• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.1
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• pp.63-69
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• 2015

The primary aim of this paper is to evaluate the probabilistic fatigue crack propagation models using the residual of a random variable and to present the probabilistic model fit for the probabilistic fatigue crack growth behavior in Mg-Al-Zn alloys under maximum load conditions. The models used in this study were prepared by applying a random variable to empirical fatigue crack propagation models such as the Paris-Erdogan model, Walker model, Forman model, and modified Forman model. It was verified that the good models for describing the stochastic variation of the fatigue crack propagation behavior in Mg-Al-Zn alloys under maximum load conditions were the 'probabilistic Paris-Erdogan model' and 'probabilistic Walker model'. The influence of the maximum load conditions on the stochastic variation of fatigue crack growth is also considered.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.2
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• pp.143-156
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• 2015

The stress and displacement fields at the crack tip were studied during the unsteady propagation of a mode III crack in a direction that was different from the property graduation direction in functionally graded materials (FGMs). The property graduation in FGMs was assumed based on the linearly varying shear modulus under a constant density and the exponentially varying shear modulus and density. To obtain the solution of the harmonic function, the general partial differential equation of the dynamic equilibrium equation was transformed into a Laplace equation. Based on the Laplace equation, the stress and displacement fields, which depended on the time rates of change in the crack tip speed and stress intensity factor, were obtained through an asymptotic analysis. Using the stress and displacement fields, the effects of the angled property variation on the stresses, displacements, and stress intensity factors are discussed.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.21 no.4
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• pp.383-390
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• 2008

This paper presents the formulation and numerical implementation of a spectral scheme specially developed to simulate dynamic fracture events in unidirectional and cross-ply fiber-reinforced composites. The formulation is based on the spectral representation of the transversely isotropic elastodynamic relations between the traction stresses along the fracture plane and the resulting displacements. Example problem of dynamically propagating cracks in fiber-reinforced composites is investigated and compared with reference solutions available in the literature and/or experimental observations. This scheme can be directly applicable to the interfacial fracture analysis in the FRP reinforced concrete structures.

• Journal of the Society of Naval Architects of Korea
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• v.38 no.3
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• pp.84-92
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• 2001

The development of a crack propagation simulation model in consideration of crack closure behavior was discussed in the accompanying paper by the authors, Kim et al(2001). To verify crack propagation behavior under variable amplitude loading based on the model, calculations of effective crack driving stresses and corresponding propagation lives are carried out for load spectrums with various stress ratios, overload and underload. Good agreement is confirmed between test results in the literatures and simulations using the developed model.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.10a
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• pp.233-233
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• 2003

• Proceedings of the Korean Nuclear Society Conference
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• 2004.10a
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• pp.859-860
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• 2004

• CORROSION AND PROTECTION
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• v.12 no.1
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• pp.12-23
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• 2013

원자력 발전소 주요 부품에 사용되는 Alloy 600의 PWSCC 개시와 전파기구를 살펴보고 그 억제 기술을 소개하였다. ○ 균열은 경화된 표면 산화층이 깨질 경우, 입계부식, 공식(pitting), 열처리 또는 물속에 노출되었을 때 일어나는 선택부식(selective corrosion), MnS등 게재물의 용출등에 의해 시작된다. ○ 균열의 전파는 '느린 성장'과 '빠른 성장'으로 구별해 볼 수 있는데 빠른 균열성장은 균열 선단에서의 응력확대 계수(K_I)가 균열이 전파하는 임계값(K_Iscc)을 넘는 경우에 일어난다. ○ Slip Dissolution/Film Rupture Model, Enhanced surface mobility model, Hydrogen assisted creep rupture, Internal oxidation 등의 모델이 제시되어 있으며 Internal oxidation 모델이 여러 실험자료로 잘 뒷 받침되고 있다. ○ PWSCC 억제 방안으로는 부식환경과의 격리 및 보수용접이 대표적이며 부품의 교체를 통한 안전 확보의 방안도 있다. 수소량 조절을 통한 억제 방안도 제시되어 있다. ○ Alloy 600 PWSCC열화 관리 전략프로그램은 결함 발생 가능성이 높은 부위 선정, 우선 순위에 따른 계획적인 검사, 결함이 발견될 경우 완화조치를 취하거나 필요시 교체/보수를 실시하고 그 운영프로그램을 지속적으로 갱신관리하는 방안으로 유지되어야 한다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.11
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• pp.1361-1368
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• 2011

Fatigue crack propagation behavior and the fatigue life in-high performance steel were investigated by means of fatigue crack propagation tests under constant loading conditions of 'R=0.1 and f=0.1 Hz', 'R=0.3 and f=0.3 Hz', and 'R=0.5 and f=0.5 Hz' for the load ratio and frequency, respectively. A modified Forman model was developed to describe the fatigue crack propagation behavior for the conditions. The modified Forman model is applicable to all fatigue crack propagation regions I, II, and III by implementing the threshold stress intensity factor range and the effective stress intensity factor range caused by crack closure. The results show that predicted fatigue lives of Forman and modified Forman models were 8,814 and 12,292 cycles, respectively when the crack propagated approximately 5.0 mm and the load ratio and frequency were both 0.1. Comparison of the test results indicates that the modified Forman model showed much more effective fatigue crack propagation behavior in high-performance steel.

• Journal of Welding and Joining
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• v.6 no.3
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• pp.43-55
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• 1988

An experimental study was carried out to identify the fatigue fractue behavior of weld zone in generally rolled steel for marine structure. The bending an shear loads were applied simultaneously on the specimens to simulate real load condition for marine structure. The effect of the stress intensity factor under mode I with II loading condition on the initiation and the propagation of a crack were investigated, with particular emphaiss on mode II. When the $K_{II}$ stress intensiy factor in mode II was applied under mode I load condition, the growth behavior of a crack seems to be affected mainly by the anisotropic characteristic of materials. Especially, when the crack was located in and near the weld zone and parallel to th weld line, the propagation behaviour was turned out to be quite different from that of the base metal along the direction transverse to the weld line. In general, the propagation veiocity of the cracks in and near the weld zone was found to be slower that the velocity in base metal.

• Journal of the Society of Naval Architects of Korea
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• v.39 no.1
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• pp.90-99
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• 2002

The prediction of stress intensity factor(SIF) is one of the most important factors to analyse the propagation behavior of cracks in hull structural members. Up to now, however, simplified prediction method of SIF has not yet been established for the cracks experienced in large complex structures. As a first step to predict crack propagation behavior in a ship structure with very large structural redundancies, simplified SIF prediction formulas for various crack shapes were derived based on the results of the stress analysis under a non-crack condition in this study. The adequacy of the proposed method was then verified in comparison with other experimental and analysis results.