Theory of shear banding in metallic glasses and molecular dynamics calculations

Shimizu, Futoshi ; Ogata, Shigenobu*; Li, J.*

Shear bands form in most bulk metallic glasses (BMGs) within a narrowrange of uniaxial strain . We propose this critical condition corresponds to embryonic shear band (ESB)propagation, not its nucleation. To propagate an embryonic shear band, the far-field shear stress must exceed the quasi steady-state glue traction glue of shear-alienated glass until the glass-transition temperature is approached internally due to frictional heating, at which point ESB matures asa runaway shear crack. The magnitude of is governed by recovery, which are extremely fast downhill dissipative processes of timescale comparable to atomic vibrations, which molecular dynamics (MD) simulations can well capture. We model 4 metallic glasses: a binary Lennard-Jones (LJ) system, twobinary embedded atom method (EAM) potential systems, and a quinternary EAM system. Despite vast differences in the structure and interatomic interactions, the glue values from the four MD calculations give predictions in the range of . Large-scale MD simulations of a binary LJ system reveal ESB as shear transformation zones coalesced. Under the condition , ESB is seen to develop into mature shear bands with approaching , while if , ESB does not propagate, becomes diffuse, and eventually dies.