Mechanism analysis and prediction of explosive formed projectile's axial fracture

To explain the axial fracture phenomenon of Explosively Formed Projectile (EFP), the fracture mechanism of long rod EFP during the forming phase is analyzed by the stress wave theory. When the velocity gradient δv between the head and tail parts exceeds the critical value δvcr, the EFP would fracture in the axial direction. Based on the Johnson-Cook constitutive model parameters and the special conditions in the forming phase of EFP, the critical velocity gradient δvcr can be determined by theoretical calculation and then validated by experimental results for both copper and tantalum EFPs. The experimental results for EFP's fracture agree well with the prediction of the theoretical analysis. The theoretical analysis method can be applied as an important measure to determine the critical velocity gradient and predict the fracture of long rod EFP, providing reference for the application of new kinds of high density materials in the EFP research area.