Abstract
Crystalline materials at yield behave as anisotropic, highly viscous fluids. A microscopic inspection reveals a structural adjustment of the crystal lattice to the material flow carried by dislocations.
The resistance to this flow determines the strength of ductile materials. The deformation microstructure evolves within a common framework up to very high strains > 100.
To avoid energetically costly multislip, materials are subdivided into regions which deform by fewer slip systems. To maintain compatibility, the regions defined as deformation bands occur in a form of elongated alternately misoriented domains filled with fairly equiaxed dislocation cells.
In the proposed continuum mechanics model, the formation of deformation bands of a lamellae type is interpreted as a spontaneous deformation instability caused by an anisotropy of hardening. However, such a model of the bands predicts their extreme orientation and their width tends to zero.
This trend is opposed by hardening caused by a bowing stress of dislocations within the cells.