Shear Localization Influences on Assessment of Deformation Behaviors of Pure Iron in Impact Loading Process

In high-speed impact loading experiments, localized deformation is readily taken place, which may result in differences in assessment of strain, strain rate, and further related deformation behaviors of a material in high rate deformations. In this paper, double-notch shear experiments of pure iron specimens were carried out by an improved split Hopkinson pressure bar (SHPB) device with impact speed ranging 16-64 m/s. The development of shear localization and fracture in shear deformation of the specimens was captured by a high-speed camera. Microstructures of localized shear band (LSB) in the shear zone of the specimens at different strain rate were analyzed by metallographic microscope. The nominal strain and strain rate in the deformation zone and the strain and strain rate in LSB were calculated based on the video frames and metallographic photomicrographs. Fracture strains of the shear bands at different impact speed were obtained. Results show that the deformation process of the specimens at different impact speeds includes uniform deformation, localized formation, microscopic crack, and macroscopic fracture; the formation of the LSB results in the decrease of the effective width of the shear band and causes the strain and strain rate to increase rapidly comparing with the nominal strain and strain rate.