Satoshi Sumikawa

Elasto‐Plasticity Behavior of Type 5000 and 6000 Aluminum Alloy Sheets and Its Constitutive Modeling

To examine the deformation characteristic of type 5000 and 6000 aluminum alloy sheets, uniaxial tension, biaxial stretching and in‐plane cyclic tension‐compression experiments were performed, and from these, r‐values (r0, r45 and r90), yield loci and cyclic stress‐strain responses were obtained. For the accurate description of anisotropies of the materials, high‐ordered anisotropic yield functions, such as Gotoh’s biquadratic yield function and Barlat’s Yld2000‐2d, are necessary. Furthermore, for the simulation of cyclic behavior, an advanced kinematic hardening model, such as Yoshida‐Uemori model (Y‐U model), should be employed. The effect of the selection of material models on the accuracy of the springback prediction was discussed by performing hat bending FE simulation using several yield functions and two types of hardening laws (the isotropic hardening model and Y‐U model).

Plastic deformation behavior of high strength steel sheet under non-proportional loading and its modeling

This paper deals with plastic deformations of a high tensile strength steel sheet (HTSS sheet) under biaxial stress condition including strain path. Using a cruciform specimen of a HTSS sheet of 780MPa-TS, experiments under proportional and non-proportional loadings were investigated. Numerical simulations of stress-strain responses for several strain paths after biaxial stretching were conducted using a large-strain cyclic plasticity model (Yoshida-Uemori model). The results of numerical simulation agrees well the corresponding experimental results, which is attributed to the accurate modeling of the backstress evolution of the anisotropic yield function.

Enlargement of measurable strain range in biaxial cruciform test

In order to improve the accuracy of FEA in the assessment of crack and wrinkle risk, and in the amount of springback, the plastic anisotropy of a material should be measured over a wide strain range by a biaxial test, especially by a cruciform test. In this study, slit arm strengthening of a cruciform test specimen was investigated: its slit arms were melted by laser irradiation, and then mertensitized by quenching. One and a half times or larger measureable strain range was obtained by one laser irradiated line in a slit arm of a cruciform specimen compared with a specimen without laser irradiation.

Springback of Aluminum Alloy Sheet Metal and its Modeling

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 Youngs 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.

Constitutive Equations of Stress-Strain Responses of Aluminum Sheet under Stress Path Changes

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 weak features such as strong plastic anisotropy of yield stress, large Lankford value, and so on. 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 an aluminum sheet metal. In the present research, several experimental procedures were carried out to reveal the mechanical properties of an aluminum sheet under proportional and non-proportional loading. From the comparisons between experimental data and the corresponding calculated results by the proposed constitutive model, the performance of our model was evaluated. The evaluation of some springback analyses were also carried out. The calculated results show good agreements with the corresponding experimental data.