Deformation macrolocalisation and fracture in ultrafine-grained armco iron

The banded structure formed in armco iron specimens as a result of equal-channel angular extrusion causes their strong shear localisation under quasi-static tension. Applying transmission electron microscopy technique, a fine structure of meso- and macroscopic shear bands was revealed. The character of shear band propagation was studied by calculation of the maximum in-plane shear strain through a digital image correlation procedure. It was shown two different patterns of macroband propagation: two parallel shear bands with oppositely directed shears or a cross of shear bands oriented along the conjugate direction of maximum tangential stresses. The necking was revealed to be caused by the disturbance of self-consistent propagation of deformation macrobands.