Explosively Formed Penetrator (EFP)

The Explosively Formed Penetrator (EFP) is an important conventional weapon in which an explosive is used to simultaneously form a projectile and propel it. The development and optimization of the EFP is greatly assisted through the use of finite element simulations. An example simulation is shown here to illustrate the use of the DYNA3D finite element code in optimization of an EFP design.

An important characteristic of EFP performance is the aerodynamic stability of the penetrator shape. One approach to improving the aerodynamic stability is to form fins on the trailing edge of the penetrator. This can be achieved by controlling or enhancing the buckling that naturally occurs in EFPs, as shown in Figure 1. Understanding and modeling the processes that lead to dynamic plastic buckling in EFP liners allows the designer to control the buckling process to gain enhanced aerostability.

The simulation of the EFP is performed by modeling the complete process, including the detonation of the explosive and the interaction of the explosive with the EFP case and liner. The early time simulation of the explosive detonation and initial penetrator formation are shown in Movie 1. The subsequent formation and motion of the penetrator are shown in Movie 2. This particular design produced too large of a velocity gradient along the length of the penetrator, which leads to an undesirable failure of the penetrator.

The dynamic plastic buckling of annealed OFHC copper cylindrical shells is treated by experiment, finite element code calculation, and analysis. Initial velocity imperfections of the impulsive loading were obtained from sheet explosive thickness measurements. The Johnson-Cook relation was adopted for the copper. A comparison of the final profiles, their modal content, and amplification functions showed good agreement among experimental code and analytical results.

References

• Florence, A.L., Gefken, P.R., and Kirkpatrick, S.W., 1991, "Dynamic Plastic Buckling of Copper Cylindrical Shells," International Journal of Solids and Structures, Vol. 27, No. 1, pp.89-103.
  Abstract
  

For inquiries or comments, please contact:
Dr. Steven Kirkpatrick
Principal Engineer
e-mail: skirkpatrick@ara.com
Dr. Robert T. Bocchieri
Principal Engineer
e-mail: rbocchieri@ara.com
Robert MacNeill
Principal Engineer
e-mail: rmacneill@ara.com

Figure 1. Buckling behaviors of EFP liners during formation.

Movie1 . EFP Detonation Simulation.

Movie 2. EFP Formation Simulation.