Hypervelocity target dynamics as seen by three-dimensional markers

Abstract

In order to observe the interior deformation and the strain field of a target under hypervelocity impact, cube-shaped copper targets 3 in. and 4 in. on an edge were made with imbedded nickel wires, arranged orthogonally, to serve as three-dimensional markers. One target was indented statically with a J-in. ball bearing for reference. Measurements of the terminal wire positions, as well as Vickers hardness, on sections of all targets indicated that the flowfields were essentially cylindrically symmetric. Calculations of the finite Lagrangian strain were thus made by using cylindrical coordinates. Comparisons of flowfields, strain invariants, and hardness profiles in the targets and the mass' velocities, and energies of the projectiles show definite qualitative correlations. The flow patterns showed that 1) only a small portion (10% to 30%) of the material that initially occupied the crater site was ejected, i.e., the evacuated volume is much smaller than the crater size, and 2) the outside surface of the lips around the crater was originally the top surface of the target. Thus, instead of being formed like the splashes of a liquid, the lips were formed by the progressive folding over of the surface material by shearing forces and pressure from a subsurface, maximum energy center during the crater expansion.