Nucleation mechanisms of shear bands in amorphous alumina

The origin of the plastic deformation in amorphous solids is a challenging issue unlike that of the plasticity in crystals. Plasticity in amorphous systems can occur by the nucleation and propagation of shear bands (SBs). In this work, we investigate the mechanical response of an amorphous alumina sample subjected to shear deformation via extensive molecular dynamics simulations. We find SBs form only within a certain range of parameter values, e.g., low quenching rates, low temperatures and high strain rates. In our proposed atomic-scale model shear transformation zones (STZs) first nucleate and act as precursors of SBs due to their high stress concentration. The results showed that STZs generate an anti-symmetric stress that is responsible for the vortex-like motion of atoms that facilitate the percolation of STZs, finally forming an SB. These results provide insight into the mechanisms of plastic deformation of similar amorphous solids.