Characterization of deformation microstructure and fractured surface of plastic shearing of copper bar

The deformation microstructure, the equivalent strain and the micro-hardness beneath the sheared surface produced by plastic shearing of copper bar under axial compressive loads are examined, and the sheared surfaces are imaged by scanning electron microscope. Three regions with different microstructure features caused by plastic deformation are observed below the sheared surface. The outer surface layer with depth of about 200 μm endures severely plastic shear deformation during shearing, in the outer surface layer of about 60 μm finely equiaxed grains nearly random oriented could be postulated and 50% increase of the micro-hardness is detected. In the second region alignment, elongation and fragmentation of grains, densely packed and nearly parallel to the shearing direction, are shown. In the inner region, grains are observed to be elongated and bent shapely along the shearing direction. The equivalent strain decreases rapidly with increase of the distance to the sheared surface. A macro-fracture zone, which takes the shape of crescent, is formed in the sheared surface. Failures originate firstly at two intersectional points of the moving blade and the fixed blade in the bar during the shearing process. The area ratio of the fracture zone decreases with increase of the applied axial compressive loads. Lots of highly developed ellipsoidal micro-voids along shearing direction, formed by mechanism of nucleation of the micro-voids, and then growth and coalescence under shear stress and shear strain, are shown in the fractured zone.