研究者詳細 - 上森　武

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

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

2016 11th International Microsystems, Packaging, Assembly and Circuits Technology Conference (IMPACT) 164 - 167 2016年10月

冷間多段鍛造による非調質ボルトの成形および強度解析に及ぼす硬化則の影響査読

成田忍, 上森武, 早川邦夫, 久保田義弘

塑性と加工 57 ( 670 ) 1070 - 1076 2016年

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：一般社団法人日本塑性加工学会

<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

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成形シミュレーションにおけるバウシンガ効果の影響と対策

上森武

塑性と加工 57 ( 662 ) 194 - 198 2016年

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

Fusahito Yoshida, Hiroshi Hamasaki, Takeshi Uemori

INTERNATIONAL JOURNAL OF PLASTICITY 75 170 - 188 2015年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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 査読

Naoya Tada, Yoshitaka Matsukawa, Takeshi Uemori, Toshiya Nakata

229 - 232 2015年10月

異種金属接着板の引張り曲げ・曲げ戻しおける接着層のせん断変形挙動査読

上森武

日本接着学会誌 51 ( 7 ) 347 - 354 2015年7月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：一般社団法人日本接着学会

<p>本研究では異種金属接着板の二種類の引張り曲げ・曲げ戻し実験とFEM 解析を行い，接着層に生じるせん断変形挙動について調べた。本研究によって得られた主な結論は，以下の通りである。（1）作成した二つの実験装置を用いて，接着層の曲げ・曲げ戻し時のせん断変形挙動を観察できた。（2）接着層のせん断変形は，ダイ半径と引張り速度の影響を強く受ける。（3）被着体の引張強さが，接着層のせん断変形挙動に大きく関係する。せん断変形を小さく抑えるには，被着体のいずれかに引張強さの小さいものを用いればよい。（4）接着板の曲げ・曲げ戻しにより生じる接着層のせん断ひずみがある値（約1.7）を超えると，接着層ははく離する。（5）先の研究で得られた接着剤の繰返し粘塑性挙動を表現した構成式をFEM に組み込んだ。接着剤の降伏関数として新たな降伏関数を提案しFEM 解析の精度向上を目指したが，期待する成果は得られなかった。</p>

DOI： 10.11618/adhesion.51.347

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

Fusahito Yoshida, Takeshi Uemori, Hiroshi Hamasaki

Advanced Structured Materials 64 571 - 585 2015年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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 査読

Fusahito Yoshida, Takeshi Uemori

60 Excellent Inventions in Metal Forming 61 - 66 2015年1月

記述言語：英語掲載種別：論文集(書籍)内論文出版者・発行元：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 査読

Hiroshi Hamasaki, Fusahito Yoshida, Takeshi Uemori

Key Engineering Materials 651-653 558 - 563 2015年

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：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 査読

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

Key Engineering Materials 626 103 - 108 2015年

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：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

アルミニウム合金板のスプリングバックに及ぼすバウシンガ効果と異方性の影響査読

主せん断ひずみエネルギーによる成形限界の評価査読

上森武

軽金属 65 ( 5 ) 190 - 195 2015年

上森武, 澄川智史, 中哲夫, 麻寧緒, 吉田総仁

軽金属 65 ( 11 ) 582 - 587 2015年

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：一般社団法人軽金属学会

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

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

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

Key Engineering Materials 626 187 - 192 2015年

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：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

中国四国支部ひずみゲージ講習会開催報告

上森武

塑性と加工 55 ( 636 ) 14 - 14 2014年

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

Takeshi Uemori, Satoshi Sumikawa, Tetsuo Naka, Fusahito Yoshida

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

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：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 査読

Fusahito Yoshida, Hiroshi Hamasaki, Takeshi Uemori

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

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：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 査読

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

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

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：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年

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：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