• Title, Summary, Keyword: 단순피로시험

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Fracture Mechanism and Micro-Practography : Fatigue Fractured Surface (파괴기구와 미시적 파면(III) : 피로파면)

  • 강정윤
    • Journal of Welding and Joining
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    • v.22 no.2
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    • pp.3-7
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    • 2004
  • 재료에 단순 인장시험에 의해 구한 항복강도의 2/3의 축응력을 부가하면, 소성변형과 파괴는 일어나지 않지만, 상당한 사이클로 반복하여 부가하면, 파괴가 일어난다. 이것을 피로파괴라고 한다 대부분의 구조물이나 기계부품은 재료의 항복응력 이하의 반복하중을 받으면서 작동되므로, 피로파괴가 자주 발생한다.(중략)

Evaluation of the Degradation Trend of the Polyurethane Resilient Pad in the Rail Fastening System by Multi-stress Accelerated Degradation Test (복합가속열화시험을 통한 레일체결장치 폴리우레탄 탄성패드의 열화 경향 분석)

  • Sung, Deok-Yong;Park, Kwang-Hwa
    • Journal of the Korean Society for Railway
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    • v.16 no.6
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    • pp.466-472
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    • 2013
  • The use of a concrete track is gradually growing in urban and high-speed railways in many part of the world. The resilient pad, which is essentially when concrete tracks are used, plays the important role of relieving the impact caused by train loads. The simple fatigue test[1] to estimate the variable stiffness of resilient pads is usually performed, but it differs depending on the practical conditions of different railways. In this study, the static stiffness levels of used resilient pads according to passing tonnages levels were measured in laboratory tests. Also, the simple fatigue test and the multi-stress accelerated degradation test for new resilient pads were performed in a laboratory. The static stiffness of the used pad was compared with the results of tests of usage times and cycles. The results of the comparison showed that the variable static stiffness levels of the used pad were similar to results of the multi-stress accelerated degradation test considering the fatigue and heat load. With a T-NT equation related to the degree of the multi-stress accelerated degradation, a model of multi-stress accelerated degradation for a resilient pad was devised. It was found through this effort that the total acceleration factor was approximately 2.62. Finally, this study proposes an equation for a multi-stress accelerated degradation model for polyurethane resilient pads.

Shape-Simplification Analysis Model for Fatigue Life Prediction of Casting Products Considering Internal Defects (내부 결함을 고려한 주조 제품의 피로수명 예측을 위한 결함 형상단순화 해석모델)

  • Kwak, Si-Young;Kim, Hak-Ku
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.35 no.10
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    • pp.1243-1248
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    • 2011
  • Internal defects are a major concern in the casting process because they have a significant influence on the strength and fatigue life of casting products. In general, they cause stress concentration and can be a starting point of cracks. Therefore, it is important to understand the effects of internal defects on mechanical properties such as fatigue life. In this study, fatigue experiments on tensile specimens with internal defects were performed. The internal defects in the casting product were scanned by an industrial CT scanner, and its shape was simplified by ellipsoidal primitives for the structural and fatigue analysis. The analysis results were compared with experimental results for casting products with internal defects. It was demonstrated that it is possible to consider internal defects of casting products in stress and fatigue analysis. The proposed method provides a tool for the prediction of the fatigue life of casting products and the investigation of the effects of internal defects on mechanical performance.

An Experimental Study on Strength Properties, Size Effect, and Fatigue Behaviour of Concrete under Biaxial Flexural Stress State (이방향 휨응력상태의 콘크리트 강도 특성, 크기효과 및 피로거동에 관한 실험적 연구)

  • Zi, Goangseup;Kim, Jihwan
    • Journal of The Korean Society of Civil Engineers
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    • v.33 no.3
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    • pp.901-907
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    • 2013
  • In this study, flexural strength properties of concrete under biaxial stress state were experimentally investigated. Tests for size effect and fatigue behaviour of concrete under biaxial stress were carried out by the ASTM C 1550 and the biaxial flexure test(BFT). The results given by the biaxial tests were compared to those by the third-point bending test. Test results showed that biaxial flexural strengths obtained from the ASTM C 1550 and the biaxial flexure test are greater than the strength by the third-point bending test. As the size increases, the uniaxial and biaxial flexural strength decreases. However, the slope of the size effect of the biaxial strength was greater than that of the uniaxial strength. Finally, the fatigue response of concrete under the biaxial stress state was similar with that for uniaxial stress state.

Hot ductility behavior of steel as low cycle high temperature fatigue (저주기 고온 피로에 따른 강의 열간 연성 거동)

  • 박병호;김현정;손광석;김동규
    • Proceedings of the Materials Research Society of Korea Conference
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    • pp.86-86
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    • 2003
  • 주편은 1차 냉각 지역인 수냉 몰드를 통과한 후, 2차 냉각 지역에서 guide roll, pinch roll 그리고 driven roll등에 의해 반복적인 압축하중을 받고 있으며, roll과 roll사이에서는 철정압에 의한 주편 bulging 현상이 발생하고 주편의 표면은 인장응력을 받게 된다. 특히 연속주조 중 주편의 변형기구가 단순 탄소성 변형 이 아닌 creep에 의한 변형임을 고려할 때, 2차 냉각 지역에서 주편의 표면은 전술한 압축 및 인장변형 이 반복되는 저주기 고온 피로 환경을 거침을 알 수 있다. 본 연구에서는 탄소함량에 따른 주편의 bulging시의 크랙 발생에 미치는 저주기 고온 피로의 효과를 조사하였다. 또한, 용체화 처리 온도에서 시험 온도까지의 냉각 속도의 영향을 조사하기 위하여 1$^{\circ}C$/s 및 1$0^{\circ}C$/s로 냉각 속도를 변화시켜 열간 연성 곡선을 작성하였다. 본 연구에서 얻어진 결과는 다음과 같다. 저탄소강의 경우는 저주기 피로의 영향이 관찰되지 않았으며, 중탄소강의 경우, 저온에서는 저주기 피로로 인해 열간 연성이 증가하였으나, 고온에서는 변형유기 페라이트의 생성으로 인해 열간 연성 이 감소하였다. 고탄소강의 경우는 저주기 피로로 인하여 열간 연성이 모든 온도 구간에서 증가하였다. 또한 용체화 처리후 시험 온도까지의 냉각 속도가 감소함에 따라 열간 연성이 증가하였는데, 이는 입 계 석출물의 조대화로 인해 열간 연성이 증가하는 것으로 판단된다.

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A Study on the Flexural Fatigue Behavior of R/C Beams Repaired with Concrete-Polymer Composites (유기 및 유기재료로 보수된 R/C 보의 휨 피로거동에 관한 연구)

  • 심종성;황의승;배인환;이은호
    • Magazine of the Korea Concrete Institute
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    • v.7 no.6
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    • pp.233-241
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    • 1995
  • In this thesis, the fatigue tests were performed on a series of R /C beams repaired with co& crete-lmlyrner composites to investigate the fatigue bahavior. The three point loading system is used in the fatigue tests. In these tests, relations between the repeated loading cycles and mid-span deflections, number of repeated loading cycles when repaired beams were fractured, the bonding performance of repair materials were observed. On this basis, the mid-span deflections, the crack growth and failure mode of repaired R /C beams were studied. A S-N curve was drawn to present the fatigue strength of repaired beams. From the test results, it was shown that behavior of R /C beams repaired with polymer-cement series were very sirnillar to control beam about bonding performance, mid-span deflections and fatigue strength according to S-N curve drawn by the regression anlysis on the fatigue test results.

Prediction of Fretting Fatigue Life for Lap Joint Structures of Aircraft (항공기 겹침이음 조립구조의 프레팅 피로수명 예측)

  • Kwon, Jung-Ho;Joo, Seon-Yeong
    • 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.

An Experimental Study on the Fatigue Behavior of T-Type Tension Joints with High Tension Bolt (고장력볼트 T-인장이음의 피로거동에 관한 실험적 연구)

  • Lee, Seung Yong;Choi, Jun Hyeok
    • Journal of Korean Society of Steel Construction
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    • v.28 no.6
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    • pp.459-465
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    • 2016
  • In this paper, it was performed the fatigue test to examine the effect of cyclic loading for the simple T-joint. Axial force of bolt by clamping and the change of the force by applied load were measured in the joint. And the bolt force, the failure mode and the fatigue strength under cyclic loading were investigated. The parameters of the tension joint were set to be the flange thickness and the diameter of bolt to a different stiffness of the joint in response to the combination. From the fatigue test, failure mode of tensile joints under cyclic loading could be evaluated using a static ultimate load of the specific failure mode in EC3. The fatigue strength of the tension joints was considerably higher than the fatigue strength of the EC3(36) that does not consider a lever action. However, the additional axial force by lever action occurs to an increase in the axial force of the bolt it requires a careful evaluation of the fatigue strength.

Fatigue Crack Growth of Welded-Structural Steel under Simple-Variable Loading (단순변동하중(單純變動荷重)을 받는 용접구조용강(鎔接構造用鋼)의 피로균열성장(疲勞龜裂成長))

  • Chang, Dong Il;Bak, Yong Gul;Lee, Bong Hak
    • Journal of The Korean Society of Civil Engineers
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    • v.7 no.4
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    • pp.103-113
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    • 1987
  • Fatigue tests using a single-peak loading and a two-step loading were carried out to examine the fatigue crack growth behaviar and to find the appropriate analysis method. C-T specimens were made using structural steel SWS58 for the tests. From this, just after a single-peak loading acceleration effect was occured and after some times retardation effect was found. And eminent retardation effect was found after High-Low two-step loading. The transition effect of crack growth due to this variable loading was occured owing to the residual stress and the plastic zone size at the crack tip. And the behaviors of these are well explained by Elber's Crack Closure Model. Also I could find that the Wheeler's Retardation Model is a simple and appropriate theory among analysis methods of fatigue crack growth under the variable loading.

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An Experimental Study on the Fatigue Flexural Bonding Characteristic of Concrete Beam Reinforced with GFRP Rebar (GFRP Rebar로 보강된 콘크리트보의 피로 휨·부착성능에 관한 실험적 연구)

  • Oh, Hong Seob;Sim, Jong Sung;Kang, Tae-Sung
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.12 no.1
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    • pp.101-108
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    • 2008
  • This study is to examine bond strength of beam reinforced with GFRP rebar under 4-point fatigue bending test by adopting BRITISH STANDARD. The variables were made to have bonding length of 5times(5db), and 15times(15db) of the nominal diameter of GFRP rebar and were done to analyze the relationship between the bonding strength and the slip. In the result of the test, pull-out failure was dominant in the 5db specimen, patterns of the pull-out failure and concrete shear failure appeared in the 15db specimen showed only concrete shear failure at the end of bonding length. Therefore, The strain development consist of three different stage : A rapid increases form 0 to about 10% of total fatigue life. A uniform increases form 10% to about 70%~90%. Then a rapid increases until failure, if failure takes place. It seems that stress level has not influence on the secant modules of elasticity. And also according to the outcome the existing strengthening method came out to be the most superiority in S-N graphs.