• 대한기계학회논문집A
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• 제35권11호
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• pp.1521-1528
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• 2011

자동차용 고무부품에 대한 유한요소 해석의 신뢰 향상을 위하여 고무소재 물성치에 대한 연구를 수행하였다. 마운트 설계를 위하여 수백 종의 고무 물성치를 모두 측정하는 것은 현실적으로 어렵다. 그래서 시험 값을 대신하는 순수전단 시험 데이타의 변환 방법을 제시하여 유효성을 확인하였다. 순수전단시험의 응력-변형 관계의 변환은 단순인장시험 데이터와 주 연신률의 함수로 정의한 푸아송의 비를 사용하였다. 카본 충진 고무의 변환 순수전단시험 데이터는 100%변형까지 시험 데이터와 상당히 유사하다. 단순인장시험 데이타와 함께, 순수전단시험의 변환 데이타와 시험 데이터를 각각 사용한 허브베어링 씰의 접촉력에 대한 유한요소해석 결과들은 시험 데이터와 거의 일치하였다. 해석에 사용된 재료상수는 Ogden 상수이다.

• 한국광학회지
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• 제4권4호
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• pp.447-451
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• 1993

용량이행형 방전회로를 이용하여 장펄스 XeCl 엑시머 레이저를 발진 시켰으며, 펄스폭은 150ns(FWHM)이었다. 펄스폭에 영향을 미치는 가스분압 및 capacitance의 비에 따른 펄스폭의 변화를 관측 하였으며, 이로부터 단펄스에서 장펄스로의 발진을 쉽게 얻을 수 있음을 알았다. 일정 가tm 혼합 비율([Xe]/[HCl]=15)의 상태에서 HCl과 Xe가스의 분압이 감소함에 따라 광 펄스폭의 최대 변화량은 125ns이었고, 일정 압력 하에서의 capacitance비(Cm/Cp) 변화에 늘어나는 광 펄스폭의 변화량은 60ns이었다.

• 전기화학회지
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• 제6권2호
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• pp.134-140
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• 2003

기능성 도판트인 dodecylbenzensulfonic acid(DBSA)와 혼합도판트{(DBSA와 $LiClO_4$, NSA(2-naphthalenesulfonic acid), DEHSA[di(2-ethylhexyl)sulfosuccinic acid]}를 사용하여 전기화학적방법에 의한 연신성 폴리피롤(Ppy-DBSA, Ppy-mixed dopants)필름을 제조하였다. 전기화학적 방법에 의해 제조된 폴리피를 괼름은 zone drawing방법을 사용하여 1.0-2.5배 연신시킬 수 있었으며, 연신된 폴리피롤 필름의 전기전도도를 측정하였다. 연신율이 증가함에 따라 필름의 전기전도도가 증가함을 볼 수 있었다. 이 현상은 연신율에 따른 결정성 증가로 설명 할 수 있었다. 1.0-2.5배 연신된 폴리피를 필름(Ppy-DBSA, Ppy-mixed dopants)을 온도변화에 따른 전하 이동 경로는 모두 power raw에 적합함을 볼 수 있었다.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 춘계학술대회 논문집
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• pp.499-502
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• 2005

A process map has been developed, which can identify the process conditions for weak mechanical bonding at the contact surface during the direct extrusion of a Cu-Ti bimetal bar. Bonding mechanism between Cu and Ti was assumed as a cold pressure welding. Then, the plastic deformation at the contact zone causes mechanical bonding and a new bonding criterion for pressure welding was developed as a function of the principal stretch ratio and normal pressure at the contact surface by analyzing micro local extrusion at the contact zone. Finite element analyses for extrusion of Cu-Ti bimetal bars were performed for various process conditions. The deformation history at the contact surface was traced and the proposed new bonding criterion was applied to predict whether the mechanical bonding at the Cu-Ti contact surface happens. Finally, a process map for the extrusion of Cu-Ti bimetal bar is suggested.

• 한국정밀공학회지
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• 제20권11호
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• pp.150-157
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• 2003

In this paper, the large deformation of hollow silicon rubber gasket is treated. The frictional contact occurs between groove and the outer part of hollow gasket, and the frictional self-contact exists in the inner parts of hollow gasket. The silicon rubber has the nonlinear elastic behavior and its material property is approximately incompressible. Hence, the stress analysis requires an existence of a strain energy function, which is usually defined in terms of invariants or stretch ratio such as generalized Mooney-Rivlin and Ogden model. Considering large compressive deformation and friction, Mooney-Rivlin 3rd model and Coulomb's friction model are assumed. The numerical analysis is obtained by the commercial finite element program MARC. But, due to large deformation, the elements degenerate in the inner parts of hollow gasket. This means that the analysis of subsequent increments is carried out with a very poor mesh. In order to continue the analysis with a sufficient accuracy, it is necessary to use new finite element modeling by remesh. Experiments are also performed to show the validity of present method. As a conclusion, numerical results by this research have good agreements with experiments.

• 소성∙가공
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• 제18권4호
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• pp.342-346
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• 2009

Forming characteristics for the bundle extrusion of Cu-Ti bimetal wires are investigated, which can identify the process conditions for weak mechanical bonding at the contact surface during the direct extrusion of a Cu-Ti bimetal wire bundle. Bonding mechanism between Cu and Ti is assumed as a cold pressure welding. Then, the plastic deformation at the contact zone causes mechanical bonding and a new bonding criterion for pressure welding is developed as a function of the principal stretch ratio and normal pressure at the contact surface by analyzing micro local extrusion at the contact zone. The averaged deformation behavior of Cu-Ti bimetal wire is adopted as a constitutive behavior at a material point in the finite element analysis of Cu-Ti wire bundle extrusion. Various process conditions for bundle extrusions are examined. The deformation histories at the three points, near the surface, in the middle and near the center, in the cross section of a bundle are traced and the proposed new bonding criterion is applied to predict whether the mechanical bonding at the Cu-Ti contact surface happens. Finally, a process map for the direct extrusion of Cu-Ti bimetal wire bundle is proposed.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2005년도 추계학술대회 논문집
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• pp.393-397
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• 2005

A process map has been developed, which can identify the process conditions for weak mechanical bonding at the contact surface during the direct extrusion of a Cu-Ti bimetal wire bundle. Bonding mechanism between Cu and Ti is assumed as a cold pressure welding. Then, the plastic deformation at the contact zone causes mechanical bonding and a new bonding criterion fur pressure welding is developed as a function of the principal stretch ratio and normal pressure at the contact surface by analyzing micro local extrusion at the contact zone. The averaged deformation behavior of Cu-Ti bimetal wire is adopted as a constitutive behavior at a material point in the finite element analysis of Cu-Ti wire bundle extrusion. Various process conditions for bundle extrusions are examined. The deformation histories at the three points, near the surface, in the middle and near the center, in the cross section of a bundle are traced and the proposed new bonding criterion is applied to predict whether the mechanical bonding at the Cu-Ti contact surface happens. Finally, a process map for the direct extrusion of Cu-Ti bimetal wire bundle is proposed.

• Journal of Mechanical Science and Technology
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• 제19권6호
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• pp.1358-1365
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• 2005

Flue gas recirculation (FGR) is widely adopted to control NO emission in combustion systems. Recirculated flue gas decreases flame temperature and reaction rate, resulting in the decrease in thermal NO production. Recently, it has been demonstrated that the recirculated flue gas in fuel stream, that is, the fuel induced recirculation (FIR), could enhance much improved reduction in NO per unit mass of recirculated gas, as compared to conventional FGR in air. In the present study, the effect of dilution methods in air and fuel sides on NO reduction has been investigated numerically by using $N_2$ and $CO_2$ as diluent gases to simulate flue gases. Counterflow diffusion flames were studied in conjunction with the laminar flamelet model of turbulent flames. Results showed that $CO_2$ dilution was more effective in NO reduction because of large temperature drop due to the larger specific heat of $CO_2$ compared to $N_2$. Fuel dilution was more effective in reducing NO emission than air dilution when the same recirculation ratio of dilution gas was used by the increase in the nozzle exit velocity, thereby the stretch rate, with dilution gas added to fuel side.

• 소성∙가공
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• 제19권6호
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• pp.337-343
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• 2010

Current need of weight reduction in automotive part increases the application for high strength steel (HSS). The various types of high strength steels have been used to produce chassis part, control arms and trailing arms for weight reduction and increasing of fatigue durability such as dual phase steel (DP) and ferrite bainite steel (FB). But, DP and FB steels have proven to show inferiority in durability as well as press formability. Edge cracking occurred often in flange forming and hole expansion processes is the major failure encountered. This paper discussed the behavior of edge stretchability of high strength steel of DP and FB steels. Experimental works have been conducted to study the effect of punch clearance and burr direction on hole expansion ratio (HER). Also finite element simulation (FEM) has been preformed to clarify the mechanism of flange crack and support the experimental results on HER of DP and FB steels. It was simulated the whole process of blanking process following by hole expansion process and ductile fracture criterion named the modified Cockcroft-Latham model which was used to capture the fracture initiation. From the hole expansion tests and FEM simulation studies it was concluded that ferrite bainite steel showed better stretch-flangeability than dual phase steel. It was attributed to the lower work hardening rate of ferrite bainite steel than dual phase steel at the sheared edge.

• Physical Therapy Rehabilitation Science
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• 제8권1호
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• pp.45-51
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• 2019

Objective: The purpose of this study was to investigate the muscle activity ratio of the lower limb according to changes in straight leg raise (SLR) test angles on hamstring muscle shortening during squat exercises. Design: Randomized controlled trial. Methods: The subjects were 14 healthy adults who were informed of and agreed to the method and purpose of the study. The participants were classified into SLR groups according to two angles (over $80^{\circ}$ or under $80^{\circ}$) assessed using the SLR tests. After training and practicing the wall squat posture to be applied to the experiment, electromyography (EMG) was used to measure changes in muscle activity during the performance of a wall squat. After stretching, a sequence of pre-stretch tests were performed again, and the active and passive SLR tests were also reconducted; thereafter, a wall squat was performed again by attaching EMG electrodes. The EMG results before and after stretching were compared. Results: The muscle activity of the vastus lateralis oblique muscle increased in both groups. The muscle activity of the vastus medialis oblique muscle decreased in over both group. Rectus femorus activity increased in the under 80-degree groups but decreased in the over 80-degree group. The muscle activity of the biceps femoris muscle decreased after stretching in the over 80-degree group and increased in the under 80-degree group, and the semitendinosus muscle activity after stretching was decreased. The quadriceps-to-hamstring muscle (Q:H) ratio before and after stretching between groups showed that the hamstring muscle ratio decreased after stretching in both groups. Conclusions: The results of this study showed that the Q:H ratio before and after stretching between groups was not significantly different.