• 소성∙가공
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• 제12권6호
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• pp.566-571
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• 2003

The metal forming behavior and defect formation in Ti-6Al-4V tube during hot backward extrusion were investigated. Dynamic material model(DMM) including Ziegler's instability criterion was employed to predict the forming defects such as shear band, inner and/or surface cracks. This approach was coupled to the internal variables generated from FE analysis. The simulation results fur the backward extrusion were compared with the experimental observation. The chilling effect and friction indicated a great influence on the deformation mode of the tube and the formation of surface cracks. The formation of forming defects in the extruded tube was attributed to non-uniform distribution of strain, strain rate and temperatures in the extruded tubes for the given test conditions.

• 마이크로전자및패키징학회지
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• 제8권3호
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• pp.25-30
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• 2001

반도체 칩과 얇은 접착제충의 계면에 존재하는 모서리 균열에 횡방향 인장변형률이 작용하는 경우에 대해 응력확대계수를 조사하고 있다. 이러한 균열들은 자유 경계면 부근에 존재하는 응력 특이성으로 인해 발생할 수 있다. 계면 응력상태를 해석하기 위해서 경계요소법이 사용되고 있다. 복합 응력확대계수의 크기는 균열의 크기에 의존하지만, 균열이 커지면 일정한 값에 수렴한다. 횡방향 인장변형률이 임계값에 도달하면, 계면 균열은 빠르게 전파되리라고 예상된다.

• Water Engineering Research
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• 제3권3호
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• pp.155-162
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• 2002

This study presents the theoretical approach for volume concentration, velocity profile, and granular discharge on the fluid-granule mixed flow downstream of the scour hole at the outlet of the hydraulic structure. Concept of dilatant model was applied for the stress-strain relationships of fluid-granule mixed flow since the flow downstream of the scour hole corresponds to debris flow, where momentum transfers through particle collisions. Mathematical formulations were derived using momentum equation and stress-strain relation of the fluid-granule mixture. Velocity profile under the assumption of uniform concentration over flowing layer showed the downward convex type. Deposition angle of downstream hump was found to be a function of an upstream slope angle, a dynamic friction angle and a volume concentration irrespective of flow itself, Granular discharge and the overflow depth were obtained with given values of inflow rates. Experimental results showed relatively good agreements with theoretical ones.

• 한국정밀공학회지
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• 제15권9호
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• pp.15-24
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• 1998

In this research. we have proposed a new technique to determine .the combination of design parameters for the process design of a hot forged product using artificial neural network(ANN) and statistical design of experiments(DOE). The investigated problem involves the adequate selection of the aspect ratio of billet, the ram velocity and the friction factor as design parameters. An optimal billet satisfying the forming limitation, die filling, load and energy as well as more uniform distribution of effective strain, is determined by applying the ability of artificial neural network and considering the analysis of mean and variation on the functional requirement. This methodology will be helpful in designing and controlling parameters on the shop floor which would yield the best design solution.

• 소성∙가공
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• 제8권1호
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• pp.38-46
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• 1999

This paper deals with the shape fixability of press formed parts through the use of a V-bending process and a U-bending one. The influence of material properties on the shape fixability in forming processes was investigated. A V-bending process had on optimum ben radius for each combination of parameters which caused maximum shape fixability. In the U-bending process the blank holder force could control the degree of shape fixability. A ha호 blank holding force resulted in a uniform strain distribution and increased shape fixability.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1997년도 춘계학술대회논문집
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• pp.25-30
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• 1997

In this study, the forming behavior of Tailor welded HS and IF steel s-rail stamping is analyzed by experiments and simulations. According to the results, uniform strain distribution in the formed part is most important to prevent springback and wrinkle formation. For that purpose, it is most effective to distribute uniformly the contact pressure of blank and bland holder.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1996년도 추계학술대회논문집
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• pp.99-104
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• 1996

A proform for engine valve was designed by finite element method. In the preform design of engine valve, various initial billets are simulated for better preform to get sound final product. Here a preform is design to get desirable metal flow in the forming so that the final product has more uniform strain distribution. after forming. The analysis of the micro-structure of the value formed through the designed process was also performed and result was compared with that of simulation.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2007년도 추계학술대회 논문집
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• pp.330-331
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• 2007

The effect of frictional rolling and subsequent heat treatment was studied on the evolution of texture of AA 3003 Aluminum alloy. With frictional rolling without lubrication it is possible to obtain a larger friction between roll and sample which lead to the formation of uniform rolling texture in the whole thickness layers.

• 대한기계학회논문집
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• 제15권3호
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• pp.1044-1056
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• 1991

본 연구에서는 균일압축력을 받으며 네변이 단순지지된 비균일 두께를 가진 평판의 좌굴응력을 Rayleigh-Ritz방법으로 해석하여 평판두께를 적절히 분포함으로써 동일한 평판중량으로 더 큰 좌굴하중을 얻을 수 있음을 보이며 또한 동일한 문제를 NASTRAN프로그램을 사용하여 해석함으로써 그 정확도를 입증한다.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1998년도 제2회 박판성형심포지엄 논문집 박판성형기술의 현재와 미래
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• pp.17-24
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• 1998

This paper deals with the springback characteristics of cold rolled sheet steel through the use of the V-bending process and U-bending one. The influence of material properties on the springback of forming processes was investigated. In the V-bending process there was an optimum bend radius for each combination of parameters which produced minimal springback. In the U-bending process the blank holder force can control the degree of springback. A high blank holding force resulted in a uniform strain distribution and reduced the level of springback.