• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.11
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• pp.1415-1422
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• 2011

Sheet aluminum alloys used in manufacturing of machine structures for transportation show the difference of crack growth speed depending on thickness under the constant fatigue stress condition. The referred thickness effect is a major fatigue failure property of sheet aluminum alloys. In this work, we identified the thickness effect in fatigue test of thick plate and thin plate of Al 2024-T3 alloy under the constant fatigue stress condition, and presented the thickness effect to a correlative equation, $U_{i}^{equ}=f(R_t)$ which is determined by the shape factor, thickness ratio, $R_t$ and the loading factor, equivalent effective stress intensity ratio depending on thickness, $U_{i}^{equ}$. And we analyzed quantitatively the crack growth retardation behavior in thin plate compared to thick plate by the thickness effect using ${\Delta}K$ conversion method. We obtained such values as decrement of thickness(DoT), decrement of stress intensity factor range, ${\Delta}K$ (DoS) and identified the relation between them to present the nature of thickness effect in this work.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.4
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• pp.437-442
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• 2014

The equipment or with a constant torque and a variable stress due to axial vibration such as the turbine-generator system in nuclear power plant show the fatigue fracture behavior. Thus this study whoul aim to measure the torsional stress and analyze the fatigue fracture behavior. To achieve this, we manufactured the equipment similar with turbine-generator system and applied various torsional vibration stress due to external load. In particular, the evaluation was conducted with the existing evaluation methods of the fatigue behavior of known stress-life, strain-life, crack growth assessment methods. With increasing the external load and independent methods tends to decrease the fatigue life was confirmed up to 10 times in 5 kV external load compared to without external load.

• Transactions of the Korean Society of Automotive Engineers
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• v.10 no.1
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• pp.187-194
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• 2002

It has been reported that cracks in mechanical joints is generally under mixed-mode and there is critical inclined angle at which mode I stress intensity factor becomes maximum. The crack propagates in arbitrary direction and thus the prediction of crack growth path is needed to provide against crack propagation or examine safety. In order to evaluate the fatigue life of cracks in mechanical joints, horizontal crack normal to the applied load and located on minimum cross section is major concern but critical inclined crack must also be considered. In this paper mixed-mode fatigue crack growth test is performed far horizontal crack and critical inclined crack in mechanical joints. Fatigue crack growth path is predicted by maximum tangential stress criterion using stress intensity factor obtained from weight function method, and fatigue crack growth rates of horizontal and inclined crack are compared.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.4 no.2
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• pp.50-56
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• 2005

To demonstrate the feasibility of utilizing FCAD chart proposed in our previous work, series of crack growth/arrest behavior in the integrally stiffened panels were simulated by numerical method using upper mentioned FCAD charts and a new crack growth rate equation. It is concluded that proposed family of FCAD curves, in the form of non-dimensional arrest load ranges, are reliable indicators of fatigue crack growth/arrest behavior of integrally stiffened panels considered here.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.4 no.2
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• pp.43-49
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• 2005

The purpose of a fatigue crack arrest design is to prevent a fatigue fracture of machine and structure resulted from unstable crack growth. In all cases of load transfer to second elements such as stringers, doublers or flanges, crack arrest is possible; arrest occurring when the fatigue crack reaches the second element. In the present work, a numerical analysis was carried out to estimate the effect of shape parameters on fatigue crack growth and arrest behavior of integrally stiffened panels. Based on these results, a set of fatigue crack arrest design chart is presented as "non-dimensional arrest load - thickness ratio" relationship.

• Journal of Welding and Joining
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• v.6 no.1
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• pp.46-52
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• 1988

Retardation or delay in fatigue crack growth due to overloads are important for the accurate prediction of fatigue lives of structural materials. In this study, retardation of fatigue crack growth in Al 6061-T6 weldments and heat affected zones (HAZ) after single overload cycle had been investigated. Retardation in both weldments and HAZ was observed. It was concluded that retardation in both weldment and HAZ was greater than in base metal due to microstructural change and crack branching and crack closure were major governing factor in retardation.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.235-240
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• 2003

Methods to predict fatigue crack growth are compared in a quantitative manner for crack growth test data of 2024-T351 aluminum alloy under narrow and wide band random loading. In order to account for the effect of load ratio, crack closure model, Hater's equation and NASGRO's equation have been employed. Load interaction effect under random loading has been considered by crack closure model, Willenborg's model and Wheeler's model. The prediction method using the measured crack opening results provides the best result among the prediction methods discussed for narrow and wide band random loading data.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.10
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• pp.1785-1792
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• 2003

Methods to predict fatigue crack growth are compared in a quantitative manner for crack growth test data of 2024- T351 aluninum alloy under narrow and wide band random loading. In order to account for the effect of load ratio, crack closure model, Hater's equation and NASGRO's equation have been employed. Load interaction effect under random loading has been considered by crack closure model, Willenborg's model and Wheeler's model. The prediction method using the measured crack opening results provides the best result among the prediction methods discussed for narrow and wide band random loading data.

• Journal of the Korean Society for Nondestructive Testing
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• v.19 no.6
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• pp.448-453
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• 1999

원전의 열성층 현상으로 발생하는 열 피로균열 및 입계응력부식균열(IGSCC) 등은 결함에 대해서 검사자의 특별한 관심과 노력 없이는 초음파를 이용해 이러한 종류의 결함검출 및 크기 측정이 쉽지 않다. 이러한 결함의 검출 및 크기 측정을 위해서 먼저 초음파 모드 변환 기법을 사용하여 결함 검출 및 결함 크기를 분류한 후에 결함 끝단에서의 초음파 회절파(tip diffraction)를 이용한 여러 가지의 초음파 기법 둥으로 정확한 결함 크기를 측정하여 가동전 중점검시 발견된 결함의 추적 관리 및 결함평가신뢰도 향상에 기여하고자 한다. 따라서, 여기서는 열 피로균열 및 입계응력부식균열 등과 같은 결함의 정확한 검출 및 크기 측정을 위해 초음파 모드 변환 기법의 특성을 철저히 이해하고 이에 관련된 초음파 신호들을 정확히 구분할 수 있는 방법을 기술하였다.

• Proceedings of the KSR Conference
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• 2003.10c
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• pp.79-84
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• 2003

A fictitious crack model was used to analyze fatigue crack growth under the influence of residual stress. In the fictitious crack model, crack is represented in terms of the separation of two adjacent interfaces and the constitutive equation between the separation and traction is assumed. The effect of fatigue loading was included in the constitutive equation by considering damage accumulation in the cohesive zone. To investigate the effect of the residual stress on the fatigue crack growth, we calculated the residual stress distribution due to transient heat flux to the specimen by finite element method. Fatigue crack growth was simulated by the fictitious crack model with repeated loading. The mode-I crack growth rates were compared for the cases with and without the compressive residual stress around the crack tip. It was observed that the mode-I crack growth can be suppressed by compressive residual stress.