Shear Band Formation

Shear Transformation Zones (STZ): In amorphous solids (metallic glasses, polymers), plastic deformation occurs through localized rearrangements of ~10–100 atoms called STZs. Under applied stress, STZs nucleate preferentially in soft spots — regions of low local yield stress. Once a band of STZs forms, it concentrates further deformation, creating a shear band. Shear bands propagate at ~10² m/s and can cause catastrophic failure. Lower temperatures and faster loading promote fewer but more intense bands. The Eshelby inclusion stress field from one STZ can trigger neighbors along the shear direction, causing autocatalytic band propagation.