The development of plastic failure modes in crystalline materials: Shear bands in Fcc polycrystals

Abstract

The structure and crystallography of shear bands formed in aluminum-3 wt pct copper polycrystals was studied by optical microscopy, electron microscopy, and convergent beam electron diffraction. The results are interpreted in light of recent finite element calculations. The importance of localized plastic deformation on material properties, particularly as a direct precursor to failure, is emphasized. Optical and electron microscopy showed that shear bands formed in aluminum-3 wt pct copper deformed in plane strain compression are not associated with microvoid formation or microfracture. Electron diffraction analyses and finite element simulations demonstrated that shear localization is promoted by local rotations of the crystal lattice that inducegeometrical softening. Regions acting as stress or strain concentrators, such as grain boundary triple points and specimen surfaces, were found to be preferential sites for shear band initiation. Texture formation promoted shear band propagation, in the sense that it reduced the misorientation between the shear band planes on each side of a grain boundary.