• Journal of the Society of Naval Architects of Korea
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• v.28 no.2
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• pp.275-284
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• 1991

Fatigure crack growth from surface defects is one of the most important subjects for the evaluation and the assurance of safety in pressure vessels, piping systems, ship hulls and other various structures. This paper attempts to analysis some practical or general problems such as the estimation of crack growth life to penetrate the plate thickness, based on fatigure crack growth from a single surface flaw and the interaction of multiple flaws. An experiment on the coalescence of multiple undercuts was carried out under cyclic tension condition as a attempt to the analysis of multiple crack problems. It is noted that the fracture strength is characterized by the analogy to that in a single crack growth.

• Journal of Ocean Engineering and Technology
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• v.15 no.2
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• pp.94-98
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• 2001

fatigue life and nondestructive evaluation were examined experimentally using surface crack specimen and compact tension specimen of 5083 aluminium alloy. Acoustic emission signals emanated during failure of aluminum alloys has been the subject of numerous investigations. Possible sources of AE during deformation have been suggested as the dislocations, fracture of brittle particles and debonding of these particles from the alloy matrix. Fatigue life and penetration behavior of long surface crack can be evaluated quantitatively using K values proposed by authors. The influence of stress ratio on the frequency characteristics of AE signals were investigated.

• Magazine of the Korea Concrete Institute
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• v.5 no.4
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• pp.135-144
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• 1993

A fatigue analysis procedure for prestressed concrete composite girder bridges is established, which includes the time-dependent effects of component materials. The procedure can take into account the movement of neutral axis depth as crack develops and give quite good agreement with experimental results available. It is also assured that Korean Standard prestressed concrete composite girder has enough fatigue resistance. The procedure in this paper gives a way to express the fatigue capacity of prestressed concrete beams in the form of S-N curve, which can be utilized under variable amplitude fatigue load.

• Journal of Aerospace System Engineering
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• v.12 no.3
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• pp.38-44
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• 2018

Military aircraft may have fatigue cracks in structurally weak areas due to multiple factors such as the accumulation of flight time while perform various missions and unpredictable air conditions. As a fatigue crack progresses, there is a risk that the structure will be destroyed in extreme cases, which can have a significant impact on flight safety. In this study, a cracking phenomenon was observed during the periodic inspection the inner support of the fairing, which is installed to protect the connection between the wing and the body of the aircraft. Therefore, a study on a series of quality improvement processes for reformation was described. In order to identify the causes of cracks, pre-load generation occurrence during the wing assembly process was investigated and a fracture analysis was performed. Also, the design of the support structure was suggested in terms of preventing recurrence of cracks. The structural integrity was verified using a stress and fatigue life analysis.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.5
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• pp.1462-1471
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• 1991

본 연구에서는 미소 결함주위에서 발생, 전파하는 균열들에 미치는 초기 결함 깊이와 상호 간섭 영향을 검토하기 위하여 기존 재료가 갖고 있는 결함이나 비금속 개 재물로 대신할 수 있다고 생각되는 미소 원공의 크기를 변화시킨 모델에 대해 유한 요 소법을 이용하여 3차원적으로 응력을 해석하였다. 실제 사용하고 있는 부재에 결함 들이 존재할 경우 응력장의 간섭으로 피로 균열 진전이 가속화됨으로 미소 원공 주위 의 응력 분포 및 미소 원공사이의 응력장의 간섭과 미소 원공에서 발생, 전파하는 표 면 균열의 응력 확대 계수에 미치는 영향에 대하여 비교검토 하였다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.5
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• pp.1186-1192
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• 1990

It is well known that the fatigue crack growth retardation following overloads can be estimated reasonably well by the models of Wheeler and Willenborg. These models, however, can not explain the delayed-retardation revealed by every experimental result. This means that they necessarily have some qualitative defects in themselves despite of a fair approximation of quantity. In fact, they did not take into account the effects of the compressive portion of the overload cycle such as the change of reversed plastic zone size. The present study is focused on the acceleration effect in the reversed plastic zone in order to analyze qualitatively delayed-retardation phenomenon following single peak overload on the fatigue crack growth behavior using 2024-T3 aluminum alloy.

• Journal of the Korean Society of Hazard Mitigation
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• v.7 no.5
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• pp.1-10
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• 2007

A laboratory investigation is conducted to characterize and quantify fatigue lives of continuously reinforced concrete pavements (CRCP) with initial design parameters. Eight specimens scaled were made based on results of finite-element analyses and stress-strain curve comparisons. Static tests were firstly performed to obtain magnitudes of static failure loads and to predict crack patterns before fatigue tests. The fatigue lives measured in the study were compared based on each initial design parameter. The comparison indicates that the fatigue lives of CRCP specimens with initial cracks increases with increasing the initial crack spacing, and CRCP specimens with reinforcements at top of the concrete slab have more fatigue lives than those with reinforcements at midheight of the concrete slab. In addition, the fatigue lives were significantly affected by soil conditions under the CRCP specimens. The results obtained in the study can be used for maintenance and retrofit of the continuously reinforced concrete pavements.

• Journal of the Korean Institute of Gas
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• v.5 no.1
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• pp.1-6
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• 2001

The main objective of this study is to determine if the sources of AE in corroded specimens of aluminum could be identified iron the characteristics of the waveform signals recorded during fatigue loading. Coupons of notched 2024-T3 aluminum with or without corrosion (at the notch) were subjected to fatigue loading and the AE signals were recorded using non-resonant, flat, wide-band transducers. The time history and power spectrum of each individual wave signal recorded during fatigue crack growth were examined and classified according to their special characteristics. Five distinct types of signals were observed regardless of specimen condition. The waveform and power spectra were shown to be dependent on specimen condition. During the initial phase of crack growth, the signals obtained in the as-received specimens are most probably due to transgranular cleavage caused by extrusion and intrusion under fatigue loading. In the corroded specimen the signal are probably generated by intergranular cleavage due to embrittlement of grain boundary neat the pitting tip. The need for additional research to further validate these findings is indicated.

• Proceedings of the KSR Conference
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• 2003.10b
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• pp.557-562
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• 2003

The responses of the floor system of a railway bridge are investigated for fatigue life prediction of damaged members using fracture mechanics approach. Numerical analysis of the structure is performed in order to see the influence of track-structure interaction and continuity of the truss connection on the response of the bridge members. Fatigue crack growth analysis is carried through equivalent stress obtained from time-history analysis. The results of time-history analysis agree with measured responses. The fatigue propagation life increases as the curvature in the coped stringer increases.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.2
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• pp.475-485
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• 1995

In this study, statistical analysis of fatigue data which had obtained from respective 24 fatigue crack, was examined for SiC whisker reinforced aluminium 6061 composite alloy (SiC$_{w}$/A16061) and aluminium 6061 alloy. SiC volume fraction in composite alloy is 25%. The analysis results stress intensity factor range and 0.1 mm fatigue crack initiation life for SiC$_{w}$/A16061 composite & A16061 matrix are the log-normal distribution. And regression analysis by linear model, exponential model and multiplicative model were performed to find out the relationship between fatigue crack growth rate(da/dN) and stress intensity for find out the relationship between fatigue crack growth rate(da/dN) and stress intensity factor range(.DELTA.K) in the SiC$_{w}$/A16061 composite and examine the applicability of Paris' equation to SiC$_{w}$A16061 composite. Also computer simulation was performed for fatigue life prediction of SiC$_{w}$/A16061 composite using the statistical results of this study.udy.