Some considerations for 3D EFP computations

This article identifies some issues, options and results associated with 3D Explosively Formed Penetrator (EFP) computations. The three broad categories of interest (for Lagrangian computations) are the sliding/contact interfaces, the type and arrangement of elements, and the generation of the grid. The sliding/contact algorithm uses a virtual particle approach that is very robust, and it is described in detail. Tetrahedral elements are considered for both symmetric and non-symmetric arrangement, each with some advantages and disadvantages. A mixed element algorithm is also considered for the non-symmetric arrangement, in an effort to eliminate some of the locking that occurs for the non-symmetric arrangement. Hexahedral (brick) elements are not considered herein, but some of the effects (for tetrahedral elements) also apply to hexahedral elements. For axisymmetric EFPs there are also some trade-offs (symmetric grid vs. equally sized elements) associated with the generation of the grid. Computational results are provided to illustrate each of the issues and effects. The virtual particle algorithm is also well suited for high-velocity impact computations, and an example is included to demonstrate this capability for a complex problem.