Mechanism of deformation localization and homogeneous flow in bulk metallic glasses

A modified coupled thermo-mechanical constitutive model for bulk metallic glasses (BMGs), which is generalized to the multiaxial stress state and considers all the effects of free volume, heat and hydrostatic stress is proposed. Besides, a failure criterion of critical free volume concentration is introduced. The constitutive model and the failure criterion are implemented into the LS-DYNA commercial software through the user material subroutine (UMAT). Then the finite element method simulations of BMGs at different initial material temperatures and strain rates are conducted, and the evolutions of physical parameters and corresponding macroscopic mechanical behavior of material are analyzed. The analysis result shows that the deformation and failure characters in the shear band zones of BMGs are significantly different from those in the matrix at room temperature, and consequently high deformation localization occurs in the material. In the supercooled liquid region, the mechanical behaviors in the shear band zones are similar to those in the matrix, and thus BMGs usually has homogeneous flow characteristics.