Mechanics of Amorphous Metals (Elastic-Plastic Finite Element Analyses Using Inhomogeneous Defects Theory)

Abstract

Plastic deformation of amorphous metals is dependent on a mean stress (hydrostatic pressure), that is, compressible due to the random atomic structure. This property leads their intrinsic anisotropy on deformation. In addition, the localized shear bands occurring just after an elastic region do not allow the sufficient elongation. This is the crucial drawback of that material which has been strongly tried to overcome. In the present paper, a constitutive law based on the inhomogeneous defects theory and an evolutional law of defects density (equivalent to free volume) were formulated with the mean stress-dependent yield function. Several parameters used in the constitutive and the defects evolution laws were fitted to the experimental results. Finite element analyses were first performed using one element model to obtain the perfectly uniform deformation. Yield curves under some multiaxial stress states were obtained at room temperature. Employing the elastic limit as a yield stress and the parameter κ of 0.09 in Drucker-Prager yield criterion, the prediction agrees well to the FEM solutions. The uniaxial deformation behavior with an initial fluctuation of defects density using a block model, then, exhibits the localized shear bands after the maximum point, and the anisotropic angles of such bands to the stress axis were coincident with the experimental and the other computational results.