• 한국도로학회논문집
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• 제20권3호
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• pp.1-9
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• 2018

PURPOSES : In order to evaluate a crack resistance at cold joint, sealing tape was adopted to apply at cold joint instead of typical tack coat material(RSC-4). The sealing tape was made by hot sealing material. The crack resistance as function of environmental and traffic loading was measured with visual observation. METHODS : In this study, the crack resistance was evaluated as function of environmental and traffic loading. The freeze-thaw method was adopted for environmental loading of asphalt pavement. condition. The damage of cold joint under freeze-thaw action is initiated by ice expansion load and accelerated by the interfacial damage between new and old asphalt pavement. The traffic loading was applied with wheel tracking machine on the cold joint area of the asphalt pavement for 3 hours at $25^{\circ}C$. The evaluation of crack resistance was measured with visual observation. The freeze-thaw results shows that the sealing tape was significantly increased the crack resistance based on. RESULTS : To estimate the crack resistance at cold joint area due to the environmental loading, the Freeze-thaw test was conducted by exposing the product to freezing temperature(approximately $-18^{\circ}C$) for 24 hours, and then allowing it to thaw at $60^{\circ}C$ for 24 hours. The tack coat material(RSC-4) was debonded after 21 cycles of the Freeze-thaw test. The first crack was observed after 14 freeze-thaw cycle with RSC-4 material. But, the sealing tape was not debonded after 24 cycle test. Also, the sealing tape shows the better performance of the crack resistance under the traffic loading with wheel track test. The crack was generated the under traffic loading with RSC-4(tack coating), however, the crack was not shown with sealing tape. It indicates that the sealing tape has a strong resistance of tensile stress due to traffic loading. CONCLUSIONS :Based on limited laboratory test result, a performance of crack resistance using the sealing tape is better than that of general tack coat material(RSC-4). It means that the sealing tape is possible to extend a pavement service life because the crack, one of the main pavement distresses, will be delayed.

• Journal of Welding and Joining
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• 제18권5호
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• pp.33-40
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• 2000

Fatigue crack propagation life of weld toe crack through residual stress field was estimated with Elber's crack concept. Propagation of weld toe crack is heavily influenced by residual stress caused by welding process, so it is essential to take into account the effect of residual stress on the propagation life of weld toe crack. Fatigue crack at transverse and longitudinal weld toe was studied respectively, which represent typical weld joint in ship structure. Numerical and experimental studies are performed for both cases. Residual stress near weldment was estimated through nonlinear thermo-elasto-plastic finite element method, and residual stress intensity factor with Glinka's weight function method. Effective stress intensity factor was calculated with Newman-Forman-de Koning-Henriksen equation which is based on Dugdale strip yield model in estimating crack closure level U at different stress ratio. Calculated crack propagation life coincided well with experimental results.

• 한국생산제조학회지
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• 제7권3호
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• pp.104-109
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• 1998

This document is a experimental study on fatigue life of brace mounting weld joint. A brace is used to put sub-frame together on the main frame with high strength bolts. It has low fatigue life so a patch is in need for improving a fatigue characteristics of welded joint in brace mounting This paper presents the most pertinent patch size for truck. For this, a critical stress is computed at the point of fatigue crack occurred on truck frame by finite Element Analysis. Using by this critical stress. Designers are able to determin whether fatigue crack is occurred and are able to select a pertinent patch type. And then, with a selected patch type, structural joint stiffness was estimated to compare to the conventional and other patch type or brace mounting Finally, fatigue test were performed to prove a suitability of selected prototype compare with the conventional and other patch type or brace mounting.

• 터널과지하공간
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• 제19권2호
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• pp.86-94
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• 2009

암석파괴역학과 파괴인성(rock fracture toughness) 이하의 응력확대계수(stress intensity factor)에서 균열이 성장하는 현상을 이용하여 암석 절리면의 비선형 강도특성과, 시간의 경과에 따라 파괴가 진행되는 특성을 고려한 수치해석용 3차원 절리면 요소를 개발하였다. 이 절리면 요소를 사용하여 암석 절리면 전단시험을 수치해석으로 모사한 결과, 전단응력이 증가하고 시간이 경과함에 따라 절리면 사이에 연결된 절리면 내 접점(asperity in joint)에서 암석의 파괴인성보다 응력확대계수가 작음에도 불구하고 균열이 발생하였고 시간이 경과하면서 균열이 성장, 절리면 내 접점이 파괴되었다. 이와 같이 각각의 절리면 내 접점의 파괴에 따라 절리면의 강도는 감소하고, 절리면의 전단응력은 응력경화와 응력연화 후 잔류응력에 도달하는 비선형거동을 보이면서 시간의 경과에 따라 점진적으로 파괴되었다.

• 한국항공우주학회지
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• 제31권1호
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• pp.8-17
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• 2003

항공기 주구조에서 맞대기중첩연결(Butt Lap Joint) 구조는 저속균열성장 개념의 손상허용설계를 한다. 이러한 연결부 구조는 볼트나 리벳 구멍 가장자리의 부재간 접촉면에서 프레팅에 의한 피로균열이 발생되어 다지점 균열성장 거동을 하는 경우가 많다. 본 연구에서는 초기 모서리균열을 내재한 볼트연결 맞대기중첩연결 구조시편에 프레팅 조건을 달리하여 비행하중스펙트럼 하에서 피로균열 성장거동을 실험적으로 분석하고 잔여강도를 비교하여 프레팅이 균열성장과 손상허용성에 미치는 영향을 고찰하였다. 또한 기존의 응력강도식으로 모서리균열의 성장패턴을 예측하고 실험결과와 비교 분석하였다.

• International Journal of Concrete Structures and Materials
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• 제5권1호
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• pp.11-18
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• 2011

Carbonation in RC (reinforced concrete) structure is considered as one of the most critical deteriorations in urban cities. Although RC column has one mix condition, carbonation depth is measured spatially differently due to its various environmental and internal conditions such as sound, cracked, and joint concrete. In this paper, field investigation was performed for 27 RC columns subjected to carbonation for eighteen years. Through this investigation, carbonation distribution in sound, cracked, and joint concrete were derived with crack mappings. Considering each related area and calculated PDF (probability of durability failure) of sound, cracked, and joint concrete through Monte Carlo Simulation (MCS), repairing timings for RC columns are derived based on several IPDF (intended probability of durability failure) of 1, 3, and 5%. The technique of equivalent probability including carbonation behaviors which are obtained from different conditions can provide the reasonable repairing strategy and the priority order for repairing in a given traffic service area.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2005년도 봄학술 발표회 논문집(I)
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• pp.447-450
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• 2005

A prefabricated composite hollow slab with perforated I-beams was suggested for the replacement of deteriorated concrete decks or the construction of new composite bridges with long-span slabs. Composite slabs with embedded I-beams have considerably higher stiffness and strength. For the application of prefabricated composite slabs to bridges, joints between slabs should satisfy the requirements of the ultimate limit state and the serviceability limit state. In this paper, three types of the detail for loop joints were selected and their structural performance in terms of strength and crack control was investigated through static tests on continuous composite slabs. A main parameter was the detail of the joint, such as an ordinary loop joint and loop joint with additional reinforcements. Even though there was no connection of the steel beams at the joints, the loop joints showed good performance in terms of strength. In terms of crack control, the loop joint with additional reinforcements showed better performance. In ultimate limit state, the continuous composite slabs showed good moment redistribution and ductility.

• 비파괴검사학회지
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• 제29권1호
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• pp.43-48
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• 2009

The fatigue crack growth behavior of high strength X80 pipeline steel was investigated with compact tension specimens that crack growth directions were aligned either parallel or normal to the rolling direction of the pipeline. Also, the fatigue crack growth rates for welded joint of X80 pipeline steel were investigated with compact tension specimens that crack growth directions were aligned either parallel or normal to the welding line. The experimental results indicated the fatigue crack growth behavior was markedly different in three zones, weld metal, heat affected zone and base metal of welded joints. There was a trend toward increment in the fatigue life of weld metal and heat affected zone as compared with the X80 pipeline steel.

• 한국해양공학회지
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• 제11권3호
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• pp.20-28
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• 1997

The fatigue crack propagation properties and fatigue life of two kinds of Al body panel for automobile were examined experimentally by using the plate specimen and the single spot welding specimen. The fatigue limit of spot welding specimens was lower than that of a plate specimen. The fatigue limit was similar in two kinds of spot welding specimen. The shape and size of crack propagation were observed and measured on beach mark of fracture surface. The crack propagation of surface crack specimen showed almost same tendency to that of a thick plate as almost semi-elliptical. In spot welding specimen, the fatigue crack occurred in inside surface of nugget area was almost semi-elliptical. The crack growth rate can be explained using equation of stress intensity factors.

• 한국해양공학회지
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• 제13권3호통권33호
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• pp.57-67
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• 1999

Welding is widely applicable and reliable process and is mainly adopted for fabricating heavy structures. Recently, weld metal transverse cracks in butt and fillet weld joint is a serious problem, and they must be eliminated for improving weld joint reliability. The weld metal transverse crack susceptibility of butt and fillet joint was carried out by cantilever type tensile crack testing jig and CTS test. In this view of point, this study investigated the potential factors for weld metal transverse crack. The main results obtained were as follows: 1. The content o fdiffusible hydrogen in weld metal played an important role for weld metal transverse cracks. 2. From cantilever type tensile crack tests, it was pointed out that the higher the diffusible hydrogen content and tensile restraint, the more susceptible to weld metal transverse craking. 3. The TSN(thermal severity number) and diffusible hydrogen were important factors for determining weld metal transverse cracks in fillet weld joints.