Journal of Japan Institute of Light Metals
Online ISSN : 1880-8018
Print ISSN : 0451-5994
ISSN-L : 0451-5994
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Volume 65, Issue 11
Displaying 1-10 of 10 articles from this issue
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REVIEW
RESEARCH ARTICLE
  • Formulation of the differential hardening of 5000 series aluminum alloy sheet for enhancing the predictive accuracy of sheet metal forming simulations
    Junpei Kawaguchi, Toshihiko Kuwabara, Takeo Sakurai
    Article type: RESEARCH ARTICLE
    2015 Volume 65 Issue 11 Pages 554-560
    Published: November 30, 2015
    Released on J-STAGE: December 30, 2015
    DOIhttps://doi.org/10.2464/jilm.65.554
    JOURNAL FREE ACCESS
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    The deformation behavior of 5000 series aluminum alloy sheets under biaxial tension was precisely measured for linear stress paths, using servo-controlled biaxial tensile tests with both cruciform and tubular specimens. The tubular specimens were fabricated by bending and laser-welding as-received flat sheet materials. Differential hardening (DH) behavior was observed; the shapes of the contours of the plastic work constructed in the principal stress space changed with an increase in plastic work. A new constitutive model that can reproduce the DH behavior was proposed; the model is based on the Yld2000-2d yield function (Barlat et al., 2003) with an exponent and material parameters changing as functions of plastic work. Finite element analysis of hydraulic bulge forming was performed using both the proposed DH model and the conventional isotropic hardening model based on selected yield functions. The calculated results based on the DH model were in closest agreement with the experimental results. Thus, the DH model has been verified to be effective for improving the accuracy of the forming simulation.
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  • Material modeling and forming simulation of 5182 aluminum alloy sheet using numerical biaxial tensile test based on homogenized crystal plasticity finite element method
    Akinori Yamanaka, Keisuke Hashimoto, Junpei Kawaguchi, Takeo Sakurai, ...
    Article type: RESEARCH ARTICLE
    2015 Volume 65 Issue 11 Pages 561-567
    Published: November 30, 2015
    Released on J-STAGE: December 30, 2015
    DOIhttps://doi.org/10.2464/jilm.65.561
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    This paper proposes a material modeling methodology of sheet metals using a numerical biaxial tensile test based on the crystal plasticity finite element (CPFE) method and the mathematical homogenization method. To demonstrate the feasibility of the proposed methodology, the biaxial tensile deformation behavior of 5182 aluminum alloy sheet was predicted by the numerical biaxial tensile tests of the sheet. The stress–strain curves and the shapes of the contours of plastic work calculated by the numerical biaxial tensile tests were quantitatively verified by the experimental biaxial tensile test using the cruciform specimen. Parameters of the Yld2000-2d yield function were identified using the results of experimental and numerical biaxial tensile tests. For comparison, von Mises's and Hill's yield functions were identified using the experimental data. To elucidate the effects of the yield functions on the accuracy of sheet metal forming simulation, finite element simulations of hydraulic bulge forming were performed using the identified yield functions. The simulation results demonstrated that the forming simulation using the Yld2000-2d yield function identified by the numerical biaxial tensile tests showed better accuracy than that of the Mises's and Hill's yield functions and was comparable to that of the Yld2000-2d yield function calibrated experimentally.
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  • Determination of flow stress equation of Al–Mg alloy for sheet metal forming analysis
    Toru Kazaoka, Keiko Natori, Ryo Matsumoto, Hiroshi Utsunomiya
    Article type: RESEARCH ARTICLE
    2015 Volume 65 Issue 11 Pages 568-572
    Published: November 30, 2015
    Released on J-STAGE: December 30, 2015
    DOIhttps://doi.org/10.2464/jilm.65.568
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    In order to improve the accuracy of forming analysis for aluminum alloys, it is important to determine precise flow stress equation for aluminum alloys. In case of 5000 series aluminum alloys, formability is difficult to predict due to non-uniform deformation such as dynamic strain aging and stretcher-strain. To identify flow stress curve of A5182-O for wider strain range, the methods using rolling-tensile test and Vickers hardness test was investigated and compared with conventional regression curve obtained by uniaxial tensile test. The three methods were assessed in prediction of neck formation. It is found that stress-strain relationship without dynamic strain aging effect is required for precise prediction of uniform elongation. Plastic instability condition was predicted more precisely by either rolling-tensile test or Vickers hardness test than by conventional tensile test.
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  • Friction characteristics in press forming of 5000 series aluminum alloy sheet
    Shinichi Nishida, Ryosuke Kurihara, Ryosuke Okushima, Hayato Aso, Yosh ...
    Article type: RESEARCH ARTICLE
    2015 Volume 65 Issue 11 Pages 573-577
    Published: November 30, 2015
    Released on J-STAGE: December 30, 2015
    DOIhttps://doi.org/10.2464/jilm.65.573
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    Demand of press forming of aluminum alloy sheet is increasing for improvement of fuel efficiency. FEM analysis of press forming is required to be more accurate. The objective of this study is to clarify the effect of friction coefficient on analytical accuracy in press forming FEM analysis. Spherical forming experiment and FEM analysis were performed to measure the contact pressure and sliding speed of the blank against the punch. Sliding friction test was performed to measure the friction coefficient with low pressure and low speed. The measured friction coefficient was input to the commercial FEM analysis soft PAM-STAMP2G as varied friction coefficient. The experimental thickness strain distributions were compared with the calculated results. FEM analysis results using varied friction coefficient had a better accuracy than those using constant friction coefficient.
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  • Simulation of forming prediction for 5000 series aluminum alloy using finite element analysis
    Shinichi Nishida, Ryosuke Kurihara, Ryosuke Okushima, Masaru Fujita, H ...
    Article type: RESEARCH ARTICLE
    2015 Volume 65 Issue 11 Pages 578-581
    Published: November 30, 2015
    Released on J-STAGE: December 30, 2015
    DOIhttps://doi.org/10.2464/jilm.65.578
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    Forming limit prediction of 5182-O aluminum alloy sheet was carried out by using finite element analysis. JSTAMP/NV was used in the finite element analysis. Length of aluminum specimen was 120 mm, and the width was varied from 10 to 120 mm, and the thickness was 1.0 mm. Stretching test was operated by Erichsen test. Forming limit prediction and necking limit prediction by using finite element analysis was proposed. Forming limit diagram (FLD) of analytical results were indicated relatively good conformability with the FLD of experimental results. Also, spherical stretch forming experiments of 5182-O aluminum alloy sheet were carried out to research the formability on biaxial stress by several companies. The forming simulations were carried out using commercial software PAM-STAMP 2G. Effects of friction coefficient and yield function were investigated in the simulation. Simulation results by using YLD-2000 yield function agreed well with experimental results compared with that of Hill′48 yield function. Those were benefit for analytical simulations of sheet metal forming.
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  • Influence of Bauschinger effect and anisotropy on springback of aluminum alloy sheets
    Takeshi Uemori, Satoshi Sumikawa, Tetsuo Naka, Ninshu Ma, Fusahito Yos ...
    Article type: RESEARCH ARTICLE
    2015 Volume 65 Issue 11 Pages 582-587
    Published: November 30, 2015
    Released on J-STAGE: December 30, 2015
    DOIhttps://doi.org/10.2464/jilm.65.582
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    For accurate springback calculations, the development of accurate constitutive equation “Yoshida–Uemori model” must always be taken into account. However, several springback calculations of other sheet metals by Yoshida–Uemori model have shown wrong agreements with the corresponding experimental data. The reason is why most of them have been calculated from the view point of the accuracy of Bauschinger effect without the strong anisotropy of sheet metal. In the present paper, we have investigated how the initial anisotropy affects the amount of springback for aluminum sheet metals with Bauschinger effect. Specifically, hat bending experiments in R.D. and T.D. were compared with the corresponding calculations. From the above mentioned comparisons, we found that the optimum combination of an anisotropic yield functions and Yoshida–Uemori model is very important for accurate springback analysis.
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