• 한국해양공학회지
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• 제8권1호
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• pp.154-164
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• 1994

In this paper, fatigue testing was carried out under the change of aging time(0.5,1.5.10hrs) by electric heating method which is one of the useful method in the application of Robot's actuator. Fatigue degradation behaviors such as cyclic deformation property, amount of deformation, decrease in recovery and variation of transformation temperature for each specimen were examined closely, and the effect of aging time condition was studied on their fatigue degradation behaviors.

• The Korean Journal of Ceramics
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• 제7권2호
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• pp.63-69
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• 2001

We investigated strength degradations from cyclic contact fatigue in self-toughened glass-ceramics. Hertzian indentation was used to induce cyclic contact load. Dynamic fatigue was also performed with changing stress rates from 0.01 to 10000 MPa/sec. After that, strength data and fracture origins were analysed. As the number of contact cycles increased or stressing rate decreased, severe strength degradation occurred by as much as 50% because of radial cracks developed from microcrack coalescence.

• 상하수도학회지
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• 제32권1호
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• pp.27-35
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• 2018

The stability of liquid ferrate(VI) produced by an innovative method was confirmed and the degradation characteristics of cyclic compounds(Benzene, Aniline, Toluene, 1,4-Dioxane) by liquid ferrate(VI) were investigated under the same reaction conditions. When it was compared with the ferrate manufactured by the wet oxidation method, the liquid ferrate was more stable. And the stability of liquid ferrate was tested at the storage temperature. As a result, only 17.7% of liquid ferrate(VI) has decomposed at the storage temperature($4^{\circ}C$) for 28 days. Among the cyclic compounds, the aniline was rapidly degraded compare to other cyclic compounds, which seems to be due to the electron-donating ability of the substituent, $-NH_2$ group. Especially, when 1,4-dioxane was compared with benzene, the decomposition rate of 1,4-dioxane was lower than that of benzene, suggesting that oxygen atoms hinder the electrophilic reaction. Among 4 cyclic compounds, it was observed that aniline has the highest rate constant than those of other cyclic compounds.

• Structural Engineering and Mechanics
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• 제74권3호
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• pp.407-423
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• 2020

The pre-peak cyclic shear mechanism of two-order asperity degradation of rock joints in the direct shear tests with static constant normal loads (CNL) are investigated using experimental and numerical methods. The laboratory testing rock specimens contains the idealized and regular two-order triangular-shaped asperities, which represent the specific geometrical conditions of natural and irregular waviness and unevenness of rock joint surfaces, in the pre-peak cyclic shear tests. Three different shear failure patterns of two-order triangular-shaped rock joints can be found in the experiments at constant horizontal shear velocity and various static constant normal loads in the direct and pre-peak cyclic shear tests. The discrete element method is adopted to simulate the pre-peak shear failure behaviors of rock joints with two-order triangular-shaped asperities. The rock joint interfaces are simulated using a modified smooth joint model, where microscopic scale slip surfaces are applied at contacts between discrete particles in the upper and lower rock blocks. Comparing the discrete numerical results with the experimental results, the microscopic bond particle model parameters are calibrated. Effects of cyclic shear loading amplitude, static constant normal loads and initial waviness asperity angles on the pre-peak cyclic shear failure behaviors of triangular-shaped rock joints are also numerically investigated.

• 한국지반환경공학회 논문집
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• 제22권10호
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• pp.31-36
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• 2021

풍력발전기 기초의 누적 회전각과 침하량을 예측하는 것은 매우 중요하다. 하지만 반복하중에 따른 버킷기초의 장기거동을 분석하는 연구는 거의 이루어지지 않았다. 본 연구에서는 사질토 지반에 설치된 버킷기초의 다양한 3차원 유한요소해석을 수행하였다. 반복 삼축압축시험으로부터 도출된 강성감소 경험식을 수치모델에 사용자 서브루틴으로 적용하여 해석을 수행하였다. 강성감소 모델을 사용하여 버킷기초의 누적 회전각을 산정하였으며, 반복하중 작용 시 거동에 영향을 주는 주요인자에 대한 분석이 이루어졌다.

• Structural Engineering and Mechanics
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• 제17권5호
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• pp.627-639
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• 2004

The objective of this research was to evaluate the performance of metal-plate-connected truss joints subjected to cyclic loading conditions that simulated seismic events in the lives of the joints. We also investigated the duration of load factor for these joints. We tested tension splice joints and heel joints from a standard 9.2-m Fink truss constructed from $38-{\times}89-mm$ Douglas-fir lumber: 10 tension splice joints for static condition and for each of 6 cyclic loading conditions (70 joints total) and 10 heel joints for static condition and for each of 3 cyclic loading conditions (40 joints total). We evaluated results by comparing the strengths of the control group (static) with those of the cyclic loading groups. None of the cyclic loading conditions showed any strength degradation; however, there was significant stiffness degradation for both types of joint. The results of this research show that the current duration of load factor of 1.6 for earthquake loading is adequate for these joints.

• 한국해양공학회지
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• 제9권1호
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• pp.101-110
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• 1995

In SMA(Shape Memory Alloy), the degradation by fatigue is one of the most important problems to be overcome, when SMA is used for robot-actuator materials. The actuator is operated repetitively for long time and its repeating operation develops the fatigue degradation of SMA. The fatigue degradation changes the transformation temperature and deformation behavior and results in inaccurate operation and deformation which results form repeating operation is to be investigated in advance and the scheme to resolve those problems have to be made for the design of actuator. In this paper, for the improvement of the fatigue degradation by repetive movement and better control of the correct movement by the stability of martensite transformation in the development of Robots actuator, Pre-strain(0, 1.5, 5, 8%) are loaded in the specimens and fatigue testing were carried out by the method of heating and cooling in direct condition. From the results of these experiments, the effect on pre-strain which affect the transformation characteristic and fatigue degradation phenomena were correctly investigated.

• 콘크리트학회논문집
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• 제15권1호
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• pp.17-24
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• 2003

지진하중을 받는 철근콘크리트구조의 취성파괴의 원인은 철근과 콘크리트사이의 급속한 부착손상에 의해 발생되는 국부 부착-슬립이다. 본 연구는 반복하중하에서 부착손상에 대한 철근의 마디높이의 효과를 평가하는 것이다. 큰 상대마디면적을 가진 가공된 철근을 사용하여 부착 시험체를 제작하였다. 또 다른 변수로서 연직방향 철근에 의해 횡구속 철근량의 정도가 고려되었다. 실험결과로부터 에너지 소산력의 크기가 산정되고 여러 변수들에 대해서 비교되었다. 실험결과로서, 하중의 반복이 증가함에 따라 부착강도와 부착강성은 현저히 감소함을 알 수 있다. 횡구속량이 크고 상대마디면적이 큰 철근에서 단조하중시에 비해서 반복하중시의 부착강도의 감소가 줄어들고 국부부착저하를 지연시키는데 효과가 있음을 알 수 있다. 에너지 소산량 또한 횡구속량과 마디상대면적이 증가함에 따라 증가한다. 그러나, 마디가 매우 높은 철근의 부착실험에서 높은 강성 때문에 부착이 적은 슬립에서 손상을 입는다는 것을 알 수 있다. 본 연구는 반복하중하에서 부착저하기구를 이해하고 높은 상대마디면적을 가진 새로운 이형철근의 개발에 유용할 것이다.

• Structural Engineering and Mechanics
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• 제30권2호
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• pp.147-164
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• 2008

Recently, many researches have been done to examine the behavior of fiber reinforced concrete (FRC) subjected to the static loading. However, a few studies have been devoted to cyclic behaviors of FRC. A main objective of this paper is to investigate the cyclic behavior of FRC through theoretical method. A new cyclic bridging model was proposed for the analysis of fiber reinforced cementitious composites under cyclic loading. In the model, non-uniform degradation of interfacial bonding under cyclic tension was considered. Fatigue test results for FRC were numerically simulated using proposed models and the proposed model is achieving better agreement than the previous model. Consequently, the model can establish a basis for analyzing cyclic behavior of fiber reinforced composites.

• Structural Engineering and Mechanics
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• 제81권1호
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• pp.11-28
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• 2022

This paper considers the combination of cyclic and axial loads to investigate the hysteretic performance of H-section 6061-T6 aluminum alloy members. The hysteretic performance of aluminum alloy members is the basis for the seismic performance of aluminum alloy structures. Despite the prevalence of aluminum alloy reticulated shells structures worldwide, research into the seismic performance of aluminum alloy structures remains inadequate. To address this deficiency, we design and conduct cyclic axial load testing of three H-section members based on a reliable testing system. The influence of slenderness ratios and bending direction on the failure form, bearing capacity, and stiffness degradation of each member are analyzed. The experiment results show that overall buckling dominates the failure mechanism of all test members before local buckling occurs. As the load increases after overall buckling, the plasticity of the member develops, finally leading to local buckling and fracture failure. The results illustrate that the plasticity development of the local buckling position is the main reason for the stiffness degradation and failure of the member. Additionally, with the increase of the slenderness ratio, the energy-dissipation capacity and stiffness of the member decrease significantly. Simultaneously, a finite element model based on the Chaboche hybrid strengthening model is established according to the experiment, and the rationality of the constitutive model and validity of the finite element simulation method are verified. The parameter analysis of twenty-four members with different sections, slenderness ratios, bending directions, and boundary conditions are also carried out. Results show that the section size and boundary condition of the member have a significant influence on stiffness degradation and energy dissipation capacity. Based on the above, the appropriate material constitutive relationship and analysis method of H-section aluminum alloy members under cyclic loading are determined, providing a reference for the seismic design of aluminum alloy structures.