Faculty Profiles - UEMORI Takeshi

Papers - UEMORI Takeshi

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Modeling of Bauschinger Effect During Stress Reversal Reviewed

Takeshi Uemori, Satoshi Sumikawa, Fusahito Yoshida

STEEL RESEARCH INTERNATIONAL 84 ( 12 ) 1267 - 1272 2013.12

Language：English Publishing type：Research paper (scientific journal) Publisher：WILEY-V C H VERLAG GMBH

It is widely known that the constitutive model of Bauschinger effect is one of key points to conduct the accurate sheet metal stamping. In the present research, the elasto-plasticity behaviors of thin sheet metals were investigated by conducting in-plane cyclic tension-compression tests in the different angle from the pre-strained direction. In order to evaluate the accuracy of constitutive models for describing the above mentioned elasto-plasticity behaviors, including the Bauschinger effect, some numerical experiments were conducted for the corresponding stress paths calculations by using three kinds of constitutive models: the isotropic hardening model (hereafter IH model), Yoshida-Uemori model (hereafter Y-U model), and the modified Yoshida-Uemori kinematic hardening model (hereafter modified Y-U model). From the comparisons, it is found that the author's present constitutive model shows a good agreement with the experimental stress-strain responses.

DOI： 10.1002/srin.201300048

A user-friendly 3D yield function to describe anisotropy of steel sheets

Fusahito Yoshida, Hiroshi Hamasaki, Takeshi Uemori

INTERNATIONAL JOURNAL OF PLASTICITY 45 119 - 139 2013.6

Language：English Publishing type：Research paper (scientific journal) Publisher：PERGAMON-ELSEVIER SCIENCE LTD

A sixth-order polynomial type 3D yield function, which has a high flexibility of describing anisotropic behavior of steel sheet, is proposed. The yield function is constructed as a sum of several components of the Cazacu and Barlat, 2001 which was derived as an extension of the J2-J3 Drucker yield criterion (Drucker, 1949) to orthotropy using the linear transformation of the stress deviator, so that the convexity of the yield locus is perfectly guaranteed. The model was validated by comparing the numerical predictions of planar anisotropy of r-values and flow stress directionality, as well as the shape of yield loci, with the corresponding experimental data on several types of steel sheets (high r-valued IF steel and SPCE, and high strength steel sheets of 440-980 MPa TS grades). For most of steel sheets, the model using the sum of two J(2) components, which involve eight anisotropic coefficients, is sufficient for the description of their anisotropies. Further it was found that the consideration of J(3) effect improves the description of anisotropy for some steel sheets (e.g., high r-valued IF steel and 980 MPa grade dual phase HSS). (C) 2013 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ijplas.2013.01.010

Description of Anisotropy and the Bauschinger Effect on Various Types of Steel Sheets Reviewed

Fusahito Yoshida, Hiroshi Hamasaki, Takeshi Uemori

11TH INTERNATIONAL CONFERENCE ON NUMERICAL METHODS IN INDUSTRIAL FORMING PROCESSES (NUMIFORM 2013) 1532 158 - 165 2013

Language：English Publishing type：Research paper (international conference proceedings) Publisher：AMER INST PHYSICS

To describe the anisotropy of sheets a sixth-order polynomial type 3D yield function is proposed. The yield function is constructed as a sum of several components of the Cazacu-Barlat function (2001) which was derived as an extension of the J2-J3 Drucker yield criterion (1949) to orthotropy using the linear transformation of the stress deviator. In this framework of modeling, the convexity of the yield locus is perfectly guaranteed. The model was validated by comparing the numerical predictions of planar anisotropy of r-values and flow stress directionality, as well as the shape of yield loci, with the corresponding experimental data on several types of steel sheets (high r-valued IF steel and SPCE, and high strength steel sheets of 440-980MPa TS grades). For most of steel sheets, the model of the sum of two J2 components, which involve eight anisotropic coefficients, is sufficient for the description of their anisotropies. For the description of the Bauchinger effect and cyclic workhardening characteristic, Yoshida-Uemori kinematic hardening model (2002a, 2002b, 2003) was employed, which includes a new proposal to describe non-saturation type workhardening.

DOI： 10.1063/1.4806820

Influence of Anisotropic Yield Functions on Parameters of Yoshida-Uemori Model Reviewed

Hirotaka Kano, Jiro Hiramoto, Toru Inazumi, Takeshi Uemori, Fusahito Yoshida

CURRENT STATE-OF-THE-ART ON MATERIAL FORMING: NUMERICAL AND EXPERIMENTAL APPROACHES AT DIFFERENT LENGTH-SCALES, PTS 1-3 554-557 2440 - 2452 2013

Language：English Publishing type：Research paper (international conference proceedings) Publisher：TRANS TECH PUBLICATIONS LTD

The Yoshida-Uemori model (Y-U model) can be used with any types of yield functions. The calculated stress strain response will be, however, different depending on the function chosen and on the effective plastic strain definition. Thus several modifications to the Y-U model were proposed in the 10th International Conference on Technology of Plasticity [1]. It was ascertained that in the modified Y-U model, the same set of material parameters can be used with von Mises, Hill's 1948, and Hill's 1990 yield function. In this study, Yld2000-2d and Yoshida's 6th-order polynomial type 3D yield function were examined and it was clarified that the same set of Y-U parameters can be used with these yield functions.

DOI： 10.4028/www.scientific.net/KEM.554-557.2440

Temperature and Processability of Magnesium Alloy AZ31 on Rectangular Cup Deep Drawing Reviewed

Yasuhide Nakayama, Tetsuo Naka, Takeshi Uemori, Ichiro Shimizu

ADVANCES IN ENGINEERING PLASTICITY XI 535-536 326 - + 2013

Language：English Publishing type：Research paper (international conference proceedings) Publisher：TRANS TECH PUBLICATIONS LTD

The magnesium alloys, that have high specific strength, are often applied to the industrial products. However, the magnesium alloys exhibit low ductility at the room temperature on account of its hexagonal close-packed structure. It is difficult to give large deformation to the magnesium alloys at room temperature. Therefore, the plastic forming of a magnesium alloy sheet needs the process at warm temperature. In the present work, the procedure of thermal-mechanical coupled analyses are employed. The numerical simulations of warm deep drawings have been performed in order to evaluate the dependence of the temperature on the plastic forming of a magnesium alloy AZ31 sheet. The mechanical properties of the magnesium alloy AZ31 shall be described as the functions depending on temperature. The shapes of punches and die holes are rectangle whose aspect ratios are 1.5 or 2.0. The corners of punches and dies are heated locally at 473K. The influence of local heating on the formability have been investigated. The relation between the blank size and the formability has been also estimated. As the results of numerical simulations, it was shown that the formability of deep drawing was improved by local heating to the punch and the die. When the blanks of various sizes were tried, the distributions of the plastic strain rate around the die corner were changed. Therefore, the deviation of the plastic flow and the temperature distribution arose in a sheet. Consequently, it is necessary to optimize the blank sizes according to the shape of die holes in addition to the forming temperature.

DOI： 10.4028/www.scientific.net/KEM.535-536.326

Constitutive equations of stress-strain responses of aluminum sheet under stress path changes

2012.12

Description of Planer Anisotropy and Cyclic Plasticity Behavior of Aluminum Sheet Based on Crystal Plasticity Theory Reviewed

Takumi Kobayashi, Kohshiroh Kitayama, Takeshi Uemori, Fusahito Yoshida

MATERIALS AND COMPUTATIONAL MECHANICS, PTS 1-3 117-119 1397 - + 2012

Language：English Publishing type：Research paper (international conference proceedings) Publisher：TRANS TECH PUBLICATIONS LTD

In sheet metal forming, the anisotropy and the Bauschinger effect of sheets affect greatly their formability. This paper discusses how the planar anisotropy and cyclic plastic behavior (the Bauschnger effect and cyclic workhardening characteristics) correlate with the crystallographic texture based on the crystal plasticity analysis on A5052-O sheet. The analytical predictions of r-values and the cyclic stress-strain responses are compared with the experimental observations (S. Tamura et al., Materials Trans, 52-5 (2011), pp.868-875).

DOI： 10.4028/www.scientific.net/AMM.117-119.1397

Direct selective laser sintering of WC-CO cemented carbide by premixing of additives Reviewed

Hideki Kyogoku, Takeshi Uemori, Akihiko Ikuta, Kenichi Yoshikawa, Hitoshi Ohmori

ASME/ISCIE 2012 International Symposium on Flexible Automation, ISFA 2012 465 - 468 2012

Language：English Publishing type：Research paper (international conference proceedings) Publisher：American Society of Mechanical Engineers (ASME)

In this study, the fabrication conditions of WC cemented carbides by direct selective laser melting were investigated. The effects of additives, such as Co, Cu-20%Sn and Cu powders, and laser scanning conditions on laser sintering process were examined to fabricate a sound laser-scanned body of WC cemented carbides. The optimum laser power, scan speed and scan pitch were found out by experiments. It was found that the continuously smooth single-scan track can be obtained at a lower laser power and a higher scan speed by the addition of 30% Cu powder. The smooth surface of the laser-scanned body could be fabricated at a laser power of 9 W, a scan speed of 20 mm/s and a scan pitch of 0.05 mm. Copyright © 2012 by ASME.

DOI： 10.1115/ISFA2012-7182

Elasto-plasticity Behavior of IF Steel Sheet with Planar Anisotropy and Its Macro-meso Modeling

Kohshiroh Kitayama, Takumi Kobayashi, Takeshi Uemori, Fusahito Yoshida

ISIJ INTERNATIONAL 52 ( 4 ) 735 - 742 2012

Language：English Publishing type：Research paper (scientific journal) Publisher：IRON STEEL INST JAPAN KEIDANREN KAIKAN

Elasto-plasticity behavior of an IF steel sheet was investigated by performing uniaxial tension tests in three directions (0 degrees, 45 degrees and 90 degrees to the rolling direction of the sheet), in-plane cyclic tension compression test and bi-axial tension test. The sheet has strong planar anisotropy (r(0) = 2.15, r(45) = 2.12 and r(90) = 2.89) but very weak flow stress directionality. Equi-biaxial flow stress is as large as 1.23 times of the uniaxial flow stress. These elasto-plasticity deformation characteristics, as well as the Bauschinger effect and cyclic hardening behavior, are well described by a macro-plasticity model (Yoshida-Uemori model incorporating with the 4th-order anisotropic yield function). Further, the simulation of elasto-plasticity stress strain responses of the sheet were conducted by two types of crystal plasticity models, i.e., Taylor hypothesis based model and CPFEM, using the crystallographic orientation distribution data measured by neutron diffraction method. The models capture most of the above-mentioned deformation characteristics qualitatively, but the predicted anisotropy and the Bauschinger effect are weaker than those of the real material. The CPFEM gives more realistic results than the Taylor model.

DOI： 10.2355/isijinternational.52.735

OS0303 Experimental Observations of In-Plane Cyclic Tension-Compression Test for Magnesium Alloy Sheet and Its Modelling

UEMORI Takeshi, KATAHIRA Takuji, YOSHIDA Fusahito, KOHTSU Masahide, ADACHI Daiki

The Proceedings of the Materials and Mechanics Conference 2012 ( 0 ) _OS0303 - 1_-_OS0303-2_ 2012

Language：Japanese Publisher：一般社団法人日本機械学会

To investigate the deformation behavior of a magnesium sheet, the finite element calculation was carried out under tension and in-plane cyclic tension-compression test. From the experimental data, the twin deformation was observed during the tensile deformation after uniaxial compression. For the accurate description of the above mentioned twin deformation, we have developed the constitutive equation of twining behavior. From the comparison, it is found that the developed constitutive equations can calculate stress-strain response accurately.

Porous titanium dental implants fabricated using metal injection molding

Hideki Kyogoku, Makiko Yonehara, Takeshi Uemori, Hideki Nakayama

Proceedings of the International Euro Powder Metallurgy Congress and Exhibition, Euro PM 2012 3 2012

Language：English Publishing type：Research paper (international conference proceedings) Publisher：European Powder Metallurgy Association (EPMA)

The porous titanium implants were tried to fabricate by metal injection molding process. Gas-atomized Ti powder and PMMA powders of various mean particle diameters between 20 and 185 μm were used. The pore size was approximately proportional to the diameter of PMMA powder. The relative density and tensile strength of the sintered compact decreased with increasing the mean particle diameter of PMMA powder. The tension and compression tests were performed to examine the mechanical properties of the porous sintered compacts. The tensile strength of the porous sintered compact added 30 vol.%PMMA of diameter of 185 μm was around 300 MPa. It was found that the strength of the porous compact decreases with increasing the amount of addition of PMMA powder. The design of dental implants was investigated by using a FEM analysis. As a result, the porous dental titanium implants were successfully fabricated by metal injection molding process.

Influence of Yield Functions on Parameters of the Yoshida-Uemori Model

Steel Research International 830 - 835 2011.10

Constitutive Equations of Bauschinger Effect under Stress Path Change

Steel Research International 819 - 823 2011.10

Experimental Observation of Elasto-Plasticity Behavior of Type 5000 and 6000 Aluminum Alloy Sheets Reviewed

Shohei Tamura, Satoshi Sumikawa, Takeshi Uemori, Hiroshi Hamasaki, Fusahito Yoshida

MATERIALS TRANSACTIONS 52 ( 5 ) 868 - 875 2011.5

Language：English Publishing type：Research paper (scientific journal) Publisher：JAPAN INST METALS

Elasto-plasticity behavior of type A5052-O and AA6016-T4 aluminum alloy sheets was examined by performing several experiments of uniaxial tension, biaxial stretching and in-plane cyclic tension-compression. Both sheets exhibit apparent r-value planar anisotropy, especially for AA6016-T4 it is extremely strong. while their flow stress directionality under uniaxial tension is not so significant. Both the sheets show strong cyclic hardening with weak Bauschinger effect. Such material behavior is well described by Yoshida-Uemori kinematic hardening model combined with an appropriate choice of anisotropic yield function. [doi:10.2320/matertrans.L-MZ201101]

DOI： 10.2320/matertrans.L-MZ201101

Elasto-plasticity Behavior of IF Steel Sheet with Planar Anisotropy and Its Macro-Meso Modeling Reviewed

Koushirou Kitayama, Takumi Kobayashi, Takeshi Uemori, Fusahito Yoshida

TETSU TO HAGANE-JOURNAL OF THE IRON AND STEEL INSTITUTE OF JAPAN 97 ( 4 ) 221 - 229 2011.4

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：IRON STEEL INST JAPAN KEIDANREN KAIKAN

Elasto-plasticity behavior of a IF steel sheet was investigated by performing uniaxial tension tests in three directions (0 degrees, 45 degrees and 90, to the rolling direction of the sheet), in-plane cyclic tension compression test and bi-axial tension test. The sheet has strong planar r-value anisotropy (r(0) = 2.15, r(45) = 2.12 and r(90) = 2.89) but very weak flow stress directionality. Equi-biaxial flow stress is as large as 1.23 times of the uniaxial flow stress These elasto-plasticity deformation characteristics, as well as the Bauschinger effect and cyclic hardening behavior, are well described by a macro plasticity model (Yoshida-Uemori model incorpolating with the 4th-order anisotropic yield function). Further, the simulation of elasto-plasticity stress-strain responses of the sheet were conducted by two types of crystal plasticity models, i.e., Taylor hypothesis based model and CPFEM, using the crystallographic orientation distribution data measured by neutron diffraction method. The models capture most of the above-mentioned deformation characteristics qualitatively, but the predicted anisotropy and the Bauschinger effect are weaker than those of the real material. The CPFEM gives more realistic results than the Taylor model.

A User-friendly 3D Yield Function for Steel Sheets and Its Application Reviewed

Fusahito Yoshida, Shohei Tamura, Takeshi Uemori, Hiroshi Hamasaki

8TH INTERNATIONAL CONFERENCE AND WORKSHOP ON NUMERICAL SIMULATION OF 3D SHEET METAL FORMING PROCESSES (NUMISHEET 2011), PTS A AND B 1383 807 - + 2011

Language：English Publishing type：Research paper (international conference proceedings) Publisher：AMER INST PHYSICS

A 6th-order polynomial type 3D yield function, which has a high flexibility of describing anisotropic behavior of steel sheets is proposed. A user-friendly scheme of material parameter identification for the model, where only limited experimental data of r-values and yield stresses in three directions (r(0),r(45),r(90) and alp sigma(0),sigma(45),sigma(90)) plus equi-biaxial yield stress (sigma(x) = sigma(y) = sigma(b)) are needed, is presented. The accuracy of this yield function is verified by comparing the numerical predictions with the corresponding experimental data on planar anisotropy of r-values and flow stress directionality, as well as the shape of yield loci, on several types of steel sheets (high r-value IF steel and high strength steel sheets of 440-980MPa TS levels). The advantage of this model is demonstrated by showing a numerical simulation of hole-expansion test.

DOI： 10.1063/1.3623689

Experimental observation of elasto-plasticity behavior of type 5000 and 6000 aluminum alloy sheets Reviewed

Shohei Tamura, Satoshi Sumikawa, Takeshi Uemori, Hiroshi Hamasaki, Fusahito Yoshida

Keikinzoku/Journal of Japan Institute of Light Metals 61 ( 6 ) 255 - 261 2011

Language：Japanese Publishing type：Research paper (scientific journal)

Elasto-plasticity behavior of type A5052-O and AA6016-T4 aluminum alloy sheets was examined by performing several experiments of uniaxial tension, biaxial stretching and in-plane cyclic tension-compression. Both sheets exhibit apparent r-value planar anisotropy, especially for AA6016-T4 it is extremely strong, while their flow stress directionality under uniaxial tension is not so significant. Both the sheets show strong cyclic hardening with weak Bauschinger effect. Such material behavior is well described by Yoshida-Uemori kinematic hardening model combined with an appropriate choice of anisotropic yield function.

DOI： 10.2464/jilm.61.255

Elasto-plasticity behavior of if steel sheet with planar anisotropy and its macro-meso modeling

Koushirou Kitayama, Takumi Kobayashi, Takeshi Uemori, Fusahito Yoshida

Tetsu-To-Hagane/Journal of the Iron and Steel Institute of Japan 97 ( 4 ) 221 - 229 2011

Language：Japanese Publishing type：Research paper (scientific journal)

Elasto-plasticity behavior of a IF steel sheet was investigated by performing uniaxial tension tests in three directions (0°, 45° and 90, to the rolling direction of the sheet), in-plane cyclic tension-compression test and bi-axial tension test. The sheet has strong planar r-value anisotropy (r0=2.15, r45=2.12 and r90=2.89) but very weak flow stress directionality. Equi-biaxial flow stress is as large as 1.23 times of the uniaxial flow stress. These elasto-plasticity deformation characteristics, as well as the Bauschinger effect and cyclic hardening behavior, are well described by a macro-plasticity model (Yoshida-Uemori model incorpolating with the 4th-order anisotropic yield function). Further, the simulation of elasto-plasticity stress-strain responses of the sheet were conducted by two types of crystal plasticity models, i.e., Taylor hypothesis based model and CPFEM, using the crystallographic orientation distribution data measured by neutron diffraction method. The models capture most of the above-mentioned deformation characteristics qualitatively, but the predicted anisotropy and the Bauschinger effect are weaker than those of the real material. The CPFEM gives more realistic results than the Taylor model.

DOI： 10.2355/tetsutohagane.97.221

Elasto-Plasticity Behavior of High Strength Steel Sheet in Biaxial Stress Path Change

Takeshi Uemori, Tohru Kuramitsu, Yuji Mito, Ryutaro Hino, Tetsuo Naka, Fusahito Yoshida

MATERIALS TRANSACTIONS 51 ( 10 ) 1814 - 1818 2010.10

Language：English Publishing type：Research paper (scientific journal) Publisher：JAPAN INST METALS

The elasto plasticity behavior of a high strength steel sheet of 980 MPa TS was investigated by performing biaxial tension experiments In order to evaluate the accuracy of constitutive models of plasticity in describing such elasto plasticity behavior numerical simulations of stress strain responses were conducted for the same stress paths as those in the experiments using two types of constitutive models the isotropic hardening model (IH model) and the kinematic hardening model proposed by the present authors (Yoshida Uemori model) In this work special emphasis is placed in the cases of stress path change In experiments on radial loadings after equi balanced tension preloading It was found that flow stresses are considerably lower than uniaxial tension flow stress The IH model can hardly describe this phenomenon although it is sufficient for stress strain analysis of proportional loading cases In contrast to this the Yoshida Uemori model can well predict every stress strain response in biaxial stress path changes [doi 10 2320/matertrans P M2010817].

DOI： 10.2320/matertrans.P.M2010817

Prediction of Fracture for High Strength Steel Sheets under Stretch Bending Reviewed

Tetsuo Naka, Takanori Kurose, Takeshi Uemori, Ryutaro Hino, Fusahito Yoshida

STEEL RESEARCH INTERNATIONAL 81 ( 9 ) 841 - 844 2010.9

Language：English Publishing type：Research paper (scientific journal) Publisher：WILEY-V C H VERLAG GMBH

Since high strength steel sheets have low ductility, fracture sometimes occurs in their press forming, especially at a die corner under stretch bending. In the present work, the fracture limits of high strength steel sheets under stretch bending were investigated by performing three-points stretch bending experiments with various punch-radii on six types of high strength steel sheets (590-1180MPa). From the experiment, it was found that stronger the sheet lower the fracture limit measured by limit wall stretch, L-max/L-0(L-max: limit wall length of a sheet, L-0: initial wall length). It comes from a fact that the workhardening exponent (n-value) decreases with increasing the strength of the sheet. To predict the fracture limits, a fracture criterion proposed by Yoshida et al., in which limit wall stretch is explicitly given as a function of non dimensional bending radius, t(0)/R (t(0): sheet thickness, R: bending radius) and materials' n-value, was employed. The predicted limit wall stretch, as well as the limit forming height, was in good agreement with the corresponding experimental results.

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