DETERMINATION OF CONSTITUTIVE PARAMETERS BY FORMING-LIMIT TESTS

Goya and Ito have developed a constitutive expression of plastic mater ials introducing two essential parameters mu(alpha) and beta(alpha) wh ich denote the magnitude and directional angle of the plastic strain i ncrement, respectively, where alpha denotes the directional angle of t he stress increment in the deviatoric stress space. In this report, th e authors investigate specific forms of mu(alpha) and beta(alpha), and determine the values of material constants through the application of the linear-comparison solid theory to the localized necking problem o f a rigid-plastic plate subjected to biaxial stretching, The specified forms of the transition parameters are described as follows: beta(alp ha) = (beta(max)/alpha(max))Phi(($) over bar Theta)alpha, mu(alpha) = {cos(alpha - beta)}(1+0.9 Phi), Phi(($) over bar Theta) = (1 - 2K(0)) (1 - ($) over bar Theta)r - K-0, where gamma and K-0 are new material constants, and ($) over bar Theta denotes the deviation of the curren t stress state from the uniaxial stress state.