Faculty Profiles - UEMORI Takeshi

Papers - UEMORI Takeshi

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Tensile Test of Copper-Cored Lead-Free Solder Joints Using Non-Contact Type Testing Device with Permanent Magnets Reviewed

Naoya Tada, Takeshi Uemori, Toshiya Nakata

SEM Annual 2017 Proceedings 478 - 478 2017

Springback analysis of aluminum alloy sheet metals by yoshida-uemori model Reviewed

Takeshi Uemori, Kento Fujii, Toshiya Nakata, Shinobu Narita, Naoya Tada, Tetsuo Naka, Fusahito Yoshida

Key Engineering Materials 725 566 - 571 2017

Language：English Publishing type：Research paper (international conference proceedings) Publisher：Trans Tech Publications Ltd

During the last few decades, the enhancement of prediction capability of the sheet metal forming have been increasing dramatically. High accurate yield criteria and wokhardening model (especially, non-linear kinematic hardening model) have a great importance for the prediction of the final shapes of sheet metal. However, the predicted springback accuracy of aluminum alloy sheet metal is not still good due to their complicated plastic deformation behaviors. In the present research, the springback deformation of aluminum alloy sheet metals were investigated by finite element calculation with consideration of initial anisotropy and the Bauschinger effect. In order to examine the effect of the initial and deformation induced anisotropy on the springback deformation, several types of high accurate yield function and hardening rules are utilized in the present research. The calculated springback by Yoshida 6th yield function [1] and Yoshida-Uemori model [2] shows an excellent agreement with the corresponding experimental data, while the other models underestimate the springback.

DOI： 10.4028/www.scientific.net/KEM.725.566

Evaluation of bonding strength of thin copper wire and lead-free solder by pullout tests Reviewed

Naoya Tada, Takuhiro Tanaka, Hirotsugu Tabata, Takeshi Uemori, Toshiya Nakata

2016 11th International Microsystems, Packaging, Assembly and Circuits Technology Conference (IMPACT) 164 - 167 2016.10

Language：English Publishing type：Research paper (international conference proceedings) Publisher：IEEE

Recently, copper wires have been attracting much attention for LSI (Large Scale Integration) bonding because of its excellent mechanical and electrical properties, and low material cost. On the other hand, the end of these wires are usually joined to the pads or through-holes on the printed circuit board, and lead-free soldering is one of the popular bonding methods. Since the solders are weaker than copper wires, the stress and strain tend to be concentrated on the interface of solder/wire interface. The fracture frequently occurred there and may influence the quality of product. It is therefore important to evaluate the bonding strength of thin copper wire and lead-free solder. In this paper, pullout tests of thin copper wires from lead-free solder were carried out and the pullout behavior of the wires were observed. A method of bonding strength evaluation was proposed and the results were examined.

DOI： 10.1109/impact.2016.7799989

Effect of Hardening Rule on Analysis of Forming and Strength of Multistage Cold Forged Bolt without Heat Treatment Reviewed

Shinobu NARITA, Takeshi UEMORI, Kunio HAYAKAWA, Yoshihiro KUBOTA

Journal of the Japan Society for Technology of Plasticity 57 ( 670 ) 1070 - 1076 2016

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Japan Society for Technology and Plasticity

<p>The isotropic hardening model for an elastic-plastic material have often been used for simulation of cold forging processes, by which, however, it is difficult to represent the Bauschinger effect properly. On the other hand, considering the Bauschinger effect is essential for more precise simulation of the forming process as well as the strength of the forged part without heat treatment. One example is a cold-forged bolt of stainless steel. In the present paper, for two multistage cold forming processes of non-heat-treated stainless steel bolts, the simulations of the forming process and the strength were performed by FE analysis using the YU model that is one of the kinematic hardening models being able to express the Bauschinger effect. As a result, the Bauschinger effect during the forming process can be expressed properly. Moreover, by carrying out the analysis on the tensile test of the forged bolt, the difference in strength by between the isotropic and the kinematic hardening models can be estimated clearly. Furthermore, the effect of the forming process on the strength of the forged bolt can also be evaluated appropriately.</p>

DOI： 10.9773/sosei.57.1070

Influence of Bauschinger Effect on Forming Simulation Result and Its Solution

UEMORI Takeshi

Journal of the Japan Society for Technology of Plasticity 57 ( 662 ) 194 - 198 2016

Modeling of anisotropic hardening of sheet metals including description of the Bauschinger effect Reviewed

Fusahito Yoshida, Hiroshi Hamasaki, Takeshi Uemori

INTERNATIONAL JOURNAL OF PLASTICITY 75 170 - 188 2015.12

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

The present paper proposes a framework for constitutive modeling of plasticity to describe the evolution of anisotropy and the Bauschinger effect in sheet metals. An anisotropic yield function, which varies continuously with increasing plastic strain, is defined as an interpolation between two yield functions at two discrete levels of plastic strain. Several types of nonlinear functions of the effective plastic strain are proposed for the interpolation. A framework for a combined anisotropic-kinematic hardening model of large-strain cyclic plasticity with small elastic strain is presented, and the details of modeling which is based on the Yoshida-Uemori, model (Yoshida et al., 2002, Yoshida and Uemori, 2002, 2003) are described. The shape of the yield surface and that of the bounding surface are assumed in the model to change simultaneously. The model was validated by comparing the calculated results of stress strain responses with experimental data on r-value and stress-directionality changes in an aluminum sheet (Hu, 2007) and a stainless steel sheet (Stoughton and Yoon, 2009), as well as the variation of the yield surface of an aluminum sheet (Yanaga et al., 2014). Furthermore, anisotropic cyclic behavior was examined by performing experiments of uniaxial tension and cyclic straining in three sheet directions on a 780-MPa advanced high-strength steel sheet. (C) 2015 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ijplas.2015.02.004

Microscopic deformation of polycrystalline pure copper wire during tension Reviewed

Naoya Tada, Yoshitaka Matsukawa, Takeshi Uemori, Toshiya Nakata

2015 10th International Microsystems, Packaging, Assembly and Circuits Technology Conference (IMPACT) 229 - 232 2015.10

Language：English Publishing type：Research paper (international conference proceedings) Publisher：IEEE

In order to clarify the inhomogeneous deformation of thin copper wire, an interrupted tensile test was carried out on the stage of the digital holographic microscope (DHM). The inhomogeneity was evaluated based on the non-uniform change in height distribution on the surface of thin wire specimen during the test. Microscopic plastic deformation by a unit of crystal grain and large gradient in height distribution along grain boundaries were observed. The increase in average height of grain between two earlier loading steps corresponded to that between two later loading steps. This result suggests that the microscopic deformation at the latter stage of tension is predictable from that at the early stage of the tension.

DOI： 10.1109/impact.2015.7365226

Shear Deformation Behavior of Adhesive Layer in Stretch-bending/unbendingof Adhesively Bonded Dissimilar Sheet Metals Reviewed

TOKUDA Taro, YOSHIDA Tetsuya, UEMORI Takeshi, TAKIGUCHI Michihiro, YOSHIDA Fusahito

Journal of The Adhesion Society of Japan 51 ( 7 ) 347 - 354 2015.7

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Adhesion Society of Japan

<p>In this study, the shear deformation behavior of adhesive layer in stretch-bending/unbending foradhesively bonded dissimilar sheet metals was investigated by two types of experiments and finiteelement analysis. Major results obtained are summarized as follows:（1）The shear deformation behaviorof adhesive layer was observed in bending/unbending tests with two experimental apparatus.（2）The shear deformation of adhesive layer was influenced by the die corner radius and the tensilespeed.（3）The tensile strength of adherend has a large influence on the shear deformation behavior ofadhesive layer. It is possible to suppress the shear deformation of adhesive layer by using a materialwith small tensile strength as one of the two adherends.（4）The delamination of adhesive layer wasoccurred when the shear strain of adhesive layer in stretch-bending/unbending exceeded a certainvalue（approximately 1.7）.（5）FEM analysis was carried out with using constitutive equations possibleto express the visco-plastic behavior obtained in previous research. However the new yield functionwas proposed in this study for improving the precision of FEM analysis, an expected result was notobtained.</p>

DOI： 10.11618/adhesion.51.347

Modeling of large-strain cyclic plasticity including description of anisotropy evolution for sheet metals Reviewed

Fusahito Yoshida, Takeshi Uemori, Hiroshi Hamasaki

Advanced Structured Materials 64 571 - 585 2015.6

Language：English Publishing type：Research paper (scientific journal) Publisher：Springer Verlag

The present paper describes a framework for the constitutive modeling of a large-strain cyclic plasticity to describe the evolution of anisotropy and the Bauschinger effect of sheet metals that is based on the Yoshida-Uemori kinematic hardening model. In the model, the shapes of the yield and the bounding surfaces are assumed to change simultaneously with increasing plastic strain. An anisotropic yield function that varies continuously with the plastic strain is defined by a nonlinear interpolation function of the effective plastic strain using a limited number of yield functions determined at a few discrete points of plastic strain. With this modeling framework, any type of yield function can be used and the convexity of the yield surface is always guaranteed. A set of kinematic parameters can be identified experimentally independent of the anisotropic parameters.

DOI： 10.1007/978-3-319-19440-0_26

Cyclic plasticity model for accurate simulation of springback of sheet metals Reviewed

Fusahito Yoshida, Takeshi Uemori

60 Excellent Inventions in Metal Forming 61 - 66 2015.1

Language：English Publishing type：Part of collection (book) Publisher：Springer Berlin Heidelberg

The use of a plasticity model that properly describes material behavior is of vital importance for accurate numerical simulation of sheet metal forming, especially for the prediction of springback. For that purpose a large-strain cyclic plasticity model, so-called Yoshida-Uemori model, was proposed in the kinematic hardening modeling framework. It is able to describe properly material behavior, such as the Bauschinger effect, the workhardening stagnation, strain-range dependent cyclic workhardening, as well as the degradation of unloading stress-strain slope with increasing plastic strain. The model has been implemented into several FE commercial codes, and it is widely used in sheet metal forming industry. By using it, the accurate springback prediction, especially for high strength steel sheets, is made possible.

DOI： 10.1007/978-3-662-46312-3_10

Implicit stress integration and consistent tangent matrix for Yoshida's 6th order polynomial yield function combined with yoshida-uemori kinematic hardening rule Reviewed

Hiroshi Hamasaki, Fusahito Yoshida, Takeshi Uemori

Key Engineering Materials 651-653 558 - 563 2015

Language：English Publishing type：Research paper (international conference proceedings) Publisher：Trans Tech Publications Ltd

This paper describes fully implicit stress integration scheme for Yoshida's 6th order yield function combined with Yoshida-Uemori kinematic hardening model and its consistent tangent matrix. Cutting plane method was employed for accurate integrations of stress and state variables appeared in Yoshida-Uemori model. In the present scheme, equivalent plastic strain, stress tensor and all the state variables are treated as independent variables in order to handle the 6th order yield function which is not the J2 yield function, and the equilibriums for each variables are solved for the stress integration. Subsequently, exact consistent tangent matrix which is necessary for implicit static finite element simulation was obtained. The proposed scheme was implemented into finite element code LS-DYNA and deep drawing process for aluminum alloy sheet was calculated. The earing appearance after drawing was compared with the experiment.

DOI： 10.4028/www.scientific.net/KEM.651-653.558

Die-dending of adhesively bonded sheet metals Reviewed

Michihiro Takiguchi, Taro Tokuda, Tetsuya Yoshida, Takeshi Uemori, Fusahito Yoshida

Key Engineering Materials 626 103 - 108 2015

Language：English Publishing type：Research paper (international conference proceedings) Publisher：Trans Tech Publications Ltd

In this paper, the deformation behavior of adhesive layer in die-Bending for adhesively bonded sheet metals was investigated by experiments and finite element method (FEM). We paid special attention to the bending/unbending shear deformation of the adhesive layer during the die-Bending of adhesively bonded sheet metals by using highly ductile acrylic adhesive. Major results obtained are summarized as follows: (1) The bending/unbending shear deformation of the adhesive layer was observed during the die-Bending. (2) The punch radius has a large influence on the die-Bending in the adhesively bonded sheet metals. (3) It is desirable to perform die-Bending at high speed as well as air-Bending. © (2015) Trans Tech Publications, Switzerland.

DOI： 10.4028/www.scientific.net/KEM.626.103

Evaluation of forming limit by principal shear strain energies Reviewed

Hidenori Yoshimura, Hiroya Horita, Takeshi Uemori, Tetsuo Naka, Yutaka Mihara

Keikinzoku/Journal of Japan Institute of Light Metals 65 ( 5 ) 190 - 195 2015

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Japan Institute of Light Metals

In sheet metal forming, crack in the formed sheets is one of the serious defects, and it is tried to avoid the crack by use of numerical simulation. In the simulation, period and location of the occurrence should be quantitatively evaluated by the formulated criteria. For prediction of crack occurrence, various ductile fracture criteria have been proposed. These criteria are based on the void damage theory and include effect of void growth and coalescence at the late stage of the fracture. In sheet forming, however, not only crack but also necking is problems, and it is important to obtain forming limit of the uniform deformation. Although the forming limit has been examined by M-K theory etc., the criteria does not reach the sufficient level. We consider that the plastic deformation depend on the shear deformation and the criterion by three principal shear strain energies is proposed. In order to verify applicability of the criterion, flat-die drawing tests of aluminum sheets with proportional and non-proportional strain passes were carried out and the forming limit curves predicted by the proposed criterion comparatively agrees with the test results.

DOI： 10.2464/jilm.65.190

Influence of Bauschinger effect and anisotropy on springback of aluminum alloy sheets Reviewed

Uemori Takeshi, Sumikawa Satoshi, Naka Tetsuo, Ma Ninshu, Yoshida Fusahito

Journal of Japan Institute of Light Metals 65 ( 11 ) 582 - 587 2015

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Japan Institute of Light Metals

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.

DOI： 10.2464/jilm.65.582

Finite element analysis of high tensile strength steel sheet by using complex step derivative approximations Reviewed

Takeshi Uemori, Hiroshi Miyake, Tetsuo Naka, Michihiro Takiguchi, Fusahito Yoshida

Key Engineering Materials 626 187 - 192 2015

Language：English Publishing type：Research paper (international conference proceedings) Publisher：Trans Tech Publications Ltd

The framework for the complex step derivative approximations (hereafter CDSA) to calculate the consistent tangent moduli is studied. The present methods is one of the most effective methods to implement any material constitutive equations to the commercial finite element codes and does not suffer from calculation conditions and errors. In order to confirm the efficiency of CDSA, we developed the user subroutine code based on the CDSA using associative J2 flow rules with general nonlinear isotropic hardening rules that is commonly and widely utilized in commercial finite element codes. In this study, the user material subroutine 'Hypela2' of MSC.Marc (ver.2013.0.0) was utilized. The finite element calculation result by the proposal method shows a good agreement with the corresponding result by the MSC.Marc default setting. Also we apply the Yoshida-Uemori back stress model to the CDSA and evaluate this new technique to predict the deformation behavior of high tensile strength steel sheet. © (2015) Trans Tech Publications, Switzerland.

DOI： 10.4028/www.scientific.net/KEM.626.187

Report of Strain Gauge Seminar under the Auspices of Chugoku-Sikoku Branch

UEMORI Takeshi

Journal of the JSTP 55 ( 636 ) 14 - 14 2014

Observations of cyclic deformation behaviors of aluminum sheet and constitutive modeling Reviewed

Takeshi Uemori, Satoshi Sumikawa, Tetsuo Naka, Fusahito Yoshida

11TH INTERNATIONAL CONFERENCE ON TECHNOLOGY OF PLASTICITY, ICTP 2014 81 933 - 938 2014

Language：English Publishing type：Research paper (international conference proceedings) Publisher：ELSEVIER SCIENCE BV

Aluminum sheet metals have been widely utilized for a light weight construction of automobile. However, these metals still remain one of the difficult materials to predict the accurate final shapes after press forming processes, because of several mechanical features such as plastic anisotropy of yield stress and small Lankford value. In order to solve the problems, the present author has developed a new constitutive model. The model can describe accurate non-proportional hardening behaviors of aluminum sheet metals. In the present research, some experimental procedures were carried out to reveal the mechanical properties of an aluminum sheet under proportional and non-proportional deformations. The comparisons between experimental data and the corresponding calculated results by the proposed constitutive model confirm the advantages of our model. (C) 2014 Published by Elsevier Ltd.

DOI： 10.1016/j.proeng.2014.10.120

A model of anisotropy evolution of sheet metals Reviewed

Fusahito Yoshida, Hiroshi Hamasaki, Takeshi Uemori

11TH INTERNATIONAL CONFERENCE ON TECHNOLOGY OF PLASTICITY, ICTP 2014 81 1216 - 1221 2014

Language：English Publishing type：Research paper (international conference proceedings) Publisher：ELSEVIER SCIENCE BV

Conventional plasticity models assume that shapes of yield surfaces are remain fixed throughout plastic deformation. However, some experiments show that anisotropy is changing with increasing plastic strain. This paper proposes a constitutive model that describes the evolution of anisotropy, both for the stress directionality and r-values, of sheet metals. The evolution of anisotropy is expressed by the change of the yield function as a function of the effective plastic strain. The anisotropy model is validated by comparing the experimental data on AA6022-T43 aluminium sheet (after Stoughton, T. B. and Yoon, J. W., Int J Plasticity 25 (2009) 1777-1817). This model is incorporated into the Yoshida-Uemori kinematic hardening model to describe both the Bauschinger effect and the anisotropy evolution. (C) 2014 Published by Elsevier Ltd.

DOI： 10.1016/j.proeng.2014.10.100

Springback of Aluminum alloy sheet metal and its modeling Reviewed

Takeshi Uemori, Satoshi Sumikawa, Syohei Tamura, Tetsuo Naka, Fusahito Yoshida

ADVANCES IN MATERIALS AND PROCESSING TECHNOLOGIES XVI 939 361 - + 2014

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

Aluminum alloy sheet metals have been widely utilized for a light weight construction of automobile. However, Aluminum sheet metals still remain one of the difficult materials to predict the accurate final shapes after press forming processes, because of several mechanical weak features such as lower Young's modulus, strong plastic anisotropy of yield stress, Lankford values, and so on. In order to solve the problems, the present author has developed a new constitutive model called "Modified Yoshida-Uemori model". The present model can describe accurate non-proportional hardening behaviors of Aluminum alloy sheet metals.
In the present research, several experimental procedures were carried out to reveal the mechanical properties of Aluminum alloy sheet metals. From the comparison between experimental data and the corresponding calculated results by our constitutive model, the performance of our model was evaluated. In addition to the above mentioned research, the evaluation of some springback analyses were also carried out. The calculated results show good agreements with the corresponding experimental data.

DOI： 10.4028/www.scientific.net/AMR.939.361

Deformation behavior of adhesive layer in stretch-bending/unbending for adhesively bonded sheet metals

Michihiro Takiguchi, Taro Tokuda, Tetsuya Yoshida, Takeshi Uemori, Fusahito Yoshida

ADVANCES IN MATERIALS AND PROCESSING TECHNOLOGIES XVI 939 19 - + 2014

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

In this paper, the deformation behavior of adhesive layer in stretch-bending/unbending for adhesively bonded sheet metals was investigated by experiments and finite element method (FEM). We paid special attention to the cyclic shear deformation of the adhesive layers during the plastic working. Major results obtained are summarized as follows: (1) When the adhesively bonded sheet metals is bent and pulled out at a 90 degrees angle, shear deformation due to bending of the adhesive layer starts shortly before reaching the die corner and unbending starts at the middle of the corner. (2) The die radius has a large influence on the bending behavior. (3) It is possible to suppress shear deformation of the adhesive layer by using a material with small tensile strength as one of the two adherends.

DOI： 10.4028/www.scientific.net/AMR.939.19

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