• Journal of Korean Society of Steel Construction
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• v.12 no.3 s.46
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• pp.239-250
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• 2000

This study investigates the mechanical behavior on trough rib to crossbeam joint in orthotropic steel plate decks, specially emphasizing on the effect of diaphragm inside trough rib on the fatigue behavior of slit by static and fatigue tests. In particular, the effects of diaphragm on in-plane stress and out-of-plane stress, stress concentration, propagation of fatigue cracks at the silt are studied. With the result of experiment and numerical analysis, we have estimated the fatigue strength using the nominal stress and hot-sport stress. The details with diaphragm have occurred about 50% stress reduction at trough rib part of trough rib to crossbeam joint than the detail without diaphragm, however, the lower parts of crossbeam have occurred much more stress. Initial crack size or slit have an considerable influence on the propagation of fatigue cracks due to V-notch. The fatigue strength category of the details without diaphragm has higher value than fatigue limit, whereas that of the details with diaphragm is estimated lower than fatigue limit.

• Journal of the KSME
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• v.28 no.4
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• pp.401-407
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• 1988

해수 중에 있는 구조용강에 음극방식을 실시했을 때의 피로균열진전 특성을 공기 중에서와 비교 하면서 정리하였으며 또한 몇 가지 영향인자들의 역할에 대해서도 기술하였다. 그러나, 이러한 특성들은 아직까지 그 정확한 메커니즘이 규명되지 못하고 있으며, 특히 균열선단에서의 소성 거동이 부식분위기나 수소분위기에서 어떻게 변화하는가 하는 문제에 대해서는 앞으로도 많은 연구가 이루어져야 할 것이다. 응력조건과 부식조건이 동시에 적용될 때, 재료의 거동을 직접 적으로 해석하기 어려운 경우가 많으며, 따라서 관련되는 많은 영향인자들의 역할에 대한 상세한 정보들이 요구되고 있으며, 또한 관련 정보들을 유기적으로 결합시키는 이론적인 근거를 마련 해야 할 필요가 있다.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.28 no.1
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• pp.1-8
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• 2015

In this paper, computational evaluation method for fatigue crack growth rate(FCGR) based on material viscoplastic-damage model is proposed. Viscoplastic-damage model expressing material constitutive behavior of 7% nickel steel is introduced and is implemented into commercial finite element analysis(FEA) code, ABAQUS, as a user defined material subroutine(UMAT) for application in the FEA environments. Verification of developed UMAT and material parameters of material model are carried out by uniaxial tensile test simulations of 7% nickel steel. Moreover, jump-in-cycles procedure and rearrangement of critical damage are employed and also implemented to the ABAQUS UMAT for fatigue damage analysis. Typical FCGR test results such as relationship between crack length and number of cycles and relationship between da/dN and ${\Delta}K$ could be obtained from FCGR test simulation using developed UMAT and these results are compared with experimental results in order to verify of proposed computational method.

• Computational Structural Engineering
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• v.10 no.3
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• pp.7-14
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• 1997

본 고에서는 설계자가 초기 설계시 적용할 수 있는 간이피로해석방법에 대하여 기술하였으며, 특히 선체의 각 구조상세에 대하여 산정된 응력집중계수를 이용하여 피로수명을 쉽게 평가할 수 있는 집중응력방법을 정립하였다. 이 집중응력방법을 사용하면 모든 구조상세에 대하여 한개의 S-N 선도를 적용하게 되므로 일관성 있는 피로상도해석을 수행할 수 있다. 또한 피로수명에 큰 영향을 미치는 파랑하중은 설계조건에 주어진 선급규칙에 따라 계산되어진다. 선체구조의 피로강도평가 기술은 계측, 실험, 해석 및 경험을 포함하는 광범위하고 포괄적이면서 정밀함을 요구하는 종합기술이지만 여기에는 많은 불확실성이 내포되어 있다. 따라서 이를 구명하고 모든 선체구조에 적용할 수 있는 신뢰성 있는 피로강도 평가기술을 개발하기 위하여는 실선계측을 통한 피로하중규명 선체구조에 적용할 수 있는 피로강도 Data base개발, 균열진전해석 등 많은 과제에 대한 집중적인 연구가 계속 수행되어야 한다.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2010.04a
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• pp.326-329
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• 2010

항공기는 전체 수명동안 무수한 반복하중에 노출되기 때문에, 동체에 피로로 인한 다중균열이 불가피하게 발생하게 된다. 이 다중균열은 기체의 강성을 저하시킬 뿐 만 아니라, 종국적으로는 해당 기체구조의 파단을 야기할 수 있다. 초기 결함과 운용 중에 작용되는 응력 스펙트럼은 구조물의 피로수명에 영향을 끼치며 고려해야 한다. 본 논문에서는 초기결함 특성을 파악하기 위한 등가초기결함크기 분포를 산출하고 리벳 시편의 다중균열모델에 대해서 초기결함과 응력배열을 고려한 해석을 수행하였다.

• Bulletin of the Society of Naval Architects of Korea
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• v.30 no.3
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• pp.23-27
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• 1993

현재까지 SFCP 해석법은 기초단계에 있으며, 아직도 정립된 방법이 없는 것이 사실이다. 따라서, 이 분야에는 많은 개선을 필요로 하고 있다. 이와 같은 개선은 이론적인 연구뿐만이 아니라, 실험적인 연구가 바탕이 되어야 라며, 동시에SFCP에 영향을 주는 초기균열의 변동성, 하중의 변동성 등을 정확한 모델링 방법에 대한 연구가 병행되어야 한다. 그리고 더 나아가서 실제 구 조물에서 피로파괴에 영향을 주는 중요한 요소인 잔류응력, 부식 등의 고려하는 방법에 관한 연구가 수행 되어져야 할 것이다. 또한, 지금까지의 연구가 주로 구조부재에 하나의 균열이 존 재한다는 가정을 내포하고 있는데, 실구조물에 적용하기 위해서는 여러개의 균열이 동시에 존 재하는 경우에 대한 연구와 균열이 성장하면서 합체(coalescence)하는 경우에 대한 연구도 수행 되어야 한다. 이와 같은 연구가 꾸준히 진행되어 소기의 성과를 거둠으로써, 구조물의 피로파괴 확률을 정확하게 추정할 수 있을 것이며, 이에 따라 합리적인 설계가 가능해질 것이다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.7
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• pp.693-700
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• 2015

To estimate the fatigue crack propagation behavior of compact tension shear (CTS) specimen under mixed-mode loads, crack path prediction theories and Tanaka's equation were applied. The stress intensity factor at a newly created crack tip was calculated using a finite element method via ANSYS, and the crack path and crack increment were then obtained from the crack path prediction theories, Tanaka's equation, and the Paris' equation, which were preprogrammed in Microsoft Excel. A new method called the finite element crack tip updating method (FECTUM) was developed. In this method, the finite element method and Microsoft Excel are used to calculate the stress intensity factors and the crack path, respectively, at the crack tip per each crack increment. The developed FECTUM was applied to simulate the fatigue crack propagation of a single-edge notched bending (SENB) specimen under eccentric three-point bending loads. The results showed that the number of cycles to failure of the specimen obtained experimentally and numerically were in good agreement within an error range of less than 3%.

• Journal of the Korean Society for Nondestructive Testing
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• v.23 no.2
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• pp.156-164
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• 2003

STS316L had been used as the structural material for energy environmental facilities, because austenite stainless steels like 316L have superior mechanical properties of which toughness, ductility, corrosion resistant and etc. However, those welded structures are receiving severe damage due to increasing of the aged degradation. Most studies until now have been carried out against fatigue behaviors of weldments, and were not well studied on nondestructive evaluation methods. In this study, the fatigue crack propagation behavior of STS316L weldment usually used for vessels of the nuclear power plant was investigated. Also, the degradation characteristics of 316L stainless steel weldments were evaluated by the ultrasonic parameter such as ultrasonic velocity, attenuation factor and time-frequency analysis. The results of this study can be used as a basic data for the prediction of the fatigue crack life of weldments structures without disjointing or stopping service of structures in service.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.3
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• pp.461-471
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• 1989

For the mixed-mode crack problems the direction of crack growth, the crack path and the rational representation of fatigue crack growth rates should be studied to predict fatigue life and safety of structures. In this study, a round specimen which produce nearly identical effects in all loading directions is proposed to make an easy measurement of initial direction of crack growth. The mode I and mode II stress intensity factors of the specimen were calculated using finite element method, in which the square root singular stresses at the crack tip are modeled by means of four rectangular quarter-point eight-noded elements surrounding the crack tip. Experimental results for high strength aluminum alloy showed that the direction of mixed-mode crack growth agree well with maximum principal stress criterion as well as minimum strain energy density criterion, but not with maximum shear stress criterion. From data of fatigue crack growth rates using crack geometry projected on the line perpendicular to the loading direction it is easily established that mixed-mode fatigue crack growth in 5083-H115 aluminum alloy goes predominantly with mode I crack growth behaviors.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.7
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• pp.2159-2166
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• 1996

The stochastic properties of variation in fatigue crack growth are important in reliability and stability of structures. In this study,the stochastic model for the variation of fatigue crack growth rate was proposed in consideration of nonhomogeneity of materials. For this model, experiments were ocnducted on 7075-T6 aluminum alloy under the constant stress intensity factor range. The variation of fatigue crack growth rate was expressed by random variables Z and r based on the variation of material coefficients C and m in the paris-Erodogan's equation. The distribution of fatigue life with respect to the stress intensity factor range was evaluated by the stochastic Markov chain model based on the Paris-Erdogan's equation. The merit of proposed model is that only a small number of test are required to determine this this function, and fatigue crack growth life is easily predicted at the given stress intensity factor range.