• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.9
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• pp.1328-1336
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• 2004

According to our fatigue tests carried out at 20 Hz, R=0.1 on transversely butt-welded joints, fatigue strengths of as-welded specimens, that is, specimens having residual stress are higher than those of annealed specimens in short life range, but vice verse in long life range. This behavior seems to be concerned mainly with residual stress relaxation by applied loading. After analyzing the welding process, we conducted finite element analysis to quantify the degree of residual stress relaxation. By taking into account residual stress relaxation, modified Goodman diagram, and nominal stress, we evaluated the fatigue life of the welded joint from the S-N curve for the parent material. The estimated results are in a good agreement with the experimental results.

• Proceedings of the KAIS Fall Conference
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• 2011.05b
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• pp.832-835
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• 2011

최근까지 용접구조물의 피로설계는 용접품질 수준에 따라 공칭응력 또는 핫스팟 응력에 의한 S-N선 도로부터 수행하였다. 본 연구에서는 유한요소망의 크기에 덜 민감하면서 기존의 하중모드형식, 두께 효과 및 용접결합형식에 상관없는 등가구조응력(E2S2) 접근법을 이용한 Master S-N선도로부터 철도차량 대차프레임의 피로수명을 평가하고자 한다. 또한 합리적인 철도차량 용접대차프레임의 피로해석 연구일환으로서, 다축피로조건인 EN규격의 피로시험조건하에 이의 피로수명을 평가하고자 한다.

• 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.

• Journal of Ocean Engineering and Technology
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• v.4 no.2
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• pp.59-72
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• 1990

본 논문은 해양 구조물에 대한 확률적 기법을 이용한 스펙트럴 피로해석 방법에 대하여 기술하고 있다. 환경조건 특히 파도 및 관련된 해상상태, 파도 스펙트럼에 대하여 조사하였다. 각종 공식을 이용한 응력 집중계수와 유한요소법을 이용한 응력 집중계수 산출 방법 및 피로수명에 대한 그 영향에 대하여 연구하고, S-N선도의 선택과 해상상태의 간략화 문제등에 관해서도 다루었다. 마지막으로 스펙트럴 피로해석 기법을 응용한 실제 피로해석 사례 연구를 통하여 본 방법의 유용성을 입증하였다.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.108-113
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• 2004

According to our fatigue tests carried out at 20 Hz, R=0.1 on transversely butt~welded joints, fatigue strengths of as-welded specimens, that is, specimens having residual stress are higher than those of annealed specimens in short life range, but vice verse in long life range. This behavior seems to be concerned mainly with residual stress relaxation by applied loading. After analyzing the welding process, we conducted finite element analysis to quantify the degree of residual stress relaxation. By taking into account residual stress relaxation, modified Goodman diagram, and nominal stress, we evaluated the fatigue life of the welded joint from the S-N curve for the parent material. The estimated results are in a good agreement with the experimental results.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.7
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• pp.642-652
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• 2009

Most of lap jointed aircraft structures encounter the fretting damages, which provoke fretting cracks prematurely and lead to significant reduction of fatigue life. In the case of ageing aircrafts especially, this fretting fatigue problem is a fatal threat for the safety and airworthiness. Recently, as the service life extension program(SLEP) of ageing aircrafts has become a hot issue, the prediction of fretting fatigue life is also indispensable. On these backgrounds, a series of experimental tests of fretting fatigue on bolted lap joint specimens, were performed. And the fretting crack initiation and propagation life of each specimen were evaluated using existing and newly proposed prediction models with the fretting parameters obtained from the FEA results for elasto-plastic contact stress analyses. The validations of prediction models were also discussed, comparing the prediction results with experimental test ones.

• Proceedings of the KSME Conference
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• 2005.11a
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• pp.119.1-119.1
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• 2005

• Journal of Ocean Engineering and Technology
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• v.3 no.2
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• pp.587-587
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• 1989

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.9
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• pp.3176-3183
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• 2010

A multi-scale fatigue life prediction methodology of composite pressure vessels subjected to multi-axial loading has been proposed in this paper. The multi-scale approach starts from the constituents, fiber, matrix and interface, leading to predict behavior of ply, laminates and eventually the composite structures. The multi-scale fatigue life prediction methodology is composed of two steps: macro stress analysis and micro mechanics of failure based on fatigue analysis. In the macro stress analysis, multi-axial fatigue loading acting at laminate is determined from finite element analysis of composite pressure vessel, and ply stresses are computed using a classical laminate theory. The micro stresses are calculated in each constituent from ply stresses using a micromechanical model. Three methods are employed in predicting fatigue life of each constituent, i.e. a maximum stress method for fiber, an equivalent stress method for multi-axially loaded matrix, and a critical plane method for the interface. A modified Goodman diagram is used to take into account the generic mean stresses. Damages from each loading cycle are accumulated using Miner's rule. Monte Carlo simulation has been performed to predict the overall fatigue life of a composite pressure vessel considering statistical distribution of material properties of each constituent, fiber volume fraction and manufacturing winding angle.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.2
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• pp.175-183
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• 2016

The endurance reliability assessment of a highly complex mechanism is generally predicted by the fatigue life based on simple stress analysis. This study discusses various fatigue life assessment techniques for an automobile clutch snap ring. Finite element analyses were conducted to determine the structural stress on the snap ring. Structural stress that is insensitive in regards to the mesh size and type definition is presented in this study. The structural stress definition is consistent with elementary structural mechanics theory and provides an effective measure of a stress state that pertains to fatigue behavior of welded joints in the form of both membrane and bending components. Numerical procedures for both solid models and shell or plate element models are presented to demonstrate the mesh-size insensitivity when extracting the structural stress parameters. Conventional finite element models can be used with the structural stress calculations as a post-processing procedure. The two major implications from this research were: (a) structural stresses pertaining to fatigue behavior can be consistently calculated in a mesh-insensitive manner regardless of the types of finite element models; and (b) by comparing with the clutch snap-ring fatigue test data, we should predict the fatigue fractures of an automobile clutch snap ring using this method.