Microscopic Mechanism of Shear Bands in Amorphous Solids

The fundamental instability responsible for the shear localization which results in shear bands in amorphous solids remains unknown despite an enormous amount of research, both experimental and theoretical. As this is the main mechanism for the failure of metallic glasses, understanding the instability is invaluable in finding how to stabilize such materials against the tendency to shear localize. In this Letter we explain the mechanism for shear localization under shear, which is the appearance of highly correlated lines of Eshelby-like quadrupolar singularities which organize the nonaffine plastic flow of the amorphous solid into a shear band. We prove analytically that such highly correlated solutions in which N quadrupoles are aligned with equal orientations are minimum energy states when the strain is high enough. The line lies at 45 degrees to the compressive stress.