temperature range was set to -20~40℃ which was 1 cycle for 6 hours. The freeze-thaw cycle was composed of time which reached to set temperature for 1 hour and holding time for 2 hours. On the basis of this cycle, surface of samples was observed by CLSM after each 20 freeze-thaw cycle. From this research, according to increase freeze-thaw cycle, there were 7, 10, 19 each cracks and High pressured sample's accumulate length was longer than low pressured sample's. High pressured sample's crack velocities were also faster than low pressured sample's which were calculated by accumulate length and freeze-thaw cycle.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.4
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• pp.1177-1185
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• 1996

The crack growth under creep condition is one of the major damage mechanisms which determines remaining life of the component operating at high temperatures. In this paper, the creep crack growth by grain boundary cavitation is studied, which is frequently observed failure mechanism for creep brittle materials. As a result of diffusive growth of creep cavities, it is shown that the crack-tip stress field is modified from the original stress distribution by the amount of singularity attenuation parameter which is function of crack growth rate and material properties. Also, the stress relaxation at crack-tip results in the extension of cavitating area by the load dump effect to meet the macroscopic force equilibrium conditdion.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.2
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• pp.646-652
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• 2014

It is the primary aim of this paper to propose the empirical fatigue crack propagation model fit to describe a crack growth behavior of AZ31 magnesium alloys under the different specimen thickness conditions. The empirical models estimated are Paris-Erdogan model, Walker model, Forman model, and modified-Forman model. The parameters of each model are estimated by maximum likelihood method. The statistical crack growth data needed for an estimation of empirical models are obtained by fatigue crack propagation tests under the three cases of specimen thickness. It is found that the good empirical models fit to describe a crack growth behavior of AZ31 magnesium alloys under the different specimen thickness conditions are Paris-Erdogan model and Walker model. It is also verified that a fatigue crack growth rate exponent of a empirical model may be a material constant at the specimen thickness conditions of 4.75mm and 6.60mm.