Study of fracture evolution in copper sheets by in situ tensile test and EBSD analysis

Abstract

Microstructural changes during plastic deformation and fracture evolution play an important role in the understanding of fracture mechanisms. However, most publications have focused on the initial stages of deformation where the latter is uniform. The current study was focused on the last stages of fracture, the necking, and crack propagation. Tensile specimens were examined by in situ scanning electron microscope equipped with a tensile module and electron backscatter diffraction. It was demonstrated that the fracture evolution consists of scanty diffuse necking followed by pronounced localized necking, in which the deformation band spread through the width of the specimen in two combined mechanisms—shearing and dimpling. The microstructural changes inside the deformation band adjacent to crack edge were compared to those in the uniform deformation zone. In the deformed areas, the grains became elongated and preferentially orientated in the loading direction. The relative frequency of twin boundaries at 60° was reduced in the deformed areas compared to non-deformed areas, while the misorientations at low angles of 3°–15°, which imply on a dislocation pileups subgrained structure, were increased to greater extent at the crack edge. Inside the deformation band, the amount of deformation was increased compared to the uniformly deformed region with grain fragments as a result of the complexity of stresses, although similar deformation mechanisms were identified.