Computational study of density fluctuation-facilitated shear band formation in bulk metallic glasses

Seemingly identical Bulk Metallic Glasses (BMG) often exhibit strikingly different mechanical properties despite having the same composition and fictive temperature. A postulated mechanism underlying these differences is the presence of “defects” and density variations. Motivated by this perspective, we introduce physically realistic and quantitatively controllable density fluctuations in molecular dynamics simulations to systematically examine their role in shear band formation under applied stress. We find that the critical shear strain is strongly dependent on the magnitude and size of the fluctuations, revealing a nonlinear activation behavior associated with localized rejuvenation. This finding also elucidates why, historically, critical shear stresses obtained in simulations have differed so much from those found experimentally, as typical simulations setups might favor unrealistically uniform geometries.