• Tunnel and Underground Space
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• v.21 no.4
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• pp.307-319
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• 2011

Cyclic loading due to traffic, excavation and blasting causes microcrack growth in rocks over long period of time, and this type of loading often causes rock to fail at a lower stress than its monotonically determined strength. Thus, the crack growth and coalescence under cyclic loading are important for the long-term stability problems. In this research, experiments using gypsum as a model material for rock are carried out to investigate crack propagation and coalescence under monotonic and cyclic loading. Both monotonic and cyclic tests have a similar wing crack initiation position, wing crack initiation angle, cracking sequence and coalescence type. Three types of crack coalescence were observed; Type I, II and III. Type I coalescence occurs due to a shear crack and Type II coalescence occurs through one wing or tension crack. For Type III, coalescence occurs through two wing or tension cracks. Fatigue cracks appear in cyclic tests. Two types of fatigue crack initiation directions, coplanar and horizontal directions, are observed.

• 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 Korean Society of Steel Construction
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• v.8 no.4 s.29
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• pp.95-103
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• 1996

단순 전단연결 구조를 가진 강철도교의 세로보 단부의 절취부위에서 많은 피로균열이 발견되었으며, 이러한 부위의 피로균열은 피로손상의 전형적인 예이다. 피로균열을 가진 세로보 절취부위의 보강방법을 연구하기 위하여 가로보 및 세로보의 상부 플랜지에 인장판을 부착한 경우와 부착하지 않은 경우로 구분하여 피로실험을 수행하였다. 피로실험에 사용된 하중은 현장에서 측정된 실동응력을 기초하여 빈도해석을 통해 산정하였다. 피로실험 결과, 인장판으로 보강한 모멘트 저항 연결구조상세가 철도교에서 균열성장을 효과적으로 정지시킬 수 있는 것으로 판명되었으며, 피로손상을 가진 절취부위의 보강방법으로 제시될 수 있을 것으로 사료된다.

• Journal of the Korean Society of Mechanical Technology
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• v.13 no.2
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• pp.31-37
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• 2011

Sheet aluminum alloys have been used in manufacturing of machine structures. In fatigue crack propagation behavior of thin sheet aluminum alloys, it is important that fatigue crack growth rate is affected by crack closure phenomenon. In this work, we analyzed the characteristics of fatigue crack propagation behavior in experiment of constant stress condition for thin sheet Al 2024-T3 alloys, and identified the retardation behavior of crack growth by comparing experimental results of thin and thick plate specimen. We attempt to operate the fatigue life estimating process using the fatigue related material constants from referred fatigue crack propagation analysis. And we analyzed the experimental and prediction results of fatigue life of thin sheet aluminum alloy in order to identify the relation between retardation behavior of fatigue crack growth and crack closure phenomenon.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.7
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• pp.3121-3126
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• 2013

The integrity evaluation of pipes in nuclear power plant are essential for the safety of reactor vessel, and integrity must be assured when flaws are found. Accurate stress intensity analyses and crack growth rate data of surface-cracked components are needed for reliable prediction of their fatigue life and fracture strengths. Fatigue design and life assessment are the essential technologies to design the structures such as pipe, industrial plant equipment and so on. The effect of crack spacing on stress intensity factor K values was studied using three-dimensional finite element method (FEM). For the case of cylinder under internal pressure, a significant increase in K values observed at the deepest point of the surface crack. Also, this paper describes the fatigue analysis for cracked structures submitted to bending loads.

• Proceedings of the KSME Conference
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• 2005.11a
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• pp.140.2-140.2
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• 2005

• Korean Journal of Materials Research
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• v.3 no.1
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• pp.84-94
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• 1993

This paper deals with the fatigue properties of chopped strand glass mat/polyester composite to understand the effect of water absorption on fatigue behavior of GFRP. The fatigue crack in the both no water and a water absorption materials initiated at the initial of cycle. Thereafter, it was divided with two regions that one decreased with the crack extension and the other increased with the crack extension. The absorption of distilled water degrades the bond strength between fiber and matrix, there, by the tendency of fiber pull-out is increased in perpendicular to crack growth deirection and the debonding of fibers increased to the place which is parallel to crack growth direction. Therefore, the reduction of fatigue strength was caused by these factors.

• Journal of the Korean Society for Railway
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• v.12 no.1
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• pp.16-24
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• 2009

In this study, fatigue crack growth rate of a cracked railway bogie frame under variable amplitude loading is predicted by applying linear elastic fracture mechanics. For this purpose, we find the critical points by reference surveying on cracked railway bogie frames. And we make an effective load history by synthesizing the dynamic load measured from the critical points of railway bogie frame during commercial line operation and the static load calculated from structural analysis. Crack growth analyses are performed at the 3 critical points under the commercial operation loading condition by assuming an initial crack size as 40 mm. and the results are compared with the experimental results from Japanese railway bogie frame crack growth case. From the analysis results, we find that around 500,000 km operating distance is necessary to bring crack growth from the initial crack to unstable crack. And it takes around 3.8 normal operating years. We conclude that it is enough time to detect the crack between normal maintenance period.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.6
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• pp.717-723
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• 2010

Many researchers have studied woven fabric carbon-fiber-reinforced composite (CFRP) materials but the study of fatigue crack propagation in composites has been insufficient. It has known that the crack propagation behavior differs depending on the load and the fiber direction. In this study, the fatigue crack propagation along two different fiber array directions ($0^{\circ}$, $45^{\circ}$) in plain woven CFRP composite was investigated. Fatigue crack propagation tests were conducted on the woven CFRP composite under a sinusoidal waveform load with stress ratios of 0.1 at a frequency of 10 Hz. Once the results of the tests were obtained, fatigue crack propagation rates (da/dN) were plotted against the energy release rate amplitude (${\Delta}G$), and it was observed that either mode I crack propagation or mixed mode crack propagation occurs depending on the fiber array direction.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2011.04a
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• pp.493-498
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• 2011

구름접촉피로는 차륜과 레일의 반복적인 접촉으로 인하여 발생하는 표면손상현상으로 점차 증가하는 레일손상 중 하나이다. 접촉마모 및 주기적 그라인딩보다 균열의 성장속도가 더 빨라 균열진전이 시작되는 최소균열크기(minimum crack size for growth)는 레일의 파괴방지 및 유효한 유지보수전략을 수립하는데 기초자료로 활용된다. 본 연구에서는 최소균열크기를 예측하기 위하여 차륜레일의 접촉에 영향을 미치는 주요 파라미터를 변화시키면서 최소균열크기의 변화를 살펴보았다. 이를 위하여 Fletcher와 Kapoor의 "2.5D"모델을 적용한 시뮬레이션 소프트웨어를 개발하였으며, 최대접촉하중(1174MPa), 표면마찰계수(0.1, 0.2, 0.3 and 0.4), 잔류응력, 접촉에 의한 표면마모(1.0nm/cycle), 그라인딩량(0.3mm/10MGT)을 파라미터로 하여 해석을 수행하였다. 해석결과 최소균열크기는 해석조건에 따라 1.41-1.95mm로 계산되었다.