Analysis of long rod penetration at hypervelocity impact

Abstract

The hypervelocity impact (>3 km/sec) of a long rod penetrator against thin targets of like material was studied analytically with the aid of the HELP code, a two-dimensiona l, finite-difference Eulerian computer code. The results were compared with experimental data. The analytical examination of the effect of strength showed no perturbation. The computations of projectile residual speed deviated by no more than 3% from the experimental data; of residual mass by no more than 16%; of final rod length by no more than 5%; and of target exit diameter by no more than 8%. This agreement demonstrated that the HELP code can serve as a useful analytical tool for the study of kinetic energy projectile penetration of hypervelocity impact. HE study of the dynamic response of materials to intense impulsive loading may be approached from three distinct points of view: experimental, analytical, and numerical. In the experimental approach tests are conducted to deduce relationships between various parameters from the observed results. Generally many data points (therefore many tests) are required, so that this approach becomes both time consuming and expensive, especially in the hypervelocity regime (striking velocities > 3 km/sec). To obtain some knowledge of the physics of the deformation process and at the same time reduce the number of tests, recourse is made to analytical methods. Simplifying assumptions are introduced into the governing equations of continuum physics, and these are reduced to a set of partial differential equations which characterize the elastic-plastic hydrodynamic response of a material or structure. Very often the resulting differential equations are mathematically intractable and further ap- proximations must be introduced to obtain an approximate analytical solution, at the expense of reducing the scope of the problem. With the present availability of large digital com- puters, however, there now exists the realization that systems of differential equations never attempted before can be solved. The main advantage of computer utilization is that parameters can be varied easily and quickly in any problem and their effects noted and compared. Furthermore, even if only a part of the problem can be formulated correctly, several methods of complete formulation can be assumed and a determination of which is the best or most sensible solution can be made. The objectives of this study were twofold: to ascertain the effect of material strength on target and projectile defor- mations with varying target thickness, and to determine the applicability of the HELP code to study hypervelocity (HV) impact of long rod kinetic energy penetrators by validating, if possible, the numerical results with experimental data.