• Title/Summary/Keyword: 교번응력

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고속 연접봉의 응력 변동

  • 김재호;신영재
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.15 no.2
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    • pp.404-412
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    • 1991
  • In the design of high speed machinery, designers must consider the problem of possible structural failure due to excessive dynamically varying stresses, which are induced by the varying external loads and internal inertia forces, in the links of the mechanism. A study of the dynamically induced stresses would indicate what values of the minimum permissible fatigue strength should be for safe mechanism operation. This paper investigates the nature of the stress fluctuation in high speed mechanism on the basis of the effects of both the loads and the friction. The latter is apt to be neglected in the usual analysis in spite of the fact that it is always generated in the operating machinery. The analysis is performed on the coupler of the slider-crank mechanism for illustrative purposes and the results are expressed in a non-dimensional form for design applications.

A Fundamental Study on the Fracture Mechanism of Steel Plates under Completely Alternating Load (완전교번하중하(完全交番荷重下)에서의 강판(鋼板)의 파괴기구(破壞機構)에 관한 기차적(基磋的) 연구(研究))

  • Chang, Dong Il;Chung, Yeong Wha
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.2 no.3
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    • pp.1-13
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    • 1982
  • Transition process of plastic region. displacements, stresses and strains ahead the flaw tips were analysed by the finite element method on the steel plate with the circular hole and the one with the elliptical hole under completely alternating load (repetition of tensile loading, unloading and compressive loading). As the results, the followings were obtained. Transition process of elastic failure (yielding) region was estimated. From this the tendency was confirmed that the fracture would be initiated from ahead the flaw tip, and propagated along the $45^{\circ}$ direction. The fundamental data available in estimating the stress intensity factor that was considered as the core in analysing the fracture mechanism of steel plates were obtained. It was indicated that when unloading after tension the effect of compressive loading, and even the compressive reyield, was occured ahead the flaw tip. Similarly it was indicated that when unloading after compression the effect of tensile loading, and even the tensile reyield, was occured ahead the flaw tip. It was considered that these phenomena were occured because the unloading effect was constrained by the residual strains when unloading. It was considered that the fatigue phenomenon was occured ahead, the flaw tip by repetition of tensile yield, the above compressive reyield, compressive yeild and the above tensile reyield. In addition, the tendency was confirmed that the fracture ahead the flaw tip was occured as the flaw was changed from the circular hole to the elliptical hole and became to be the crack lastly.

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Density Variation within Specimen as Affected by Vibration (진동으로 인한 모래 공시체내의 밀도변화에 관한 연구)

  • 장병욱
    • Geotechnical Engineering
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    • v.3 no.3
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    • pp.7-20
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    • 1987
  • To obtain meaningful data of the tests for cyclic loading triaxial test, cyclic loading simple shear test ; and Shake table studies, it is necessary to test uniformly densified specimens. However, there is still some question about the assumed uniform density within a specimen when subjected to the process of densification. A study is conducted to investigate the density variation It within the specimen and analyze the effect of various parameters during the process of vibratory densification. It is found that variation of the ideally graded sand having a homogeneous initial density results in large inhomogeneities within the specimen after vibration. The degree of density variation within the speimen becomes more pronounced by the gradation of sand, surcharge and the intensity of acceleration.

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Structural Integrity Evaluation of Large Main Steam Piping by Water Hammering (수격 현상에 근거한 대형 주증기관의 구조건전성 평가)

  • Jo, Jong-Hyun;Lee, Young-Shin;Kim, Yeon-Whan;Jin, Hai Lan
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.36 no.9
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    • pp.1103-1108
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    • 2012
  • A main steam pipe system is a branch pipe that connects a boiler with a turbine. Water hammering analysis is very important for limiting the damage caused to pipe systems by operation conditions. Water hammering created by an unsteady flow in pipeline systems can cause excessive change in pressure, vibration, and noise. The main steam pipe structure should be designed to safely maintain the pressure pulsation and several vibrations under operation environments. This study evaluated the structural integrity of a main steam pipe during suspended and normal operation by using the ASME fatigue life methodology and finite element analysis. In the analysis, water hammering was used for transient analysis. The calculated alternating stress and fatigue stress were compared with the applicable limits of ASME fatigue life. All the evaluation results satisfied the requirements of the ASME fatigue life.

Local Behavior of Structural Details for Orthotropic Steel Deck Bridge with Longitudinal Rib of Open Section and Retrofitting Method of Fatigue Cracks (개단면리브를 갖는 강바닥판 교량의 국부거동 분석 및 피로균열 보강방안)

  • Lee, Sung Jin;Kyung, Kab Soo;Lee, Hee Hyun;Jeon, Jun Chang
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.17 no.2
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    • pp.33-44
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    • 2013
  • Although many studies have been performed for the structural details of orthotropic steel deck, most of them were focused on the trough rib of standard type, but not for orthotropic steel deck with longitudinal rib of open section used at beginning of the deck. In order to investigate the cause of fatigue crack for orthotropic steel deck bridge serviced 31 years with longitudinal rib of open section, in this study, the behavior characteristics of target structural details were analyzed based on measurement data under real traffic condition. Also the typical loading truck passing the target bridges was estimated with the structural analysis detailed, and the stresses and deformation patterns of target structural details were analyzed by performing the detailed structural analysis. Based upon the analysis, retrofitting methods of the fatigue crack were suggested and its validation was examined. From this study, it was clarified that fatigue crack of longitudinal rib with open section were affected with the stress increment by shear deformation in the rib and the occurrence of alternative stress due to moving vehicle. In addition, it was known that it is important to perform fatigue design reflected the local behavior of the structural details.

Identification on Fatigue Failure of Impeller at Single Stage Feedwater Pumps During Commissioning Operation (단단 주 급수 펌프 임펠러에서 시운전 중 발생한 피로 절손에 관한 규명 연구)

  • Kim, Yeon-Whan;Kim, Kye-Yean;Bae, Chun-Hee;Lee, Young-Shin
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.18 no.9
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    • pp.937-942
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    • 2008
  • This paper presents a case history on failures of impeller and shaft due to pressure pulsation at single stage feed water pumps in 700 MW nuclear power plant during commissioning operation. The pumps had been service and had run for approximately $40{\sim}50$ hours. For the most part, the failures of impeller occurred with the presence of a number of fatigue cracks. All cracks were associated with the deleterious surface layer of impeller by visual and metallurgical examination. On-site testing and analytical approach was performed on the systems to diagnose the problem and develop a solution to reduce the effect of exciting sources. A major concern at high-energy centrifugal pump is the pressure pulsation created from trailing edge of the Impeller blade, flow separation and recirculation at centrifugal pumps of partial load. Pressure pulsation due to the interaction generating between impeller and casing coincided with natural frequencies of the impeller and shaft system during 1ow load operation. It was identified that dynamic stress exceeding the fatigue strength of the material at the thin shroud section due to the hydraulic instability at running condition below BEP.

Influence of Cardiac Contraction and its Phase Angle with Coronary Blood flow on Atherosclerosis of Coronary Artery (심장의 수축운동과 관상동맥 혈류와의 위상차가 관상동맥 혈관의 동맥경화 민감성에 미치는 영향)

  • 김민철;이종선;김찬중;권혁문
    • Journal of Biomedical Engineering Research
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    • v.23 no.6
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    • pp.437-449
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    • 2002
  • Coronary arteries are subjected to very different flow conditions compared to other arteries in systemic blood circulation. We Performed a computational fluid dynamic research to investigate influence of such flow conditions in coronary arteries on development and progress of atherosclerosis in the same. The results showed big differences in the flow field of the coronary artery compared to the abdominal and femoral arteries. The coronary artery showed higher wall shear stresses due to the small vessel diameter. On the other hand, it showed only one vortex distal to the stenosis throat during a whole pulse cycle. However. several vortices were observed in the abdominal and femoral arteries in both proximal and distal sides of the stenosis throat The wall shear stresses and extent of recirculation area were increased with impedance phase angle increasing toward more negative values. Therefore, cardiac contraction and the negative impedance phase angle as large as -110。 may induce a flow field that accelerates atherosclerosis.

Multi-scale Progressive Fatigue Damage Model for Unidirectional Laminates with the Effect of Interfacial Debonding (경계면 손상을 고려한 적층복합재료에 대한 멀티스케일 피로 손상 모델)

  • Dongwon Ha;Jeong Hwan Kim;Taeri Kim;Young Sik Joo;Gun Jin Yun
    • Composites Research
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    • v.36 no.1
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    • pp.16-24
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    • 2023
  • This paper presents a multi-scale progressive fatigue damage model incorporating the model for interfacial debonding between fibers and matrix. The micromechanics model for the progressive interface debonding was adopted, which defined the four different interface phases: (1) perfectly bonded fibers; (2) mild imperfect interface; (3) severe imperfect interface; and (4) completely debonded fibers. As the number of cycles increases, the progressive transition from the perfectly bonded state to the completely debonded fiber state occurs. Eshelby's tensor for each imperfect state is calculated by the linear spring model for a damaged interface, and effective elastic properties are obtained using the multi-phase homogenization method. The fatigue damage evolution formulas for fiber, matrix and interface were proposed to demonstrate the fatigue behavior of CFRP laminates under cyclic loading. The material parameters for the fiber/matrix fatigue damage were characterized using the chaotic firefly algorithm. The model was implemented into the UMAT subroutine of ABAQUS, and successfully validated with flat-bar UD laminate specimens ([0]8,[90]8, [30]16) of AS4/3501-6 graphite/epoxy composite.