Numerical Simulation and Mechanism Analysis of EFP's Fracture in Forming Process

In order to study the fracture mechanism of explosively-formed projectile (EFP) in axial direction, the forming and fracturing processes of OFHC EFP with typical charge structure are simulated by using LS-DYNA software, in which Johnson-Cook failure model and adaptive algorithm are introduced. Hemispherical liners with different extrinsic curvatures are simulated, and the simulated results of fracture are validated through experiment. The stress wave theory is used to analyze the fracture mechanism of long rod EFP, and confirm the critical velocity gradient. The results show that the fracture phenomenon of EFP can be well simulated by using LS-DYNA software based on Johnson-Cook failure model and adaptive algorithm. For certain EFP charge structure with hemispherical liner, a critical liner curvature which makes the long rod EFP fracture in forming process exists. The critical value of 60~83 m/s calculated from stress wave theory agrees well with the critical velocity gradient (76 m/s) of EFP fracture. The theoretical analysis method can be used to confirm the critical velocity gradient of long rod EFP fracture.