• Title/Summary/Keyword: Stretching Sheet

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Spring-Back Prediction for Sheet Metal Forming Process Using Hybrid Membrane/shell Method (하이브리드 박막/쉘 방법을 이용한 박판성형공정의 스프링백 해석)

  • 윤정환;정관수;양동열
    • Transactions of Materials Processing
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    • v.12 no.1
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    • pp.49-59
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    • 2003
  • To reduce the cost of finite element analyses for sheet forming, a 3D hybrid membrane/shell method has been developed to study the springback of anisotropic sheet metals. In the hybrid method, the bending strains and stresses were analytically calculated as post-processing, using incremental shapes of the sheet obtained previously from the membrane finite element analysis. To calculate springback, a shell finite element model was used to unload the final shape of the sheet obtained from the membrane code and the stresses and strains that were calculated analytically. For verification, the hybrid method was applied to predict the springback of a 2036-T4 aluminum square blank formed into a cylindrical cup. The springback predictions obtained with the hybrid method was in good agreement with results obtained using a full shell model to simulate both loading and unloading and the experimentally measured data. The CPU time saving with the hybrid method, over the full shell model, was 75% for the punch stretching problem.

Spring-back prediction for sheet metal forming process using hybrid membrane/shell method (하이브리드 박막/쉘 방법을 이용한 박판성형공정의 스프링백 해석)

  • F. Pourboghrat
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 1999.03b
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    • pp.62-65
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    • 1999
  • To reduce the cost of finite element analyses for sheet forming a 3D hybrid membrance/sheel method has been developed to study the springback of anisotropic sheet metals. in the hybrid method the bending strains and stresses were analytically calculated as post-processing using incremental shapes of the sheet obtained previously from the membrane finite element analysis. To calculate springback a shell finite element model was used to unload the final shape of the sheet obtained from the membran code and the stresses and strains that were calculated analytically. For verification the hybrid method was applied to predict the springback of a 2036-T4 aluminum square blank formed into a cylindrical cup. the springback predictions obtained with the hybrid method was in good agreement with results obtained using a full shell model to simulateboth loading an unloading and the experimentally measured data. The CPU time saving with the hybrid method over the full shell model was 75% for the punch stretching problem.

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Thermal residual stress behavior in fiber metal laminates (섬유금속적층판의 경화 시 발생하는 열 잔류응력에 관한 연구)

  • Kim, Se-Young;Choi, Won-Jong;Park, Sang-Yoon;Moon, Cho-Rok
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.33 no.6
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    • pp.39-44
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    • 2005
  • Due to mismatch of thermal expansion coefficients between aluminum sheet and glass/epoxy sheet, thermal residual stresses generally appear in the FML. These stresses will affect the yield and fatigue strength of the FML. The numerically determined residual stresses in the Fiber-Metal-Laminates(FML) have been compared to the residual stresses measured from the curvature and tensile test methods. These two experimental methods have been developed for assessing the influence of residual stress in FML. Post-stretching process has been applied to remove the thermal residual stress and reverse the stress distribution. After post-stretching process, the residual stress has been measured from experiments. The results obtained show that analytical and experimental data are well agreed. The thermal residual stress can be removed by post-stretching process and it will increase the yield strength of FML.

Optimum Design of the Process Parameter in Sheet Metal Forming with Design Sensitivity Analysis using the Direct Differentiation Approach (I) -Design Sensitivity Analysis- (직접미분 설계민감도 해석을 이용한 박판금속성형 공정변수 최적화 (I) -설계민감도 해석 -)

  • Kim, Se-Ho;Huh, Hoon
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.26 no.11
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    • pp.2245-2252
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    • 2002
  • Design sensitivity analysis scheme is proposed in an elasto -plastic finite element method with explicit time integration using a direct differentiation method. The direct differentiation is concerned with large deformation, the elasto-plastic constitutive relation, shell elements with reduced integration and the contact scheme. The design sensitivities with respect to the process parameter are calculated with the direct analytical differentiation of the governing equation. The sensitivity results obtained from the present theory are compared with that obtained by the finite difference method in a class of sheet metal forming problems such as hemi-spherical stretching and cylindrical cup deep-drawing. The result shows good agreement with the finite difference method and demonstrates that the preposed sensitivity calculation scheme is a pplicable in the complicated sheet metal forming analysis and design.

Rigid-Plastic Explicit Finite Element Formulation for Two-Dimensional Analysis of Sheet Metal Processes (2차원 박판성형공정해석을 위한 강소성 외연적 유한 요소수식화)

  • 안동규;정동원;양동열
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 1993.10a
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    • pp.206-211
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    • 1993
  • The explicit scheme for finite element analysis of sheet metal forming problems has been widely used for providing practical solution since it improves the convergency problem,memory size and computational time especially for the case of complicated geometry and large element number. In the present work, a basic formulation for rigid-plastic explicit finite element analysis of plain strain sheet metal forming problems has been proposed. The effect of some basic parameters involved in the dynamic analysis has been studied in detail. A direct trial-and-error method is introduced to treat contact and friction. In order to show the validity and effectiveness of the proposed explicit scheme, computation are carried out for cylindrical punch stretching and the computational results are compared with those by the implicit scheme as well as with a commercial code. The proposed rigid-plastic explicit element method can be used as a robust and efficient computational method for analysis of sheet method forming.

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Some Remarks on the Experiment and Finite Element Analysis to Evaluate to Forming Limit of Sheet Metals (금속판재의 성형성 평가를 위한 실험 및 유한요소해석에 관한 고찰)

  • 곽인구;신용승;김형종;김헌영
    • Transactions of Materials Processing
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    • v.9 no.4
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    • pp.379-388
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    • 2000
  • This study aims to examine the influence of experimental and numerical factors on the results of the test and finite element simulation to evaluate the formability of sheet metals. The stretch-forming test with a hemispherical punch is carried out to obtain the limiting dome height (LDH) and forming limit diagram (FLD) for several kinds of aluminium and steel sheet. The results of the LDH and FLD tests are analysed to find any correlation with the uniaxial tensile properties. It proves that the size of the prescribed grid has great influence on the measured value of strain. The finite element analysis of the punch stretching process is also carried out and the result is compared with the experimental data. The influence of the numerical parameters such as friction coefficient, element size and anisotropy model on the simulation results tms out to be very considerable.

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Investigation of Properties of the PET Film Dependent on the Biaxial Stretching (PET 필름의 이축연신에 따른 물성변화 연구)

  • Lee, Jung-Gyu;Park, Sang-Ho;Kim, Seong-Hun
    • Polymer(Korea)
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    • v.34 no.6
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    • pp.579-587
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    • 2010
  • To investigate the properties of PET films, PET films were extruded at various temperature above $T_m$ and quenched at $18^{\circ}C$ for amorphous sheet, and stretched along a direction defined as the machine direction (MD) with a transverse direction (TD) above $T_g$ at various stretching ratios and then annealed at various temperatures produced by SKC PET line. Thermal shrinkage of MD and TD increased with decreasing annealing temperature and extruding temperature, and increasing stretching ratio. The degree of crystallinity, density, heat of fusion (${\Delta}H$) and pre-melting point ($T_m'$) increased with increasing annealing temperature and extruding temperature. Number average molecular weight ($M_n$) and intrinsic viscosity decreased with increasing extruding temperature. Tensile strength and modulus increased with increasing stretching ratio, however decreased with increasing annealing temperature. Reflective index of both stretching and thickness direction increased with increasing stretching ratio and annealing temperature.

A Study on the Springback Characteristics and Bracket Formabilities Enhancement of Aluminum Alloy Sheets for Autobody Application (차체용 알루미늄합금 판재의 스프링백 특성과 브래킷 성형성 향상에 관한 연구)

  • 최문일;강성수
    • Transactions of the Korean Society of Automotive Engineers
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    • v.5 no.6
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    • pp.64-76
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    • 1997
  • This paper deals with development of brackets by using aluminum alloy sheets which is indispensable for weight reduction of autobody. The press formability of aluminum alloy sheet is estimated by means of tensile test, V bending test, sample manufacturing test and photograph of microstructure. The results show that the elongation, strength, work hardening exponent, plastic anisotropy coefficient of Al 6***series are better than those of Al 5***series, but for general press formability, Al 5***series are better than Al 6***series due to lower yield strength. Since most of mechanical properties of aluminum sheet are generally inferior to those of cold-rolled steel sheet, shape fixability and press formability of aluminum sheet are very poor. For making components of autobody by use of die for steel sheet application, it is essential that die should be nodified for least bending and stretching. With the modified die for aluminum, it could be possible to make brackets, the component of autobody. Microstructure of Al 5***series has fine grain and small the 2nd phase and that of Al 6***series has relatively coarse grain. Therefore, it seems that fine grain and small the 2nd phase of Al 5***series is one of the factor of lower yield strength, resistance to stamping work, formation of Luder's line.

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Fabrication of Microfibrous Structures with Rolled-Up Forms using a Bilayer Self-Assembly Process (이중층 자가조립 공정을 활용한 롤형태의 생체의료용 마이크로섬유 구조체 제작)

  • Kim, Yeong-Seo;Park, Suk-Hee
    • Journal of the Korean Society of Manufacturing Process Engineers
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    • v.21 no.2
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    • pp.79-86
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    • 2022
  • Numerous fabrication techniques have been used to mimic cylindrical natural tissues, such as blood vessels, tendons, ligaments, and skeletal muscles. However, most processes have limitations in achieving the biomimetic properties of multilayered and porous architectures. In this study, to embrace both features, a novel self-assembly method was proposed using electrospun microfibrous sheets. A bilayer microfibrous structure, comprising two sheets with different internal stresses, was fabricated by electrospinning a polycaprolactone (PCL) sheet on a uniaxially stretched thermoplastic polyurethane (TPU) sheet. Then, by removing the stretching tension, the sheet was rolled into a hollow cylindrical structure with a specific internal diameter. The internal diameter could be quantitatively controlled by adjusting the thickness of the PCL sheet against that of the TPU sheet. Through this self-assembly method, biomimetic cylindrical structures with multilayer and porous features can be manufactured in a stable and controllable manner. Therefore, the resulting structures may be applied to various tissue engineering scaffolds, especially vascular and connective tissues.