• International Journal of Naval Architecture and Ocean Engineering
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• 제4권2호
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• pp.132-140
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• 2012

This study aims to assess fatigue property by the static overload and average load in the fillet welded joints which is on the ship structural steel having gusset welds. To this end, a small specimen was made, to which the same welding condition for the actual ship structure was applied, to perform fatigue tests. In this study, a method to simply assess changes in welding residual stress according to different static overload was suggested. By measuring actual strain at the weld toe, the weld stress concentration factor and property which is determined by recrystallization in the process of welding were estimated to investigate the relation between overload and fatigue strength.

• 대한토목학회논문집
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• 제32권1A호
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• pp.39-48
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• 2012

본 논문에서는 V형 노치 및 반원형 노치 균열을 갖는 패치보강 적층판의 응력확대계수 산정을 위하여 수치해석적 방법을 사용한다. p-수렴 비등매개변수 모델이 고려되고, 이와 같은 비등매개변수 모델의 결과를 활용한 3차원 가상균열닫힘법에 대한 식이 표현된다. 1차원 로바토 함수로부터 확장된 3차원 계층적 형상함수를 가지고서, 임의의 요소에서의 변위장의 변위-변형률 관계와 3차원 구성방정식이 표현된다. 원형경계의 기하형상을 나태내기 위해 초유한사상기법을 사용한다. 응력집중계수, 응력분포, 자유도, 그리고 무차원 응력확대계수 등의 항목에 대해서, 제안된 모델의 정확도와 단순성이 기존의 결과들과의 비교를 통해 설명된다. 균열 적층판의 폭, 높이, 노치근입부의 반경, V형 노치의 경사각, 균열길이 등의 변화에 따른 응력확대계수가 산정된다.

• 동의생리병리학회지
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• 제31권1호
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• pp.65-74
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• 2017

Sleep deprivation is an extremely common event in today's society. It has caused learning cognitive skill deterioration and poor concentration, increased disease such as heart disease, diabetes and obesity, sexual function decrease, infertility increase, depression and autonomic nervous system disorder. Sleep deprivation-induced stress caused NADPH oxidase and oxidative stress. And this oxidative stress induces apoptosis. Lilii bulbus and Nelumbins semen are known to mental and physical relaxation effects. In this study, we induced sleep deprivation(SD) in Sprague-Dawley rats in water for 5 days and thereafter administered orally L. bulbus and N. semen for 5 days. Brain tissues were observed by histochemical, immunohistochemical and tunel staining. The immunoreactives of Tumor necrosis factor ${\alpha}$, Neuronal nitric oxide synthases, Phospho-SAPK/JNK and gp91-phox of the L. bulbus administered group and N. semen administered group were weaker than those of sleep deprivation group. In the L. bulbus administered group and N. semen administered group, apoptosis was decreased than that of sleep deprivation group. Proapoptotic p53, Bax, Cleaved caspase 3 immunoreactives of the administered group were weaker than those of sleep deprivation group, whereas anti-apoptotic Bcl-2 immunoreactity was stronger in the L. bulbus administered group and N. semen administered group. Antioxidant mechanism such as DJ-1, superoxide dismutase 1, Nuclear factor-like 2 immunoreactives of the L. bulbus and N. semen administered group were stronger than those of sleep deprivation group. These results demonstrate that L. bulbus, N. semen had the neuroprotective effects on the sleep deprivation-induced oxidative stress in the hippocampus.

• Journal of Ship and Ocean Technology
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• 제3권4호
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• pp.35-51
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• 1999

Fatigue strength assessment procedures have been implemented in the ship design rules by many classification societies. However, a large variation tin the details of the different approaches exists in practically all aspects influding load history assessment, stress evaluation and fatigue strength assessment. In order to assess the influences of thesd variations on the prediction of fatigue lives. a comparative study is organized by the ISSC Committee III.2 Fatigue and Fracture. A pad detail on the top of longitudinal hatch coaming of a panamax container vessel is selected for fatigue calculation. The work described in this paper is one set of results of this comparative study in which the ABS dynamics approach is applied. Through this analysis the following conclusions can be drawn. (1) With the original ABS approach, the fatigue life of this pad detail is very low, only 2.398 years. (2) The treatment of the stillwater bending moment in the ABS approach might be a source of conservatism. If the influence of stillwater bending moment is ignored, then the fatigue life for this pad detail is 7.036 years. (3) The difference between the nominal stress approach and the hot spot stress approach for this pad detail is about 26%.

• 대한기계학회논문집A
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• 제29권2호
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• pp.284-292
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• 2005

Material flaws in the from of pre-existing defects can severely affect the crack initiation. Stress distribution and crack initiation life of engineering materials such as monolithic aluminum alloy and Al/Glass fiber laminate may be different according to the defect location. The aim of this study is to evaluate effects of relative location of defects around the circular hole in monolithic aluminum and Al/Glass fiber laminates under cyclic bending moment. Stress distribution and crack initiation behavior near a circular hole are considered. Results of Finite Element (FE) model indicated the features of different stress field due to the relative defects positions. Especially, the defects positions at ${\theta}=0^{\circ}\;and\;{\theta}=30^{\circ}$ was strongly effective in stress concentration factor ($K_t$) and crack initiation behavior.

• 대한지역사회영양학회지
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• 제8권3호
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• pp.349-355
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• 2003

We developed a dietary supplement using natural herbs and nutrients for the growth and exercise performance improvement. It called 50-22 supplement containing distilled extracts of natural herbs to remove bitterness and the addition of Vitamin B1, B6, Ca and xylitol. We investigated on the effect of 10-22 supplementation on the maximal exercise performance, IGF-1 (insulin like growth factor-1) concentration and antioxidant activity in SD rat model. In result, JR-22 supplement group was better than control group about 10％ in exercise performance test and increased about 63％ of IGF-1 concentration in blood. In addition, the oxidative damage induced by exercise was reduced by JR-22 supplementation. Therefore, we suggested that 50-22 supplementation enhanced effectively exercise performance and IGF-1 concentration and reduced to oxidative stress in muscles. Also, we analysed biochemical factors in blood for the safety of JR-22 supplement. We known that there is no change of blood lactic acid, ammonia, inorganic phosphorous ion and creatine kinase activity. (Korean J Community Nutrition 8(3) : 349∼355, 2003)

• 대한기계학회논문집
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• 제16권10호
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• pp.1890-1899
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• 1992

본 연구에서는 이종재료간의 Ⅴ-노치균열의 노치각도 및 재료의 종류에 따른 응력특이성지수와 응력강도 계수 해석에 각각 뉴톤-랍슨법(newtonraphson method), 뉴톤-랍슨법과 최소자승법을 이용한 선점법(collocation method)인 수치해석적 방법을 응용하고, 광탄성 등색선 무늬를 컴퓨터 그래픽하여 응력특이성지수와 응력강도계수가 모우드(mode)에 미치는 특성과 경계요소법(boundary element method)으로 응력해석한 결과로써 선점법을 이용하여 응력강도계수를 해석하고 기존의 결과등과 비교, 검토하 고자 한다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회A
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• pp.66-71
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• 2007

Isochromatics obtained from photoelastic experiment shows the stress distributions of full field of a structure under a load. Therefore stress distributions of the structure can be read at a glace through isochromatics. Many experimental data are obtained from isochromatics. And then, the various photoelastic experimental hybrid methods have been developed. Until now, monochromatic light has been used for photoelastic experimental hybrid method. Therefore the photoelastic experimental hybrid method used until now is called the photoelastic experimental hybrid method for black and white isochromatics. When stresses are analyed by photoelastic experimental hybrid method, many experimental data are needed. Therefore some fringe orders of isochromatics are needed for the photoelastic experimental hybrid method for white and black isochromatics. Therefore in this paper, the photoelastic experimental hybrid method for color isochromatics is developed. In this case, two fringe orders are enough for the experimental data of photoelastic experimental hybrid method for color isochromatics. Applying the method to stress concentration problems, its validity is confirmed. In the precision, the photoelastic experimental hybrid method for color isochromatics is better than the photoelastic experimental hybrid method for white and black isochromatics when fringe orders of isochromatics are few. When fringe orders are few, the photoelastic experimental hybrid method for color isochromatics can be used to analyze stress through few fringe orders of isochromatics.

• 대한조선학회논문집
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• 제38권4호
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• pp.75-82
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• 2001

건조 후 수행하는 수압시험 또는 화물의 적재 등과 같은 정하중은 파랑변동하중에 비하여 선체구조물에 상당히 큰 응력을 유발한다. 이러한 정하중이력에 의하여, 선체구조물의 응력집중으로 인해 피로강도가 문제되는 용접이음부에서는, 재료의 탄소성 거동에 의하여 초기용접잔류응력이 상당히 이완될 것으로 예상된다. 따라서, 이러한 용접이음부의 피로강도를 평가할 때에는 이완된 잔류응력의 영향을 고려하는 것이 보다 합리적이다. 본 연구에서는 선체구조물의 여러 가지 용접형태 중 Padding plate가 용접된 형태에 대하여 정하중이력($0.5{\sigma}Y,\;0.85{\sigma}Y$)에 의한 초기 용접잔류응력의 변화를 측정하며, 잔류응력의 변화가 피로강도에 미치는 영향을 검토한다.

• Steel and Composite Structures
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• 제21권6호
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• pp.1227-1250
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• 2016

Most of the research work has been conducted on K-joints under static loading. Very limited information is available in consideration of fatigue strength of K-joints with concrete-filled chord. This paper aims to describe experimental and numerical investigations on stress concentration factors (SCFs) of concrete-filled circular chord and square braces K-joints under balanced axial loading. Experiment was conducted to study the hot spot stress distribution along the intersection of chord and braces in the two specimens with compacting concrete filled in the chord. The test results of stress distribution curves of two specimens were reported. SCFs of concrete-filled circular chord and square braces K-joints were lower than those of corresponding hollow circular chord and square brace K-joints. The corresponding finite element analysis was also conducted to simulate stress distribution along the brace and chord intersection region of joints. It was achieved that experimental and finite element analysis results had good agreement. Therefore, an extensive parametric study was carried out by using the calibrated finite element model to evaluate the effects of main geometric parameters and concrete strength on the behavior of concrete-filled circular chord and square braces K-joints under balanced axial loading. The SCFs at the hot spot locations obtained from ABAQUS were compared with those calculated by using design formula given in the CIDECT for hollow SHS-SHS K-joints. CIDECT Design Guide was generally quite conservative for predicting SCFs of braces and was dangerous for predicting SCFs of chord in concrete-filled circular chord and square braces K-joints. Finally SCF formulae were proposed for circular chord and square braces K-joints with concrete-filled in the chord under balanced axial loading. It is shown that the SCFs calculated from the proposed design equation are generally in agreement with the values derived from finite element analysis, which were proved to be reliable and accurate.