Article ID: 250901
Goya and Ito[Goya, M. et al.:Trans. Jpn. Soc. Mech. Eng., Ser. A, 54-504(1988), 1617-1622.] proposed an expression of plastic constitutive law in which both the direction and magnitude of the plastic strain increment ε ̇P are expressed as functions of the stress increment σ ̇' and unit normal nN of the plastic potential function. The expression is developed through the introduction of two independent transition parameters μ(α) and β(α), which denote the magnitude and direction angle of the plastic strain increment, respectively, and are defined as functions of the direction angle α of the stress increment. The angle α is defined as the direction measured from the unit normal nN in deviatoric stress space. Then, the authors[Ito, K. et al.:Trans. Jpn. Soc. Mech. Eng., Ser. A, 57-533(1991), 141-146.] investigated specific forms of μ(α) and β(α) through the application of the linear-comparison solid theory to the local necking problem of a rigid plastic plate subjected to biaxial stretching. The specific forms were proposed as functions of three material parameters KC|Uniaxial Direction, K0 and γ. In this paper, we report on a method to explicitly estimate the parameter values using a forming limit diagram, which has been widely used in many industries as a useful test to evaluate the formability of thin metallic sheets.
