Plastic deformation: Shearing mountains atom by atom

Conventional wisdom established atomistic defects, dislocations, as agents of plastic deformation. On macroscopic scale, rock, wood, steel, tough ceramics, fiber reinforced composites, and silicon all deform in the same way and produce the same pattern; shear bands. The argumentation presented here, starts on the largest length scale of the problem at hand and leads through a number of hierarchical levels down to the atomistic mechanism. Shear bands develop discontinuously by the motion of a process zone. Locally, i.e. in the process zone, deformation proceeds perpendicularly to the macroscopic shear, in combination with a rotation. The microscopic shear itself may occur again in a discontinuous manner and again orthogonally to the intermediate level and so on at ever smaller scale. Material properties come into play at the highest hierarchical level, i.e. at the smallest length scale where they control the well-known micromechanisms.