Shear bands as translation-rotation modes of plastic deformation in solids under alternate bending

The paper studies the shear banding developing in corrugated surface layers of commercial titanium, hydrogenated Ti surface layers and high-purity aluminum foils glued onto commercial aluminum A7 plates against elastic deformation of their bulk under alternate bending at room temperature. In surface layers of commercial titanium under alternate bending up to fracture, plastic flow develops through microscale twinning against the background of dislocation substructure and shear banding is absent. Early in the alternate bending (up to N = 103 cycles which corresponds to strain ε∼ 55-60%), shear banding in hydrogenated Ti surface layers and Al foils is also absent. At N = 104-106 cycles, severe shear banding is detected in hydrogenated Ti surface layers and Al foils. Two types of meso- and macroscale shear bands are revealed and analyzed: planar shear bands with continuous misorientations in slightly corrugated surface layers and three-dimensional shear bands which propagate in highly corrugated surface layers. The latter shear bands are responsible for submicro- and/or nanofragmentation of material and culminate in plastic collapse and fracture of solids. Shear bands are treated as translation-rotation modes of plastic deformation in solids with high crystal lattice curvature. Shear banding is a multiscale noncrystallographic mechanism of a curved crystal lattice fragmentation that transforms an elastic lattice curvature of a deformed solid to its inelastic rotation.