• 한국정밀공학회지
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• 제20권4호
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• pp.158-164
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• 2003

The air circuit breaker (ACB) with the spring-actuated mechanism was studied to improve the fatigue-proof characteristics of its link. The low-cycle fatigue fracture phenomenon occurred on the critical link, called h-link, of ACB from the repeated rapid closing and opening operations. To analyze the cause of failure, dynamic FE-analysis on the b-link part of ACB was performed considering tile velocity and acceleration of the links per time as boundary conditions, which were obtained by using ADAMS. Also, the S-N curve obtained by experiments was used to investigate requirement on the fatigue-proof characteristics. Then, to reduce the maximum tensile stress on the h-link, three types of h-link were examined and one of them was selected.

• Structural Engineering and Mechanics
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• 제83권1호
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• pp.109-121
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• 2022

Twelve push-out test specimens were conducted with various parameters to study the static and fatigue performance of a new through-bolt shear connector transferring the shear forces of interface between prefabricated hybrid fiber reinforced concrete (HFRC) slabs and steel girders. It was found that the fibers could improve the fatigue life, capacity and initial stiffness of through-bolt shear connector. While the bolt-hole clearance reduced, the initial stiffness, capacity and slippage of through-bolt shear connector increased. After the steel-concrete interface properties were improved, the initial stiffness increased, and the capacity and slippage reduced. Base on the test results, the equation of the load-slip curve and capacity of through-bolt shear connector with prefabricated HFRC slab were obtained by the regression of test results, and the allowable range of shear force under fatigue load was recommended, which could provide the reference in the design of through-bolt shear connector with prefabricated HFRC slabs.

• 대한기계학회논문집A
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• 제33권4호
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• pp.388-395
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• 2009

An accelerated fatigue test is essentially required to maintain the reliability of the actual structures of KTX under operation conditions. However, actual fatigue life cannot be obtained because the conventional fatigue tests are not adequate to the real load conditions. Moreover foreign component makers have not provided data of the loading stresses (S) versus cycles at the failure (N). In this study, we suggested a deduction method of the S-N curve for establishing an accelerating test under various load levels. Load history was acquired from the field tests. A Rainflow method was used on the cycle counting of the field load data. After that, an S-N curve was obtained through the iteration process under the condition that the damage index satisfies to 1 in the Miner's rule. The deduced S-N curve was applied to the performance evaluation of Korean-made sealed knuckles compared with imports.

• 콘크리트학회지
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• 제4권1호
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• pp.81-87
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• 1992

본 논문에서는 강섬유 혼입량과 강섬유 형상비에 대한 강섬유보강콘크리트의 휨 피로거동을 분석하기 위하여 일련의 강섬유보강콘크리트 시험체에 대하여 피로실험을 수행하였다. 피로실험은 3점 휨 실험법으로 실시하였으며, 실험시 각 시험체의 하중반복회수에 대한 중앙처짐과 피로파괴시의 반복회수를 조사하였다. 이들 실험 결과를 토대로 반복회수에 대한 강섬유보강콘크리트의 중앙처짐, 비탄성변형에너지 및 탄성변형형에너지등을 비교 분석하였으며, 강섬유보강콘크리트의 S-N선도를 작도하였다. 연구결과, 강섬유 혼입량이 클수록 영구변형에 손실되는 에너지가 크게 감소하고, 균열 확대에 소모되는 에너지가 증가하였으며, 동일한 강섬유 혼입량을 갖는 강섬유콘크리트의 경우 강섬유 형상비가 클수록 탄성변형에너지는 작았다. 아울러 본 피로실험 결과를 회귀분석하여 구한 S-N선도에 의하면 강섬유 혼입량이 1.0%인 강섬유보강 콘크리트의 반복회수 200만회에 대한 피로초기균열 발생시의 정적강도의 약 70%로 나타났다.

• 대한기계학회논문집A
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• 제30권8호
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• pp.976-984
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• 2006

Time-temperature superposition has been studied to determine the long-term fatigue life over millions of cycles for glassy polymers. π le superposition is supposed to make an accelerated lifetime testing (ALT) technique possible. Dog-bone shaped specimens made of carbon filled Polycarbonate (PC) were tested under fatigue, based on the stress-lifetime approach (S-N curve). Fatigue-induced localized yield-like deformation is considered as the defect leading to fatigue and its evolution behavior is characterized by a modified energy activation model in which temperature is considered as fatigue acceleration factor. This model allows the reduced time concept to account for effects of different temperature in short-term fatigue data to determine long-term fatigue life through the use of time-temperature superposition that is applicable under a low frequency and isothermal conditions. The experimental results validated that the proposed technique could be a possible method for accelerated lifetime testing (ALT) of time-dependent polymeric materials.

• 한국농공학회논문집
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• 제46권6호
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• pp.47-58
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• 2004

As concrete structures are getting larger, higher, longer and more specialized, it is more required to develop steel fiber concrete and apply to the real world. In this research, it is aimed to have fatigue strength examined, varying the steel fiber content of 0%, 0.75%, 1.00%, 1.25% by experimental study of fatigue behavior of the steel fiber reinforced concrete continuous beams under cyclic loading. The ultimate load and initial load of flexural cracking were measured by static test. In addition, the load versus strain relation, load versus deflection relation, crack pattern and fracture mode by increasing weight were observed. On the other hand, the crack propagation and the modes of fracture according to cycle number and the relation of cyclic loading to deflection relation and strain relation were investigated by fatigue test. As the result of fatigue test, continuous beam without steel fiber was failed at 60 ~ 70% of The static ultimate strength and it could be concluded that fatigue strength to two million cyclic loading was arround 67.2% by S-N curve. On the other hand, that with steel fiber was failed at 65 ~ 85% of the static ultimate strength and it could be concluded fatigue strength to two million cyclic loading around 71.7%.

• 한국자동차공학회논문집
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• 제1권1호
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• pp.131-139
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• 1993

Low cycle fatigue characteristics of cast aluminum alloy A356 with a yield strength and ultimate strength of 229 and 283 MPa respectively was evaluated using smooth axial specimen under strain controlled condition. Reversals to failure ranged from 16 to 107. The cast aluminum alloy exhibited cyclically strain-gardening behavior. The results of low cycle fatigue tests indicated that the conventional low cycle fatigue tests indicated that the conventional low cycle fatigue life model was not a satisfactory representation of the data. This occurred because the elastic strain-life curve was not-log-log linear and this phenomena caused a nonconservative and unsafe fatigue life prediction at both extremes of long and short lives. A linear log-log total strain-life model and a bilinear log-log elastic strain-life model were proposed in order to improve the representation of data compared to the conventional low cycle fatigue life model. Both proposed fatigue life models were statistically analyzed using F tests and successfully satisfied. However, the low cycle fatigue life model generated by the bilinear log-log elastic strain-life equation yielded a discontinuous curve with nonconservatism in the region of discontinuity. Among the models examined, the linear log-log total strain-life model provided the best representation of the low cycle fatigue data. Low cycle fatigue life prediction method based on the local strain approach could conveniently incorporated both proposed fatigue life models.

• 한국가스학회지
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• 제9권4호
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• pp.1-5
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• 2005

소성가공으로 제작되는 575 304재료 멤브레인의 피로 특성에 대하여 조사하였다. 소성 가공량에 의한 영향을 파악하고자 5종류의 시험편에 대하여 피로 시험을 실행하였다. 피로 시험은 실온과 저온에서 수행하였으며, 모든 시험 결과는 지하식 저조 지침에서 제시하는 피로 시험 데이터와 비교 분석하였다. 이러한 결과를 기본으로 프레스 가공 제작 KOGAS 멤브레인 피로 수명 평가에 RPIS 설계 피로 곡선을 적용할 수 있음을 확인하였다.

• Composites Research
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• 제12권3호
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• pp.26-35
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• 1999

복합재료내의 결함을 원공노치로 가정하고 노치의 크기에 따른 정하중 및 피로실험을 수행하였다. 원공이 존재하는 복합재료에 대하여 다양한 수리기법을 적용하여 정하중 실험을 수행하였다. 수리기법중에 precured double patched 방식과 cure-in-place 방식의 수리는 가장 우수한 결과를 보여 평활재의 약 60∼80%의 강도복구효과를 보였다. 우수한 결과기법을 나타낸 수리기법중에 보다 실제적인 방식이라고 사료되는 cure-in-place 방식으로 수리된 재료에 대하여 피로실험을 수행하였다. 수리된 재료는 정하중 및 피로의 경우에 있어서 향상된 결과를 보였으며 피로시 평활재의 거동을 나타낸다. 참고계수를 도입하여 회귀분석된 피로수명예측식(MFLPE's)은 수리된 시편에 비해 타 예측식에 비해 더 좋은 결과를 나타낸다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.13-18
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• 2004

The objective of this study is to investigate fracture toughness and fatigue crack propagation behavior in the Reduced Activation Ferritic Steel (RAFs) JLF-I. The fracture toughness tests were performed with various size(plane size and thickness) and various side groove of specimens. The fatigue crack propagation behavior of the JLF-I steel was investigated by the constant-amplitude loading test for the stress ratios R=O.I, 0.3 and 0.5 respectively. The effects of stress ratios and specimen size on the fatigue crack growth behaviors for JLF-I steel were discussed within the Paris law. The test results showed the standard CT specimen with the side groove of 40 % represented a valid fracture toughness. The fracture resistance curve increased with increasing plane size and decreased with increasing thickness. However, the fracture resistance curve of half size specimen was similar to that of the standard specimen. The fatigue crack propagation rate of a half size specimen was similar to that of a full size specimen at the stress ratios of 0.1, 0.3 and 0.5 respectively. The fatigue crack propagation behavior of this material were evaluated by using a half size specimen.