A PLASTIC CONSTITUTIVE MODEL FOR ANISOTROPIC MATERIALS AND FINITE-ELEMENT ANALYSIS OF STRAIN LOCALIZATION PROCESS

A plastic constitutive model for initially orthotropic but subsequentl y skewed anisotropic materials is proposed in this paper. The variatio n of anisotropic axes is discussed within the framework of objectivity , and the evolution of the axes is formulated. It is shown that the yi eld function proposed is identical to Hill's quadratic yield function when the anisotropic axes lie along the base vectors. Applying the con ventional laws for both work-hardening and material flow to the yield function, an anisotropic constitutive model is completed. A finite ele ment equation is obtained next, based on the updated Lagrangian formul ation. A fully three-dimensional analysis is carried out to predict th e strain localization behavior of anisotropic sheet metals. The direct ion of strain localization is strongly affected by the initial configu ration of the anisotropic axes, and the simulated result shows fairly good agreement with the experimental one.