• Steel and Composite Structures
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• 제33권3호
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• pp.433-444
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• 2019

Fatigue failure of a grid structure using bolt-sphere joints is liable to occur in a high-strength bolt due to the alternating and reciprocal actions of a suspension crane. In this study, variable amplitude fatigue tests were carried out on 20 40 Cr steel alloy M30 high-strength bolts using an MTS fatigue testing machine, and four cyclic stress amplitude loading patterns, Low-High, High-Low, Low-High-Low, and High-Low-High, were tested. The scanning electron microscope images of bolt fatigue failure due to variable amplitude stress were obtained, and the fractographic analysis of fatigue fractures was performed to investigate the fatigue failure mechanisms. Based on the available data from the constant amplitude fatigue tests, the variable amplitude fatigue life of an M30 high-strength bolt in a bolt-sphere joint was estimated using both Miner's rule and the Corten-Dolan model. Since both cumulative damage models gave similar predictions, Miner's rule is suggested for estimating the variable-amplitude fatigue life of M30 high-strength bolts in a grid structure with bolt-sphere joints; the S-N fatigue curve of the M30 high-strength bolts under variable amplitude loading was derived using equivalent stress amplitude as a design parameter.

• 대한한의학방제학회지
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• 제17권2호
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• pp.163-174
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• 2009

Reactive oxygen species(ROS) can induce hepatotoxicity and trigger apoptosis in the liver. In this study, we investigated the sulfated polysaccharide A-1 from Opuntia ficus-indica against alcoholic oxidative stress in human liver Hep G2 cell. An antioxidant substance A-1 obtained from the enzymatic extract of Opuntia ficus-indica fruit was purified by DEAE-cellulose ion exchange and sephadex G-100 gel permeation chromatography. The purification yield and molecular weight were 14.3% and 1.8 KDa, respectively. The A-1 predominately contained arabinose, galactose, rhamnose and also sulfate group. The structure of A-1 was investigated by periodate oxidation, FT-IR spectroscopy, $^1H$-NMR spectroscopy. The A-1 mainly composed of alternating unit of ${\rightarrow}4$)-$\alpha$-L- Rapp-2-$SO_3^-$-$\alpha$-L-Galp-($1{\rightarrow}$ and branched linkage of $\beta$-D-Arbp- ($5{\rightarrow}$. The antioxidative activity was measured using the SOD, CAT activity and GSH assay, respectively. The expression of Nrf2 protein was analyzed by western blotting. The viable cell count analyzed by autofluorescence. Oxidative stress induced by ethanol(1 M) were dramatically reduced by A-1 treatment. A-1 also prevented cell death induced by oxidative stress. It also increased expression Nrf2 protein level. We concluded that sulfated polysaccharide A-1 from Opuntia ficus-indica effectively protect Hep G2 liver cell from alcoholic oxidative stress.

• 대한기계학회논문집
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• 제16권4호
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• pp.609-620
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• 1992

본 연구에서는 텅스텐 할로겐 램프를 이용한 급속 열처리 장치로 웨이퍼를 가 열할 때 시간에 따라 변하는 웨이퍼의 2차원 온도 분포와 온도 구배에 의해 발생하는 열응력을 실리콘 웨이퍼의 결정방향에 따라 다른 값을 갖는 탄성계수를 고려하여 계산 하고, 슬립의 발생 시기, 웨이퍼의 가열속도와 슬립량의 관계, 그리고 웨이퍼에 발생 한 슬립의 진전 특성에 대하여 살펴보고 실험결과와 비교하였다.

• Journal of Acupuncture Research
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• 제23권3호
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• pp.231-239
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• 2006

Functional medicine is a system which utilizes certain investigative and treatment methods that are primarily oriented toward the recognition of functional disorder. Functional disorders take place on an energetic plane. This plane is not capturable using our regular investigatory techniques, such as X -ray. ultrasound, computer tomography and laboratory analyses. The 7-zone-diagnostic system(VEGA-DFM 722 and ABR-2000, etc) is a diagnostic device Which applies pulse signals to predetermined bodily locations. Applying alternating positive and negative stress to tissues with positive and negative pulses first manifests itself as negative and positive wave forms. The skin has many functions as an organ. It is the organism's interlace with the outsider world. Hence, the manner in which the skin reacts to external stimuli reflects the current state of the organism(as meridian systems). This system make a diagnosis of functional disorder or some typical organic diseases include stress of the mind or the body, and the energetic situation, reserves. We are known a disorder or disease throw the result chart. This result chart contain disorder flow wave forms and some valuable diagnostic hints (letters ; S, OM, RA, etc). In spite of this 7-zone-diagnostic system that is applied plentifully in the clinical application, there is not a statistics which is suitable. Therefor we must carry out many various research in the future.

• 대한토목학회논문집
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• 제12권4호
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• pp.1-10
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• 1992

프리스트레스트 콘크리트 교량을 압출공법으로 가설하는 과정에서는 구조계가 계속하여 변하므로 교량의 주형에는 사용하중 상태에서와는 상이한 교번 단면력이 발생하게 된다. 이러한 단면력의 크기는 경간 길이, 추진코의 길이 및 강성등에 영향을 받게 된다. 본 논문에서는 많은 예제를 해석하여 이러한 요소들이 주형에 발생하는 최대 단면력에 미치는 영향을 연구하였다. 주프로그램의 복잡한 입력작업을 쉽게 처리할 수 있는 선처리 프로그램과 더불어 주형압출시 변화되는 구조계의 다단계 해석을 수행하여 최종적인 결과를 종합 출력할 수 있는 전산프로그램을 개발하였다. 압출공법으로 시공되는 박스거더교를 대상으로 하여 여러 가지 경간길이에 대한 구조해석을 수행한 결과로부터 경간 길이에 따른 최적 추진코길이와 강성비의 상호 관계를 제안하였다.

• 비파괴검사학회지
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• 제29권1호
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• pp.21-26
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• 2009

이차원 표면균열을 가진 재료의 모드 I 응력확대계수($K_1$)를 교류전위차법으로 효과적으로 계측할 수 있는 방법을 결정하기 위해 하중이 가해질 때 균열면을 포함한 시험편 내부 및 외부의 자속 변화 해석이 필요하여 이를 이론적 및 실험적으로 규명하였다. 이론 해석 결과 균열면 사이의 공기중 자속은 시험편에 하중을 가하여도 변하지 않았으며, 실험 결과와 일치하였다. 따라서 유도기전력을 많이 유도할 수 있도록 제작된 계측계로 측정한 하중에 따른 교류전위차 변화는 시험편의 내부 인덕턴스 변화와 시험편 내부 인덕턴스 변화와 관련된 상호 인덕턴스 변화에 의하여 발생한다.

• Steel and Composite Structures
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• 제25권5호
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• pp.571-579
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• 2017

The grid structure with bolt-sphere joints is widely adopted by industrial plants with suspending crane. The alternating reciprocating action of the suspending crane will cause fatigue problems of the grid structure with bolt-sphere joints with respect to the rod, the cone, the sealing plate, the bolt ball and the high strength bolt; while the fatigue of the high strength bolt is the key issue of fatigue failure. Based on efficient and smooth loading equipment with the AMSLER fatigue testing machine, this paper conducted a constant amplitude fatigue test on 18 M20 and 14 M30 high strength bolts with 40Cr material, and obtained 19 valid failure points, 9 unspoiled points with more than 2 million cycles, and 4 abnormal failure points. In addition, it established the constant amplitude fatigue design method, ${[{\Delta}{\sigma}]_{{2{\times}10}}{^6=58.91MPa}$, and analyzed the stress concentration and the fatigue fracture of high strength bolts. It can be explained that the geometrical stress concentration of high-strength bolt caused by spiral burr is severe.

• Journal of Acupuncture Research
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• 제23권5호
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• pp.11-21
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• 2006

The 7-zone-diagnostic system(ABR-2000, BIO MEDIC 700Plus, CP-6000A, OMD 3000, VEGA-DFM 722) is a diagnostic device which applies pulse signals to predetermined bodily locations. Applying alternating positive and negative stress to tissues with positive and negative pulses first manifests itself as negative and positive wave forms. This system make a diagnosis of functional disorder or some typical organic diseases include stress of the mind or the body, and the energetic situation, reserves. We are known a disorder or disease throw the result charts. And these result represents various characteristic signals are assisted diagnosis and care. These result chart contains disorder flow wave forms and some valuable diagnostic hints or marks. But we have several various products for the 7-zone-diagnostic system. I think that we need the comparative analysis of the general rule and the decipher for each equipment. Because these letters(marks) each product are different, we necessary various plentiful research and suitable statistics in these points. And we must carry out many various research in the future.

• Nuclear Engineering and Technology
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• 제46권1호
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• pp.101-108
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• 2014

About 40% of reactors in the world are being operated beyond design life or are approaching the end of their life cycle. During long-term operation, various degradation mechanisms occur. Fatigue caused by alternating operational stresses in terms of temperature or pressure change is an important damage mechanism in continued operation of nuclear power plants. To monitor the fatigue damage of components, Fatigue Monitoring System (FMS) has been installed. Most FMSs have used Green's Function Approach (GFA) to calculate the thermal stresses rapidly. However, if temperature-dependent material properties are used in a detailed FEM, there is a maximum peak stress discrepancy between a conventional GFA and a detailed FEM because constant material properties are used in a conventional method. Therefore, if a conventional method is used in the fatigue evaluation, thermal stresses for various operating cycles may be calculated incorrectly and it may lead to an unreliable estimation. So, in this paper, the modified GFA which can consider temperature-dependent material properties is proposed by using an artificial neural network and weight factor. To verify the proposed method, thermal stresses by the new method are compared with those by FEM. Finally, pros and cons of the new method as well as technical findings from the assessment are discussed.

• 비파괴검사학회지
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• 제19권1호
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• pp.1-7
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• 1999

교류전위차법 (alternating current potential drop : ACPD)을 이용하여 이차원 표면균열을 갖고 있는 상자성체 (paramagnetic material)의 모드 I (opening mode) 응력확대계수($K_I$)를 실험적으로 평가하기 위하여 하중에 따른 교류전위차 변화(change in ACPD)를 연구하였다. 아울러 하중에 의한 전위차 변화의 원인 그리고 전위차 변화에 미치는 자속(magnetic flux) 탈자(demagnetization) 및 균열길이의 영향을 연구하였다. 상자성체의 교류전위차는 인장하중을 증가시킬수록 선형적으로 감소하였다. 전위차 감소의 원인은 균열선단 주위의 도전율(conductivity)이 인장하중의 증가에 따라 증가하고 이는 시험편의 저항과 내부 인덕턴스를 감소시키기 때문이다. 도전율의 변화는 균열선단 주변의 응력상태에 의존하기 때문에 일정 $K_I$ 변화에 따른 전위차 변화량은 균열길이에 의존하지 않는다. 하중에 의한 전위차변화량은 시험편 주위의 자속의 유무에 영향을 받지만 탈자의 유무에는 영향을 받지 않는다.