• The Korean Journal of Rheology
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• v.6 no.2
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• pp.139-146
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• 1994

미연신, 비결정 PET 필름의 띠연신조건(띠연신 응력, 띠연신 온도, 띠열판의 상승속 도)에 따른 필름의거동을 연구하였다. 띠열판의 상승속도가 10, 20, 30, 50 mm/min일 때 온 도(Td) 이하에서는 임계네킹응력이 띠연신 온도가 증가함에 따라 급격히 감소하고 그 온도 이상에서는 거의 변하지 않고 일정했으며 임계온도 이하에서는 임계온도와 띠연신 온도의 온도차(Tc-Td)가 임계네킹응력과 비례관계를 가져 다음과 같은 간단한 실험식을 얻었다. $\sigma$c=0.838 (Tc-Td)+$\sigma$0 임계네킹응력에서 띠연신한 필름의 치수는 연신 온도와 띠열판의 상 승속도에 거의 의존하지 않고 일정한 값을 나타내었다. 임계네킹응력 이상에서는 연신 조건 에 따라 필름의 폭, 두께, 그리고 연신비가 거의 변하지 않았다.

• Nuclear Engineering and Technology
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• v.17 no.3
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• pp.193-199
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• 1985

Iodine-induced stress corrosion cracking tests of Zircaloy-4 cladding were undertaken using the modified infernal pressurization method. The effects of iodine concentration and applied stress were studied. The critical iodine concentration for SCC was found to be about 0.2 mg/$\textrm{cm}^2$ at 603$^{\circ}$K. The threshold stress was dependent on the test temperature and the mechanical properties of the specimen. The fracture surface showed that the crack propagated stepwise iron one grain to others until the material was unstable and then ruptured mechanically. The initial region showed the transgranular feature and the wedge-shaped cracks. As the crack proceeded, the transgranular and ductile-tearing mired feature appeared in the middle region.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.4
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• pp.491-496
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• 2013

Finite element simulations of tensile tests were performed to determine the equivalent stress - equivalent plastic strain curves, critical equivalent stresses, and critical equivalent plastic strains. Then, the curves were used as inputs to finite element simulations of fracture toughness tests to determine the plane strain fracture toughness. The critical COD was taken as the COD when the equivalent plastic strain at the crack tip reached a critical value, and it was used as a crack growth criterion. The relationship between the critical COD and the critical equivalent plastic strain or the reduction of area was found. The relationship between the plane strain fracture toughness and the product of the critical equivalent stress and the critical equivalent plastic strain was also found.

• Proceedings of the Korean Nuclear Society Conference
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• 1996.05c
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• pp.188-192
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• 1996

재결정 Zircaloy-2의 요드에 의한 응력부식균열의 전파속도를 직류전압강하측정법 (DCPD, Direct Current Potential Drop)을 이용하여 측정하고 임계응력집중계수( $K_{ISCC}$)를 구하였다. 임계요드농도 이상인 0.01 MPa의 요드농도에서, $K_{ISCC}$는 300 $^{\circ}C$의 경우 약 15 MPa√m, 350 $^{\circ}C$의 경우 약 12 MPa√m의 응력계수였으며, plateau 구역에서의 균열속도는 $10^{-4}$~ $10^{-3}$ mm/sec 영역이었다.

• Nuclear Engineering and Technology
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• v.10 no.2
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• pp.65-72
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• 1978

In this paper, it is attempted to investigate the phenomena of iodine stress corrosion cracking of Zircaloy-4 cladding failures in reactor through the results of similar out-of-pile test in iodine vapour. The main result of this experiment is a finding of the relation between the threshold stress which can lead to iodine stress corrosion cracking of Zircaloy-4 tube and the iodine concentration. The values of critical stress and the critical iodine concentration are also obtained. A model which relates failure time of Zircaley-4 tube to failure stress and iodine concentration is suggested as follows: log t$_{F}$ =5.5-(3/2)log$_{c}$-4log $\sigma$ where t$_{F}$ : failure time, minutes c: iodne concentration, mg/㎤ $\sigma$: stress, 10$^4$psi.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.05a
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• pp.385-390
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• 2009

The gas turbine engine structures usually are placed on high thermal mechanical stress condition. For general low cycle fatigue evaluation, simple fatigue criterion based on critical plane approach is developed. LCF life of turbine wheel is evaluated with this criterion and process contrived together.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.11 s.254
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• pp.1384-1391
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• 2006

The problem of an infinite anisotropic material with a crack inclined with respect to the principal material axes is analyzed. The material is subjected to uniform biaxial load along its boundary. It is assumed that the material is homogeneous, but anisotropic. By considering the effect of the horizontal load, the distribution of stresses at the crack tip is analyzed. The problem of predicting critical stress in anisotropic solids which is a subject of considerable practical importance is examined and the effect of load biaxiality is made explicitly. The present results based on the normal stress ratio theory show significant effects of biaxial load, crack inclination angle and fiber orientation on the critical stress. The analysis is performed for a wide range of the crack angles and biaxial loads.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.37-42
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• 2003

The problem of an orthotropic material with a central crack is studied. The material is subjected to uniform biaxial loading along its boundary. The normal stress ratio theory is applied to predict fracture strength behavior in cracked orthotropic material. The dependence of the critical stress with respect to the biaxial loading and the crack orientation is discussed. Our analysis shows significant effects of biaxial loading on the critical stress. The additional tenn in the asymptotic expansion of the crack tip stress field appears to provide more accurate critical stress prediction.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.1358-1361
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• 2003

In this study, intrinsic static/dynamic fracture toughness of Al 7175-T74 are evaluated from the apparent static/dynamic toughness of notched specimen. The notch/crack critical average stress fracture model is suggested to establish the relationship to predict the intrinsic fracture toughness from the apparent fracture toughness of a notched specimen. The notch/crack critical average stress fracture model is established using the relation between the notch root radius and the effective distance calculated by finite element analysis. It is conclude that the true fracture toughness can be estimated from test results of apparent fracture toughness measured by using a notched specimen. Also, critical notch root radius can be predicted by notch/crack critical average stress fracture model.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.1021-1026
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• 2003

The problem of predicting the fracture strength behavior in orthotropic plate with a crack inclined with respect to the principal material axes is analyzed. Both the load to cause fracture and the crack direction of crack growth arc of interest. The theoretical results based on the normal stress ration theory show significant effects of biaxial loading and the fiber orientation on the crack growth angle and the critical stress. The additional term in the asymptotic expansion of the crack tip stress field appears to provide more accurate critical stress prediction.