• Title/Summary/Keyword: Stretching process

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Measurement of Friction Coefficient in Stretching of Coated Steel Sheets (각종 도금강판의 신장성형시 마찰계수측정)

  • Kwon, Jae-Wook;Kim, In-Soo;Lee, Dong-Nyung
    • Transactions of Materials Processing
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    • v.1 no.1
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    • pp.75-86
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    • 1992
  • Coated sheet steels have been increasingly used in automotive industry for improving corrosion resistance. One of the arised concerns is frictional behavior of coated sheet steel in stamping process. But analyses of the frictional behavior are complex and difficult. A tensile strip test has been developed for evaluating friction under the condition which simulate the stretching of sheet. Tests are conducted under different die radius and lubrication conditions. Electro-galvanized steel sheets show a lower coefficient of friction than bare steel sheets whose coated layers have been chemically removed. The coefficients of friction are independent of die radius.

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Effect of Shot Blasting Treatment on the Formability of Thin High Strength Steels (고강도 강판의 성형성에 미치는 Shot Blasting 가공 조건의 영향)

  • Park, K.C.;Kim, J.I.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2008.05a
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    • pp.341-344
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    • 2008
  • In order to study the effect of shot blasting condition on the formability of thin high strength steels, specimens were made by changing line speed of a commercial shot blasting plant with maintaining constant impeller condition. Surface roughness of prepared specimens was multiplied by lowering line speed or increasing density of shot impact. Formability was reduced as increasing shot impact. The elongation and stretching formability of shot blasted sheet were decreased by about 10% compared to original sheet. More significant decrease in bending formability was observed after shot blasting. This might be due to the concentrated impact near the surface where major strain occurs during bending process.

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Generation of Solenoidal Modes in Turbulence Driven by Compressive Driving

  • Lim, Jeonghoon;Cho, Jungyeon;Yoon, Heesun
    • The Bulletin of The Korean Astronomical Society
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    • v.44 no.2
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    • pp.47.3-47.3
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    • 2019
  • In this talk, we present numerical simulations of driven hydrodynamic and magnetohydrodynamic (MHD) turbulence with weak/strong imposed magnetic fields. We mainly focus on turbulence driven compressively (∇ × f = 0). Our main goal is to examine how magnetic fields play a role in generating solenoidal modes in compressive turbulence. From our simulation analysis, we find that solenoidal energy densities in hydrodynamic and weak magnetic field cases are generated up to ~ 30% of total ones. On the other hand, in the case of strong magnetic fields, solenoidal energy densities are excited up to ~ 70%. To interpret the results, we further analyze vorticity (w = ∇ × u) equation and find that magnetic fields directly create solenoidal motions, and magnetic tension is most effective in this sense. In hydrodynamic simulations, however, we find that viscous dissipation provides vorticity seeds at the very early stage and they are amplified via stretching process. Lastly, in weak magnetic fields cases, we find that solenoidal motions are created by the effects of magnetic fields, viscosity, and stretching in conjunction.

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A Simplified Approach for Predicting Springback in U-Draw Bending of Sheet Metals (용접 판재의 U 드로오 벤딩에서 스프링백 예측을 위한 이론적 단순화)

  • Chang S. H;Seo D. G.
    • Transactions of Materials Processing
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    • v.13 no.8
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    • pp.678-688
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    • 2004
  • The U-draw bending operation is known as a representative test method for springback evaluation of sheet metals since the sheet in U-draw bending operation undergoes stretching, bending and unbending deformations occurred at the stamping process. In this study, a simplified approach was proposed for predicting springback and side-wall curls of tailor-welded blank in U-draw bending operations, using moment-curvature relationships derived for sheets undergoing stretching, bending and unbending deformation. Two different welded strips were adopted to compare the effects of weld-line locations on the springback. One (type A) was welded along the centerline of the strip-width and the other (type B) was welded along the centerline of the strip-length. To investigate the effect of different thickness combination on the springback, the tailor-welded strips were joined by the laser welding process and consisted of three types of thickness combinations of sheets, SCP1 0.8t * SCP1 1.2t, SCP1 0.8t * SCP1 1.6t and SCP1 0.8t * TRIP 1.0t. Some calculated results by the simplified formula were compared with experimental results.

Elastic-Plastic Finite Element Analysis of Sheet Metal Forming Processes(II) - Analysis of Metal Forming Processes with Contact Condition - (탄소성 유한요소법에 의한 박판성형 공정의 해석 II - 접촉 조건을 가지는 박판성형 공정의 해석 -)

  • 심현보;정완진;양동열
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.14 no.5
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    • pp.1129-1137
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    • 1990
  • Based on the formulation which incorporates large deformation and anisotropy, an elastic-plastic finite element code is developed with membrane element to include the contact treatment. For the analysis of the general sheet metal forming process with contact condition, the treatment of contact is considered by employing the successive skew coordinate system. Three kinds of sheet metal forming processes with contact conditions are analyzed; stretching of a square diaphragm with a hemispherical punch, deep drawing of a circular cup and deep drawing of a square cup. Then the computational results are compared with the experiment. The computed loads and the distribution of the thickness strain are in good agreement with the experiment for all cases. However, the computational results of the thickness strain show the effect of bending can not be ignored in the deep drawing process whereas the effect of bending is negligible in stretching.

Characterization of the PVDF Fibers Fabricated by Hybrid Wet Spinning (하이브리드 습식 공정을 통한 PVDF 섬유의 제조 및 특성에 관한 연구)

  • Jeong, Kun;Kim, Seong-Su
    • Composites Research
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    • v.29 no.4
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    • pp.145-150
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    • 2016
  • Polyvinylidene fluoride (PVDF) as a representative polymer with the piezoelectric property has been studied since the 1960s. Crystalline structure of poly(vinylidene fluoride) polymer is composed of five different crystal structure of the polymer as a semi-crystalline. Among the various crystal structures, ${\beta}-type$ crystal exhibits a piezoelectricity because the permanent dipoles are aligned in one direction. Generally ${\beta}-form$ crystal structure can be obtained through the transformation of the ${\alpha}-form$ crystal structure by the stretching and it can increase the amount through the after treatment as poling process after stretching. ${\beta}-form$ crystal structure the PVDF fibers produced by wet spinning is formed through a diffusion mechanism of a polar solvent in the coagulation bath. However, it has a disadvantage that the diffusion path of the solvent remains as pores in the fiber because the fiber solidification occurs simultaneously with the diffusion of the polar solvent. These pores play a role in reducing effect of poling process owing to effect of disturbances acting on the polarization by the electric field. In this work, the drying method using the microwave was introduced to remove more effectively the residual solvent and the pore within PVDF fibers produced through wet-spinning process and piezoelectric PVDF fibers was produced by transformation of the remaining ${\alpha}$ form crystal structure into ${\beta}-crystal$ structure through the stretching process.

Study of Development for Multi-Cavity Preform Mold (Multi-Cavity Preform 금형시스템 개발에 관한 연구)

  • 서태일;허영무;이성희;이영훈;박용석
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2003.05a
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    • pp.381-388
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    • 2003
  • The paper presents our study of development for multi-cavity preform mold system which consists of hot runner system and valve gate. For this purpose, stretching blow molding process and preform injection process were simulated by Polyflow and Moldflow. Based on various results of the preform injection process analysis, process planning was established. The sectional thickness distribution of preform was optimized. Preform injection mold system was designed by these technical analysis data. Finally, 24-cavity preform mold system was successfully developed.

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Effect of Post-Process on Physical Properties of Electrospun PEI/PVdF Blend Nonwoven Web (전기방사법으로 제조한 PEI/PVdF 블렌드 웹의 물리적 특성에 대한 후처리 영향)

  • Seok, Hoon;Park, Cheol-Min;Kim, Dong-Young;Jo, Seong-Mu
    • Polymer(Korea)
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    • v.36 no.5
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    • pp.606-611
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    • 2012
  • Polyetherimide (PEI) and poly(vinylidene fluoride) (PVdF) blend web was prepared by electrospinning technique. In order to improve low mechanical properties, post processes like hot-pressing and heat-stretching were employed, and a study on the effects of post processes on their mechanical properties was performed. To confirm the physical properties of the web, scanning electron microscopy and tensile measuring instrument were used. The mechanical strength of webs pressed in the ratios of 1/2, 1/3, 1/4 and 1/5 at $180^{\circ}C$ were improved four-to-five times compared to pristine webs. Also they showed an additional increase by 2~8MPa, by heat-stretching 30 to 40% at $220^{\circ}C$.

A Study on the Reproduction of Fine Lines according to Angle Change in Screen Printing (Screen 인쇄에 있어서 망사각도 변화에 따른 미세선화 재현성에 관한 연구)

  • 신종현
    • Journal of the Korean Graphic Arts Communication Society
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    • v.11 no.1
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    • pp.1-16
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    • 1993
  • In screen printing process, printers are stretching screen meshs of an angle of 45deg. This angle need much more screen mesh’s quantity of 15% than 22.5deg. To search mesh angles have affect on reproducting fine line pattern, we modeled the expecting image according on screen angles change and reconfirmed it’s useful and valid from experimentation.

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Vibrational Structure and Predissociation of Ar-CO2 by CO2 Symmetric Stretching Mode Coupled with Ar Motion

  • Jung, Jae-Hoon;Sun, Ho-Sung
    • Bulletin of the Korean Chemical Society
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    • v.23 no.2
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    • pp.245-252
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    • 2002
  • The computationally simple quantum mechanical method (VSCF-DWB-IOS) has been applied to studying the Ar-$CO_2$ vibrational predissociation phenomenon. The new methodology utilizes the vibrational self-consistent field method to determine the vibrational structure of the van der Waals complex, the distorted-wave Born approximation for dissociating process, and the infinite-order sudden approximation for the continuum dissociating product of $CO_2$. The dissociation due to the coupling of the symmetric stretching vibrational motion of $CO_2$ with the motion of the Ar van der Waals mode has been extensively investigated. The lifetimes of transient excited vibrational states, linewidths of absorption peak, and the rotational state distributions of the product, $CO_2$ have been computed. It has been found that the lifetime of the Ar-$CO_2$ in excited vibrational state is very long compared with that of triatomic van der Waals complexes and the product $CO_2$ carries a major portion of dissociation energy as a rotational energy.