• 오토저널
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• 제15권1호
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• pp.100-106
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• 1993

This paper aims to synthesize the research on fatigue fracture mechanisms of high strength aluminum alloys which are widely used in motorcars or airplanes to prevent accidents. To measure the data of crack opening ratio, the same materials and method are used for evaluating the fatigue crack propagation rate as an effective stress intensity factor. But, many researchers have brought different results. An exact crack opening ratio was, therefore, proposed for getting a more accurate fatigue crack propagation rate. The main conclusions obtained are as follows. (1) As a result of the fatigue test, the value of the crack opening ratio is the same regardless of the stress ratio. (2) The value of crack opening ratio is different according to the measuring point. After measuring the crack propagation rate by using an effective stress intensity factor, the crack opening ratio value measured at the crack mouth by a clip gage, or measured rear of the specimen by a strain gage is more accurate than that by any other measuring test.

• 한국물환경학회지
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• 제25권1호
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• pp.84-89
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• 2009

Our nation's water resources remain susceptible to contamination by phenolic agrichemicals. These compounds can be toxic to a variety of organisms including humans. Their disposal is restricted in many countries with strict limits for acceptable concentrations in drinking water. Enzyme-mediated in situ stabilization has been advocated as an approach for the treatment of phenolic compounds in soils and groundwater. This study reports the development of a new approach to quantify the activity of the HRP enzyme in aqueous systems. The method is based on the coupled processes of energy transfer and enhanced chemiluminescence using a luminol-$H_2O_2$-HRP system. In this study, the effects of solution pH, ionic strength and aqueous concentrations of HRP, $H_2O_2$ and enhancer were evaluated on the p-iodophenol-enhanced, HRP-catalyzed chemiluminescence reaction intensity in Tris-HCl buffer. All assay components were found to affect the maximum chemiluminescene intensity. The calibration curve for HRP showed the linear relationship with maximum light intensity.

• Advanced Composite Materials
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• 제16권4호
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• pp.315-334
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• 2007

In the present study, chopped henequen natural fibers without and with surface modification by electron beam (E-beam) treatment were incorporated into a polypropylene matrix. Prior to composite fabrication, a bundle of raw henequen fibers were treated at various E-beam intensities from 10 kGy to 500 kGy. The effect of E-beam intensity on the interfacial, mechanical and thermal properties of randomly oriented henequen/polypropylene composites with the fiber contents of 40 vol% was investigated focusing on the interfacial shear strength, flexural and tensile properties, dynamic mechanical properties, thermal stability, and fracture behavior. Each characteristic of the material strongly depended on the E-beam intensity irradiated, showing an increasing or decreasing effect. The present study demonstrates that henequen fiber surfaces can be modified successfully with an appropriate dosage of electron beam and use of a low E-beam intensity of 10 kGy results in the improvement of the interfacial properties, flexural properties, tensile properties, dynamic mechanical properties and thermal stability of henequen/polypropylene composites.

• Journal of Welding and Joining
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• 제29권3호
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• pp.76-81
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• 2011

Recently, the structural failures due to fatigue occur frequently with the increase of size of ships and offshore structures. In this respect, the assessment of fatigue life and the residual strength are very important. Currently, the smart materials technology has demonstrated a variety of possibilities for a diagnosis of structural strength and structural health condition for large structures. The benefits and feature of the MFC sensor are more flexible, durable and reliable than conventional smart material. In this study, Micro Fiber Composite (MFC) sensor for the measurement of stress intensity factor (SIF) of two dimensional cracks induced in a structure is developed. Two MFC sensors are placed in the vicinity of the crack tip close to each other with the crack tip in between them. The SIFs of Mode I($K_I$) as well as of Mode II($K_{II}$) based on the piezoelectric constitutive law and fracture mechanics are calculated. In this study, the SIF values measured by MFC sensors are compared with the theoretical results and measured value.

• 조명전기설비학회논문지
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• 제15권4호
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• pp.23-30
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• 2001

본 연구에서는 교류유전체장벽형 코로나방전을 이용하여 선대원통형 전극구조의 방전리액터내의 NO입자의 방전 Image와 형광방출파장대역[236[nm], 247[nm], 259[nm]에서의 수평방향과 수직방향의 신호강도를 ICCD카메라를 이용하여 측정하였다. 또한 방전메카니즘을 알기 위해서 방전진전시간에 따른 방전 Image와 신호강도 측정을 행하였다. NO입자의 수평과 수직방향의 신호강도는247[nm]대역에서 가장 큰 것을 확인 할 수 있었으며, 방전진전시간에 따른 수평과 수직방향의 신호강도는 큰 변화가 없었다. 특히 측정된 데이터로부터 반응장치 내부에서 일어나는 현상의 Image와 형광방출파장의 신호강도를 비교할 수 있었다.

• Journal of Advanced Marine Engineering and Technology
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• 제31권4호
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• pp.385-393
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• 2007

The strength evaluation of the most weakest junction part is required for the safety design of all structures. Most of all. in order to enhance the reliability and safety of the welding part. whose use is the highest, it is very important to establish the efficient structure manufacturing technology by studying and investigating the evaluation of fatigue strength in various environments. This study analyzed the relations of da/dN, and th according to the welding methods of SMAW, FCAW, and SAW. In the stage II. the value of stress intensity factor range was the highest in SMAW welding method of stress ration R=0.1, and appeared under the sequence of FCAW and SAW and as the completion section of stress intensity factor was low, threshold stress intensity factor was lowly formed in da/dN - The fatigue life of each welding method is sensitively worked in high stress ratio. judging from the fact that the width of life reduction increases in the high stress ratio zone compared to the width of life reduction in the low stress ratio zone. In the fatigue limit of welding methods before corrosion. the welding of SMAW and FCAW shows the same fatigue limit compared to Base metal, and SAW holds the lowest fatigue limit value.

• Structural Engineering and Mechanics
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• 제72권1호
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• pp.31-41
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• 2019

Structural integrity assessment of piping components is of paramount important for remaining life prediction, residual strength evaluation and for in-service inspection planning. For accurate prediction of these, a reliable fracture parameter is essential. One of the fracture parameters is stress intensity factor (SIF), which is generally preferred for high strength materials, can be evaluated by using linear elastic fracture mechanics principles. To employ available analytical and numerical procedures for fracture analysis of piping components, it takes considerable amount of time and effort. In view of this, an alternative approach to analytical and finite element analysis, a model based on relevance vector machine (RVM) is developed to predict SIF of part through crack of a piping component under fatigue loading. RVM is based on probabilistic approach and regression and it is established based on Bayesian formulation of a linear model with an appropriate prior that results in a sparse representation. Model for SIF prediction is developed by using MATLAB software wherein 70% of the data has been used for the development of RVM model and rest of the data is used for validation. The predicted SIF is found to be in good agreement with the corresponding analytical solution, and can be used for damage tolerant analysis of structural components.

• International journal of advanced smart convergence
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• 제12권2호
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• pp.167-172
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• 2023

In this study, the absolute and relative strength of six upper extremity resistance exercises were measured by classifying resistance exercise experts and non-experts. As a result, the skilled group showed higher absolute and relative muscle strength than the unskilled group in the 6 upper extremity resistance exercises. These results are judged to be the hypertrophy of fast-twith muscles, the mobilization of motor units, and the increase in the speed of nerve conduction while the skilled person consistently performs resistance exercise. Experts use intermuscular coordination efficiently to stably perform the load according to the movement and exercise intensity performed during exercise, whereas the inexperienced person uses relatively large muscle groups rather than efficiently using intermuscular coordination. It is considered that exercise motion and load were performed by mobilizing. In addition, as a result of comparing the absolute and relative muscle strength between the 6 types of upper limb resistance exercises, there was a difference between the 6 types of upper limb resistance exercises in the two groups. It can be judged that greater muscle strength and endurance were created through liver coordination.

• 한국응용과학기술학회지
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• 제37권1호
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• pp.17-27
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• 2020

본 연구는 6주간의 고강도 복합 훈련 프로그램을 통해 카누 선수의 심폐기능(Cardiorespiratory Function), 체간 등속성 근력(Isokinetic Trunk Strength) 그리고 무산소성 파워(Anaerobic Power)에 미치는 영향을 확인하는데 있다. 이를 위해 고등학교 카누 선수 9명을 대상으로 고강도 복합 훈련 프로그램을 적용하였으며, 고강도 훈련 프로그램은 주 2회의 유산소 운동(화, 목), 주 3회의 무산소 운동(월, 수, 금) 그리고 주 5회의 유연성 운동을 실시하였다. 고강도 복합 훈련 프로그램의 핵심은 무산소성 훈련 프로그램으로 기존 1RM의 퍼센트(%)를 나누어 훈련하던 방식과는 달리 횟수에 대한 100%의 중량을 가지고 하는 훈련이며, 유산소성 운동과 짐볼운동은 보조적인 개념으로 실시하였다. 연구결과, 고강도 복합 훈련 프로그램에 따른 신체구성에서 신장과 근육량은 통계적으로 의한 차이가 있었으며, 체중, 체지방율, BMI는 통계적으로 유의한 차이는 없는 것으로 나타났다. 심폐기능의 경우, 최대산소섭취량과 총 운동시간은 통계적으로 유의한 차이가 있는 것으로 나타났다. 체간 등속성 근력의 경우, 각속도 30°/sec에서는 Flexors 운동시 Peak Torque 항목에서만 통계적으로 유의한 차이가 있는 것으로 나타났다. 각속도 120°/sec에서는 Extensors 운동시 Total Work 항목에서만 통계적으로 유의한 차이가 있는 것으로 나타났다. 무산소성 파워의 경우, Peak Power, Average Power, Peak Drop의 모든 항목에서 통계적으로 유의한 차이가 없는 것으로 나타났다. 이상의 결과를 종합해보면 심폐기능에서는 유의한 개선효과가 있었지만 체간 등속성 근력과 무산소성 파워 항목에서 증가하는 경향은 있었지만 통계적인 차이는 없는 것으로 나타났다. 결론적으로 선수 개개인의 근력과 파워가 개선되는 경향이 나타난 것을 고려하면 훈련기간을 6주 이상으로 구성하고 사례수가 보강된다면 체계적인 결과를 얻을 수 있을 것으로 생각된다. 본 연구에서 적용한 고강도 복합 훈련 프로그램은 카누 선수들의 경기력 향상 효과를 기대할 수 있는 훈련 프로그램으로 적용될 수 있을 것으로 판단된다.

• 대한기계학회논문집A
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• 제23권6호
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• pp.961-967
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• 1999

A model is constructed to evaluate the mode III stress intensity factor(SIF) for orthotropic three-layered material with a center crack subjected to uniform anti-plane shear loading. A mixed boundary value problem is formulated by Fourier integral transform method and a Fredholm integral equation of the second kind is derived. The integral equation is numerically analyzed to evaluate the effects of the ratio of shear modulus, strength of each layer and crack length to layer thickness on the stress intensity factor.