On the mechanism of deformation and failure in bulk metallic glasses

Based on the coupled thermo-mechanical model, a constitutive model for bulk metallic glasses (BMGs), which considers the effects of free volume, temperature and hydrostatic stress, has been further deduced and generalized to the multi-axial stress status in the present manuscript. Besides, a failure criterion of critical free volume concentration is introduced from the coalescence mechanism of free volume. Then the constitutive model and the failure criterion are implemented into LS-DYNA commercial software through the user material subroutine (UMAT). Integrated with the related test data, FEM simulations for different deformation scenarios are conducted. The evolutions of different material parameters and the corresponding mechanical behaviors of BMGs are analyzed, and especially the effects of strain rate, initial temperature and hydrostatic stress as well as the initial free volume concentration on the deformation and failure of BMGs are discussed in detail. It demonstrates that the multi-axial-stress-status constitutive model and the failure criterion are able to describe the mechanical behaviors of BMGs at different initial temperatures (below and within the supercooled liquid region) and strain rates universally.